You cannot create a route based on the query string, but you still can retrieve query string values in your code:
amu_hal.publicationsPerYear:
path: '/publications/{year}'
defaults:
_controller: '\Drupal\amu_hal\Controller\AmuHalController::publicationPerYear'
_title: 'publicationPerYear'
year: 2016
requirements:
_permission: 'access content'
public function publicationPerYear($year) {
$url = \Drupal::request()->query->get('url') ?: 'default';
}
