Selecting and evaluating sources is about credibility - the credibility of the authors of the sources and your own credibility. Consider the quality of the source, whether the author is trustworthy on that topic, and what the source offers (does it offer facts? an opinion? a new idea?).
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Searching the library's database is the best way for you to get access to the full-text of scholarly and peer-reviewed articles. Most of the library's database allow you to limit your searches to receive only scholarly results. This "limiter" is often found by clicking on "Advanced Search" or by using the "Refine Results" or "Limit Results" menu on a search results screen.