Article indexes are a type of bibliography. The purpose of bibliography is to list documents, usually published documents like books and articles. This type of bibliography is more accurately called "enumerative bibliography". An enumerative bibliography will attempt to be as comprehensive as possible, within whatever parameters established by the bibliographer.
Think of a bibliography as a guide to the source base for a specific field of inquiry. A high quality bibliography will help you understand what kinds of sources are available, but also what kinds of sources are not available (either because they were never preserved, or because they were never created in the first place).
For more information on the role of bibliography in historical research, see our guide to Bibliography and Historical Research.
Bibliographies can be as short as a few pages, or as long as several hundred volumes. Bibliographies can also be published as databases, and these are the bibliographies that are often called "article indexes" or "indexing and abstracting services" because they index the contents of journals:
Because article indexes are a form of bibliography, and not a catalog, you can use them to discover articles from journals the Library doesn't even own. An article index, therefore, enables you to cast the widest possible net within whatever field the article index covers. If you discover an article from a journal that the Library does not own, you can request a copy of the article through interlibrary loan:
There are several major collections of full-text electronic journals. In these databases you can browse individual issues of journals, or you can do a search across the entire database. Most of the journals in the following collections are scholarly journals: