@article{ref1,
title="Sleep and nocturnal air traffic",
journal="Nederlands Tijdschrift voor Geneeskunde",
year="1991",
author="Ettema, J. H.",
volume="135",
number="37",
pages="1667-1668",
abstract="<p>[Abstract unavailable]</p> <p>Language: nl</p>",
language="nl",
issn="0028-2162",
doi="",
url="http://dx.doi.org/"
}