@article{su2009urban,
  title = {Urban ecosystem health assessment based on emergy and set pair analysis—A comparative study of typical Chinese cities}
  author = {Su, M. R.; Yang, Z. F.; Chen, B.; Ulgiati, S.},
  journal = {Ecological Modelling},
  url = {http://www.sciencedirect.com/science/article/pii/S0304380009003974},
  doi = {10.1016/j.ecolmodel.2009.06.010},
  year = {2009}
}