<script>
        
window.onload=function()
{
   for(var i=0;i<document.getElementsByTagName("input").length;i++)
   {
      var thisObj=document.getElementsByTagName("input")[i];
      if(thisObj.getAttribute("type")=="text")
      {
         thisObj.onkeydown=function()
         {
            if(event.keyCode==13)
            {
               event.keyCode=9;
               event.returnValue=false;
               $(" <%=btnSearch.ClientID% >").click();
            }
         }
      }
   }
}
        
</script>

------解决方案--------------------
<script type="text/javascript">
var flag = true;
function document.onkeydown()    
{           
   if(flag)
   {  
       if(event.keyCode==13)      
       {  
           event.keyCode=9;    
           event.returnValue=false;    
           $('<%=Button1.ClientID %>').click(); 
       }  
   } 
} 
  
function document.onclick()
{
   var obj = event.srcElement;
   if(obj.type=="textarea")
   {
       flag = false;
   }
   else  
   {
       flag = true;
   }
}
</script>