每10秒刷新一次div，为什么SetTimeout()不起作用？

非常简单的任务，每10秒刷新一次div：

function upd(){
    alert('asd');
    $('#maincontent').load('providerpage.php?allimages=1 #maincontent > *');

}
window.onload=function(){
    setTimeout('upd()',10000);
}

但是上面的代码不起作用，伙计们请告诉我，它有什么问题？我为测试设置了警报，但在第一次迭代时，它只显示了一次。

As stated by Juhana and others in the comments:

That's what setTimeout() does, runs the function once. You probably want setInterval()

I don't know why no one put that as an answer (instead of a comment) so he can accept the answer, and we all leave this question alone (instead of posting closing votes).

Zheka: you can also put the answer yourself once you know the solution if no one else does.