Extensive online encyclopedia organized alphabetically and by topic.
DiracDelta Science and Engineering Encyclopedia
Dirac Delta is a small consultancy formed from a group of people with very different skills in engineering, physics and software engineering. The encyclopedia was created to store and share information needed on a daily basis. After a number of years of using the database (the CD version that is) the group decided to share the information to others.
Encyclopaedia Britannica Online
An online version of the widely-used Encyclopedia Britannica. It contains more than 120,000 articles, thousands of images and videos, online dictionary and many more.
Encyclopedia.com gives free access to nearly 200,000 reference entries from sources you can cite. Plus, more than 50,000 topic summaries feature related pictures, videos, topic summaries, and newspaper and magazine articles from around the world. Encyclopedia.com also provides innovative tools that allow you to rate and sort the reference content you find to be the most useful.