Zero to 2 million in 10 years… 
PubMed Central (PMC) is the free digital archive of biomedical and life sciences journal literature from the U.S. National Institutes of Health (NIH) . With PubMed Central, the National Library of Medicine has taken the lead in preserving and maintaining access to the electronic literature: NLM believes that giving all users free access to the material in PubMed Central is the best way to ensure the durability and utility of the archive as technology changes over time.
PubMed Central is now 10 years old. In February 2000, PMC contained only 2 journals: Proceedings of the National Academy of Sciences of the United States of America and Molecular Biology of the Cell. Currently, there are more than 600 full deposit journals as well as collections of NIH-funded articles, author manuscripts, books and other documents in the PMC archive. On a typical weekday, about 420,000 users are accessing 740,000 of PMC’s over 2 million articles.
ยป Read more in the NLM Technical Bulletin.