参考百度百科http://baike.baidu.com/link?url=aOA8FtaYKH8XKKOcquatuzGBtRhbCsNP_IB77JaHIFR59a1JHs7x36BCvqVwYrQM0Gd4AhJUXlv9hzI1R0unOBxNarms6AQqFZARA0N48F7