This little video from the American Psychological Association, which is really only about two minutes long, will clearly explain what a DOI is and where you can find it in three different places. When it starts the part about finding it in PsycInfo you can skip to the 2:38 mark where it demonstrates the ProQuest platform that we use.
Almost all journal articles now have DOIs, but that wasn't always the case. Now it is common practice for the DOI to be clearly printed on the first page of the journal article. But what if it's not? The fact that a DOI does not appear on the article itself does not necessarily mean that it doesn't have one. It may be that the publisher has gone back and retroactively assigned DOIs to all of their older issues. What is the best way to start your search? The answer really is "whatever works best for you!" But here are the best possibilities for you to check:
There are still some journals that do not assign DOIs. For example, there is a highly cited journal called "Alcohol Research: Current Reviews" that does not use them. And there are also publishers that have not gone back and retroactively assigned DOIs to their older issues. If you are unsure whether or not you may have missed something, remember that you can always use our Ask a Librarian chat service or contact me.