@book { WerttreiberimMittelstand,
    title = "Werttreiber im Mittelstand",
    author = "Hanno {Waltermann}",
    year = "2008",
    publisher = "Diplom.de",
    address = "Hamburg, Deutschland",
    doi = "10.3239/9783836618007",
    url = "https://m.diplom.de/document/226073"
}