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 ;