Raw Source
progman32 / Single-click PDF access 

// ==UserScript==
// @name        Single-click PDF access
// @namespace   giferrari.net
// @include     http://www.alldatasheet.com/view.jsp*
// @version     1
// @grant       none
// @require       http://ajax.googleapis.com/ajax/libs/jquery/1.6/jquery.js
// ==/UserScript==

// Grab all links that appear to redirect to a PDF page.
// There isn't a class that we can key off of, so we look for all
// anchors that have a PDF icon in them.
var datasheetPdfLinks = $('img[src="http://other.alldatasheet.com/etc/electronic_parts_datasheet.gif"]').closest('a');

// Open in same window instead of a new one.
datasheetPdfLinks.attr('target', null)

// Go to the PDF page directly.
datasheetPdfLinks.attr('href', function(i, oldHref) {
  // From:
  // http://www.alldatasheet.com/datasheet-pdf/pdf/317775/COMSET/2N2222.html
  // To:
  //http://pdf1.alldatasheet.com/datasheet-pdf/view/317775/COMSET/2N2222.html
  
  return oldHref
   .replace(/^http:\/\/www.alldatasheet.com/, 'http://pdf1.alldatasheet.com')
   .replace(/\/pdf\//, '/view/');
});