@Book{Klandt.1999,
  author = {Klandt, Heinz},
  title  = {Gr\"undungsmanagement: der integrierte Unternehmensplan},

  year   = {1999},
  number = {},
  url    = {},

  const  = {\ text}
}
@Book{Vahrenkamp.1994,
  author = {Vahrenkamp, Richard},
  title  = {Produktions- und Logistikmanagement},

  year   = {1994},
  number = {},
  url    = {http://www.gbv.de/dms/ilmenau/toc/15676573X.PDF},

  const  = {\ text}
}