Is there any shortcut keys to open nautilus

By default there is none, but you can set one:

System Settings -> Keyboard -> Shortcuts -> Custom shortcut

Then press the + Button. The command to run is nautilus.

After creating the shortcut, click 'disabled' then press the desired key combination (e.g., Super + E) to set the new shortcut.

Super+1 opens Nautilus, at least in the default Ubuntu + Unity installation.

Super+t = Trash, it uses nautilus to show you the Trash! Works fine for me.