title: requests.get returns 403 while the same url works in browser
body: <p>I'm trying to use the search form at <a href="http://www.rlsnet.ru" rel="noreferrer">rlsnet.ru</a>. Here is the form's definition I've extracted from the source file:  </p>
  
  <pre><code>&lt;form id="site_search_form" action="/search_result.htm" method="get"&gt;
      &lt;input id="simplesearch_text_input" class="search__field" type="text" name="word" value="" autocomplete="off"&gt;
      &lt;input type="hidden" name="path" value="/" id="path"&gt;
      &lt;input type="hidden" name="enter_clicked" value="1"&gt;
      &lt;input id="letters_id" type="hidden" name="letters" value=""&gt;
      &lt;input type="submit" class="g-btn search__btn" value="Найти" id="simplesearch_button"&gt;
      &lt;div class="sf_suggestion"&gt;
          &lt;ul style="display: none; z-index:1000; opacity:0.85;"&gt;
          &lt;/ul&gt;
      &lt;/div&gt;
      &lt;div id="contentsf"&gt;
      &lt;/div&gt;
  &lt;/form&gt;
  </code></pre>
  
  <p>Here is the code I used to send the search request:</p>
  
  <pre><code>import requests
  from urllib.parse import urlencode 
  
  root = "http://www.rlsnet.ru/search_result.htm?"
  response = requests.get(root + urlencode({"word": "Церебролизин".encode('cp1251')})
  </code></pre>
  
  <p>Each time I do it, the response status is 403. When I enter the same request URL (i.e. <code>http://www.rlsnet.ru/search_result.htm?word=%D6%E5%F0%E5%E1%F0%EE%EB%E8%E7%E8%ED</code>) into Safari/Chrome/Opera, it works fine and returns the expected page. What am I doing wrong? Googling the issue only brought this SO question: <a href="https://stackoverflow.com/questions/25097093/why-url-works-in-browser-but-not-using-requests-get-method">why url works in browser but not using requests get method</a>, which was of little use.</p>