Nuclear magnetic resonance (N.M.R) is a physical phenomenon in which a nucleus in a strong constant magnetic field is disturbed by a weak oscillating magnetic field (near magnetic field) and responds by generating an electromagnetic signal with the frequency characteristics of the magnetic field at the nucleus.
This process occurs near resonance when the vibration frequency matches the natural frequency of the nucleus. It depends on the strength of the static magnetic field, the chemical environment, and the magnetic properties of the isotopes involved.