@article{ref1,
title="A simple classification of the present and future stages of manned flight",
journal="Journal of aviation medicine",
year="1956",
author="Strughold, H.",
volume="27",
number="4",
pages="328-331",
abstract="<p>[Abstract unavailable]</p> <p>Language: en</p>",
language="en",
issn="0095-991X",
doi="",
url="http://dx.doi.org/"
}