function navover(object){
  //主菜单
  var mm=document.getElementById("nav_"+object);
  mm.className="nav_over";
  //初始主菜单先隐藏效果
  if(def!=0){
    var mdef=document.getElementById("nav_"+def);
    mdef.className="nav_def";
  }
}

function navout(object){
  //主菜单
  var mm=document.getElementById("nav_"+object);
  mm.className="nav_def";
  //初始主菜单还原效果
  if(def!=0){
    var mdef=document.getElementById("nav_"+def);
    mdef.className="nav_over";
  }
}