Use AND to search for specific terms, usually retrieves fewer results.
Use OR to search for synonyms or variations of terms, usually retrieves more search results.
beaver AND duck = platypus
source: http://i.imgur.com/8BFAq.png
Comprehensive index to international medical literature with links to full text.
Index to full text journal articles in the medical disciplines.
Multi-disciplinary source for scholarly, popular, professional, and news publications. This is a good place to start many searches or to gather material from various disciplines at once.