@book { ModerneEntwicklungenimSeniorenmarketing,
    title = "Moderne Entwicklungen im Seniorenmarketing",
    author = "Petra {Kühnel}",
    year = "2001",
    publisher = "Diplom.de",
    address = "Hamburg, Deutschland",
    doi = "10.3239/9783832434458",
    url = "https://m.diplom.de/document/219113"
}