When you find a book that is relevant to your topic, always check the bibliography for other sources and then ask a librarian for help with finding them. The author of the book has already done much of your research for you, and he/she spent many weeks/months/years of his/her life doing research. Take advantage of it!
Search the full text of books that Google has scanned and stored in its digital database. The books come from large research university and public libraries. Full text is available for books published before 1923. For books still under copyright protection, only a small snippet of text is available.
You may also explore OWHL's collection by youself via NOBLE Catalog to get titles like this:
Republican Beijing: The City and Its History from ebrary
Wen xue = Literature 中国传统文化双语读本
Books in bilingual 中英对照双语书
Note, we always welcome your recommendations. To make a recommendation to this list, please contact Ms. Pei via her email. Thank you in advance for your participation.