There are various measures used for assessing scholarly impact. Three commonly used "bibliometric" measures are: journal impact factors, citation counts and the h-index.
Impact factors are a measure of impact for a particular publication. These can be found for each year using the Journal Citation Reports (JCR) database produced by Thomson Reuters.
To access the database you will need to enter your NetID. To search for a specific journal title use the "Master Search" on the top left under "Go to Journal Profile". When the Journal Profile is returned it should include the raw Journal Impact Factor for each year measured in the results column third from the left.
NOTE: If a journal title can not be found in the JCR then this indicates that it is not indexed by the JCR database and it does not have a JCR Impact Factor.
A citation count is the number of times a particular publication has been cited by other authors. The most frequently used databases for citation counts are Google Scholar, Scopus and Web of Science (WoS). For example, when using WoS a search for the article title “The basics of general relativity theory” should return a citation count of 700+.
The h-index, devised by Jorge Hirsch in 2005, is a measure that seeks to gauge the impact of a particular author's body of work.* The databases Google Scholar, Scopus and Web of Science are all able to provide an h-index.
NOTE: As each of these databases index different sets of papers they will often return different results when searching for the same author.
Using Web of Science as an example: To find the h-index for a particular author first find all the indexed papers for that author. This is done by either searching by author or by searching for each of the individual papers. To assist in this process and to avoid author ambiguities the Library recommends scholars sign up for a ResearcherID and "claim" your papers within Web of Science. Once a conclusive list is established then a citation report can be generated using the "Create Citation Report" option on the right hand side of the results list. Included in the results of the citation report is a total citation count for all the documents and an h-index for the papers overall. Scopus works in a very similar manner.
* Hirsch, J. E. (2005). 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.