BioOne (http://www.bioone.org/) searches over 200 leading titles in the biological, ecological, and environmental sciences.
ScienceDirect (http://www.sciencedirect.com/) searches in peer-reviewed journals, articles, book chapters and open access content.
WorldWideScience is a global science gateway to national and international scientific databases and portals. (https://worldwidescience.org/)
Primary sources in the sciences are publications which provide a full description of original research and the presents the results of that research. For example, an article describing a research study which is published in a peer-reviewed journal. A secondary source would be an article that provides an overview of the topic or one that analyzes the original research study,
Interactive graphic from North Carolina State University
Click on this interactive graphic to see the different parts of a scholarly article.