string(230) "get document error：https://zhidao.baidu.com/search?lm=0&rn=10&pn=0&fr=search&dyTabStr=null&word=%E8%AE%BA%E6%96%87%E6%91%98%E8%A6%81%E7%9A%84%E6%A0%BC%E5%BC%8F%E8%A6%81%E6%B1%82 => Received HTTP code 403 from proxy after CONNECT"
论文摘要的格式要求
