code: def get_dois(query_str, count=100):
      
      url = '%s/%s' % (elsevier_search_url, query_str)
      params = {'query': query_str,
                'count': count,
                'httpAccept': 'application/xml',
                'sort': '-coverdate',
                'field': 'doi'}
      res = requests.get(url, params)
      if not res.status_code == 200:
          return None
      tree = ET.XML(res.content, parser=UTB())
      doi_tags = tree.findall('atom:entry/prism:doi', elsevier_ns)
      dois = [dt.text for dt in doi_tags]
      return dois
docs: Search ScienceDirect through the API for articles.
  
      See http://api.elsevier.com/content/search/fields/scidir for constructing a
      query string to pass here.  Example: 'abstract(BRAF) AND all("colorectal
      cancer")'