What is the readers guide to periodic literature?

It seems you're asking about a resource called "Readers Guide to Periodic Literature." However, there is no known publication or database with that exact name. It's possible you're thinking of a similar resource, or perhaps there's a slight misunderstanding.

To help me understand what you're looking for, could you please provide more context? For example:

* What kind of literature are you interested in? (e.g., scientific journals, literary magazines, historical periodicals)

* What is your purpose for using this resource? (e.g., finding specific articles, researching a topic, keeping up with current events)

* Are there any other keywords or phrases you remember associated with this resource?

Once I have a better understanding of your needs, I can help you find the right resource or guide.