documentclass{elsart}

usepackage{hyperref}

begin{document}

begin{frontmatter}
  title{The title}
  author{The author}
  address{The address}

  begin{abstract}
    ...
  end{abstract}

end{frontmatter}

section{Section}
label{sec1}

This is a reference without an hyperlink: ref{sec1}

end{document}

newenvironment{NoHyper}{}{}

documentclass{elsart}

usepackage{hyperref}

begin{document}

begin{frontmatter}
  title{The title}
  author{The author}
  address{The address}

  begin{abstract}
    ...
  end{abstract}

end{frontmatter}
endNoHyper % Magic!

section{Section}
label{sec1}

This is a reference with an hyperlink: ref{sec1}

end{document}