$text = '<a href="http://www.xxx.com/yapim_yili/2013" rel="tag"><b>2013</b></a>';
$ifade = '/<a href=".+" rel=".+"><b>([0-9]+)<\/b><\/a>/';

preg_match_all($ifade, $text, $match);

$yapimyili = $match[1][0];