Visit PubMed Central: http://www.ncbi.nlm.nih.gov/pmc/
From the PubMed Central (PMC) Overview:
- PMC is a free archive of biomedical and life sciences journal literature at the National Library of Medicine (NLM), one of the institutes that make up the U.S. National Institutes of Health (NIH).
- It is the official repository for papers submitted in accordance with the NIH Public Access Policy.
- As an archive, PMC is designed to provide permanent access to all of its content.
- All PMC literature is free, but are still under copyright protection and some may be delayed by an embargo of up to 12 months, as requested by some publishers.
- While some journals in PMC are fully 'open access', there are key differences between Public Access and Open Access.