There are, however, several lists of online periodicals. Because of the constantly changing nature of electronic resources, it is impossible for any index to be complete and up to date, but several resources are useful starting points. The University of Pennsylvania Library's index of electronic journals by category is one such source. MetaGrid provides links to international newspaper and magazine sites. Some newspapers such as The New York Times and The Times of London are free but require a brief registration.
Online publications vary widely in the availability of their contents free on the Web.
Some provide all the contents for issues going back three or four years. Others offer only the contents of the latest issues. Some give only partial contents. Very few publications, such as Studies in Bibliography , provide free access to all issues. Most publishers of academic journals charge fees.