如何在latex中实现这样的数学公式排版？

这样还存一个问题，对于不同部分如果高度不一样，最后得到的横线貌似不在同一水平位置：

\documentclass[border=2pt,tikz]{standalone}
\usetikzlibrary{tikzmark}
\begin{document}
\begin{tikzpicture}[remember picture]
     \node [right] at (0,0) {
         $\tikzmarknode{a}{\frac{\partial f_{nk}(r,t)}{\partial t}}+\tikzmarknode{b}{v_{nk}\cdot \nabla_r f_{nk}(r,t) + \frac{F}{\hbar}\cdot \nabla_k f_{nk(r,t)}}
         =\tikzmarknode{c}{\mathcal{I}[f_{nk}]}$
     };
     \draw [red, line width = .35pt]  ([yshift=-5pt]a.south west) -- ([yshift=-5pt]a.south east) node [midway,below=1pt,scale=.5,text=black] {电子占据随时间的演变};
     \draw [blue,line width = .35pt]  ([yshift=-5pt]b.south west) -- ([yshift=-5pt]b.south east) node [midway,below=1pt,scale=.5,text=black] {外场导致的漂移项};
     \draw [cyan,line width = .35pt]  ([yshift=-5pt]c.south west) -- ([yshift=-5pt]c.south east) node [midway,below=1pt,scale=.5,text=black] {碰撞项};
  \end{tikzpicture}
\end{document}

@u3379 可以考虑使用vphantom插入一个虚拟的盒子占位，把tikznode撑大

\documentclass[border=2pt,tikz]{standalone}
\usetikzlibrary{tikzmark}
\begin{document}
\begin{tikzpicture}[remember picture]
     \node [right] at (0,0) {
         $\tikzmarknode{a}{\frac{\partial f_{nk}(r,t)}{\partial t}}+\tikzmarknode{b}{v_{nk}\cdot \nabla_r f_{nk}(r,t) + \frac{F}{\hbar}\cdot \nabla_k f_{nk(r,t)}}
         =\tikzmarknode{c}{\vphantom{\frac{\partial f_{nk}(r,t)}{\partial t}}\mathcal{I}[f_{nk}]}$
     };
     \draw [red, line width = .35pt]  ([yshift=-5pt]a.south west) -- ([yshift=-5pt]a.south east) node [midway,below=1pt,scale=.5,text=black] {电子占据随时间的演变};
     \draw [blue,line width = .35pt]  ([yshift=-5pt]b.south west) -- ([yshift=-5pt]b.south east) node [midway,below=1pt,scale=.5,text=black] {外场导致的漂移项};
     \draw [cyan,line width = .35pt]  ([yshift=-5pt]c.south west) -- ([yshift=-5pt]c.south east) node [midway,below=1pt,scale=.5,text=black] {碰撞项};
  \end{tikzpicture}
\end{document}

@u70550 哎呀....忘记调用ctex支持中文了...我不管了...这是你评论里mwe的问题😡

@u70550 好滴，好滴，另外还想问一下，为什么我这里画的线不是从公式的左下角开始而是偏左一点呢,从您给出的图也能看到，不是从左下角开始的？

\documentclass[border=2pt,tikz]{standalone}
\usepackage{ctex}
\usetikzlibrary{tikzmark}
\begin{document}
\begin{tikzpicture}[remember picture]
     \node [right] at (0,0) {
         $\tikzmarknode{a}{\frac{\partial f_{nk}(r,t)}{\partial t}}+\tikzmarknode{b}{v_{nk}\cdot \nabla_r f_{nk}(r,t) + \frac{F}{\hbar}\cdot \nabla_k f_{nk(r,t)}}
         =\tikzmarknode{c}{\vphantom{\frac{\partial f_{nk}(r,t)}{\partial t}}\mathcal{I}[f_{nk}]}$
     };
     \draw [red, line width = .35pt]  ([yshift=-5pt]a.south west) -- ([yshift=-5pt]a.south east) node [midway,below=1pt,scale=.5,text=black] {电子占据随时间的演变};
     \draw [blue,line width = .35pt]  ([yshift=-5pt]b.south west) -- ([yshift=-5pt]b.south east) node [midway,below=1pt,scale=.5,text=black] {外场导致的漂移项};
     \draw [cyan,line width = .35pt]  ([yshift=-5pt]c.south west) -- ([yshift=-5pt]c.south east) node [midway,below=1pt,scale=.5,text=black] {碰撞项};
  \end{tikzpicture}
\end{document}

@u3379 你所说的不正确间距，有可能是因为tikzmarknode不是零宽造成的，如果确需刚好卡在盒子的“正确四角”，可以使用overlay模式。

但是使用overlay模式后，如果遇到高低不平的情况且存在过高的数学元素，行内公式可能需要手动添加额外的垂直间距，以规避重叠的情况，行间公式你可以自己测试一下。

\documentclass{article}
\usepackage[margin=.5cm,papersize={5cm,6cm},showframe]{geometry}
\usepackage{xcolor}
\usepackage{tikz}
    \usetikzlibrary{tikzmark}
\def\myvp{\displaystyle\sum_{n=1}^{i}x^2}
\begin{document}
\pagecolor{gray}
%%对照组：
$\tikzmarknode{a}{e^{\pi i}}+
 \tikzmarknode{b}{\frac1x}\not=
 \tikzmarknode{c}{\displaystyle\sum_{n=1}^{i}x^2}$
\begin{tikzpicture}[remember picture,overlay]
%%绿色的是辅助线，可以不看
    \draw [green,dotted] 
        ([yshift=2pt]a.north west) -- ([yshift=2pt]a.north east);
    \draw [green,dotted] 
        ([yshift=2pt]a.north west) -- ([yshift=-30pt]a.north west);
    \draw [green,dotted] 
        ([yshift=2pt]a.north east) -- ([yshift=-30pt]a.north east);
    \draw [green,dotted] 
        ([yshift=2pt]b.north west) -- ([yshift=2pt]b.north east);
    \draw [green,dotted] 
        ([yshift=2pt]b.north west) -- ([yshift=-30pt]b.north west);
    \draw [green,dotted] 
        ([yshift=2pt]b.north east) -- ([yshift=-30pt]b.north east);
    \draw [green,dotted] 
        ([yshift=2pt]c.north west) -- ([yshift=2pt]c.north east);
    \draw [green,dotted] 
        ([yshift=2pt]c.north west) -- ([yshift=-40pt]c.north west);
    \draw [green,dotted] 
        ([yshift=2pt]c.north east) -- ([yshift=-40pt]c.north east);
%%对照组，下方的横线与注释
    \draw [red]  ([yshift=-2pt]a.south west) -- ([yshift=-2pt]a.south east) node [midway,below=1pt,scale=.5,text=black] {What};
    \draw [blue] ([yshift=-2pt]b.south west) -- ([yshift=-2pt]b.south east) node [midway,below=1pt,scale=.5,text=black] {is};
    \draw [cyan] ([yshift=-2pt]c.south west) -- ([yshift=-2pt]c.south east) node [midway,below=1pt,scale=.5,text=black] {this?};
\end{tikzpicture} 
\vskip.5cm
Hello, this is what? Hello, this is what? 
\vskip.5cm
%%实验组：
$\tikzmarknode{A}{e^{\pi i}\vphantom{\myvp}}+
 \tikzmarknode{B}{\frac1x\vphantom{\myvp}}\not=
 \tikzmarknode{C}{\myvp\vphantom{\myvp}}$
\begin{tikzpicture}[remember picture,overlay]
%%绿色的是辅助线，可以不看
    \draw [green,dotted] 
        ([yshift=2pt]A.north west) -- ([yshift=2pt]A.north east);
    \draw [green,dotted] 
        ([yshift=2pt]A.north west) -- ([yshift=-40pt]A.north west);
    \draw [green,dotted] 
        ([yshift=2pt]A.north east) -- ([yshift=-40pt]A.north east);
    \draw [green,dotted] 
        ([yshift=2pt]B.north west) -- ([yshift=2pt]B.north east);
    \draw [green,dotted] 
        ([yshift=2pt]B.north west) -- ([yshift=-40pt]B.north west);
    \draw [green,dotted] 
        ([yshift=2pt]B.north east) -- ([yshift=-40pt]B.north east);
    \draw [green,dotted] 
        ([yshift=2pt]C.north west) -- ([yshift=2pt]C.north east);
    \draw [green,dotted] 
        ([yshift=2pt]C.north west) -- ([yshift=-40pt]C.north west);
    \draw [green,dotted] 
        ([yshift=2pt]C.north east) -- ([yshift=-40pt]C.north east);
%%实验组，下方的横线与注释
    \draw [red]  ([yshift=-2pt]A.south west) -- ([yshift=-2pt]A.south east) node [midway,below=1pt,scale=.5,text=black] {What};
    \draw [blue] ([yshift=-2pt]B.south west) -- ([yshift=-2pt]B.south east) node [midway,below=1pt,scale=.5,text=black] {is};
    \draw [cyan] ([yshift=-2pt]C.south west) -- ([yshift=-2pt]C.south east) node [midway,below=1pt,scale=.5,text=black] {this?};
\end{tikzpicture} \color{yellow!1}Hello, this is what? Hello, this is what? 
\end{document}

@u101077 如果不嫌麻烦，自己手动调节横线的左右偏移量也是可以的，就在yshift那个中括号里，加上英文逗号和xshift=...就可以了，表示括弧里的坐标向左右偏移

@u101077 好滴好滴，谢谢大佬

@u3379 我的上一个评论是完全基于你的评论给出的代码，你评论的代码画线本来就有

不是从公式的左下角开始而是偏左一点

的问题。

听从@u101077 老师的建议即可...