7. A non-transitory computer-readable medium storing instructions, the instructions comprising: one or more instructions that, when executed by at least one processor, cause the at least one processor to: receive a search query; identify documents based on the search query; generate a plurality of substrings based on the search query; calculate, for a particular substring of the plurality of substrings, a value based on the identified documents and the particular substring; determine that the calculated value for the particular substring satisfies a particular threshold associated with identifying compounds; select the particular substring, as a semantic unit, from the plurality of substrings based on the calculated value for the particular substring satisfying the particular threshold; and refine the identified documents based on the semantic unit.
7. A non-transitory computer-readable medium storing instructions, the instructions comprising: one or more instructions that, when executed by at least one processor, cause the at least one processor to: receive a search query; identify documents based on the search query; generate a plurality of substrings based on the search query; calculate, for a particular substring of the plurality of substrings, a value based on the identified documents and the particular substring; determine that the calculated value for the particular substring satisfies a particular threshold associated with identifying compounds; select the particular substring, as a semantic unit, from the plurality of substrings based on the calculated value for the particular substring satisfying the particular threshold; and refine the identified documents based on the semantic unit. 11. The non-transitory computer-readable medium of claim 7 , where the one or more instructions to identify the documents comprise: one or more instructions that, when executed by the at least one processor, cause the at least one processor to: generate a list of relevant documents based on search terms of the search query, and identify the documents, from the list of relevant documents, that are most relevant to the search query.