屢試不爽　

◎ 屢試不爽 lǚshì-bùshuǎng

[be found officious as often as it is tried;be often tried and often succeeded;effective every time it is used] 每次使用都有效;多次試驗(yàn)都不錯(cuò)

這種新農(nóng)藥效果良好,屢試不爽