有临界点http://cache.baidu.com/c?word=%BE%C6%BE%AB%3B%C1%D9%BD%E7%3B%B5%E3&url=http%3A//210%2E34%2E15%2E249/wuji/yanjiuxingxuexi/13%2Edoc&b=0&a=41&user=baidu
http://cache.baidu.com/c?word=%BE%C6%BE%AB%3B%C1%D9%BD%E7%3B%B5%E3&url=http%3A//210%2E34%2E15%2E249/wuji/yanjiuxingxuexi/13%2Edoc&b=0&a=41&user=baidu