@misc{Kukla_Stanisław_Free,
 author={Kukla Stanisław and Rychlewska Jowita},
 howpublished={online},
 publisher={Wydaw. Politechniki Częstochowskiej},
 language={eng},
 type={czasopismo},
 title={Free vibration analysis of functionally graded beams},
 keywords={free vibration problem, funcionally graded beams},
}