Many printed/published documents such as books, government documents, maps, films, etc. are primary, e.g. are first hand accounts. Library catalogs help identify such sources. Interlibrary loan (ILLIAD) services can retrieve them.
[Topic, e.g. United States > History > Civil War, 1861-1865 >] Sources
"What was the most interesting thing you read in researching your new book?
Some magazines are digitized in Google Books, lncluding Life Magazine (digitized and keyword searchable from 1935-1972, no printing.) Use the link to browse a list of other titles available. Or, do an advanced search of Google books, limiting to magazines, notice you can also select a date range. Mostly articles from U.S. during 20th century
JStor includes historical sources.. For example currently in JStor American Naturalist is available from 1867-2015, American Scholar runs 1932-2011 and American Sociologist 1965-2013. Some JStor journals date to the 19th century, many started in the early 20th.
Lane Library's Special Collections houses The Inkwell, Armstrong's student newspaper from the first issue (September 1935) through current issues. See below for links to the digitized back issues from 1935-1947, 1955, & 1960-1971 and the current, online issues.