Most subject encyclopedias and all scholarly journal articles include citations of books and articles that the author used, which in turn will include more citations. Titles and authors of books and titles of journals can be searched in InfoHawk, which will be going away, or SmartSearch, which will become the entry point to finding a wider range of resources that seem to be related to your search term.
InfoHawk can be searched by subject as well as by a specific author or title. The options are search by "subject beginning with" or "keyword in subject." "Keyword in subject" is more flexible since the words do not need to be in a particular order as prescribed by LCSH (Library of Congress Subject Headings). A full record display will include the subject headings assigned to the book. These are linked to similar records and can lead to additional sources.
SmartSearch retrieves records from virtually anything that has a footprint in cyberspace. The basic search has some options to direct the search toward what is really wanted. The Advanced search option has a few more ways to limit a search. Simply searching "crusades" retrieves 204,693 citations; limited to "in subject," brings the citations down to 5,350; "medieval crusades" cuts the results down to 238, which can be further filtered down to 40 English language books and knocked down to 34 by location in the Main Library. Going back to the 238 results and filtering first by type (articles), then by "peer review" (academic journals), language (English), and date (after 2005), the result set is down to 39, actually a few less since some citations duplicate.
A primary source can be a document, narrative, letter, literary work, art, music. What makes it a primary source is that it was produced in the past, in this case, in the medieval period. It does not have to be the actual item: it can be a text reproduced in print, a translation of a document written in Latin or Old French, an image from ARTSTOR.
A keyword subject search with "Middle Ages" and "sources" in InfoHawk, or SmartSearch, is one starting point. An increasing amount of primary source materials is accessible online.
Below are some of the primary source collections that are online:
Medieval sources Online contains topical collections of medieval documents in translation.
The Internet Medieval Sourcebook is a large collection of a variety of texts including saints' lives, government and legal documents, chronicles, and literature.
CELT is a searchable online corpus of multilingual texts in Irish literature and history.