The majority of articles in databases come from scholarly peer-reviewed journals, but you should still critically assess your sources to ensure that they have been peer-reviewed.
Your search words should be only the words that express the main concepts in your research topic. Words that don't convey main concepts should not be used as search terms. They can cause many useful things to be left out of your search results.
Here are some types of words to avoid:
Different words can be used to represent the same main concept. Be prepared to think of synonyms or related terms. They can help you
Example: pollution OR degradation
Example: Sandinis* = sandinista, sandinistas, sandinismo, etc.