@book { DienstleistungenimMaschinenbau,
    title = "Dienstleistungen im Maschinenbau",
    author = "Paul {Morgenthaler}",
    year = "2002",
    publisher = "Diplom.de",
    address = "Hamburg, Deutschland",
    doi = "10.3239/9783832457624",
    url = "https://m.diplom.de/document/221223"
}