全站搜索时，想要搜索几个指定栏目的内容应该怎么设置

全站搜索时，想要搜索几个指定栏目的内容应该怎么设置；下边是现在用的

<form class="search-form" action="/index.php" method="get">
          <input type="hidden" name="c" value="api">
          <input type="hidden" name="m" value="search">
          <input type="hidden" name="dir" id="dr_search_module_dir" >
            <div class="input-group-btn btn-group" style="display: none;">
                            <button id="dr_search_module_name" type="button" class="btn default dropdown-toggle" data-toggle="dropdown" aria-expanded="false">
                                <i class="fa fa-angle-down"></i>
                            </button>
                            <ul class="dropdown-menu">
                                <!--这是来列出全部可以搜索的内容模块-->
                                {php $top_search=[];}
                                {list action=cache name=module}
                                {if !$t.setting.search.close}
                                {php !$top_search && $top_search=$t;}
                                <li><a  target="_blank" href="[removed]dr_search_module_select('{$t.dirname}', '{$t.name}');"> {$t.name} </a></li>
                                {/if}
                                {/list}
                            </ul>
                        </div>
          <input type="text" name="keyword" value="请输入关键词" class="s_w" onblur="if (this.value ==&#39;&#39;){this.value=this.defaultValue}"
            onclick="if(this.value==&#39;请输入关键词&#39;)this.value=&#39;&#39;" />
          <input type="submit" name="submit" value="" class='an' style="border:0; padding: 0;" />
          <script>
                        // 这段js是用来执行搜索的
                        function dr_search_module_select(dir, name) {
                            $("#dr_search_module_dir").val(dir);
                            $("#dr_search_module_name").html(name+' <i class="fa fa-angle-down"></i>');
                        }
                        dr_search_module_select('{php echo defined('MOD_DIR') ? MOD_DIR : $top_search.dirname}', '{php echo defined('MODULE_NAME') ? MODULE_NAME : $top_search.name}');
          </script>
        </form>