Google Scholar has adapted the h-index method of impact for publications and an h5 variation for five complete calendar years.
From Google Scholar:
Two examples of Google Scholar journal metric are below:
Scholar Metrics currently cover articles published between 2007 and 2011, both inclusive. The metrics are based on citations from all articles that were indexed in Google Scholar as of November 15th, 2012. This also includes citations from articles that are not themselves covered by Scholar Metrics.
Since Google Scholar indexes articles from a large number of websites, we can't always tell in which journal a particular article has been published. To avoid misidentification of publications, we have included only the following items:
Furthermore, we have specifically excluded the following items:
Overall, Scholar Metrics cover a substantial fraction of scholarly articles published in the last five years. However, they don't currently cover a large number of articles from smaller publications.