HttpWebRequest乱码问题

public static string getWebContent(string Url, string referer, string ch)

        {

            string strResult = "";

            try

            {

                HttpWebRequest request = (HttpWebRequest)WebRequest.Create(Url);

                request.Timeout = 30000;//设置连接超时时间

                request.UserAgent = "Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 5.2; ccdotnet ; .NET CLR 1.1.4322; .NET CLR 2.0.50727)";

                request.Referer = referer;//设置标头

                request.AllowAutoRedirect = true;

                //不用缓存

                //request.Headers.Set("Pragma", "no-cache");//不用缓存的话，对方服务器返回500错误

                HttpWebResponse response = (HttpWebResponse)request.GetResponse();

                Stream streamReceive = response.GetResponseStream();

                Encoding encoding = Encoding.GetEncoding(ch);

                StreamReader streamReader = new StreamReader(streamReceive, encoding);

                strResult = streamReader.ReadToEnd();

            }

            catch (Exception ex) { HttpContext.Current.Response.Write(ex.ToString()); }

            return strResult;

        }

//抓取的地址http://www.qidian.com/BookReader/180029.aspx

//编码设置为gb2312，目标网址编码也是gb2312，但是返回结果是乱码，有什么解决的办法没？