composer require package fail

[xueji...@gmail.com]

D:\phpStudy>composer require laravel/laravel

Search for a package: laravel/laravel

Enter the version constraint to require (or leave blank to use the latest version):

Using version ^5.4 for laravel/laravel

Search for a package: 

Downloading other dependencies is the same , Please explain why, how to solve？thank you very much！