The database America: History and Life is the best place to search for research articles on any topic in US and Canadian history.
The following two journals, which are both indexed in America: History and Life, focus on the Pacific Northwest.
At right: The Two Sentries by Frank H. Nowell, 1914, from the University of Washington Digital Collections via Flickr Commons.
Books (also called monographs) are essential to historians. Books can be written by one person or include a series of essays by several historians. One strategy to find books on your topic is to use a keyword search to find relevant subjects. For example, I searched the keyword phrase chinatown portland in the Portland State Library Catalog (PSU Library selected only). The fifth result seemed very relevant, a book called Sweet Cakes, Long Journey: The Chinatowns of Portland, Oregon. I clicked on the book title, then I looked at the subject headings listed. Clicking on a subject heading will get me quickly to many more books on the same topic.