PubMed Central
PubMed Central (PMC) is NLM's digital archive of medical and life sciences journal articles and an extension of NLM's permanent print collection. It was launched in early 2000 with a single issue each of two journals, and has grown steadily since. As of June 2013, it contained over 2.7 million articles; more than 1200 journals were depositing all their published content in PMC, and a few thousand other journals were depositing selected articles. (See http:/www.ncbi.nlm.nih.gov/pmc/ for current counts and titles. Almost all the articles in PMC have a corresponding citation in PubMed. The exceptions are a few types of material, such as book reviews, that PubMed does not cover.