Use general resources listed below or search in the catalogue using keywords e.g. Sartre for individual reference books available in print and online formats. Below is a list of examples of what I mean:
A scholarly array of classic handbooks of historical subject on 17th, 18th, 19th Century, Renaissance, Late antiquity, Medieval, Greek, Jewish and general philosophy.
Authoritative handbooks on state of the art areas in philosophy giving the reader an overview of the major problems, positions, issues, and battle lines.