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Unfortuantely no. The issue is energy. The kinetic energy of the impactor has to go somewhere, and since it's hitting the Earth, all the energy is transfered to the Earth. With large impactors this will cause enough heating to bring about the conflagration of the biomass of the planet, or a large percentage thereof.
The other issue is that these damn things are so huge, our nuclear arsenels don't have enough umph to break up the solid ones, not to mention that the numerious "rubble pile" astreriods and comets are fantastically resistent (read completely immune) to this sort of effect.
Nukes are not the answer to cosmic impactors, not because tree hugging nuts don't like them, but because they won't work. Taking ones science from Hollywood is a mistake.