Cross-database search engine from the National Center for Biotechnology Information at the NIH. Searches PubMed as well as databases for proteins, nucleotides, genes, SNPs and provides many tools for gene and molecular visualization.
Web of Science-Web of Knowlege is a suite of citation databases including Science Citation Index Expanded, Social Sciences Citation Index, and Arts & Humanities Citation Index.
SciFinder covers literature in chemistry, biochemistry, chemical engineering, materials science and more. Search by chemical substance, reactions, research topic, etc.