Scholarly article databases collect and index literature published in academic periodicals. 

Database diversity

Some databases are interdisiciplinary and collect literature from periodicals across a range of the social sciences, the humanities, or both.  Interdisciplinary databases offer greater sensitivity but less precision (i.e., you will be casting a wide net and catching more fish, though you may be after only largemouth bass.  Few fish will escape your net, but it may take significant time to sift through your haul to find the bass).

Other databases assume narrower scopes; these databases are subject-specific and collect literature from only one or two disciplines or an isolated area of interdisciplinary interest.  Subject-specific databases offer less sensitivity but greater precision (i.e., your net will be smaller and you will catch less fish, but of those that you do catch, a large proportion will be largemouth bass.  It is likely that the narrower net allows some largemouth bass to escape).

Periodical diversity

There is variation not only among article databases, but among the periodicals from which they draw their content. 

These periodicals may be published annually, biannually, quarterly, etc. -- journal names often indicate publication frequency (e.g., The Quarterly Journal of Economics, Annual Review of Political Science, Philosophical Quarterly, etc.).  

The periodicals may publish literature across a wide range of topics in a single field (generalist journals) or they may be focused on a subfield or a couple subfields within a discipline (specialist or subfield journals).  Still other journals assume an interdisciplinary focus (interdisciplinary journals) and invite submissions from scholars who work in various fields.

See below for a selection of interdisciplinary and subject-specific article databases.