When you perform a search, the system interprets the query intent, which determines the nature/number of results returned. If you're presented with Query Interpretation, click it to view how your query was searched.
In the below example, the query "What are the applications of supramolecular self-assembly in creating new nanomaterials?" was interpreted and searched as: applications + supramolecular + self-assembly + nanomaterials.
The interpretation means results must have all four terms; in this case, there are 2,280 results. Clicking Search Original Query returns 1,349,553 results.