$(document).ready(function() {
  
  var 
  sites_header = $('#sites_header'),
  sites = $('#sites').hide(),
  books_header = $('#books_header'),
  books = $('#books').hide(),
  research_header = $('#research_header'),
  research = $('#research').hide(),
  videos_header = $('#videos_header'),
  videos = $('#videos').hide();
  
  books_header.click(function() {
    $(books).slideToggle("fast");
  });
  
  sites_header.click(function() {
    $(sites).slideToggle("fast");
  });
  
  research_header.click(function() {
    $(research).slideToggle("fast");
  });
  
  videos_header.click(function() {
    $(videos).slideToggle("fast");
  });
  
});