HEATKEYS

Comprehensive encyclopedia of mathematics with 13,000 detailed entries. Continually updated, extensively illustrated, and with interactive examples.

Princeton University is a vibrant community of scholarship and learning that stands in the nation's service and in the service of all nations.

Science, astronomy, and space flight news, science and renewable energy encyclopedias. Maintained by science writer David Darling, Ph.D.

Dictionary.com - the largest and most trusted free online dictionary. Instantly look up accurate and extensive definitions and word meanings, and hear audio pronunciations.

wiseGEEK: clear answers for common questions

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The Khan Academy is a not-for-profit 501(c)(3) with the mission of providing a world-class education to anyone, anywhere. Despite being the work of one man, Salman Khan, this 1600+ video library is the most-used educational video resource as measure...

XahLee.org ? a intellectual excursion in math, programing, visual arts, and humanities. Math reference works, programing tutorials, photo galleries, social commentaries, classical literature collection. 5360 pages total.

Infoplease.com, a free, authoritative, and respected reference for Internet users, provides a comprehensive encyclopedia, almanac, atlas, dictionary, and thesaurus. Infoplease.com contains facts on all subjects including sports, entertainment, techno...