string(252) "get document error：https://zhidao.baidu.com/search?lm=0&rn=10&pn=0&fr=search&dyTabStr=null&word=%E7%AE%80%E8%BF%B0b2b%E6%A8%A1%E5%BC%8F%E6%A6%82%E5%BF%B5%E5%8F%8A%E7%89%B9%E5%BE%81 => Failed to connect to 101.89.143.195 port 38175: Connection refused"
简述b2b模式概念及特征
