This page goes over some search strategies that can help you find articles published in Political Science journals.
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The Academic Search Complete database is a good place to find scholarly articles. It searches journals in many disciplines, not just Political Science. Despite its name, it is not a "complete" collection of all the journals to which the library subscribes, but it is a good collection of high-quality journals.
Use two or more search boxes (Advanced Search).
Brainstorm alternate keywords
There is no exact way to limit your search to Political Science journals. Here is a "hack" you can use to find some Political Science journals, although it may exclude some relevant journals and include some irrelevant ones. Put this string of terms into a box, using the SO Journal Title drop-down:
Look at the journal title. Often it will have a descriptive name like American Political Science Review or The Journal of Politics.
If you are not sure whether this is a Political Science journal, try searching for the journal's website.
Another thing to try: See whether the database record lists the author's academic department. Or do a Web search for the author to see where they work.