Efficacy differences of electroacupuncture with single acupoint or matching acupoints for chemotherapy-induced nausea and vomiting: study protocol for a randomized controlled trial oleh Bo Chen, Yang Guo, Xue Zhao, Li-li Gao, Bo Li, Tian-yi Zhao, Qi-wen Zhang, Jin-xing Zou, Ming-yue Li, Yong-ming Guo, Yi Guo, Xing-fan Pan