PMC Beta Search User Guide

As the next step in the ongoing modernization of the PubMed Central (PMC) website, NCBI is updating PMC's search functionality and user experience. In preparation for a planned transition to the new search later this year, PMC has made a beta version available for you to preview, test, and provide feedback on the updated search technology and design.

This guide is meant to help you use PMC Beta Search to find articles of interest to you. To provide feedback on PMC Beta Search, please use the green "Provide Feedback" button located in the top left corner of the beta search page (see area #7 in Figure 1 below).

Please note: PMC Beta Search represents the initial set of features that will be launched to the main PMC website later this year.

Search for Articles

To navigate to PMC Beta Search, type a term or concept into the search box at the top of any PMC page and click the "Try this search in PMC Beta Search" link instead of the "Search in PMC" button to run the search (see image below). You can then conduct subsequent searches by typing your search query into the search box at the top of the page. Suggestions will display as you type your search terms.

For many searches, it is not necessary to use special tags or syntax, though, like the current PMC search, PMC Beta Search does support more structured searching and filters to refine your results and help you find the information you are seeking.

Conduct a search by:

Author | Journal | Volume and Issue | Collection | Funder | License | Date | Article Property

Other search topics:

• UPDATED Searching for a Specific Article
• Phrase Searching
• NEW Proximity Searching
• UPDATED Truncating Search Terms
• Combining Search Terms with Boolean Operators
• UPDATED Using Search Field Tags

By Author

In the Search box, enter the author's full name or their last name followed by initials, without punctuation. If you only know the author's last name, use the author search field tag[au] as shown in an example below.

Author names are automatically truncated to account for varying initials and designations such as Jr. To turn off the truncation, use double quotes around the author's name with the author search field tag [au] as shown in an example below.

By Journal

In the Search box, enter the journal title, the NLM journal title abbreviation, or the ISSN, the 8-digit standardized international code used to identify journals.

By Volume or Issue

To retrieve all the articles in PMC from a specific volume or issue of a journal, include the volume number or the volume and issue number in a journal search query.

By Collection

Explore the contents of collections in PMC by entering the appropriate preset PMC search filter(s):

By Funder

Use or append the preset search filters shown in the Search Query column below to find articles supported by funding organizations that have formally partnered with NLM to use PMC as a repository for their funded research.

By License

Limit your search results to articles in the PMC Open Access Subset with specific Creative Commons (CC) licenses by appending the preset search filters shown in the Search Query column below. For descriptions of these licenses, please see the Creative Commons site, About the Licenses. Please note that not all articles in the Open Access Subset have a CC license.

These filters are based on license information provided in the articles by publishers and other content providers.

By Date

To search by a single date, use the format YYYY/MM/DD[date field]. The month and day are optional.

The available date fields are:

• Date of Publication [dp] - The date an article was first made available in print or electronic format, based on data provided to PMC
• Electronic Publication Date [epdat] (if applicable)
• Print Publication Date [ppdat] (if applicable)
• PMC Live Date [pmcrdat] - The date the PMCID is accessible in PMC. For embargoed articles, this date is updated when the embargo lifts
• Entry Date [edat] - Date used for PMC processing, such as PMC Live Date sort order. This date is not populated for embargoed articles

Deposit date data are not available.

By Article Property

Search or append a search with any of the following queries to find articles with these specific properties in PMC:

Searching for a Specific Article

UPDATED FEATURE: Searching by article title has been improved in PMC Beta Search.

To search for a specific article in PMC, paste the article title into the search box without quotes or punctuation. Alternatively, you can include citation details such as the author, journal name and the year the article was published in the search box and the citation sensor will automatically analyze your query for citation information to return the correct record. You do not need to use field tags or Boolean operators.

You can also search for a specific article using a location ID, such as a DOI. For more information, see the details about the Location ID [lid] field tag.

Phrase Searching

Many phrases are recognized by the subject translation table used in PMC's automatic term mapping feature (ATM). For example, if you enter influenza in birds, PMC recognizes this phrase as a MeSH concept.

You can bypass ATM and search for a specific phrase using the following formats:

When you enter search terms as a phrase, PMC will not perform automatic term mapping that includes the MeSH term and any specific terms indented under that term in the MeSH hierarchy. For example, "health planning" will include citations that are indexed to the MeSH term, Health Planning, but will not include the more specific terms, e.g., Health Care Rationing, Health Care Reform, Health Plan Implementation, that are included in the automatic MeSH mapping.

Quoted phrase not found

PMC uses a phrase index to provide phrase searching. Phrases may appear in a PMC record but not be in the phrase index. To search for a phrase that is not found in the phrase index, use a proximity search with a distance of 0 (e.g., "cognitive impairment in multiple sclerosis"[tiab:~0]); this will search for the quoted terms appearing next to each other, in any order.

Automated processes regularly add new phrases to the index based on standard criteria such as phrase frequency and length.

Proximity Searching

NEW FEATURE: Proximity search is now available in PMC Beta Search.

You can use proximity searching to search for multiple terms appearing in any order within a specified distance of one another in the following fields:

To create a proximity search in PMC, enter your terms using the following format:

"search terms"[field:~N]

More information about proximity searching:

• Results will include your quoted terms in any order. If you would like to search for an exact phrase with terms appearing in a specific order, use a phrase search instead.
• Automatic Term Mapping is not applied to the quoted terms.
• Proximity searching is not compatible with wildcards (*). If the double quoted terms in a proximity search include a wildcard (*), the proximity operator will be ignored.
• You can combine proximity searches with other terms using Boolean operators; for example, "hip pain"[Title:~4] AND stretching
• Booleans and stopwords included in quoted terms for proximity search are searched like regular keywords.

Example

Search PMC for records with the terms "rationing" and "healthcare" appearing within 2 words of each other - in any order - in the Title field:

"rationing healthcare"[Title:~2]

Search results may include: rationing healthcare, healthcare rationing, rationing in healthcare, rationing scarce healthcare, rationing strategies in healthcare, rationing limited healthcare and more.

Example

Search PMC for records with the terms "patient," "physician", and "relationship" appearing next to each other - in any order - in the Title/Abstract fields:

"patient physician relationship"[Title/Abstract:~0]

Since N=0, the quoted terms must appear next to each other with no other words in between them, although they can still appear in any order. Search results may include patient physician relationship, physician patient relationship, etc.

Example

You can build queries that combine proximity searches with other terms using Boolean operators (AND, OR, NOT):

"accidental overdose"[Title/Abstract:~3] AND acetaminophen

Truncating Search Terms

UPDATE: PMC Beta Search searches for unlimited variations of truncated terms. Additionally, multiple wildcards can now be used in the same term.

To create a wildcard search in PMC, use an asterisk (*) to substitute for 0 or more characters in a term or phrase. For example, flavor* finds terms that begin with the root term flavor, such as flavored, flavorful, flavoring, and more variations of this term.

• A wildcard (*) substitutes for 0 or more characters
• Terms must begin with at least 4 characters before the first wildcard: colo*
• Multiple wildcards can be used in the same term: organi*ation*

To use wildcards in a phrase search, use any of the following formats:

• Enclose the phrase in double quotes: "clinical laboratory test*"
• Use a search tag: clinical laboratory test*[tiab]
• Use a hyphen: clinical-laboratory-test*

Phrases can include more than one wildcard: "uter* muscle*"

Wildcards turn off Automatic Term Mapping (ATM) and the process that includes the MeSH term and any specific terms indented under that term in the MeSH hierarchy. For example, "brain neoplasm*" will not map to the MeSH term Brain Neoplasms or include any of the more specific terms, e.g., Cerebral Ventricle Neoplasms, Infratentorial Neoplasms, etc.

Wildcards can be particularly useful to capture variations of a phrase, since phrase searches already turn off automatic term mapping and do not otherwise include alternate spellings or singular/plural forms. For example, searching for "tumo*r associated macrophage*" retrieves variations of the phrase such as: "tumor associated macrophage", "tumour associated macrophage", "tumor associated macrophages", and "tumour associated macrophages".

Combining Search Terms with Boolean Operators (AND, OR, NOT)

Enter Boolean operators in uppercase characters to combine or exclude search terms:

• AND retrieves results that include all of the search terms.
• OR retrieves results that include at least one of the search terms.
• NOT excludes the retrieval of terms from your search.

Use parentheses to group terms as desired.

Using Search Field Tags

You can search for a term in a specific field by including a search field tag after the term; for example, UCLA[ad] will search for the term UCLA in the affiliation field only.

More information about using search field tags:

• The search field tag must be enclosed in square brackets.
• Case and spacing do not matter: cancer[mh] = Cancer[mh].
• Search field tags turn off Automatic Term Mapping (ATM), limiting your search to the specified term only.
• Using a search field tag after multiple terms will attempt to search those terms as a phrase: kidney allograft[tiab]. If the phrase is not found in the phrase index, the individual terms will be combined with the Boolean AND, and the search tag will only be applied to the final term.
• To search multiple terms in the same field, each term must be tagged individually: child[ti] nutrition[ti] development[ti].

Search Field Descriptions and Tags

UPDATE: Some search fields have been added or updated in PMC Search beta. New items are highlighted with NEW. Removed and replaced search fields are listed below this table.

Search field descriptions and their corresponding tags are listed in the table below.

Please note: The following search tags apply only to MEDLINE indexed articles. Use of these tags will restrict the retrieval of search results to the MEDLINE-indexed subset of PMC.

Acknowledgements [ack]

Includes all words in the acknowledgement section of an article (e.g., "National Institutes of Health[ack]").

Affiliation [ad]

Includes the institutional affiliation and address (including email address, when available) of the authors of the article as it appears in the journal.

Searching for terms in the affiliation field searches in all author affiliations on a record. For example, a search for Hopkins[ad] AND Bloomberg[ad] can find these terms spread across multiple authors' affiliations on the same record.

To search for multiple terms appearing within the same affiliation, use a proximity search. You can also search affiliations using a phrase search; however, we suggest using a proximity search for more comprehensive results because affiliation data may be provided in a variety of ways for the same institution. For example, a search for "Hopkins Bloomberg"[ad:~25] will find any record where the words "Hopkins" and "Bloomberg" appear in the same affiliation, with no more than twenty-five words between each term.

All Fields [all]

Untagged terms and terms tagged with [all] are processed using Automatic Term Mapping (ATM). Terms that do not map are searched in all search fields except for Entry Date, MeSH Date, and Modification Date. Terms enclosed in double quotes or including wildcards (*) will be searched in all fields and not processed using Automatic Term Mapping. PMC ignores stopwords. Replaces Text Word [tw].

Author [au]

To search for an author, enter the last name followed by a space and up to the first two initials followed by a space and, if applicable, a suffix abbreviation. Initials and suffixes may be omitted when searching.

PMC automatically truncates author names to account for varying initials, e.g., o'brien j[au] will retrieve o'brien ja, o'brien jb, o'brien jc jr, as well as o'brien j. To turn off this automatic truncation, enclose the author's name in double quotes and qualify with [au] in brackets, e.g., "o'brien j"[au] to retrieve just o'brien j.

Author – Identifier [auid] NEW

The author identifier includes a unique identifier associated with an author, corporate or investigator name, if supplied by a publisher. The field includes the organization authority that established the unique identifier, such as, ORCID, ISNI, VIAF, e.g., "orcid 0000-0001-5027-4446"[auid].

Body - All Words [body] NEW

Includes all words and numbers in the body of an article except for the Abstract and References. Replaces Article Body [article].

Conflict of Interest Statement [coi] NEW

The conflict of interest statement from the published article. Conflict of interest statements are available when supplied by the publisher.

To retrieve all articles that contain conflict of interest statements, use the query hascois.

Corporate Author [cn] NEW

Corporate author identifies the corporate or collective authorship of an article. Corporate names display exactly as they appear in the journal.

Data Availability [das] NEW

Includes all words and numbers from the data availability statement, when available.

EC/RN Number [rn]

EC/RN numbers are assigned by:

• The Food and Drug Administration (FDA) Substance Registration System for Unique Ingredient Identifiers (UNIIs), e.g., Y92OUS2H9B[rn]
• The Enzyme Commission (EC) to designate a particular enzyme, e.g., "EC 1.1.1.57"[rn]
• The Chemical Abstracts Service (CAS) for Registry Numbers, e.g., 2751-14-6[rn]

The EC/RN number search field includes both the Registry Number and the Related Registry Number (available in the NLM MeSH Browser).

Use of the [rn] tag will restrict the retrieval of search results to the MEDLINE-indexed subset of PMC.

Editor [ed] NEW

Includes the editors of the article.

Electronic Publication Date [epdate]

The date of the electronic publication, when available. Dates or date ranges must be entered using the format YYYY/MM/DD [epdat] (e.g., 2021/04/06[epdat]). The month and day are optional (e.g., 2021[epdat] or 2021/03[epdat]). To enter a date range, insert a colon (:) between the dates (e.g., 2020:2021[epdat] or 2021/01:2021/04[epdat]).

Entry Date [edat]

This date represents the date the full text of the article is publicly available. For most articles, this is the same as PMC Live Date. However, this date is not populated for embargoed articles. This date is used primarily for PMC processing.

Figure/Table Caption [capt]

Includes all words and numbers in the figure and table captions of an article.

Filter [filter]

Technical tags used by PMC to qualify results. See the Search PMC sections for examples of tagged search filters.

First Author Name [fauth] NEW

The first personal author name on an article.

Full Author Name [fau]

The full author names from all articles for which full names are provided to PMC from the publisher. Full author searching can be entered in natural or inverted order, e.g., "julia s wong" or "wong julia s". See Author [au] for more information on author searching.

Grant Number [gr]

The grant number search field includes research grant numbers, contract numbers, or both that designate financial support by agencies of the US PHS (Public Health Service), and other national or international funding sources. The four parts of the grant data are:

1. number, e.g., LM05545
2. PHS 2-character grant abbreviation, e.g., LM
3. institute acronym, e.g., NLM NIH HHS
4. country, e.g., United States

Each individual grant part can be searched using [gr], e.g., NIH[gr]

More information about NIH grant numbers and tips for searching: NIH grant numbers, e.g., 5R01CA101211-03, typically have three main parts:

1. A prefix that indicates the type of grant, e.g., 5R01.
2. An 8-character serial number consisting of a 2-letter NIH institute/center code and a 6-digit number, e.g., CA101211.
3. A suffix that includes additional data such as grant year.

To search for an individual NIH grant number, use the 8-character serial number and the [gr] tag (e.g., ca101211[gr]).

Investigator [ir] NEW

Names of principal investigator(s) or collaborators who contributed to the research. Search names following the author field format, for example: soller b[ir].

Issue [iss]

The number of the journal issue in which the article is published.

Journal Title [ta]

The journal title abbreviation, full journal title, or ISSN number (e.g., J Biol Chem, Journal of Biological Chemistry, 0021-9258). If a journal title contains parentheses or brackets, enter the name without the parentheses or brackets, e.g., Proc (Bayl Univ Med Cent) as "Proc Bayl Univ Med Cent.

The PMC Journal List is available to browse journal titles, holdings and embargo information. Or use the Journals Database look up the full name, abbreviation, and ISSN number of a journal.

Language [la] NEW

The language search field includes the language in which the article was published. You may search using either the language or the first three characters of most languages, e.g., chi[la] retrieves the same results as chinese[la]. The most notable exception is jpn[la] for Japanese.

Last Author Name [lauth] NEW

The last personal author name on an article.

Location ID [lid] NEW

Includes the DOI or publisher ID that serves the role of pagination to locate an online article. For the best results when searching on DOIs, enclose the entire DOI is double quotes, e.g., "10.1093/nar/gkr1184"[lid]. Replaces DOI [doi].

MeSH Major Topic [majr]

A MeSH term that is one of the main topics discussed in the article. See MeSH Terms below.

Use of [majr] will restrict the retrieval of search results to the MEDLINE-indexed subset of PMC.

MeSH Subheadings [sh] or [subHeading]

MeSH Subheadings are used with MeSH terms to help describe more completely a particular aspect of a subject. For example, the drug therapy of asthma is displayed as asthma/drug therapy. See "MeSH/Subheading Combinations" in the More information about MeSH Terms and Topic Search Fields box below.

The MeSH Subheading field allows users to "free float" Subheadings, e.g., "hypertension[mh] AND toxicity[sh]".

MeSH Subheadings automatically include the more specific Subheading terms under the term in a search. To turn off this automatic feature, use the search syntax [sh:noexp], e.g., "therapy[sh:noexp]".

In addition, you can enter the MEDLINE two-letter MeSH Subheading abbreviations rather than spelling out the Subheading (e.g., dh[sh] = diet therapy[sh]). See PubMed Help: MeSH Subheadings for a full list of abbreviations.

Use of [sh] or [subHeading] will restrict the retrieval of search results to the MEDLINE-indexed subset of PMC.

MeSH Terms [mh]

NLM's Medical Subject Headings controlled vocabulary of biomedical terms that is used to describe the subject of each journal article in MEDLINE. MeSH contains more than 23,000 terms and is updated annually to reflect changes in medicine and medical terminology. MeSH terms are arranged hierarchically by subject categories with more specific terms arranged beneath broader terms.

MEDLINE articles are automatically indexed with MeSH terms using a well-refined algorithm. Applying the MeSH vocabulary ensures that articles are uniformly indexed by subject, whatever the author's words. For more information, see Frequently Asked Questions about Indexing for MEDLINE.

Use of [mh] will restrict the retrieval of search results to the MEDLINE-indexed subset of PMC.

Methods [meth]

UPDATE: All terms from the methods field are now indexed and searchable in PMC Beta Search. Previously, only key terms from the methods field were indexed.

Includes words from the methods section of the article.

NLM Unique ID [jid] NEW

The NLM ID is the alpha-numeric identifier for the cited journal that was assigned by the NLM Integrated Library System LocatorPlus, e.g., 0375267[jid].

Pagination [pg]

Enter only the first page number on which the article appears. The result will display the full pagination of the article, but this field is searchable using only the first page number.

PMCID [uid]

Unique identifier for a PMC article. Search without the PMC prefix when using the [UID] field tag, e.g., 10040002[UID].

Users can also search for PMC or NIH manuscript identifiers without a field tag using the appropriate prefix followed by the ID number, e.g., PMC2600426

To retrieve all NIH manuscripts, use the query hasnihmsid.

PMC Live Date [pmcrdat]

The date the article was first available in PMC. For embargoed articles, this is the date that the PMCID and the citation was made available. When the embargo lifts, this date is updated to the date the full text became available.

Dates or date ranges must be entered using the format YYYY/MM/DD, e.g. "2021/04/06[pmcrdat]". The month and day are optional (e.g., "2021[pmcrdat]" or "2021/03[pmcrdat]". To enter a date range, insert a colon (:) between each date (e.g., "2020:2021[pmcrdat]" or "2021/01:2021/04[pmcrdat]").

PubMed ID [pmid]

Unique identifier for the PubMed record for a PMC article.

Print Publication Date [ppdat] NEW

The date of the print publication, when available. Dates or date ranges must be entered using the format YYYY/MM/DD[ppdat] (e.g., 2021/04/06[ppdat]). The month and day are optional (e.g., 2021[ppdat] or 2021/03[ppdat). To enter a date range, insert a colon (:) between the dates (e.g., 2020:2021 [ppdat] or 2021/01:2021/04[ppdat]).

Publication Date [dp]

The date that the article was published. The date on which the article was first made available in final, edited form, whether in print or electronic ( i.e., online) format.

Dates or date ranges must be searched using the format YYYY/MM/DD, e.g. "1998/03/06[dp]". The month and day are optional (e.g., "2021[dp]" or "2021/03[dp]").

To enter a date range, insert a colon (:) between each date (e.g., "2019:2021[dp]" or "2021/01:2021/04[dp]").

Use the following format to search X days, months, or years immediately preceding today's date where X = numeric value:

• "last X days"[dp]
• "last X months"[dp]
• "last X year"[dp]

Reference [refr]

Includes words and numbers in the titles in an article references section.

Reference Author [refa]

Includes authors cited in an article references section.

PMC references do not list the full author name. The format to search for a reference author is the same as article Author searching.

Section Title [sect]

Includes words and numbers in an article section title.

Supplementary Concept [nm]

Includes chemical, protocol or disease terms. Synonyms to the supplementary concepts will automatically map when tagged with [nm]. This field was implemented in mid-1980; however, many chemical names are searchable as MeSH terms before that date.

Use of the [nm] tag will restrict the retrieval of search results to the MEDLINE-indexed subset of PMC.

Title [ti]

Words and numbers included in the title of an article.

Title/Abstract [tiab] NEW

UPDATE: This field replaces the previous Abstract [ab] field and now includes the title data in addition to abstract data.

Includes all words and numbers in the title and abstract of an article. English language abstracts are taken directly from the published article. If an article does not have a published abstract, PMC does not create one.

Volume [vol]

The number of the journal volume in which an article is published.

View Your Search Results

UPDATE: PMC Beta Search includes an updated search results page that is more mobile-friendly and consistent with the rest of the PMC website. These updates include:

Understand the Search Results Page | Sort Your Search Results Display | Filter Your Search Results | View the Search Details

Understand the Search Results Page

As shown in Figure 1, on the beta search results page, you can:

1. Click on the record title to access an article.
2. See snippets and highlighted terms that are displayed below the article citation. Snippets are selected based on relatedness to your query.
3. Sort your results by Live in PMC Date, Relevance, or Publication date. Click the up/down arrow next to the selected sort option to toggle between ascending or descending order. The reverse sort option will not display when relevance sort order is selected.
4. Expand the search details bar to view how PMC translated your query by clicking on the green "Search Details" box.
5. Select "Include" to include embargoed articles in your search results; select "Exclude" to exclude embargoed articles from your search results.
6. See the total number of articles returned by your search is listed below the Search Details.
7. Provide feedback on PMC Beta Search.
8. Filter your search results by Results by Year Timeline, Publication Date, Publication Stage, or Collection.

Filter Your Search Results

UPDATE: The filters interface has been streamlined to include the most-used filters.

Use the filters on the left-hand side of the page (see area #8 in Figure 1) to narrow your search results.

Filter your results by:

Results by Year Timeline

Click and drag the sliders on the Publication Date timeline to change the date range for your search. Click the download button to download a CSV file including the number of records retrieved per year.

To reset the timeline, click “Clear filters” in the green banner at the top of your search results.

Publication Date

To filter your results by Publication Date, click 1 year, 5 years, 10 years, or enter a custom range. Only a year is required.

Publication Stage

• Published journal article - content published in a scholarly journal
• Author manuscript - peer-reviewed author manuscripts accepted for publication in a journal
• Preprint - preprint versions of articles collected through the NIH Preprint Pilot, made public prior to peer review

Collections

• PMC Open Access Subset - The PMC Open Access Subset includes journal articles and preprints that are made available under license terms that allow reuse
• Historical back issues - Historical back issues refers to digitized content from print journals made available in PMC through the Biomedical Journal Digitization Projects

Sort Your Search Results

PMC Beta search results are displayed by default in order of availability in PMC with 10 results per page.

As shown in Figure 2, you can use the "Sort by" drop-down menu at the top of the search results page to change the sort order.

• PMC Live Date (default) – Articles sorted by PMC Live Date are displayed in reverse date added order: last in, first out. PMC Live Date is the date is the date an article became fully available in PMC, not the publication date. Embargoed articles display at the end of the search results. The secondary sort is PMCID.
• Relevance – PMC Beta Search Relevancy sort uses the BM25 algorithm to return articles related to your search term(s).
• Publication Date – Articles sorted by Publication Date are displayed in reverse chronological order: newest to oldest.

When sorting by PMC Live Date or by Publication Date, you can reverse the sort order by clicking the up/down arrow next to the selected sort option to toggle between ascending or descending order. The reverse sort option will not display when Relevance sort order is selected.

View the Search Details

PMC may modify or add additional search terms to your search to optimize retrieval, such as: MeSH terms, British/American spellings, singular/plural word forms, and other synonyms.

You can view the details of how PMC translated your search in the green expandable Search Details bar below the search bar (see area #4 in Figure 1). Only the translation of your most recent search will be available in the Search Details box.

Appendices

Automatic Term Mapping (ATM) | Stopwords | Character Conversions

Automatic Term Mapping (ATM)

Untagged terms that are entered in the search box are matched (in this order) against a Subject translation table (including MeSH - Medical Subject Headings), a Journals translation table, the Author index, and an Investigator (Collaborator) index.

When a match is found for a term or phrase in a translation table the mapping process is complete and does not continue on to the next translation table.

To see how your terms were translated, check the Search Details. If you want to report a translation that does not seem accurate for your search topic, please send the information to the NLM Help Desk.

1. Subject Translation Table

UPDATED: The Subject Translation Table has been augmented to include additional British and American spellings, singular and plural word forms, and other synonyms to provide more consistent and comprehensive search retrieval.

The Subject Translation Table contains:

• British and American spellings
• Pairs: singular and plural word forms, synonyms, and other closely related terms
• Drug brand name to generic name translations
• MeSH terms
• The See-Reference mappings (also known as entry terms) for MeSH terms
• MeSH Subheadings
• Terms derived from the Unified Medical Language System (UMLS) that have equivalent synonyms or lexical variants in English
• Supplementary concept (substance) names and their synonyms

If a match is found in this translation table, the term will be searched as MeSH (that includes the MeSH term and any specific terms indented under that term in the MeSH hierarchy), and in all fields.

For example, if you enter bacterial infections in the search box, PMC will translate this search to: "bacterial infections"[MeSH Terms] OR ("bacterial"[All Fields] AND "infections"[All Fields]) OR "bacterial infections"[All Fields]

If you enter an entry term for a MeSH term, the translation will also include an all fields search for the MeSH term associated with the entry term. For example, a search for sore throat will translate to: "pharyngitis"[MeSH Terms] OR "pharyngitis"[All Fields] OR ("sore"[All Fields] AND "throat"[All Fields]) OR "sore throat"[All Fields]

Substance name mappings do not include a mapping for individual terms in a phrase, e.g., IL-22 will not include IL[All Fields] AND 22[All Fields].

MeSH term mappings that include a standalone number or single character do not include a mapping for individual terms in a phrase, e.g., Protein C will not include Protein[All Fields] or C[All Fields].

2. Journals Translation Table

The Journals translation table contains the:

• full journal title
• title abbreviation
• ISSN and eISSN number

These will automatically map to the journal abbreviation that is used to search journals in PMC and in all fields. For example, a search for tissue barriers will translate to: "tissue barriers"[Journal] OR ("tissue"[All Fields] AND "barriers"[All Fields]) OR "tissue barriers"[All Fields]

3. Author Index

If the term is not found in the above tables, and is not a single term, PMC checks the author index for a match.

More information about author searching:

• PMC automatically truncates a search for an author's name to account for varying initials, e.g., colins c retrieves colins cc, colins cl, colins cm, colins cp, as well as colins c.
• When combining multiple authors, to avoid a match with full author names, include initials or use the [au] search tag, e.g., ryan[au] james[au]. Author names comprised of only stopwords, e.g., as a, are not searched as authors if they are part of phrase, chemical burn as a danger, unless the search only includes the author name, e.g., as a.
• You can search for a name in natural or inverted order, e.g., julia s wong or wong julia s.
• A comma following the last name for searching is optional. For some names, however, it is necessary to distinguish which name is the last name by using the comma following the last name, e.g., james, ryan.
• Omit periods after initials and put all suffixes at the end, e.g., vollmer charles jr
• Initials and suffixes are not required, if you include a middle initial or suffix, you will only retrieve citations for articles that were published using the middle initial or suffix.
• To distinguish author initials that may match a full author name use the [fau] search tag, e.g., peterson do[fau].

4. Investigator (Collaborator) Index UDPATED

If the term is not found in the above tables, except for Author, and is not a single term, the investigator index is consulted for a match. The investigator (collaborator) index includes full names, if available. Enter a full investigator name in natural or inverted order, e.g., harry janes or janes harry.

5. If No Match is Found?

PMC breaks apart the phrase and repeats the above automatic term mapping process until a match is found. PMC ignores stopwords in searches.

If there is no match, the individual terms will be combined (ANDed) together and searched in all fields.

When a search includes terms that were tagged with a search field during the automatic term mapping process and retrieves zero results, the system triggers a subsequent search using "Schema: all". "Schema: all" modifies the search by removing the automatically added search field tags and then searches each term in all fields.

Stopwords

PMC searches use the same stopwords that are used in PubMed. Stopwords are common, but uninformative words such as "a" or "about" that are eliminated from searches. See PubMed Stopwords for the list.

Please note, stopwords in phrase searches and proximity searches are not ignored.

Character Conversions

Special characters (e.g., pound sign, dollar sign) included in a PMC search may hold specific search syntax meaning, whereas others are converted to spaces. (See PubMed Character Conversions for more information.) However, in the abstracts and full-text of PMC articles, all characters are represented as accurately as possible

Provide Feedback and Request Search Help

Please reach out to the NLM Help Desk with any questions. To provide feedback on PMC Beta Search, please visit PMC Beta Search Feedback Survey.

For information about PMC features that are not related to the Beta Search, please see the regular PMC User Guide.