Once you have found a citation for a useful article in an index or database, where can you view the full text of the article?
Look for Advanced Search options to limit your results to German language. These databases don't have a primary focus on German language or literature, but they may have some applicability, depending on your research topic.
Academic Search Complete, Historical Abstracts, and MLA International Bibliography are all EBSCOhost databases. They have the same basic search interface, so once you learn how to search one, you can easily search the others.
EBSCO Publishing has a YouTube channel with tutorials. Here's one on using the Advanced Search features: