Use get_post_format()
inside your loop:
if (have_posts()) :
while (have_posts()) :
the_post();
$format = get_post_format();
if (false === $format) {
get_template_part('content', get_post_format());
}
endwhile;
twentyfourteen_paging_nav();
else :
get_template_part('content', 'none');
endif;