https://www.plakaterogsager.dk/vare-tag/gopel/
gopel Arkiv - Plakater og Sager
arkivplakaterogsager
https://catalogo.share-cat.unina.it/sharecat/resource?uri=UNICASRMS0019423&v=l&dcnr=5
3: Chemical and biochemical sensors. 2 / edited by W. Gopel ... \et al.!