86de5828_User_Tips__SERP_URL_Parameters__Description
[URL Parameter] as_rights [Format Example] http://google.com/search?q=cheese& as_rights=cc_publicdomain [Description] 
Restrict results to re-usable (Creative Commons licensed) content. This is probably a more straightforward exercise from the Advanced Search screen, but if you’re feeling adventurous, cc_publicdomain is public domain, cc_attribute is re-usable with attribution, cc_sharealike means you’d have to offer the derivative works under a Creative Commons license, cc_nonderived means no derivative works allowed, and cc_noncommercial means non-commercial use only. You can combine these into groups with parentheses and pipe symbols, and minus signs to exclude certain license types such as the commercially restricted license. For example, (cc_publicdomain | cc_attribute | cc_sharealike).-(cc_noncommercial | cc_nonderived) is equivalent to “free to use, share or modify, even commercially.” There should not be spaces in the above (they were merely added for readability).
Google Power User Tips: SERP URL Parameters
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