\documentclass[a4paper]{article}

\usepackage{natbib}
\usepackage[colorlinks=true]{hyperref}

\begin{document}

% \nocite{*}

\input{thielemann}

\bibliographystyle{plain}
\bibliography{hackage}

% with alpha style, BibTeX generates identifiers like Ant09{ that cannot be handled by LaTeX
% \bibliographystyle{alpha}
% \bibliographystyle{plain}
% \bibliography{hackage-b}

\end{document}