Overviews and allows text-based searches of over 25 of the bibliographic databases and biomolecular data resources held at NCBI (the National Center for Biotechnology Information), including PubMed, OMIM, Entrez Gene, and Entrez Taxonomy; this site performs a simultaneous search of the various databases and reports back the number of hits in each -- you can then select an individual database to view detailed search results.

http://www.ncbi.nlm.nih.gov/gquery/gquery.fcgi/?otool=umnbmlib