1. One or more tangible computer storage media storing computer-useable instructions that, when used by a computing device, cause the computing device to perform a method comprising: receiving a search query; reformulating the search query to identify one or more atoms used to query a search index, the search index storing a plurality of atoms, the plurality of atoms comprising one or more n-grams, one or more n-tuples, and one or more near n-tuples; identifying an initial set of documents from the search index based on the one or more atoms identified in the reformulated search query; computing preliminary scores for each document in the initial set of documents using both a simplified scoring function and pre-computed scores stored in the search index for document/atom pairs for the one or more atoms and the initial set of documents, wherein a pre-computed score for each document/atom pair represents the importance of an atom extracted from the document, and wherein the simplified scoring function is derived at least in part from ranking features of a full ranking algorithm; selecting a pruned set of documents from the initial set of documents based on the preliminary scores; computing a ranking score for each document in the pruned set of documents using the full ranking algorithm different from the simplified scoring function to provide a set of ranked documents; and providing search results for presentation to an end user based on the set of ranked documents.