Credo Reference - online library with publications on a variety of topics.
The following Reference Books are authoritative, informative, and concise. Of the three, authoritative counts the most.
from the Library home page:
Do books count as scholarly sources?
Scholarly books are written for scholars/researchers in the author's field, and are typically intended to share research findings and contribute to the ongoing scholarly "conversation." Textbooks, encyclopedias, and books published for commercial audiences often do not count as scholalry.
Consider these questions when you're deciding if a book is academic or not: