I found the following webpage that lists the differences between the PubMed and MEDLINE databases:
http://www.nlm.nih.gov/pubs/factsheets/dif_med_pub.html .
MEDLINE is a component of PubMed and both deal with the life sciences. PubMed is free and while it may be easier to use, MEDLINE will be more specialized and will link to more full-text. Both databases are still very useful to know. The USF Libraries gives you access to MEDLINE via different platforms; the OVID platform contains a subject headings map (a list of predetermined descriptors) – the MeSH – to help you formulate your queries. It is also available in PubMed. A common strategy is to use PubMed to draft a search query you will then use in MEDLINE.
After reading http://catherin.blog.usf.edu/2006/06/27/the-differences-between-pubmed-and-medline, I thought this might be a useful resource for your site:
http://www.biomedsearch.com
The site is free, and perhaps the most comprehensive biomedical site on the web. It has all PubMed and MedLine documents, plus mililons more including full-text journal articles and a large database of theses and dissertations.
And, you don’t have to register but if you do you can use portfolios to save documents, share documents (and comment on them) between users, and set up automatic alerts.