function change_city(){
  var city_ul = document.getElementById('city_ul');
  var city_ad = document.getElementById('city_ad');

  if(city_ul.style.display == "none"){
		$('embed, object,select').css({ 'visibility' : 'hidden' });
		$("#city_ul").css({
			//大图的位置根据窗口来判断
			"left":($(window).width()/2-350>20?$(window).width()/2-345:20)
		});
		document.getElementById('city_ul').style.display = 'block';
		document.getElementById('city_ad').style.display = 'none';
	}else{
		$('embed, object, select').css({ 'visibility' : 'visible' });
		city_ul.style.display = "none";
		city_ad.style.display = "block";
	}
}