This site from the American Library Association helps the researcher identify, locate and evaluate primary source documents on the web.
As a history researcher, you may want to consider Google Scholar as a third-tier or "mop-up" resource. You may occasionally find articles or citations that have eluded you elsewhere. Not all sources in Google Scholar are peer-reviewed.
If you find useful titles in Google Book Search, you can check the OPAL Catalog to determine whether Watson Library owns a copy; or search for them in the OhioLINK Catalog and request a copy. If the title you are looking for is not in the OPAL or OhioLINK catalogs, Watson Library may be able to get them for you through Inter-library Loan. Ask one of your librarians at Watson Library for details!
Or, you can reverse the process; use Google Book Previews through the OPAL and OhioLINK catalogs. Sometimes you can read the entire book, sometimes portions of the book. Look for "Limited Preview at Google Books," or to help you decide whether to request the title.