@book { Marketingstrategien,
    title = "Marketingstrategien",
    author = "Gabriele {Bayer}",
    year = "2000",
    publisher = "Diplom.de",
    address = "Hamburg, Deutschland",
    doi = "10.3239/9783832427658",
    url = "https://m.diplom.de/document/218499"
}