BibTeX

@ARTICLE{iumj57014,
    author = "Jack Hale",
     title = "Sufficient Conditions for the Existence of Periodic Solutions of Systems of Weakly Nonlinear First and Second Order Differential Equations",
   journal = "Indiana Univ. Math. J.",
  fjournal = "Indiana University Mathematics Journal",
    volume = 7,
      year = 1958,
     issue = 2,
     pages = "163--171",
      issn = "0022-2518",
     coden = "IUMJAB",
   mrclass = "",
}

amsrefs

\bib{iumj57014}{article}{
     author = {Hale, Jack},
      title = {Sufficient Conditions for the Existence of Periodic Solutions of Systems of Weakly Nonlinear First and Second Order Differential Equations},
    journal = {Indiana Univ. Math. J.},
     volume = {7},
       year = {1958},
     number = {2},
      pages = {163 \ndash 171},
}