c# 用webBrowser读取网页源代码

//不能用 this.webBrowser.DocumentText 读取网页源代码，读出来是乱码

string url="http://www.yn-home.com";

this.webBrowser.Url = new System.Uri(url);            

            System.IO.StreamReader strm = new System.IO.StreamReader(this.webBrowser.DocumentStream, Encoding.GetEncoding("gb2312"));
            string docment = strm.ReadToEnd();
           // MessageBox.Show(strm.ReadToEnd());
           // return;