Established by the American Geosciences Institute, GeoRef provides access to the most comprehensive geoscience literature of the world. It includes references to all publications of the U.S. Geological Survey. Master's theses and doctoral dissertations from US and Canadian universities are included. Coverage for North American resources starts in 1669, and worldwide coverage in 1933.
Web of Science is the world's largest, high-quality interdisciplinary database back to 1965. All subject areas are covered, but the sciences are covered very well. WoS is easy to use, but it has many advanced features that make it an excellent tool for advanced researchers. See the Web of Science page for searching instructions.
You can search all these databases, or select only one.
Web of Science (Arts & Humanities Index, Science Citation Index, Social Sciences Index)
BIOSIS (the leading biological sciences database)
Current Contents (current awareness database covering more than 7,000 journals)