1. Search for a keyword broadly related to your topic in Tripod (e.g. "Ming dynasty").
2. Under the "Books and More" search results, click "More."
3. Under "Narrow Search" (at the right), try these different limits (one at a time). The links change based on the search results, so you might not be able to try all of these limits for a given search.
Try Subject Headings
Librarians assign subject headings to describe published works. You'll see them in Tripod records (example). Specific subject headings are used in library catalogs (like Tripod) to describe primary source documents that have been collected and published.
Here are some words to look out for in Library of Congress subject headings (the kind used by the Trico Libraries) that will alert you to possible primary sources. These subheadings include:
Click here for a full list of subject headings used to catalog primary sources and more information about how to search using these subject headings.