Google continues to offer new tools to estimate impact of scientific publications. Given the sheer volume of the indexed publications, it could be expected that the results are quite meaningful (as always, any numerology about publications, e.g., total number of citations, h-index, impact factor and so on, should be taken with a serious grain of salt). Now Google provides information on the top hundred scientific journals ordered by 5-year h-index. I assume, more to follow.
Here is the Google Metrics help page.