Using Boolean operations and concatenation product w.r.t special trees,quantifier hierarchies are given by way of altern......

基于网络的大规模软件应用系统面临着日益复杂的数据资源安全管理的难题．基于角色的访问控制方法(role-based access control，简称RB......

A critical review of the development of the ecosystem concept is presented in this paper. An attempt to define the conce......

生态网络分析的研究进展韩博平（厦门大学生物系，３６１００５）ＰｒｏｇｒｅｓｓｅｓｏｎｔｈｅＡｎａｌｙｓｉｓｏｆＥｃｏｎｅｔｗｏｒｋ￥ＨａｎＢｏｐｉｎｇ（ＢｉｏｌｏｇｙＤｅｐａｒｔｍｅｎｔ，ＸｉａｍｅｎＵｎｉｖｅｒｓｉｔｙ，Ｘｉａｍｅｎ３６１００５）；ＣｈｉｎｅｓｅＪｏｕｒｎａｌｏｆＥｃｏｌｏｇｙ，１９９３，１２（６）：４１－４５．Ｅｃｏｎｅｔｗｏｒｋｉｓａｓｔｒｕｃｔｕｒａｌｍｏｄｅｌｗｈｉｃｈｉｓｕｓｅｄｔｏｓｉｍｕｌａｔｅｔｈｅｆｌｏｗｏｆｍａｔｅｒｉａｌａｎｄｅｎｅｒｇｙｉｎｅｃｏｓｙｓｔｅｍ。Ｔｈ......