Periodicals can be useful either as secondary sources (recent articles in scholarly journals) or as primary sources (journals, magazines, newspapers, and others published in the time period you are researching).
The principal database for identifying journal articles in world history is:
There are several other very important article indexes, any of which might be crucial for research depending on the focus of your research:
Provides page images of back issues of the core scholarly journals in the humanities, social sciences, and basic sciences from the earliest issues to within a few years of current publication. Users may browse by journal title or discipline, or may search the full-text or citations/abstracts. New issues of existing titles and new titles are added approximately on a weekly basis. The University of Illinois has access to the following JSTOR collections: Arts & Sciences I-XV, 19th Century British Pamphlets, Business IV, Global Plants, Hebrew Journals, Ireland, Life Sciences Collection, Lives of Literature, Security Studies, Struggles for Freedom - South Africa, Sustainability, and World Heritage Sites - Africa.