Multi-discipline database searches many (but not all) journals and some books. It allows you to locate the most highly cited articles on a topic, and follow "citation trails" forward and backward in time.
Date Coverage: 1970-present; selected access back to 1823
The Hathi Trust Digital Library contains digital copies of over 10 million volumes (books and journals) in over 400 languages, printed from 1500-present. Over 3 million volumes are in the public domain and can be viewed/printed/downloaded. Other volumes can be searched, but viewing is restricted.
JSTOR contains full-text journal articles dating back to the very beginning of each journal (most journals start publishing in the mid-19th to early 20th century). If your articles were published during the years the historical events were occurring, they are likelier to be considered primary than secondary sources.
Specifically contains access to Arts and Sciences I, II, III, IV, Complement, Ecology & Botany and General Science Collections.
Free account can be created for personalization. Date Coverage: Varies by title Maximum Users: Unlimited Truncation: Plurals: +