Do We See the ``Dark Clouds'' Again? --- On Some Puzzles in Contemporary   Physics
  Some conceptual problems in physics are discussed. Do we need a change in the concept of matter structure? Why the ``$i=\sqrt{-1}$'' is introduced to quantum mechanics (QM) essentially? What is the relation between QM and special relativity (SR)? Could we modify the stationary Schr$\ddot{\rm o}$dinger equation in conformity with SR? How can a particle acquire a mass? We propose some tentative answer. Their philosophical implications are emphasized. 
Guang-jiong Ni (Department of Physics, Fudan University, P.R. China)