GeoRef -- Established by the American Geosciences Institute (AGI) in 1966, provides access to the most comprehensive geoscience literature of the world. GeoRef contains millions of references to geoscience maps, serial, and non-serial literature. The database includes references to all publications of the U.S. Geological Survey. Master's theses and doctoral dissertations from US and Canadian universities are also covered. Coverage for North American resources starts in 1669, whereas worldwide coverage starts in 1933.
National Centers for Environmental Information (NCEI), formerly National Geophysical Data Center (NGDC) -- "NCEI is responsible for hosting and providing access to one of the most significant archives on Earth, with comprehensive oceanic, atmospheric, and geophysical data. From the depths of the ocean to the surface of the sun and from million-year-old sediment records to near real-time satellite images, NCEI is the Nation’s leading authority for environmental information."
Web of Science -- Provides access to over 8700 journals from various disciplines from 1900-.
OnePetro -- provides access to over 160,000 documents from a number of petroleum related organizations including the Society of Petroleum Engineers (SPE), the Society of Petrophysicists and Well Log Analysts (SPWLA) and the American Petroleum Institute (API).
American Association of Petroleum Geologists (AAPG) Datapages -- The AAPG/Datapages online archive database includes over 60,000 articles in the field of petroleum, geology and geophysics. Collections include the AAPG Bulletin (1917 to present) and AAPG special publications, Journal of Petroleum Geology (1978-2004), Journal of Sedimentary Research (1931 to present) and publications of other geoscience societies.
Geoscience World -- Access to 46 full-text, scholarly journals from 30 geoscience publishers. It is fully linked to GeoRef.