Pick key words from your research topic.
Brainstorm synonyms for those words. These words might help you find more articles.
Don't forget to make use of Boolean connectors between your search terms. AND will limit your search results. OR with broaden them.
When you pull up an article that works really well for you, look at its subject tags or object descriptors and perform a search on them. Sometimes this can help you find more similar articles without having to sift through a large number of items that are not specifically related to what you want.