The UW Libraries has a strong collection of published primary sources dealing with history. Primary sources for other regions and time periods are also available (though often in the original language). These include books written during the period for your topic (i.e., during the Russian Revolution), books written by participants, published collections of correspondence and other personal writings, memoirs and reprints of collections of primary source material. Most books are printed but some are microfilmed.
To find these primary sources use the Advance search option on UW Libraries Search and switch "Show Only" option to UW Libraries.
By AUTHOR-- search for books written by key participants and organizations.
By SPECIAL SUBJECT HEADINGS -- do a keywords search for your topic/event and change the search label from "Any field" to "Subject" and use one of these special subject headings that designate primary sources: personal narratives, correspondence, diaries, interviews, sources. Some terms may work better than others depending on your topic.
By DATE -- narrow your search by year of publication
This is just a selection of the digitized early book collections available on the web. Additional collections early books can be found under the tabs for History by Region and History by Topic.
If you are looking for books published before 1924, check HathiTrust. More than million books (also some magazines and Parliamentary Papers) free of copyright are available full-text and can be downloaded as pdfs. Plus you can search through the entire text to find the information you seek. Note: these digitized items include books published in Britain, the United States and other countries.
The Advanced Catalog Search provides options to search for specific titles, authors and keywords and to limit your search by fulltext availability (full view only) and publication date.
Current books and books still in copyright are not available full-text but you can usually use the search feature to pinpoint the pages you might need. Then search the UW Libraries to find a copy of the printed book.