Entrez is the National Center for Biotechnology Information's, (NCBI), primary text search and retrieval system used for PubChem's three primary databases and other major NCBI databases, including PubMed, Nucleotide and Protein Sequences, Protein Structures, Genome, Taxonomy, BioSystems, Gene Expression Omnibus (GEO) and many others.
You can search the PubChem databases through Entrez by initiating a search from the PubChem home page, which also provides launch points to various PubChem services, tools, help documents and more. Or, you can begin the search from the NCBI home page.
By default, if a specific database is not selected in the search menu, Entrez searches all Entrez databases available and lists the number of records in each database that are returned for this ‘global query’. By selecting one of the three PubChem database from the result page, you can see the query result specific to that database.