\documentclass[12pt]{article}
\usepackage{amssymb,amsmath,amscd,concmath,amsfonts}
\usepackage{color}
\pagestyle{empty}
\begin{document}
\begin{equation*}
  u(t) = k_i \int\limits _0^t\,e(\tau)d\tau .
\end{equation*}
\end{document}