//menu
$(document).ready(function(){
  
  $('li.mainlevel').mousemove(function(){
  $(this).find('ul').slideDown();//you can give it a speed
  });
  $('li.mainlevel').mouseleave(function(){
  $(this).find('ul').slideUp("fast");
  });
  
});

function qiehuan(num){
		for(var id = 0;id<=6;id++)
		{
			if(id==num)
			{
				document.getElementById("mynav"+id).className="nav_on";
			}
			else
			{
				document.getElementById("mynav"+id).className="nav_off";
			}
		}
	}