Fig.2.
Percentage of publications listed in the United States National Library of Medicine (https://www.ncbi.nlm.nih.gov/pubmed/, 12-3-2018) for years 1900 through 2018 (a), 1960 through 2018 (b) and 2000 through 2018 (c), containing the keyword “hydroxyapatite” normalized to the total annual number of publications retrievable using the keyword “medicine”.