Aside from CBBcat for books, and LibrarySearch+ for books and articles, the following are places to find related secondary sources.
Topical bibliographies in the humanities and social sciences. Oxford Bibliography
U.S. and Canadian history journal articles. Citations with links to full text. Publication dates: 1964 to present
Citations to articles in biomedicine and health fields, and related disciplines such as life sciences, behavioral sciences, chemical sciences, and bioengineering.nursing dentistry veterinary
The bound and daily versions of Congressional Record, its three predecessor titles, and other important Congressional material. 1789 to present Hein online