The Digital Object Identifier (DOI) is a more stable identifier than the web address (URL). You may have noticied them in journals before, but expect to see them in citations now that the American Psychological Association (APA) and the American Medical Association (AMA) recommend their use in their style guides.
Here’s a citation based on the APA’s new recommendations. The DOI is the final element (retrieval date is no longer required by APA when a document is unlikely to change such as a journal article):
Neely, J. G., Paniello, R. C., Fraley, P. L., Salcman, J. T., Karni, R. J., Nussenbaum, B., et al. (2007). Practical guide when searching for answers: How to find the right articles. Otolaryngology Head and Neck Surgery, 137, 5-9. 10.1016/j.otohns.2007.04.018.
And the same citation in AMA style (accessed date, required by AMA when using the URL, is not required when using the DOI):
Neely JG, Paniello RC, Fraley PL, et al. Practical guide when searching for answers: How to find the right articles. Otolaryngol Head Neck Surg. 2007;137:5-9. doi:10.1016/j.otohns.2007.04.018.
To find the content from citations like these go to http://dx.doi.org and enter the DOI, in this case 10.1016/j.otohns.2007.04.018. (If you’re off campus use the orange “login to JEFFLINE” button to first authenticate your browser session with Jefferson’s proxy server to take advantage of Scott Library’s extensive collection of journal subscriptions.)
The new 10th edition of the AMA Manual of Style is available in the Reference area.
WZ 345 B244m 2007 Ref
AMA manual of style : a guide for authors and editors