It can serve as a good supplement to any quantum mechanics textbook, filling the gap between standard textbooks and higher-level books on the one hand and journal articles on the other. This book provides a detailed treatment of the scattering theory, multidimensional quasi-classical approximation, non-stationary problems for oscillators and the theory of unstable particles. It will be useful for postgraduate students and researchers who wish to find new, interesting information hidden in the depths of non-relativistic quantum mechanics.Contents: Discrete SpectrumContinuous SpectrumAnalytic Properties of Wave FunctionInverse Scattering ProblemThe Green Functions and Perturbation TheoryQuasi-classical ApproximationExact Solutions of Non-stationary Problems for OscillatorQuasi-stationary StatesAppendices:Specific Cases of the Schrödinger Equation SpectrumQuasi-classical Properties of Highly Excited Levels in the Coulomb FieldReadership: Undergraduates, academics and researchers in physics.Key Features:Presents new and exciting resultsInternal resonances in nonlinear systems are studied from a general point of view on the basis of a complex representation of equations of motionComplicated regimes of motion of nonlinear systems at free and forced oscillations are investigated, many of which have important practical applications