Citation analysis measures the impact of research via the number of times it is cited. Applications include:
Google Scholar can tell you how many times an article has been cited. This provides a measure of the article's scholarly impact.
It can also tell you where these citations appear, which leads to related articles and can show how the article was received.
Google Scholar Metrics provides a ranking of highly cited publications within languages and disciplines.
For more information, see Harzing, Anne-Wil. (2008) "Google Scholar - a new data source for citation analysis."