code: def get_piis(query_str):
      
      dates = range(1960, datetime.datetime.now().year)
      all_piis = flatten([get_piis_for_date(query_str, date) for date in dates])
      return all_piis
docs: Search ScienceDirect through the API for articles and return PIIs.
  
      Note that ScienceDirect has a limitation in which a maximum of 6,000
      PIIs can be retrieved for a given search and therefore this call is
      internally broken up into multiple queries by a range of years and the
      results are combined.
  
      Parameters
      ----------
      query_str : str
          The query string to search with
  
      Returns
      -------
      piis : list[str]
          The list of PIIs identifying the papers returned by the search