http://sf.baidu.com/baidu.php?url=&e=dj0xJms9NTk5Nzc5MyZzPWh0dHAlM0ElMkYlMkZ3d3cudWQ4OC5jb20=00e0756a7b2765acbbfa964291e7866508228595&n=baidu&rank=1&s=ecc338fb5722f9e9&query=%BC%D3%C3%CB%D2%BB%B8%F6%C8%E7%BB%A5%BB%DD%D6%AE%C0%E0%B5%C4%B3%AC%CA%D0%B4%F3%B8%C5%D0%E8%D2%AA%B6%E0%C9%D9%C7%AE去看一下专业网站的解释吧!