For some research projects you may be required to use Primary Sources. A primary source provides direct or firsthand evidence about an event, object, person, or work of art. Primary sources include:
"In the natural and social sciences, primary sources are often empirical studies - research where an experiment was performed or a direct observation was made. The results of thse first-hand empirical studies are typically found in scholarly articles or papers delivered at conferences." (http://www.ithacalibrary.com/sp/subjects/primary)
Below is a list of some well-known primary source websites. Be sure to check the [Websites] tabs on individual [Subject Guides] for other discipline-specific primary source websites.
Secondary Sources: 
Periodicals often provide secondary source materials in articles in newspapers or popular magazines, or in book or movie reviews.
If a scholarly periodical (journal) article mentions or critiques another scholar's original research, it is secondary source material.
Tertiary sources consist of information which is a compilation or distillation of primary and secondary sources. Usually information is provided factually and does not critique or provide analysis. Tertiary sources may include:
