APA style prefers a reference to the print form of a source, even if it is available on the Net. If you have read only the electronic form of an article’s print version, add “Electronic version” in brackets after the title of the article. If an on-line article has been changed from the print version or has additional information, follow the same general format for the author, date, and title elements of print sources, but follow it with a “retrieved” statement, citing the date of retrieval and the electronic address.
NOTE : Titles and subtitles of articles are not capitalized (except for the first word) or enclosed in quotation marks. (The names of periodicals are capitalized and italicized.)