1 大写罗马数字

  相应的数字$1$表示

\uppercase\expandafter{\romannumeral1}

2 小写罗马数字

\romannumeral1

3 示例

\begin{table}[!htb]\caption{Test.}\renewcommand\tabcolsep{0.005cm}\centering\setlength{\abovecaptionskip}{0pt}\setlength{\belowcaptionskip}{-5pt}\scriptsize
\begin{tabular*}{\hsize}{@{}@{\extracolsep{\fill}}lllllllllllll@{}}\bottomrule1 &  \uppercase\expandafter{\romannumeral1}    &  \romannumeral1\\2 &  \uppercase\expandafter{\romannumeral2}    &  \romannumeral2\\3 &  \uppercase\expandafter{\romannumeral3}    &  \romannumeral3\\4 &  \uppercase\expandafter{\romannumeral4}    &  \romannumeral4\\5 &  \uppercase\expandafter{\romannumeral5}    &  \romannumeral5\\6 &  \uppercase\expandafter{\romannumeral6}    &  \romannumeral6\\7 &  \uppercase\expandafter{\romannumeral7}    &  \romannumeral7\\8 &  \uppercase\expandafter{\romannumeral8}    &  \romannumeral8\\9 &  \uppercase\expandafter{\romannumeral9}    &  \romannumeral9\\
10 &  \uppercase\expandafter{\romannumeral10}   &  \romannumeral10\\
11 &  \uppercase\expandafter{\romannumeral11}   &  \romannumeral11\\
12 &  \uppercase\expandafter{\romannumeral12}   &  \romannumeral12\\
13 &  \uppercase\expandafter{\romannumeral13}   &  \romannumeral13\\
14 &  \uppercase\expandafter{\romannumeral14}   &  \romannumeral14\\
15 &  \uppercase\expandafter{\romannumeral15}   &  \romannumeral15\\
16 &  \uppercase\expandafter{\romannumeral16}   &  \romannumeral16\\
17 &  \uppercase\expandafter{\romannumeral17}   &  \romannumeral17\\
18 &  \uppercase\expandafter{\romannumeral18}   &  \romannumeral18\\
19 &  \uppercase\expandafter{\romannumeral19}   &  \romannumeral19\\
20 &  \uppercase\expandafter{\romannumeral20}   &  \romannumeral20\\\bottomrule\end{tabular*}
\end{table}

  测试如下：

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参考资料：
【1】戳戳。