You need to try and find a doi for all articles retrieved electronically (whether through a database, the library’s website, google, google scholar, etc.)
a. APA requires you to list a doi if one is available
b. Sometimes doi’s may appear in the citation sent from a database but often they are not included.
c. Check the first page of an article carefully to see if a doi is available. Doi’s often appear at the top of the page but may also appear in other places such as the side or bottom of the page or within the abstract or included in the detail record.
d. IIf there is no doi listed, you can check CrossRef, http://search.crossref.org/ to see if one is available there. Search by entering the article title in the search box.