function onKeyDown()
{
 if ((event.keyCode==116)||(window.event.CtrlKey)||(window.event.ShiftKey)||(event.keyCode==122))
 {
 event.keyCode=0;
 event.returnValue=false;
 }
}
function yxl() { 
if(window.event.altKey) 
{
window.event.returnValue=false;
}
}
document.onkeydown=yxl