Are Dumbbells enough for you to get muscles?

Yes. Just make sure you move up to heavier Dumbbells to add resistance. Any weight is appropriate to build muscle as long as you can add resistance.

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Yes, it can be done.

sure...it will be more difficult because you don't have the nautilus equipment that works every single muscle and makes you more evenly big, but yes you can just use dumb bells...you need to have a wide variety of lifts that you do though that work the muscles all the way around your arm, your obliques, and your back...you also need to be doing pushups and situps and some sort of running to keep your legs fit...and eat lots of protein!

If you know what you're doing, then dumbbells will work
If you follow Charles Atlas, you don't even need dumbbells.