$re = '/(NS[\d]{3,})/';
$str = '<div class="product-desc col-md-6"> <h1 class="product-title" id="productTitle"
itemprop="name">Шлем для крепления электродов ЭЭГ (взрослый)</h1><p>NS023211.007-02
(размер 54-62), синий</p><p>NS023211-01 (размер 48-54),
зеленый</p><p>NS023211 размер 42-48), желтый</p></div>';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php