PubMed
And finally, the king of biological science article databases: PubMed. PubMed was developed by the National Center for Biotechnology Information at the National Library of Medicine at the U.S. National Institues of Health (NIH). PubMed also provides other valuable resources for researchers including nucleotide and protein sequences, protein structures, genomes, taxonomy, OMIM (a catalog of human genes and genetic disorders) and more. Usually the abstract of each article is available. Occasionally one can find free article as well. Enjoy exploring the wonderful free tool that is PubMed.
http://www.ncbi.nlm.nih.gov/pubmed/
Here is PubMed’s archive of free digital biomedical journals