The experience of tobacco withdrawal symptoms among current smokers and ex-smokers in the general population: findings from nationwide China Health Literacy Survey during 2018-19 by Cui, Z-Y, Li, Y-H, Liu, Z, Li, L, Nie, X-Q, Zhou, X-M, Cheng, A-Q, Li, J-X, Qin, R, Wei, X-W, Zhao, L, Ladmore, D, Pesola, F, Chung, KF, Chen, Z-M, Hajek, P, Xiao, D, Wang, C