@article{702175,
     title = {Variational methods of solving linear and nonlinear boundary value problems},
     booktitle = {Differential Equations and Their Applications},
     series = {GDML\_Books},
     publisher = {Publishing House of the Czechoslovak Academy of Sciences},
     address = {Prague},
     year = {1963},
     pages = {77-92},
     mrnumber = {MR0170132},
     zbl = {0181.42501},
     url = {http://dml.mathdoc.fr/item/702175}
}

Mihlin, S. G. Variational methods of solving linear and nonlinear boundary value problems, dans Differential Equations and Their Applications, GDML_Books,  (1963), pp. 77-92. http://gdmltest.u-ga.fr/item/702175/