While books can be broad in the coverage, articles are usually short and focused. To find them go to the library website and use the OneSearch tab.
If the keyword search brings various sources (ebooks, dissertations, reports, etc.), limit the content to "journal articles". Be aware of the concept of peer-reviewed journal articles: articles that have gone through a rigorous review process by scholars in their field of study.
Google Scholar is another great source for articles. Since it is multidisciplinary, be very specific with your search terms. Also, make sure Google Scholar recognizes you as a patron of the Georgetown University: go into Settings, Library links and add in Georgetown University.
There are many online databases you can use to find scholarly articles on nationalism. A master list of all library databases you can check here. Below are several that you can find useful: