$.fn.smartfloat = function() {
	var position = function(element) {
		var top = element.position().top, pos = element.css("position");
		$(window).scroll(function() {
			var scrolls = $(this).scrolltop();
			if (scrolls > 702) {
				if (window.xmlhttprequest) {
					element.css({
						display:"block",
						position: "fixed",
						top: 0
					});	
				} else {
					element.css({
						display:"none",
						top: scrolls
					});	
				}
			}else {
				element.css({
					display:"none",
					position: pos,
					top: top
				});	
			}
		});
	};
	return $(this).each(function() {
		position($(this));						 
	});
};

//���÷���
//$("#fixed").smartfloat();