var wc = new WebClient();
            //下载网络资源到文件
            wc.DownloadFile("http://www.baidu.com/img/PCtm_d9c8750bed0b3c7d089fa7d55720d6cf.png", "d:\\1.png");
            //下载网络资源到内存
            var bytes = wc.DownloadData("http://www.baidu.com/img/PCtm_d9c8750bed0b3c7d089fa7d55720d6cf.png");
            //下载网络资源到字符串
            var html = wc.DownloadString("http://www.baidu.com");