Since 2000 there has been an effort to assign everything that exists in the digital world, e.g. 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 and AMA citation styles, use the DOI in citations whenever one is listed. See this FAQ for more information about DOIs, including what to do if you can't find the DOI.
Whether you are an experienced academic writer or this is your first paper, Webster University's Writing Center offers writing support for students. Find help with all kinds of research projects, including "reports; résumés and cover letters; admission essays and personal statements; summaries, critical analyses, and literature reviews; research and term papers; theses and dissertations; and more." Writing Center coaches are available at all stages of the writing process from brainstorming to draft revision and everything in-between.
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When you cite a full-text article retrieved from a Webster University Library database, some citation styles require you to cite the database name and/or a URL. Here’s how the University's most-used citation styles address this issue:
Publication manual of the American Psychological Association: the official guide to APA style (7th ed.) by 
The Chicago Manual of Style, 17th Edition by 
MLA Handbook (9th ed.) by 
Cite Right, Second Edition by 
A manual for writers of research papers, theses, and dissertations : Chicago Style for students and researchers by When in doubt, ask your instructor which citation style to use for your paper or project. Some of the most widely used citation styles include:
