admin URL

Hii all,

I am a newbi in codeigniter. i am creating an admin panel inside application/controller/admin, application/views/admin, application/models/admin.

but it is working but i am unable to use the images & javascript path, currently i am using
<link href="<?php echo base_url(); ?>admin/css/bootstrap.css" rel="stylesheet">.

it will not link to my css.