Of course, many bibliographies contain citations of articles too. Bibliographies can save you work and time because another researcher has pulled together the information on your topic. An index is, generally, a guide to the contents of the work, as in the indexes at the back of books. Academic Index is an index of journals of interest to academics. Essentially, the indexers must catalog and index every article in every journal.
Indexes usually cover a field or topic.
There is no such thing as an index of all the periodical literature in the world. An index usually allows you to search by personal name of author, by title of article, and by subject. After you find your subject area, the index gives you citations of articles on that subject. With the citation you can get the article. New College has also subscribed to PsychInfo in its web-style incarnation.