Is there a good exercise to build pectorals without weights?

All the areas. I'm going to be away for a while and I have no access to weights. Someone experienced in getting at least some tone without any weights or machines?
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I have tried pushups, it's not enough and it becomes more aerobic. And the idea that just pullups and situps in a cell will build your body is only in the movies.
Is there a good exercise to build pectorals without weights?
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