Since 2000 there has been an effort to assign everything that exists in the digital world such as online articles with a unique number called a Digital Object Identifier or a DOI. The DOI is unique, permanent, and persistent. It remains the same despite changes in URL's or permanent removal from the Internet.
In APA style, use the DOI in citations whenever possible. If no DOI is present, try the free DOI lookup from CrossRef. For more information, watch the short video, Citing an article with a DOI and without a DOI (University of Maryland University College). If you have questions, Webster students, faculty and staff should contact the Webster U. Library Reference Department (info in the Help box).
Visit http://www.webster.edu/writingcenter for more help with citations and writing.
These websites will assist you in building citations for your bibliographies. Always check your citations against a style manual to make sure they are correct.
Publication manual of the American Psychological Association by 
AMA manual of style : a guide for authors and editors by 
MLA Handbook for Writers of Research Papers by 
The Chicago manual of style by 
A manual for writers of research papers, theses, and dissertations : Chicago style for students and researchers by Some citation guides ask you to provide a URL for certain resources . The URL for each of the library's databases can be found on our Alphabetical list of databases page.
Contact a Librarian
Get help finding sources, narrowing or expanding your topic, and more!
Call us at (314) 968-6950
Toll-free: (800) 985-4279