Can not use jQuery UI in the View with _Layout in ASP.NET MVC.

See more:

ASP.NET

MVC

jQuery

In ASP.NET MVC 4, I wanna use datepicker() of jQuery UI plugin in index.cshtml.
The problem is:
if I use the _Layout.cshtml( return View("index")) as masterpage, the datepicker() method doesn't work;
if I don't use the _Layout.cshtml (return PartialView("index")), the datepicker() works!
The same view, without or with the _Layout.cshtml, has different effect. Is there anything wrong in _Layout.cshtml?
The script to find the element is:

$(function () {
    $("#dateBegin").attr("readonly","true").datepicker();
    $("#dateEnd").attr("readonly","true").datepicker();
});