These databases will contain article from academic journals and some primary source documents that relate to Holocaust and genocide studies. They are created by different companies, but the basic search functions and the tools to help you save and cite articles will be similar.
These academic journals are where many genocide and Holocaust researchers publish their work. Some of them may be searched in the databases listed above, but not all of them. You can search in the individual journals by clicking the link and using the search box under the "Search Inside" section.