Searches across 39 molecular and literature database maintained by NCBI (the National Center for Biotechnology Information). Results are listed by database so a single search can lead to discover of different types of data. Good for a broad overview.
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Online Index-Catalogue of the Library of the Surgeon-General's Office, an index of medical and scientific publications from 1880-1961; eTK, covering medieval Latin; eVK2, covering medieval English texts; and other selected historical resources.
Keesing's World News Archive contains about 95,000 unbiased, full-text reports of the most historically significant political, social, and economic events of the world since 1931.