1 Introduction
Modern biotechnology has significantly propelled the development of global economy and has a major impact on our life[1-2].According to the report released in March 2011 by IMS Health,the sales of the global pharmaceutical market were $856.4 billion,setting a record high.Specifically,the sales of the world's largest drug market,North America,reached $334.7 billion in 2010 by an increase of 1.9%,accounting for 39% of the global market.