\begin{landscape}
\begin{table}[!h]\renewcommand{\arraystretch}{1}\addtolength{\tabcolsep}{0 pt}
\centering
\caption{Diagnostic test statistics for all models \& Emerging markets.}
\label{T.55}
\begin{tabularx}{0.95\linewidth}{lccccc||lccccc}
\hline
\rule{0pt}{12pt}&\multicolumn{5}{c||}{$H(6)$}&\multicolumn{5}{c}{$H(6)$}\\
\hline
\rule{0pt}{12pt} Model &Linear &Quadratic &Cubic &GAM &KFMR & Model&Linear &Quadratic &Cubic &GAM &KFMR\\
\hline
\rule{0pt}{12pt}\it{Developed}&&&&&&\it {Emerging} &&&&&\\
France &4383.99&2005.36&1821.74&1948.91&95.81 & Brazil &54.97 &37.75 &37.52 &25.39 &11.07\\
&0.000 &0.000 &0.000 &0.000 &0.000 & &0.000 &0.000 &0.000 &0.013 &0.086\\
Germany &817.98 &124.25 &62.88 &59.35 &83.53 &Chile &17.20 &13.45 &11.08 &12.52 &9.56\\
&0.000 &0.000 &0.000 &0.000 &0.000 & &0.142 &0.337 &0.522 &0.405 &0.144\\
Italy &132.74 &134.65 &131.79 &115.64 &110.47&India&25.72 &26.33 &28.56 &27.08 &15.79\\
&0.000 &0.000 &0.000 &0.000 &0.000 & &0.012 &0.010 &0.005 &0.008 &0.015\\
Japan &1900.93&2163.24&2192.52&2337.99&451.05&Korea &94.92 &103.49 &102.98 &105.92 &13.39\\
&0.000 &0.000 &0.000 &0.000 &0.000 & &0.000 &0.000 &0.000 &0.000 &0.037\\
Norway &229.48 &230.47 &293.06 &268.82 &312.29&Malaysia &11.91 &12.57 &9.31 &10.54 &13.07\\
&0.000 &0.000 &0.000 &0.000 &0.000 & &0.453 &0.401 &0.676 &0.569 &0.042\\
Sweden &1054.32&75.38 &52.96 &44.84 &55.49 &Mexico &43.77 &30.22 &27.89 &23.55 &19.18\\
&0.000 &0.000 &0.000 &0.000 &0.000 & &0.000 &0.003 &0.006 &0.023 &0.004\\
Switzerland &513.14 &498.66 &413.96 &455.74 &88.40 &Poland &44.50 &45.00 &41.61 &40.49 &25.94\\
&0.000 &0.000 &0.000 &0.000 &0.000 & &0.000 &0.000 &0.000 &0.000 &0.000\\
UK &403.55 &297.95 &274.03 &169.71 &379.99&Russia &25.77 &25.76 &23.37 &19.01 &19.93\\
&0.000 &0.000 &0.000 &0.000 &0.000 & &0.012 &0.012 &0.025 &0.088 &0.003\\
USA &616.13 &598.02 &535.16 &612.09 &23.49 &SouthAfrica &28.46 &24.02 &24.58 &22.39&17.34\\
&0.000 &0.000 &0.000 &0.000 &0.000 & &0.005 &0.020 &0.017 &0.033 &0.008\\
\hline
\end{tabularx}
\end{table}
\end{landscape}
答案1
请始终发布完整的文档，而不仅仅是片段。
tabularx由于没有X列，因此没有执行任何操作，因此我切换到tabular。
\it自 LaTeX2.09（即 1993 年之前）以来，在 latex 中默认没有定义，除非需要与旧文档兼容，否则不要使用它。您可以使用该array包将字体更改插入每个单元格。
\documentclass[a4paper]{article}
\newcount\rownum
\usepackage{lscape,array}
\begin{document}
\newcommand\rowstyle{\relax\ifodd\rownum\itshape\tiny\fi}
\begin{landscape}
\begin{table}[!h]
%\renewcommand{\arraystretch}{1}
%\addtolength{\tabcolsep}{0 pt}
\centering
\caption{Diagnostic test statistics for all models \& Emerging markets.}
\label{T.55}
\begin{tabular}{>{\global\advance\rownum1 \rowstyle}l*{5}{>\rowstyle{c}}||>\rowstyle{l}*{5}{>\rowstyle{l}}}
\hline
\rule{0pt}{12pt}&\multicolumn{5}{c||}{$H(6)$}&\multicolumn{5}{c}{$H(6)$}\\
\hline
\rule{0pt}{12pt} Model &Linear &Quadratic &Cubic &GAM &KFMR & Model&Linear &Quadratic &Cubic &GAM &KFMR\\
\hline
\rule{0pt}{12pt}\normalsize Developed&&&&&&\normalsize Emerging &&&&&\\
France &4383.99&2005.36&1821.74&1948.91&95.81 & Brazil &54.97 &37.75 &37.52 &25.39 &11.07\\
&0.000 &0.000 &0.000 &0.000 &0.000 & &0.000 &0.000 &0.000 &0.013 &0.086\\
Germany &817.98 &124.25 &62.88 &59.35 &83.53 &Chile &17.20 &13.45 &11.08 &12.52 &9.56\\
&0.000 &0.000 &0.000 &0.000 &0.000 & &0.142 &0.337 &0.522 &0.405 &0.144\\
Italy &132.74 &134.65 &131.79 &115.64 &110.47&India&25.72 &26.33 &28.56 &27.08 &15.79\\
&0.000 &0.000 &0.000 &0.000 &0.000 & &0.012 &0.010 &0.005 &0.008 &0.015\\
Japan &1900.93&2163.24&2192.52&2337.99&451.05&Korea &94.92 &103.49 &102.98 &105.92 &13.39\\
&0.000 &0.000 &0.000 &0.000 &0.000 & &0.000 &0.000 &0.000 &0.000 &0.037\\
Norway &229.48 &230.47 &293.06 &268.82 &312.29&Malaysia &11.91 &12.57 &9.31 &10.54 &13.07\\
&0.000 &0.000 &0.000 &0.000 &0.000 & &0.453 &0.401 &0.676 &0.569 &0.042\\
Sweden &1054.32&75.38 &52.96 &44.84 &55.49 &Mexico &43.77 &30.22 &27.89 &23.55 &19.18\\
&0.000 &0.000 &0.000 &0.000 &0.000 & &0.000 &0.003 &0.006 &0.023 &0.004\\
Switzerland &513.14 &498.66 &413.96 &455.74 &88.40 &Poland &44.50 &45.00 &41.61 &40.49 &25.94\\
&0.000 &0.000 &0.000 &0.000 &0.000 & &0.000 &0.000 &0.000 &0.000 &0.000\\
UK &403.55 &297.95 &274.03 &169.71 &379.99&Russia &25.77 &25.76 &23.37 &19.01 &19.93\\
&0.000 &0.000 &0.000 &0.000 &0.000 & &0.012 &0.012 &0.025 &0.088 &0.003\\
USA &616.13 &598.02 &535.16 &612.09 &23.49 &SouthAfrica &28.46 &24.02 &24.58 &22.39&17.34\\
&0.000 &0.000 &0.000 &0.000 &0.000 & &0.005 &0.020 &0.017 &0.033 &0.008\\
\hline
\end{tabular}
\end{table}
\end{landscape}
\end{document}
答案2
以下用途collcell以及来自改进的\rowstyle以单元格内容作为参数和用于数组/表格单元格的计数器：
\documentclass{article}
\usepackage{pdflscape,array,collcell}% http://ctan.org/pkg/{pdflscape,array,collcell}
% https://tex.stackexchange.com/q/32861/5764
\newsavebox\TBox\newif\iffbox \fboxfalse
\newcommand{\rowstyle}[1]{\ifnum\value{storerow}>3\ifodd\value{storerow}\raisebox{\height}{\itshape\tiny#1}\else#1\fi\fi}
\newcounter{storerow}
\newcolumntype{C}{%
>{\setcounter{storerow}{\value{tabrow}}\collectcell\rowstyle}
c
<{\endcollectcell}}
% https://tex.stackexchange.com/q/65649/5764
\makeatletter
\def\insert@column{%
\the@toks \the \@tempcnta
\global\advance\c@tabcol\@ne
\ignorespaces \@sharp \unskip
\the@toks \the \count@ \relax}
\let\old@arraycr\@arraycr
\def\@arraycr{\global\c@tabcol\z@\global\advance\c@tabrow\@ne\old@arraycr}
\let\old@tabarray\@tabarray
\def\@tabarray{\global\c@tabrow\@ne\global\c@tabcol\z@\old@tabarray}
\makeatother
\newcounter{tabcol}\newcounter{tabrow}
\begin{document}
\begin{landscape}
\begin{table}[p]
\centering
\caption{Diagnostic test statistics for all models \& Emerging markets.}
\label{T.55}
\begin{tabular}{l*{5}{C}||l*{5}{C}}
\hline
\strut&\multicolumn{5}{c||}{$H(6)$}&&\multicolumn{5}{c}{$H(6)$}\\
\hline
\strut Model &Linear &Quadratic &Cubic &GAM &KFMR & Model&Linear &Quadratic &Cubic &GAM &KFMR\\
\hline
\strut\textit{Developed} & \multicolumn{5}{c||}{} & \textit{Emerging} & \multicolumn{5}{c}{} \\
France &4383.99&2005.36&1821.74&1948.91&95.81 & Brazil &54.97 &37.75 &37.52 &25.39 &11.07\\
&0.000 &0.000 &0.000 &0.000 &0.000 & &0.000 &0.000 &0.000 &0.013 &0.086\\
Germany &817.98 &124.25 &62.88 &59.35 &83.53 &Chile &17.20 &13.45 &11.08 &12.52 &9.56\\
&0.000 &0.000 &0.000 &0.000 &0.000 & &0.142 &0.337 &0.522 &0.405 &0.144\\
Italy &132.74 &134.65 &131.79 &115.64 &110.47&India&25.72 &26.33 &28.56 &27.08 &15.79\\
&0.000 &0.000 &0.000 &0.000 &0.000 & &0.012 &0.010 &0.005 &0.008 &0.015\\
Japan &1900.93&2163.24&2192.52&2337.99&451.05&Korea &94.92 &103.49 &102.98 &105.92 &13.39\\
&0.000 &0.000 &0.000 &0.000 &0.000 & &0.000 &0.000 &0.000 &0.000 &0.037\\
Norway &229.48 &230.47 &293.06 &268.82 &312.29&Malaysia &11.91 &12.57 &9.31 &10.54 &13.07\\
&0.000 &0.000 &0.000 &0.000 &0.000 & &0.453 &0.401 &0.676 &0.569 &0.042\\
Sweden &1054.32&75.38 &52.96 &44.84 &55.49 &Mexico &43.77 &30.22 &27.89 &23.55 &19.18\\
&0.000 &0.000 &0.000 &0.000 &0.000 & &0.000 &0.003 &0.006 &0.023 &0.004\\
Switzerland &513.14 &498.66 &413.96 &455.74 &88.40 &Poland &44.50 &45.00 &41.61 &40.49 &25.94\\
&0.000 &0.000 &0.000 &0.000 &0.000 & &0.000 &0.000 &0.000 &0.000 &0.000\\
UK &403.55 &297.95 &274.03 &169.71 &379.99&Russia &25.77 &25.76 &23.37 &19.01 &19.93\\
&0.000 &0.000 &0.000 &0.000 &0.000 & &0.012 &0.012 &0.025 &0.088 &0.003\\
USA &616.13 &598.02 &535.16 &612.09 &23.49 &SouthAfrica &28.46 &24.02 &24.58 &22.39&17.34\\
&0.000 &0.000 &0.000 &0.000 &0.000 & &0.005 &0.020 &0.017 &0.033 &0.008\\
\hline
\end{tabular}
\end{table}
\end{landscape}
\end{document}