Retrieve all substances included in National Drug Code Directory according to the term introduced

Statement: 
Retrieve all substances included in National Drug Code Directory according to the term introduced $substance$ (e.g. methenamine)
A limit of results per page $number$ (e.g. 12)
Query: 
select* where{ ?s<http://www.w3.org/1999/02/22-rdf-syntax-ns#type><http://bio2rdf.org/ndc_vocabulary:Substance> . ?s<http://www.w3.org/2000/01/rdf-schema#label>?label . ?label bif:contains "'??substance'" } limit ??number