documentclass{article}
usepackage{booktabs}% http://ctan.org/pkg/booktabs
usepackage{colortbl}% http://ctan.org/pkg/colortbl
usepackage{amsmath}% http://ctan.org/pkg/amsmath
usepackage{xcolor}% http://ctan.org/pkg/xcolor
usepackage{graphicx}% http://ctan.org/pkg/graphicx

colorlet{tableheadcolor}{gray!25}
newcommand{headcol}{rowcolor{tableheadcolor}} %
colorlet{tablerowcolor}{gray!10}
newcommand{rowcol}{rowcolor{tablerowcolor}} %

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 newcommand{rowmidlinecw}{arrayrulecolor{tablerowcolor}specialrule{aboverulesep}{0pt}{0pt}%
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 newcommand{bottomline}{arrayrulecolor{white}specialrule{aboverulesep}{0pt}{0pt}%
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 newcommand{bottomlinec}{arrayrulecolor{tablerowcolor}specialrule{aboverulesep}{0pt}{0pt}%
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begin{document}

begin{table}[htb!]
centering

begin{tabular}{lllccccc}
    topline
    headcol &         &                                                         & multicolumn{5}{c}{Kodierung}    \
    cmidrule {4-8}
    headcol & Einheit & Faktor $x_i$  & -2  & -1    & 0    & 1     & 2    \
    midline
    Badtemperatur            & °C      & 1      & 40  & 45    & 50   & 55    & 60   \
    rowcol Bandgeschwindigkeit      & mm/min  & 2      & 500 & 625   & 750  & 875   & 1000 \
    Trockentemperatur        & °C      & 3      & 22  & 36,5  & 51   & 65,5  & 80   \
    rowcol begin{tabular}[c]{@{}l@{}}Luftfeuchte im \ Trockenmediumend{tabular} & %      & 4                                                       & 0   & 13,75 & 27,5 & 41,25 & 55   \
    bottomlinec
end{tabular}
caption{Faktoren und ihre Kodierung}
label{tab:FaktorenKodierung}
end{table}

end{document}