The Oxford Dictionary of Philosophy [ONLINE & PRINT] by 
The Philosophy of Science: a Companion [ONLINE & PRINT] by 
The Oxford Companion to Philosophy [ONLINE & PRINT] by 
The Encyclopedia of the History of Science [ONLINE] by 
The Oxford Illustrated History of Science [PRINT] by 
Encyclopaedia of the History of Science, Technology, and Medicine in Non-Western Cultures [ONLINE] by 
Encyclopedia of Early Modern Philosophy and the Sciences [ONLINE]
The Oxford handbook of science and medicine in the classical world [ONLINE & PRINT] by A digital collection of reference sources in various subject areas. While it can be useful to see varied/multi-disciplinary angles on a particular topic, you search by, you can also limit to specific subject areas. Additionally, you can limit the results to more fulsome "subject reference" works (rather than subject-specific dictionaries containing brief definitions only).
