APA now requires a DOI (Digital Object Identifier) be added to citations of articles from electronic databases.
The DOI can often be found in a database record for an article or on the actual article text. On the text of an article the DOI is typically on either the first page or last page.
Please note that not all articles are assigned a DOI.
APA style was established by the American Psychological Association.
APA is normally used in the sciences, including sociology and psychology.