Purdue OWL is a great resource for APA, Chicago, and MLA styles.
Other styles common in 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
The Manual of Scientific Style by 
Cite Right by Having trouble deciphering a journal title that's abbreviated? Try these resources:
