Google Scholar

Fnd scholarly literature (peer-reviewed papers, theses, preprints, abstracts, technical reports) from a wide variety of academic publishers, professional societies, preprint repositories and universities and across the web. As with Google Web Search, Google Scholar presents search results in order of relevance to your query, so the most useful references should appear at the top of the page. This relevance ranking takes into account the full text of each article as well as the article's author, the publication in which the article appeared and how often it has been cited in scholarly literature. Google Scholar also automatically analyzes and extracts citations and presents them as separate results, even if the documents they refer to are not online, so search results may include citations of older works and seminal articles that appear only in books or other offline publications.

http://scholar.google.com