If you need to search for word usage across a text, texts, or corpora, check out AntConc. Built for linguists, this program should be of use to anyone interested in tracking a word or phrase throughout a text. The program only accepts .txt files.
For Chinese, make sure to change the language settings under “Global Settings” to
the appropriate encoding. If your texts shows up garbled, open your .txt file in a text editor and re-save it with UTF-8 Unicode encoding. Then set the program to use UTF-8.
Update: it appears that users are having difficulty using this program on the Mac, as the X11 environment does not easily allow for the input of Chinese characters. If anyone has been successful in this regard, please post in the comments.
See below for screenshot.
This screenshot is from AntConc running in Windows. It is the same in OS X and Linux. Click image for larger view.