Style guides from the Temple University Writing Center:
Purdue OWL is another great resource for APA, Chicago, and MLA styles.
Other styles common for the sciences and, specifially, physics are CSE and AIP:
Author, A. A., & Author, B. B. (Date of publication). Title of article.Title of Journal, volume number, page range. doi:0000000/000000000000 [or http://dx.doi.org/10.0000/0000]
If the article doesn't have a DOI (digital object identifier), then it will look like this:
Author, A. A., & Author, B. B. (Date of publication). Title of article.Title of Journal, volume number. Retrieved from http://www.journalhomepage.com/full/url/
Author, A. A., & Author, B. B. (Date of publication). Title of document. Retrieved from http://Web address
More examples of how to cite electronic sources in APA
RefWorks is a web-based personal database for storing, organizing, formatting, and sharing your citations.
Even though RefWorks and other similar programs will format your citations for you, they're not perfect and you should always double check that everything looks right.