Utiliser les facettes, par exemple :
https://api.archives-ouvertes.fr/?q=structId_i:866%26language=fr&fq=structId_i:866&wt=json&fl=docid,docType_s,fr_title_s,en_title_s,title_s,authFullName_s,doiId_s,volume_s,page_s,producedDate_tdate,producedDateD_i,producedDateM_i,producedDateY_i,keyword_s&facet=true&facet.field=keyword_s&facet.sort=count&rows=1