Android四种启动模式
http://www.cnblogs.com/fanchangfa/archive/2012/08/25/2657012.html
Android 关闭多个视图Intent.FLAG_ACTIVITY_CLEAR_TOP用法
http://blog.csdn.net/lvxiangan/article/details/42120951
http://blog.csdn.net/vfush/article/details/51482296
