function chg_date(){
 if (document.getElementById('si_it').selectedIndex == 1) {
     document.getElementById('si_ds').disabled = false; 
     document.getElementById('si_ds').style.backgroundColor = '#FFFFFF';
     document.getElementById('si_de').disabled = false;
     document.getElementById('si_de').style.backgroundColor = '#FFFFFF';
   }
 else {
     document.getElementById('si_ds').disabled = true; 
     document.getElementById('si_ds').style.backgroundColor = '#999999';
     document.getElementById('si_de').disabled = true;
     document.getElementById('si_de').style.backgroundColor = '#999999';
   }
}