Is the material published on a trustworthy website? Is the site owned by, for example, a university, a research institute, a scientific community, an EU project or some other official organization or authority?
Is the author a researcher or specialist within the field? What is his/her academic background? You can do a search on the person to ensure that he/she is really an expert.
Does the material have a scientific purpose? Is the source or research meant to be read by other researchers, i.e. peers? Is it a part of a scholarly discussion? This indicates that the target group is correct.
Is the text written objectively? Does it include strong opinions? Are things being exaggerated? Scientific research is always objective and unbiased, and all facts presented are justifiable and based on research.
Does the text include specialist terminology without spelling mistakes? Can you follow the logical thread of the research through theory, methodology, conclusions and references presented in the text?
Are the sources used in the material reliable? Are they presented correctly? Is the list of references complete and accurate?
When was the material published? Older publications may contain outdated information. Whether the material is up-to-date or not depends greatly on the topic. Are there more recent sources that support the facts presented in the material?
If these criteria are fulfilled, the source can be used.
Wikipedia is not a scientific source!
Use Google Scholar instead of Google!
Use Boolean operators, phrase search and truncation also in Google to boost your search!