There is no way to restrict the results in Google Scholar by citation number, to my knowledge. However, it is useful to understand that Scholar heavily weights the number of citations in deciding which results to return. For a broad search one can see this; the returned results will tend to be in order of decreasing number of citations. When narrow searches are done, as by using many search terms, this ordering is often not seen, presumably because the search engine finds closer term matches in obscure papers with few citations. Sometimes one can choose alternative queries which are broad enough to include the more heavily cited papers in the field.
Some insight into how the Google Scholar search engine works is available in this paper: Beel, J. Google Scholar's Ranking Algorithm: An Introductory Overview