Your website will always download the entire library.
However, there is a potential solution to reduce loading delays. Utilize a Content Delivery Network (CDN), similar to this example for Twitter:
<link rel="stylesheet" type="text/css" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.6/css/bootstrap.min.css" />
or
<script type="text/javascript" src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.6/js/bootstrap.min.js"></script>
By implementing this approach, it increases the likelihood that users have previously visited websites utilizing the same libraries you are using, resulting in cached files for bootstrap, jquery, or other popular libraries already stored in their memory.