这是我的demo.tex：
\documentclass[12pt,a4paper]{report}
\usepackage[utf8]{inputenc}
\usepackage{natbib}
\usepackage{makeindex}
\title{Demo}
\author{Some author}
\begin{document}
\maketitle
\tableofcontents
\chapter{First}
Some text with \cite{bell1998computer}.
\chapter{Second}
ToDo
\bibliography{bibliografia}
\bibliographystyle{plain}
\end{document}
这是我的 bibliografia.bib（bibliografia.bib 是参考书目名称）：
@book{bell1998computer,
title={Computer Science Unplugged: Off-line activities and games for all ages},
author={Bell, Timothy C and Witten, Ian H and Fellows, Mike},
year={1998},
publisher={Computer Science Unplugged}
}
为了编译，我在 demo.tex 上运行以下命令：LaTeX Bibtex LaTeX LaTeX
我在编译 Bibtex 时遇到以下错误：
Process started
This is BibTeX, Version 0.99d (MiKTeX 2.9.6500 64-bit) The top-level auxiliary file: relazione1.aux The style file: plain.bst Database file #1: bibliografia.bib You're missing an entry type---line 1 of file bibliografia.bib : @ :
Process exited with error(s)
有人能帮帮我吗？谢谢大家
附言：我使用 TeXmaker 和 bibtex。