string(375) "get document error：https://zhidao.baidu.com/search?lm=0&rn=10&pn=0&fr=search&dyTabStr=null&word=%E4%BA%92%E8%81%94%E7%BD%91%E5%8F%91%E5%B1%95%E7%9A%84%E5%90%84%E4%B8%AA%E9%98%B6%E6%AE%B5%E5%8F%8A%E7%9B%B8%E5%BA%94%E7%9A%84%E5%BA%94%E7%94%A8%E9%A2%86%E5%9F%9F%E5%88%86%E5%88%AB%E6%98%AF%E4%BB%80%E4%B9%88 => Failed to connect to 101.89.117.144 port 38017: Connection refused"
互联网发展的各个阶段及相应的应用领域分别是什么
