Citebase Archive - was an experimental, semi-autonomous citation index for free, online research literature

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CiteSeerX - access to the Scientific Research Digital Library

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Collection of Computer Science Bibliographies - more than 7 millions of references (mostly to journal articles, conference papers and technical reports)

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Current Index to Statistics (AMS) - more than 160 preferred journals, plus selected articles from 1,200 more and 11,000 statistics books to draw from

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Inspec - contains over 18 million records of research literature

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MathGuide - find online information sources in mathematics. The catalog offers not just a search, but a database of high quality Internet resources

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Math WebSearch - Several different search engines which allow users to search with numbers and formulas instead of text

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zbMATH Online Database - millions of entries from thousands of serials and journals dating back as far as 1826

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