Bibliographies of string instruments/music and guides to repertoire hold a wealth of useful information. Bibliographies, also known as guides to research, will provide comprehensive lists of books and articles on the instrument, on teaching techniques, and more. Repertoire guides can tell you all the music available for various instruments and can also give you a lot of details you won't get elsewhere--like durations for each movement, difficulty ratings, pitch range, and whether a piece requires extended techniques.
Most of the library's holdings in this area are in the Reference section under the call number ML128. Once you get to the ML128 section you can browse alphabetically to your instrument (don't forget, cello goes under violoncello). Here are the call numbers for each instrument:
Double Bass: ML 128.D6
String Quartets: ML 128.S68
Strings in general: ML128.S7
Instruments in general: ML 128.I66
See the Browsing the Shelf for Music tab to see how to serach online by call number.
You can also find these by searching WorldCat UMD for the subject Bibliography and your instrument. For example: su:viola su:bibliography.
A selected list of bibliographies also appears on the left.