Eric Weisstein's World of Science contains budding encyclopedias of astronomy, scientific biography, chemistry, and physics. This resource has been assembled over more than a decade by internet encyclopedist Eric W. Weisstein with assistance from the internet community.
Eric Weisstein's World of Science is written and maintained by the author as a public service for scientific knowledge and education. Although it is often difficult to find explanations for technical subjects that are both clear and accessible, this web site bridges the gap by placing an interlinked framework of mathematical exposition and illustrative examples at the fingertips of every internet user.
Hosted by wolfram, of "new science" fame.
For example - fundamental constants. I wonder if Britannica points to this site.