Is there anyplace on the Internet where I can find a listing of topics covered in magazines, similar to the print “Reader’s Guide to Periodic Literature?”
Check your local public library’s web page. It probably has a version of Reader’s Guide (or something better with full text) available to you online for free. You may have to get a library card before you start.
The major online indexes are provided either by IAC (Information Access) aka InfoTrac or UMI which was a product called ProQuest.
“Reader’s Guide” is produced by the Wilson company, whose online products aren’t that great.