$clause = array();
					if ($nb_auth != "") {
						$clause[] = "nb_auth LIKE '%$nb_author%'";
					}
					if ($nb_subj != "") {
						$clause[] = "nb_subject LIKE '%$nb_subj%'";
					}
					if ($nb_num != "") {
						$clause[] = "nb_number LIKE '%$nb_num%'";
					}
					if ($nb_type != "") {
						$clause[] = "nb_type LIKE '%$nb_type%'";
					}
					$clause = implode(' AND ', $clause);