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Articles that are "open access" in PMC are made available under a Creative Commons or similar license that allows more liberal redistribution and reuse than a traditional copyrighted work. Many articles in PMC are protected by U.S. and/or foreign copyright laws, even though PMC provides free access to it. Some journals use the label "open access" for an article that is available free at time of publication, but is still subject to traditional copyright restrictions.

Open access articles are included in the PMC Open Access Subset and can be found in PMC by searching open access[filter]. This subset also includes a number of U.S. government publications, e.g.,

• Addiction Science & Clinical Practice (vol. 1 through vol. 6)
• Alcohol Research: Current Reviews
• Emerging Infectious Diseases
• Environmental Health Perspectives
• Journal of Research of NIST
• Morbidity and Mortality Weekly Report
• Preventing Chronic Disease

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Some of the digitized articles are distributed under a Creative Commons license and note that in the article record. Those that are covered by a Creative Commons license are included in the PMC Open Access Subset.

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