@article{ref1,
title="Effort variations in relation to task difficulty, concept of own capability and achievement motivation",
journal="Archiv für Psychologie (Frankf)",
year="1978",
author="Krug, S. and Hage, A. and Hieber, S.",
volume="130",
number="3",
pages="265-278",
abstract="<p>[Abstract unavailable]</p><p>Language: de</p>",
language="de",
issn="0066-6475",
doi="",
url="http://dx.doi.org/"
}