跨源请求被阻止？！(原因：缺少CORS标头'Access-Control-Allow-Origin'）

以下是我的php代码：

<?php
    header('Access-Control-Allow-Origin: *');
    header('Access-Control-Allow-Methods: GET, POST');
    header("Access-Control-Allow-Headers: X-Requested-With");
    include 'dbconnection.php';
    try{
        if (isset($_GET['term'])){
        $return_arr = array();

        $stmt = $conn->prepare('SELECT JOBNO FROM PRTJOBHD WHERE JOBNO LIKE :term');
        $stmt->execute(array('term' => '%'.$_GET['term'].'%'));

        while($row = $stmt->fetch()) {
            $return_arr[] =  $row['JOBNO'];
        }

        } 
    }catch(PDOException $e) {
        echo 'ERROR: ' . $e->getMessage();
    }

    /* Toss back results as json encoded array. */
    echo json_encode($return_arr);
?>    

收到错误警告 "Cross-Origin Request Blocked: The Same Origin Policy disallows reading the remote resource at http://192.168.0.102/ipack/search.php?term=a. (原因：在浏览器中运行时ORS 标头Access-Control-Allow-Origin' 丢失)