PubMed is a database of citations and abstracts for over 33 MILLION ARTICLES from over 5,000 journals. One of its features is a FREE FULL TEXT FILTER that allows you to locate articles that are available for free from several thousand journal web sites and also connects you to most of the articles in PubMed Central.
PubMed Central is an electronic archive of 3.6 MILLION FREE FULL TEXT JOURNAL ARTICLES, most of which have a corresponding entry in PubMed.