public string SendRequest(string url, string requestString)
        {
            try
            {
                byte[] requestBytes = System.Text.Encoding.ASCII.GetBytes(requestString);
                request = (HttpWebRequest)WebRequest.CreateDefault(new Uri(url));
                request.ContentType = "text/html; charset=gb2312";
                request.ContentLength = requestBytes.Length;
                request.Referer = "http://www.51.com";
                request.Method = "POST";
                request.CookieContainer = cookie;
                using (Stream writer = request.GetRequestStream())
                {
                    writer.Write(requestBytes, 0, requestBytes.Length);
                }
                response = (HttpWebResponse)request.GetResponse();
                StreamReader reader = new StreamReader(response.GetResponseStream(), Encoding.GetEncoding("GB2312"));
                string str = reader.ReadToEnd();
                reader.Close();
                response.Close();
                return str;
            }
            catch (Exception ex)
            {
                throw ex;
            }
        }