You can now refine your search results in the http://google.com with the search options. These search options was launched in May and now some additional options were added to the existing search options.
You can get search options panel by clicking on the “Search Options” with plus sign which will add an extra panel to the left side with Search Options which will refine the search results.
These Search Options allow you to refine search results on Specific date range, Past Hour, Visited Pages, Not yet Visited pages, More Shopping Sites, Fewer shopping sites, Books, Blogs, News etc. You can find more at Official Google Blog.