string[] keysArray = {"你好","他好","她好","好她","asp.net"};
                string str = "你好啊为什么好她好为什么ASP。NET他，好Asp.net";
                string[] result_array=keysArray.Where(a => str.ToUpper().Contains(a.ToUpper())).ToArray();
                /*
                 *         [0]    "你好"    string
                        [1]    "她好"    string
                        [2]    "好她"    string
                        [3]    "asp.net"    string

                 */

------解决方案--------------------
楼上正解