How detect and filter noise from signal This is the spectrum of the signal:

And this is the signal:



On the FFT spectrum you can notice the high amplitude peaks and I think these frequencies are the main ones in the signal:
   

I think that the "low" harmonic must be clean, but I have the problem that low amplitude components are placed in every frequency interval.  The main problem is that I haven't got any model of the signal for a hypothesis about noise, and as result, I must detect noise components.  After this step, I must design a filter or use another method of filtering for denoising the signal.  Which methods can I apply for (1) detecting noise and (2) filtering?
Just "eyeballing" your signal, it looks like the interesting things are all down below 1Hz.  The peaks in your signal browser diagramm seem to be spaced at every 5 to 10 Seconds, which would be 0.1 to 0.2 Hz.  Your spectrum plot goes from zero to 25 Hz, and doesn't show anything really interesting.

Try zooming in on the spectrum and see what lies below 1 Hz.  Yo may well find that the signal itself lives down in the very low frequencies, and that separating the noise from the signal is as simple as using a low pass filter.