The library catalog only looks for the words you enter in a few places --book title, author's name, publisher, and official subjects assigned to the book. Using broad, general search terms is usually better than being too specific.
"color purple" AND criticism
Alice Walker AND criticism
"community college" AND success
"community college" AND outcomes
O'Brien AND crit*
To specify ebooks only in your results, select the "Full Text Online" filter.