string(231) "get document error：https://zhidao.baidu.com/search?lm=0&rn=10&pn=0&fr=search&dyTabStr=null&word=%E5%AF%BC%E6%95%B0%E7%9A%84%E6%80%A7%E8%B4%A8%E6%80%BB%E7%BB%93 => Failed to connect to 101.89.117.144 port 38022: Connection refused"
导数的性质总结
