1. A method implemented by data processing apparatus, the method comprising: obtaining search results that each satisfy a search query, the search results including a plurality of generic search results and a plurality of mobile search results, wherein the generic search results each identify a respective generic resource and have a respective search result quality score, and wherein the mobile search results each identify a respective mobile resource; and have a respective search result quality score; determining that the mobile search results fall into a plurality of non-overlapping mobile score sub-ranges based on the respective search result quality scores of the mobile search results; determining a corresponding generic score sub-range for one or more of the mobile score sub-ranges wherein the generic score sub-range is different than the mobile score sub-range; modifying the respective search result quality scores of one or more mobile search results that fall into a mobile score sub-range of the mobile score sub-ranges so that the modified respective search result quality scores fall within the corresponding generic score sub-range; ranking the search results based at least partly on the respective search result quality scores and the modified respective search result quality scores; providing the ranked search results to a client device; and wherein obtaining, determining, modifying, ranking, and providing are performed by the data processing apparatus.