Google™ Scholar Beta
Coverage varies
Google's web search tool focusing on scholarly literature, including peer-reviewed papers, theses, books, preprints, abstracts and technical reports from all broad areas of research. Includes both open access and commercial content with links to available Library full text and FindIt! linking service. Still in Beta test mode. [
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SCIRUS
for scientific information only
Scirus is a comprehensive science-specific search engine on the Internet.