There are two main databases that will be good sources of scholarly (sometimes called peer-reviewed or refereed) journal articles.One is Academic Search Premier. The other is Worldwide Political Science Abstracts, the main database for research in political science.
Click the "Scholarly (peer-reviewed)" box to limit your results.
Academic Search Premier covers many scholarly disciplines, not just political science. It will return broader results.
Limit to scholarly articles by clicking the "peer-reviewed" box before submitting your search.