@book { NaturundKulturlandschaftenBulgariens,
    title = "Natur- und Kulturlandschaften Bulgariens",
    author = "Karsten {Grunewald} and Dimitar {Stoilov}",
    year = "1998",
    publisher = "Biblion",
    address = ", Germany",
    doi = "10.3726/b12864",
    url = "https://www.peterlang.com/document/1067234"
}