function KeyDown(){ 
//屏蔽鼠标右键、Ctrl+n、shift+F10、F5刷新、退格键
//alert("ASCII代码是："+event.keyCode);
  if ((window.event.altKey)&&
      ((window.event.keyCode==37)||   //屏蔽 Alt+ 方向键 ←
       (window.event.keyCode==39))){  //屏蔽 Alt+ 方向键 →
     alert("不准你使用ALT+方向键前进或后退网页！");
     event.returnValue=false;
     }
  if ((event.keyCode==8)  ||                 //屏蔽退格删除键
      (event.keyCode==116)||                 //屏蔽 F5 刷新键
      (event.keyCode==112)||                 //屏蔽 F1 刷新键
      (event.ctrlKey && event.keyCode==82)){ //Ctrl + R
     event.keyCode=0;
     event.returnValue=false;
     }
  if ((event.ctrlKey)&&(event.keyCode==78))   //屏蔽 Ctrl+n
     event.returnValue=false;
  if ((event.shiftKey)&&(event.keyCode==121)) //屏蔽 shift+F10
     event.returnValue=false;
  if (window.event.srcElement.tagName == "A" && window.event.shiftKey) 
      window.event.returnValue = false;  //屏蔽 shift 加鼠标左键新开一网页
  if ((window.event.altKey)&&(window.event.keyCode==115)){ //屏蔽Alt+F4
      window.showModelessDialog("about:blank","","dialogWidth:1px;dialogheight:1px");
      return false;}
}