come at 和 come up to 都有“达到”的意思,两者有什么区别?

come at 和 come up to 都有“达到”的意思,两者有什么区别?

come at
vt.达到(袭击,弄清)
例句与用法:
1.She desires you to come at once.
她希望你立即来.
2.All right,I'll come at six o'clock tomorrow.
行,我明天六点钟来.
3.Put the food where dog can't come at it.
把食物放在狗够不到的地方.
come up to
符合,达到(标准),比得上
例句与用法:
1.Why don't you come up to Scotland for a few days?
你怎麽不北上到苏格兰来住几天?
2.His film performance didn't come up to expectations.
他在影片中的演出有负众望.
3.His performance didn't really come up to his usual high standard.
他没有真正表现出平日的高水平来.