@article{liu2018the,
  title = {The Statistics of Recyclable Resources in Beijing: Satus, Problems and Countermeasures}
  author = {Liu, Tingting; Wu, Yufeng; Tian, Xi; Gong, Yu; Li, Yanmei},
  journal = {IOP Conference Series: Earth and Environmental Science},
  url = {https://doi.org/10.1088%2F1755-1315%2F178%2F1%2F012040},
  doi = {10.1088/1755-1315/178/1/012040},
  year = {2018}
}