My ubuntu was remove ubuntu software center because i want to reinstall again.but i used terminal...i cannot to install ubuntu software center..

:~$ sudo apt-get install software-center
Reading package lists... Done
Building dependency tree       
Reading state information... Done
Package software-center is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source

Why?