1. One or more 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; identifying an initial set of documents from a search index based on the one or more atoms, 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; computing preliminary scores for each document in the initial set of documents using a simplified scoring function and pre-computed stores stored in the search index for document/atom pairs for the one or more atoms and the initial set of documents; 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 a full ranking algorithm to provide a set of ranked documents; and providing search results for presentation to an end user based on the set of ranked documents.