function show(id,e,f){
	var obj = document.getElementById('phtm');
    if(f){
        document.getElementById('bImg').src = "./images/"+f;
		st = document.documentElement.scrollTop; //下拉距离
		st = st ? st : document.body.scrollTop; //chrom不支持documentElement
		if(e.clientY > 320){ //离上边超过一张图,在当前位置上面显示
			cY = st + e.clientY - 340;
		}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';
	}
}