Credible websites for research papers are websites that are written, maintained or were established by a credible source such as a university, established journal, reputable magazine, authors with credits and affiliations to professional organizations, government organizations, and professional websites such as WebMD. This not an all inclusive list of credible websites and the best way to determine whether or not a website is credible is to look at its authorship and to decipher what level of fact checking occurs.
For example, an unpublished author with no professional organizational affiliation or backing is unlikely to be held accountable by any fact checking system, whereas a published author who is affiliated with a psychological journal is more likely to create fact-based websites. Look at the home page of each site and read the "About Us" section. This section should contain vital information about the page and where the content comes from, including the author, the possible sponsor of the page and any possible organizational affiliations.
Another important detail to look for on the website is the date. The date might not be as relevant when looking at a historical page, but in the scientific field where new discoveries are made every day, looking at a page from 1990 in 2015 may not yield the most credible information. Although it might have been credible in 1990, that may no longer be the case. Look at research and credible sources from the current year before using older sources to ensure that the information is up-to-date.