MathSciDoc: An Archive for Mathematician ∫

@inproceedings{george1927on,
  title={On the periodic motions of dynamical systems},
  author={George D. Birkhoff},
  url={http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203048539446406},
  booktitle={Acta Mathematica},
  volume={50},
  number={1},
  pages={359-379},
  year={1927},
}