function show(id,e,f){
var obj = document.getElementById('phtm');
    if(f){
        document.getElementById('bImg').src = ""+f;//可设地址"./images/"+f;
   st = document.documentElement.scrollTop; //下拉距离
   st = st ? st : document.body.scrollTop; //chrom不支持documentElement
   if(e.clientY > 0){ //离上边超过一张图,在当前位置上面显示
    cY = st + e.clientY - 0;//
   }else{
    cY = st + e.clientY + 20;//
   }
        obj.style.top = cY + 'px';
     obj.style.left = e.clientX + 20 + 'px';//
        obj.style.display = 'block';
    }
    else {
   obj.style.display = 'none';
}
}