I got some journals and articles, but they don't have the DOI. How can I get the DOI?
Answer
DOI stands for Digital Object Identifier. It is a unique way to identify or locate a digital object, such as an online article. Not all articles are assigned DOI numbers; so there may not be one to find.
The easiest way to find out if an article does have a DOI number is to paste all or some of the reference into the search box of CrossRef http://search.crossref.org/ . It will provide you with the DOI for an article if it exists.