Search for scholarly (aka peer reviewed) journal articles and scholarly books using SLUth Search Plus. It searches more than 100 library databases, including Art Full Text, Arts & Humanities Citation Index, JSTOR, Project Muse, ATLA Religion Database, and the SLU Libraries Catalog.
If you're looking specifically for books and ebooks, you might prefer using the Saint Louis University Libraries' Catalog.
Look for books published by university presses and scholarly associations, written by authors with degrees and credentials in the field. Scholarly or academic books will also cite their sources and will have a lengthy list of references.