答案1
也许这就是你想要的?
\documentclass{article}
\newcommand{\uint}[4]{
\ensuremath{\underset{#3}{\int_{\!{#1}}^{#2}{#4}}}
}
\newcommand*{\dd}{\mathop{}\!\mathrm{d}}
\def \integrando {\rho_{\mu \mathrm{canonico}}\frac{\dd p^{3N} \dd q^{3N}} {h^{3N}}}
\usepackage{mathtools}
\begin{document}
\[ \int_{_\mathrm{\scriptstyle Ph\mathrlap{\mathrm{aseSpace}}}} {\integrando}=1 \]
\end{document}