The Alkek library has thousands of books and other materials that are, in fact, primary sources for historical research. However, the catalog does not use that term to identify them so, here are some tips-
When looking for primary sources use the subject headings to help you tease these out. Here are some keywords to use (within subject headings) that will often result in primary sources being revealed. Try adding these to any search for primary sources-
Sources or correspondence or letters or diaries
Because subject headings can be complex the best way to perform this search is to use the "advanced search" link just below the main serch box in the catalog. This allows searching of just the subject headings for whatever terms are wanted, no matter where in the subject heading they may appear.