Yes it is readers, you can find it very much in the wikipedia article.

In all recorded cases the books were kept in a relatively small room where the staff went to get them for the readers, who had to consult them in an adjoining hall or covered walkway.


http://en.wikipedia.org/wiki/Library#Library_use

visitor-readers

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Note added at 1 hr (2009-04-14 10:34:18 GMT)
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It looks like that you need to read the definition - the text uses the word – مراجعون therefore you have to translate within the context, as you said in your clarification this is a reference library, thus revisors is your best option, see below:-

1 a: to look over again in order to correct or improve <revise a manuscript> bBritish : to study again : review
2 a: to make a new, amended, improved, or up-to-date version of <revise a dictionary> b: to provide with a new taxonomic arrangement <revising the alpine ferns>

Apparently, these are those who go to the library to review the sources in the library for their research work. مراجع means reviewer and thus fits well within this context.

In the link below one can find under the heading: Synonyms within Context, for the word 'research',

"Experiment Literature search, library research", as well as under the heading "Expressions: Research" in the same page (way down):

الأشخاص كثيرو التردد على المكتبة

Have a look at this link:
http://dictionary.reference.com/dic?q=frequenter&search=sear...

Frequenter
Fre*quent*er\, n. One who frequents; one who often visits, or resorts to customarily.
Webster's Revised Unabridged Dictionary, © 1996, 1998 MICRA, Inc.
Cite This Source
frequenter

noun
a regular customer [syn: patron]