https://vocabularyserver.com/psh/en/ Polythematic Structured Subject Heading System National Technical Library National Technical Library 1998-12-31 en 2012-03-20 15:17:20 flueways 2012-03-20 15:17:20https://vocabularyserver.com/psh/en/xml.php?skosTema=828https://vocabularyserver.com/psh/en/xml.php?skosTema=818