A subset of the total collection of books and documents in the NLM Literature Archive (NLM LitArch), accessible through the Bookshelf website, are available through the NLM LitArch Open Access subset. Contents in the NLM LitArch Open Access subset generally include works which are in the public domain, works which are available under a Creative Commons or similar license, and works whose authors or publishers have explicitly agreed to the terms of the NLM LitArch Open Access subset. Except for public domain works, works in the NLM LitArch Open Access subset are still protected by copyright, but are made available under a Creative Commons or similar license that generally allows more liberal redistribution and reuse than a traditional copyrighted work. The license terms are not the same for each work. Read the license text which is available with each downloadable file to determine terms of use.

The OLDMEDLINE subset in PubMed® represents journal article citations from two print indexes: Cumulated Index Medicus (CIM) and the Current List of Medical Literature (CLML). Created by the National Library of Medicine® (NLM®), there are approximately 2,011,000 article citations from international biomedical journals that cover the fields of medicine, preclinical sciences and allied health sciences from 1946 through 1965. OLDMEDLINE records, which are included in the MEDLINE® database, can be searched via PubMed.

The OLDMEDLINE subset in PubMed contains citations from the 1960 through 1965 Cumulated Index Medicus (CIM) print indexes and the 1946 through 1959 Current List of Medical Literature (CLML) print indexes. The OLDMEDLINE subset does not include citations from the Quarterly Cumulative Index Medicus (QCIM) print indexes. A hand search of the QCIM print indexes is necessary to ensure comprehensive review of medical periodical literature of the world from 1946 through 1956.

PubMed comprises more than 26 million citations for biomedical literature from MEDLINE, life science journals, and online books. Citations may include links to full-text content from PubMed Central and publisher web sites.

Not all articles in PMC are available for text mining and other reuse, many have copyright protection, however articles in the PMC Open Access Subset are made available for download under a Creative Commons or similar license that generally allows more liberal redistribution and reuse than a traditional copyrighted work.

PubMed Central (PMC) is a free, digital archive of full text biomedical and life sciences journal literature.

Yearly citation totals from each year of the MEDLINE/PubMed Baseline referencing citations back to year 1781. These totals may increase over time for a particular year as new citations are added. For example, 25 citations were listed for the year 1800 in the 2018 MEDLINE/PubMed Baseline, while the 2019 Baseline includes 387 citations for that year.

Information about abstracts with distinct, labeled sections (e.g., Introduction, Methods, Results, discussion) that appear in MEDLINE.