Semantic scholar uses groundbreaking ai and engineering to understand the semantics of scientific literature to help scholars discover relevant research.
Library genesis is a scientific community targeting collection of books on natural science disciplines and engineering.
Sciencedirect is the world's leading source for scientific, technical, and medical research. explore journals, books and articles.
Apollo scientific | supplying research intermediates for over 20 years
Google scholar
Swoogle -- the semantic web search engine and metadata service provider
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800+ texts of classic literature, drama, and poetry together with detailed literature study guides. large reference book and non-fiction section