One way to narrow your search to primary source documents in the DiPietro Library collection is to select "Advanced Search" (beneath the Find button), select "Subject" from the dropdown menus on the next page, then enter the type of primary source material you want to find (e.g., speeches, letters) and the historical event you are researching (such as the Vietnam War or the Black Power movement). Here's an example below of how to search for letters from the Vietnam War era.
Other primary source terms and documents you might consider searching for include: photographs, letters, correspondence, diaries, interviews, photography, pictorial works, personal narratives, memoirs.
(Adapted from "Find Primary Sources in OneSearch with Subject Terms," Alfred R. Neumann Library, University of Houston Clear Lake, https://uhcl.libguides.com/primarysources/onesearch).
"This multi-disciplinary database provides full text for more than 4,600 journals, including full text for nearly 3,900 peer-reviewed titles. PDF backfiles to 1975 or further are available for well over one hundred journals, and searchable cited references are provided for more than 1,000 titles."