Boolean Operators are short words used to combine search terms in logical operations. Most databases, discovery layers and search engines recognize them and use them to to bring search results that fulfill the requested operations.The most common are AND, OR and NOT. They are written in capitals to differentiate them from regular keywords.
Check the image below to understand how each of them affects the results of your searches. Parenthesis are used to combine different sets of instructions and to signal the order in which they should happen.
Here are a few criteria for determining if your source is scholarly:
Author(s) credentials - are they experts working or teaching in this field of study?
Length - is it a few brief paragraphs or a longer, more substantive article?
Language - is it written for other scholars in the field? Do they used specialized or technical language specific to this field of study?
References - is the author(s) citing other scholars in this field of study? Do they have a robust reference list?
Journal or Book Type - If it's a journal article, what kind of journal is the article is published in? Is it a scholarly journal, or even peer reviewed? If it’s a book, is it published by a university press or other well-respected commercial publisher known for publishing scholarly works?