这为什么有效……？
\documentclass{beamer}
\usetheme{Madrid}
\title{Title}
\subtitle{Subtitle}
\author{Me}
\begin{document}
\frame{\titlepage}
\section{References}
\begin{thebibliography}{plain}
\begin{frame}{\secname}
\bibitem{AM87}R. Abraham and J. E. Marsden (1987) \emph{Foundations of Mechanics}, Addison-Wesley, Redwood City, 2nd ed.
\bibitem{WW83}F. W. Warner (1983) \emph{Foundations of Differentiable Manifolds and Lie Groups}, Springer, New York.
\bibitem{LLM18}T. Lee, M. Leok, and N. H. McClamroch (2018) \emph{Global Formulations of Lagrangian and Hamiltonian Dynamics on Manifolds: a Geometric Approach to Modeling and Analysis}, Springer, Cham, pp: 11-42.
\bibitem{FS04}S. F. Singer (2004) \emph{Symmetry in Mechanics: a Gentle, Modern Introduction}, Birkh\"auser, Boston, \url{https://link.springer.com/book/10.1007/978-1-4612-0189-2}.
\bibitem{IA89}V. I. Arnold (1989) \emph{Mathematical Methods of Classical Mechanics}, Springer, New York, 2nd ed., pp: 163-232.
\bibitem{RR20}N. Román-Roy (2020) \emph{A summary on symmetries and conserved quantities of autonomous Hamiltonian systems}, Journal of Geometric Mechanics, \url{https://arxiv.org/abs/1806.06265v1}.
\end{frame}
\bibitem{LP20}P. G. L. Leach and A. Palianthanasis (eds.) (2020) \emph{Noether's Theorem and Symmetry}, MDPI, \url{https://doi.org/10.3390/books978-3-03928-235-7}.
\bibitem{IT08}I. Taimanov (2008) \emph{Lectures on Differential Geometry}, EMS, \url{https://www.ems-ph.org/books/book.php?proj_nr=76}.
\bibitem{GS86}V. Guillemin and S. Sternberg (1986) \emph{Symplectic Techniques in Physics}, Cambridge University Press.
\bibitem{Mar09}C.-M. Marle (2009) \emph{The Inception of Symplectic Geometry: the Works of Lagrange and Poisson During the Years
1808–1810}, Letters in Mathematical Physics, \url{https://link.springer.com/article/10.1007%2Fs11005-009-0347-y}.
\end{thebibliography}
但这（正确的方法）却不行：
\documentclass{beamer}
\usetheme{Madrid}
\begin{document}
\section{References}
\begin{frame}{\secname}
\begin{thebibliography}{plain}
\bibitem{AM87}R. Abraham and J. E. Marsden (1987) \emph{Foundations of Mechanics}, Addison-Wesley, Redwood City, 2nd ed.
\bibitem{WW83}F. W. Warner (1983) \emph{Foundations of Differentiable Manifolds and Lie Groups}, Springer, New York.
\bibitem{LLM18}T. Lee, M. Leok, and N. H. McClamroch (2018) \emph{Global Formulations of Lagrangian and Hamiltonian Dynamics on Manifolds: a Geometric Approach to Modeling and Analysis}, Springer, Cham, pp: 11-42.
\bibitem{FS04}S. F. Singer (2004) \emph{Symmetry in Mechanics: a Gentle, Modern Introduction}, Birkh\"auser, Boston, \url{https://link.springer.com/book/10.1007/978-1-4612-0189-2}.
\bibitem{IA89}V. I. Arnold (1989) \emph{Mathematical Methods of Classical Mechanics}, Springer, New York, 2nd ed., pp: 163-232.
\bibitem{RR20}N. Román-Roy (2020) \emph{A summary on symmetries and conserved quantities of autonomous Hamiltonian systems}, Journal of Geometric Mechanics, \url{https://arxiv.org/abs/1806.06265v1}.
\bibitem{LP20}P. G. L. Leach and A. Palianthanasis (eds.) (2020) \emph{Noether's Theorem and Symmetry}, MDPI, \url{https://doi.org/10.3390/books978-3-03928-235-7}.
\bibitem{IT08}I. Taimanov (2008) \emph{Lectures on Differential Geometry}, EMS, \url{https://www.ems-ph.org/books/book.php?proj_nr=76}.
\bibitem{GS86}V. Guillemin and S. Sternberg (1986) \emph{Symplectic Techniques in Physics}, Cambridge University Press.
\bibitem{Mar09}C.-M. Marle (2009) \emph{The Inception of Symplectic Geometry: the Works of Lagrange and Poisson During the Years
1808–1810}, Letters in Mathematical Physics, \url{https://link.springer.com/article/10.1007%2Fs11005-009-0347-y}.
\end{thebibliography}
\end{frame}
\end{document}
答案1
我按照 Ulrike 的建议修复了这个问题，将选项添加fragile到frame环境中