documentclass[12pt]{article}
usepackage[sort&compress,numbers]{natbib}
% Other
usepackage{hyperref}
usepackage{indentfirst}

begin{document}

section{first section}
AAAcitep{bell_beyond_2009} cccc bbbcitep{noauthor_cern_nodate}.

bibliographystyle{unsrtnat}
bibliography{bibliography/sample}
end{document}