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If you enter Vietnam War as your search terms, you wil get any item that incudes the word Vietnam AND War.
If you enter "Vietnam War" as your search term, the search engine will only retrieve items with those words in that exact order. This can greatly increase the relevancy of your search results and will help you avoid sorting through long lists of potentially-irrelevant results.
Using an Asterisk
If you enter the term soldier as your search term, you will only get results that contain this exact word.
If you enter the term soldier* as your search term, the search engine will retrieve items that contain any spelling variation of this word (for example: soldier, soldiers, soldiering, etc.). This can help to expand the number of search results that you get and will make sure that you are not limiting your search to a specific spelling of a keyword.
Is Your Book Published by an Academic Publisher?
One of the best indicators of whether or not your book or e-book is considered a "scholarly" source is its publisher. Academic publishers such as Wiley, Taylor and Francis, Brill, and Routledge (to name a few!) and university presses (Oxford University Press, for example) are responsible for publishing almost all of the scholarly books and e-books that you'll need to use in your research projects.
Check the lists linked below if you aren't sure whether or not the publisher of your book is considered scholarly or academic. If you don't see your publisher listed, you can always reach out to your professor for their input, as well.