我写的例子抓取网页源码，可得到的不是想要的：如：抓取链接"http://www.google.com.hk/search?&num=20&q=%e6%ad%a6%e5%a4%a7"的源码，得到的内容与打开此链接看到的不同。求帮助，不胜感激。。。。。。。
 class Program
  {
  static string ChangeKeywordEncoding(string keyword, string codeType)
  {
  return HttpUtility.UrlEncode(keyword, Encoding.GetEncoding(codeType));
  }
   
  static string GetHttpPageSourceCode(string url, string codeType)
  {
  //判断网页编码
  Encoding wCode;
  HttpWebRequest wReq = (HttpWebRequest)WebRequest.Create(@url);
  wReq.UserAgent = "Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 5.0; .NET CLR 1.1.4322; .NET CLR 2.0.50215;)";
  wReq.Referer = url;
  wReq.Method = "GET";
  string strWebData;
   
  //设置页面超时时间为30秒
  wReq.Timeout = 30000;

  HttpWebResponse wResp = (HttpWebResponse)wReq.GetResponse();
  Stream respStream = wResp.GetResponseStream();

  switch (codeType)
  {
  case "auto":
  wCode = Encoding.Default;
  string cType = wResp.ContentType.ToLower();
  Match charSetMatch = Regex.Match(cType, "(?<=charset=)([^<]*)*", RegexOptions.IgnoreCase | RegexOptions.Multiline);
  string webCharSet = charSetMatch.ToString();
  wCode = Encoding.GetEncoding(webCharSet);
  wCode = Encoding.Default;
  break;
  case "gb2312":
  wCode = Encoding.GetEncoding("gb2312");
  break;
  case "gbk":
  wCode = Encoding.GetEncoding("gbk");
  break;
  case "utf-8":
  wCode = Encoding.UTF8;
  break;
  default:
  wCode = Encoding.UTF8;
  break;
  }
  StreamReader reader = new StreamReader(respStream, wCode);
  strWebData = reader.ReadToEnd();
  reader.Close();
  reader.Dispose();

  return strWebData;
  }

  static void Main(string[] args)
  {
  StreamWriter sw = new StreamWriter("123.txt",false,Encoding.GetEncoding("GB2312"));
  string keyword=Console.ReadLine();
  string baseURL = "http://www.google.com.hk/search?&num=20&q="+ChangeKeywordEncoding(keyword, "utf-8") ;

  string sourceCode = GetHttpPageSourceCode(baseURL, "utf-8");
  sw.WriteLine(sourceCode);
  Console.Read();
  }
  }