The characteristics of the frequent exacerbator with chronic bronchitis phenotype and non-exacerbator phenotype in patients with chronic obstructive pulmonary disease: a meta-analy... oleh Jian-jun Wu, Hong-ri Xu, Ying-xue Zhang, Yi-xuan Li, Hui-yong Yu, Liang-duo Jiang, Cheng-xiang Wang, Mei Han