@article{1077477214,
author = {Sternberg, Robert L.},
title = {Variational methods and non-oscillation theorems for systems
of differential equations},
journal = {Duke Math. J.},
volume = {19},
number = {1},
year = {1952},
pages = { 311-322},
language = {en},
url = {http://dml.mathdoc.fr/item/1077477214}
}
Sternberg, Robert L. Variational methods and non-oscillation theorems for systems
of differential equations. Duke Math. J., Tome 19 (1952) no. 1, pp. 311-322. http://gdmltest.u-ga.fr/item/1077477214/