Primary sources in the sciences differ from primary sources in other fields. In the humanities or social sciences primary sources typically include historical records and first-hand accounts of events (diaries, interviews, recordings, etc.), while primary sources in the sciences refer to those sources reporting original research.
Primary sources in the sciences have the following characteristics...
Citation databases are used to retrieve information about the relationships among published articles -- how many times an article has been cited by other articles, where an article was cited and related articles. There are two major databases with this kind of information Scopus and Web of Science.
There is overlap among the publications covered by the two databases but there is also unique content in each. Scopus tends to be more international while WOS favors North America/Europe. More extensive coverage of engineering titles in Scopus. Try searching both WOS and Scopus. Users can set up alerts to track future citations to articles of interest.
The h-index quantifies the output of an individual scientist. This metric was developed by Jorge Hirsch, a physicist at UC San Diego.
Hirsch, J.E. An index to quantify an individual's scientific research output. Proceedings of the National Academy of Sciences of the United States of America, 102(46), 16569-16572. This article describes Hirsh's concept and rationale. Definition of h-index from WOS.
Another article on the h-index: Bornmann, L. and Hans-Dieter, D. The state of h index research. EMBO Reports, 10(1), 2-6