There are many online resources relating to the study of history during the 20th century. This list of resources, while by no means exhaustive, provides a basic starting point for your research.
"The definitive database of literature covering the history and culture of the United States and Canada, from prehistory to the present. With selective indexing for 1,700 journals from 1964 to present, this database is without question the most important bibliographic reference tool for students and scholars of U.S. and Canadian history."
Electronic version of International Index to Periodicals (1907-1955), International Index (1955-1965), Social Sciences and Humanities Index (1965-1974), and Humanities Index (1974-1996). This database should be used in conjunction with Humanities Abstracts in FirstSearch.
Provides full-text access of more than 200 history and history-related journals. Remember that in many cases the latest 3-5 years' worth of issues are NOT included due to publisher restrictions.
"An invaluable, in-depth record of contemporary art history, Art Index Retrospective allows users to search 55 years of art journalism at a keystroke. Users can research leading English-language sources, plus others published in French, Italian, German, Spanish, and Dutch. Besides periodicals, users have access to data from important yearbooks and select museum bulletins."
"Search through the complete digital edition of The Times (London), using keyword searching and hit-term highlighting to retrieve full facsimile images of either a specific article or a complete page. The entire newspaper is captured, with all articles, advertisements and illustrations/photos divided into categories to facilitate searching."