问C#HttpWebRequest类型“application/x-www-form-urlencode”--如何在内容体中发送‘&’字符？

HttpWebRequest request = (HttpWebRequest)HttpWebRequest.Create(URL);
request.Method = "POST";
request.AllowAutoRedirect = false;
request.CookieContainer = my_cookie_container;
request.Accept = "text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8";
request.ContentType = "application/x-www-form-urlencoded";

string iCalStr = GetCalendarAsString();

string strNew = "&uploadfile=true&file=" + iCalStr;

using (StreamWriter stOut = new StreamWriter(request.GetRequestStream(), System.Text.Encoding.ASCII))
 {
     stOut.Write(strNew);
     stOut.Close();
 }