The arXiv is an archive for electronic preprints of scientific papers in the fields of mathematics, physics, astronomy, computer science, quantitative biology, statistics, and quantitative finance which can be accessed online.
MathSciNet is a comprehensive database covering the world's mathematical literature since 1940 and provides access to data from Mathematical Reviews (updated monthly) and Current Mathematical Publications (updated daily). To search this database by topic, click "Free Tools." This will let you enter your keywords, and then it will map them to the MSC code actually used by the database.
1868-1930. Excellent bibliography for older mathematics research, the European Mathematical Society's online version of Jahrbuch uber die Fortschritte der Mathematik covers also has links to scanned images of classic papers.
The world’s leading citation databases provide authoritative, multidisciplinary coverage from more than 12,000 high impact research journals worldwide, including Open Access journals.
Cover-to-cover indexing of content is provided by Science Citation Index Expanded (1900 - present), Social Sciences Citation Index Expanded (1900 - present), Conference Proceedings Citation Index (1990-present),Arts & Humanities Citation Index (1975 - present), Book Citation Index (2005 - present), Current Chemical Reactions (1985 - present), and Index Chemicus (1993 - present).
Compendex is the most comprehensive bibliographic database of scientific and technical engineering research available, covering all engineering disciplines. It includes millions of bibliographic citations and abstracts from thousands of engineering journals and conference proceedings.