AccessScience is an authoritative and dynamic online resource that contains incisively written, high-quality reference material covering all major scientific disciplines. An award-winning gateway to scientific knowledge, it offers links to primary research material, videos and exclusive animations, plus specially designed curriculum maps for teachers.

The Birds of the World is a comprehensive reference collaboration by the American Ornithologists' Union, the Cornell Lab of Ornithology, and the Academy of Natural Science. This reference covers the life histories of 10,824 bird species and including illustrations, audio clips, and videos.

NSDL is the National Science Foundation's online library of resources and collections for science, technology, engineering, and mathematics education and research.

An evidence-based, peer reviewed database of clinical information, covering more than 7,700 topics in 15 medical specialties and includes more than 80,000 pages of text, graphics, links to Medline abstracts, more than 260,000 references, and a drug database.

eLS features over 4,900 peer-reviewed and citable articles in the life sciences. eLS is updated by approximately 400 articles per year, with new articles publishing on a monthly basis.

Provides access to over 1.5 million full text articles and books, including encyclopedias and other references in the sciences and other disciplines.

Information on evolution, habitat, behavior, and geographic distribution for more than 4,000 species of birds, fish, invertebrates, mammals, and reptiles. Includes more than 11,000 images, illustrations, and maps.

OneZoom Tree of Life is committed to heightening awareness about the diversity of life on earth, its evolutionary history and the threats of extinction. OneZoom allows you to explore the tree of life in a completely new way: it's like a map, everything is on one page, all you have to do is zoom in and out. OneZoom also provides free, open source, data visualization tools for science and education, currently focusing on the tree of life.

This new eighth edition has been fully revised and updated to reflect recent progress in the fields of biology, biophysics, and biochemistry, with particular expansion to the areas of ecology, cell biology, and plant and animal development. Over 150 new entries include de-extinction, ecological footprint, rewilding, and Zika virus.

This encyclopedia includes 370 entries by leading experts and researchers in evolutionary biology and related fields.

Scitable is a free science library created by Nature Publishing Group. Scitable focuses on genetics and cell biology and also offers resources for the budding scientist, with advice about effective science communication and career paths.

Compilation of 22,000 terms and definitions in the life sciences representing 26 distinct fields, such as Anatomy, Biophysics, Botany, Ecology, Genetics, Immunology, Systematics, and Zoology.

The Encyclopedia of Ecology provides includes over 500 entries covering all aspects of applied and theoretical ecology.

The Encyclopedia of Evolution includes over 200 articles highlighting the various aspects of evolutionary biology, including biographies of significant evolutionary biologists.

Henderson's Dictionary of Biology includes over 22,000 entries in all areas of the biological sciences.

This four volume set of 379 articles provides in-depth information for the various plant science disciplines.

The Oxford Dictionary of Plant Sciences includes over 4,000 entries in the fields of botany, plant sciences, environmental science, and horticulture.