<script type="text/javascript">
   window.onload = function () {
                var minSize = 10; //最小字体
                var maxSize = 20;//最大字体
                var newOne = 600; //生成雪花间隔
                var flakColor = "#f5f5f5fa"; //雪花颜色
                var flak = $("<div></div>").css({position:"absolute","top":"0px"}).html("?");//定义一个雪花
                var dhight = $(window).height(); //定义视图高度
                var dw =$(window).width()-80; //定义视图宽度
                setInterval(function(){
                var sizeflak = minSize+Math.random()*maxSize; //产生大小不等的雪花
                var startLeft = Math.random()*dw; //雪花生成是随机的left值
                var startOpacity = 0.7+Math.random()*0.3; //随机透明度
                var endTop= dhight-100; //雪花停止top的位置
                var endLeft= Math.random()*dw; //雪花停止的left位置
                var durationfull = 5000+Math.random()*3000; //雪花飘落速度不同
                flak.clone().appendTo($("body")).css({
                "left":startLeft ,
                "opacity":startOpacity,
                "font-size":sizeflak,
                "color":flakColor
                }).animate({
                "top":endTop,
                "left":endLeft,
                "apacity":0.1
                },durationfull,function(){
                $(this).remove()
                });
                },newOne);
            }
 </script>