Power Spectrum Analysis - using a NETCDF file

Hello, Im using MATLAB 2015a for spectrum analysis. I want to see the peaks in the spectrum of my netcdf file which is having monthly data of 10 variables from 1979-2017. I have used SPtoolbox, but that doesnot produce the results I need. I want to input my netcdf file, and plot the power-spectrum of the required variable (say u or v). It is possible in most of oceanographic soft wares using just a command. Is there any command where I will directly understand the variability of the data? I have tried FFT.m and SPtoolbox. Any other procedures if possible, will be appreciated. Thanks