Use the advanced search: it lets you limit your searches by domain names,allowing you to choose to avoid commercial sites. Choose sites from a specific country, or retrieve only sites from non-profit organizations, for example. Cutting down the huge numbers of items you retrieve will save you time!
Well Known and Respected sites from Government Agencies or Associations that perform or collect research are excellent sources. Sites such as EPA and the American Cancer Society for example.
Use Google Scholar if you want only scholarly writings. Many, though not all, of these will have been published in journals or books, not just on the Internet.
Never pay for an article online without talking to us first! One of the downsides of using Google is that you may think you have to buy an article that's available through the USM libraries. When in doubt, check with the library staff.