@book { DirektmarketinginUnternehmensberatungen,
    title = "Direktmarketing in Unternehmensberatungen",
    author = "Jörn {Paraat-Zierrath}",
    year = "2007",
    publisher = "Diplom.de",
    address = "Hamburg, Deutschland",
    doi = "10.3239/9783836605410",
    url = "https://m.diplom.de/document/225370"
}