// 获取指定的QueryString
function GetQueryString(fieldname)
{
    var urlstring = document.location.search;
    if(urlstring != null)
    {
         var typequ = fieldname+"=";
         var urlend = urlstring.indexOf(typequ);
         if(urlend != -1)
         {
              var paramsurl = urlstring.substring(urlend+typequ.length);
              var isend =  paramsurl.indexOf('&');
              if(isend != -1)
              {
                   return paramsurl.substring(0, isend);
              }
              else
              {
                  return paramsurl;
              }
         }
         else 
         return null;
    }
    else
        return null;
}