\usepackage{url}
@article{ zoccolan:pnas_2009,
    author={Zoccolan, D. and Oertelt, N. and DiCarlo, J. J. and Cox, D. D.},
    title={{A rodent model for the study of invariant visual object recognition}},
    journal={Proceedings of the National Academy of Sciences},    
    volume={106},
    number={21},
    pages={8748-8753},
    issn={0027-8424},
    url={http://www.rowland.harvard.edu/cox/pdfs/PNAS-2009-Zoccolan-0811583106.pdf},
    year={2009}
}