string(265) "get document error：https://zhidao.baidu.com/search?lm=0&rn=10&pn=0&fr=search&dyTabStr=null&word=%E6%A0%87%E5%87%86%E5%B7%AE%E5%92%8C%E6%96%B9%E5%B7%AE%E5%93%AA%E4%B8%AA%E6%9B%B4%E5%87%86%E7%A1%AE => Failed to connect to 14.18.117.71 port 38133: Connection refused"
标准差和方差哪个更准确
