Browse the results list of your keyword search and look at the full records to see the subject headings assigned for relevant titles. Note that the results are sorted by relevance. You can change the results to sort by date, author, or title. Click on the subject headings to find more books on your topic.
For example, for the topic: Feminist novels in the early 20th century some of the assigned subjects headings include:
After you find a relevant book on your topic, you can also browse the catalogue by the Library of Congress call numbers to find more titles.