There are other citation styles and the library has style guides both online and in print.
The new (6th) edition of APA asks for the DOI (Digital Object Identifier), if available, for citations for electronic journal articles. Note that a DOI does not always exist for an online article. If the article has one, it can sometimes be found in the database entry (but not always) or is often included with the Journal Name at either the top or bottom of the first page of the article itself.
Alternatively, if you have the citation information, you can look up the DOI number in CrossRef:
1. Go to CrossRef's Free DOI Lookup
2. Copy and paste your citation information and CrossRef will supply the DOI number, if available.