Basic keyword search:
Reference sources can offer useful overviews and background information, but typically don't include the type of primary and secondary materials needed for the majority of your research.
While the catalog and HathiTrust include secondary sources, both are also excellent tools for finding primary sources:
Examples of Sources:
The Examination of Doctor Benjamin Franklin relative to the repeal of the American Stamp Act in MDCCLXVI
Bibliographical notes on the issues of the Continental congress 1776-1779
The writings of George Washington from the original manuscript sources, 1745-1799
These databases, produced by Gale, contain digitized materials, ranging anywhere from a few to several hundred pages or more.