@book { GeschftsmodelleimECommerce,
    title = "Geschäftsmodelle im E-Commerce",
    author = "Michael {Heik}",
    year = "2011",
    publisher = "Diplom.de",
    address = "Hamburg, Deutschland",
    doi = "10.3239/9783842818774",
    url = "https://m.diplom.de/document/228554"
}