There are multiple ways to achieve this purpose

nautilus . &
xdg-open .

My preferred way is the latter. I usually make xdg-open's alias named open to be able to use the same command in Mac OS.

To make the alias, add following entry to .bashrc (or .zshrc if you uses zsh)

alias open=xdg-open

Then, to open current (or any) directory, execute

open .