function imgadapter(obj,width,height)
    {   var max_height = height;
      //设置最大高度
         var max_width = width;
            //设置最大宽度
               var real_height = obj.height;
                  var real_width = obj.width;
                     if(obj.height>max_height)
                        {     obj.height = max_height; 
                            obj.width = Math.round(obj.height*real_width/real_height); 
                              } 
                                if(obj.width>max_width) 
                                  {     obj.width = max_width;
                                       obj.height = Math.round(obj.width*real_height/real_width); 
                                         } 
                                         } 
function check(){
    if(form1.username.value==""){
     alert("请输入用户名!");
     form1.username.focus;
     return false; 
    }
 if(form1.password.value==""){
     alert("请输入密码！");
     form1.password.focus;
     return false; 
    }
     	
    return true;
   }