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%E6%9C%89%E4%BB%80%E4%B9%88%E5%8C%BA%E5%88%AB => Failed to connect to 14.18.117.71 port 38220: Connection refused"
标准差和方差有什么区别
