Effect of sequential treatment with syndrome differentiation on acute exacerbation of chronic obstructive pulmonary disease and "AECOPD Risk-Window": study protocol for a randomize... oleh Haifeng Wang, Jiansheng Li, Suyun Li, Xueqing Yu, Hailong Zhang, Zhiwan Wang, Qiyi Wu, Pankui Zhang, Zhongchao Wang, Fenglei Li, Haihong Yan