@book { CrossSellinginEnergieversorgungsunternehmen,
    title = "Cross Selling in Energieversorgungsunternehmen",
    subtitle = "Ein notwendiger Vertriebsansatz im Rahmen eines CRM",
    author = "Armin {Baumgärtner}",
    year = "2007",
    publisher = "Diplom.de",
    address = "Hamburg, Deutschland",
    doi = "10.3239/9783836601085",
    url = "https://m.diplom.de/document/225173"
}