string(285) "get document error：https://zhidao.baidu.com/search?lm=0&rn=10&pn=0&fr=search&dyTabStr=null&word=%E5%8F%98%E5%8A%A8%E6%88%90%E6%9C%AC%E8%AE%A1%E7%AE%97%E6%96%B9%E6%B3%95%E7%9A%84%E4%B8%BB%E8%A6%81%E7%89%B9%E7%82%B9 => Failed to connect to 101.89.117.144 port 38005: Connection refused"
变动成本计算方法的主要特点
