Many scholarly publishers now assign an alpha-numeric code called a DOI (Digital Object Identifier) to journal articles and other documents. APA guidelines for citing electronic resources recommend including this identifier in the citation whenever possible. The DOI can generally be found on the first page of scholarly journal articles as well as in the database record for that article.
If the DOI does not appear on the article or in the database record, it may be found by entering citation information into the free DOI Lookup on CrossRef.org.
To determine DOIs for an entire reference list, copy & paste the entire list here: Cross/Ref Simple Text Query.
Materials originally published prior to the Internet, but now available online, may not have a DOI. Use this DOI Flow Chart created by APA to help you decide what information you need to include if you cannot find a DOI.