If you nuke water in a microwave, it gets hotter. If you microwave liquid nitrogen, nothing happens. The liquid nitrogen keeps boiling off, but at the same rate as if you had it sitting on the counter.
How It WorksWater molecules are polar, which makes them able to absorb microwave energy. Each water molecule has a positive end and a negative end, making it responsive to electromagnetic fields, such as the one produced by the magnetron of a microwave. The molecules vibrate and move further apart, eventually boiling into the gas phase.
Nitrogen molecules are linear nonpolar N2 molecules. Because they don't exhibit polarity, the microwaves don't react with them. Microwaves pass through liquid nitrogen as if it wasn't even there.
Do you want to see for yourself? If you don't have access to liquid nitrogen, you can watch Jefferson Lab's video of liquid nitrogen in a microwave.