@article{PismaZhETF.25.296,
    title = {Modified conservation laws for nonlinear waves},
    author = {Karpman, V. I.},
    journal = {πΙΣΨΝΑ Χ φότζ},
    volume = {25},
    issue = {6},
    pages = {296},
    year = {1977},
    doi = {},
    url = {http://jetpletters.ru/ps/0/article_21156.shtml},
}