off hand有什么区别？

    这三个词组都含“在手头”、“在手边”的意思，用法区别甚微，只是侧重不同而已。 at hand 有二个基本用法：① “在手边”、“在附近”；②“即将到来”。常用 close、near、 ready 前置修饰之。
   ●“在手边”、“在附近”，侧重强调就在手边、近处，随时可用之，含 have something easy to reach，which can be used if needed 的意思。
    在句中可作 状语、补语或后置定语。 1）Whenever I want to write something, I always have a dictionary (close) at hand。
   每当我想写点什么，我总在手边放一本字典。   2）When he goes out on business, he likes to have his secretary (ready) at hand。
   他出去谈业务时，总喜欢他的秘书在身边。 3）I want you to be at hand during my interview with the journalists。
     我接见记者采访时希望你在跟前。 4）The judge would not admit the testimony, ruling that it was extrinsic to the matter at hand。
   法官不接受此项证词，裁定它与眼下审议的事无关。   5）The students reside in various boarding-houses near at hand。
   这些学生住在附近各个寄宿宿舍里。 6）They built a small hut by using the materials close at hand。   他们利用附近的材料建造了一个小棚屋。
   ●“即将来临”、“在眼前”，在句中一般用作连系动词 be 的表语。 1）The athletes are busy training, for the school sports meeting is (near) at hand。
     运动员们正忙于训练，因为学校运动会即将到来。 2）Although the end of the term was (close) at hand, Jenny had not completed all of the projects he had hoped to finish。
     学期结束就在眼前，可是珍妮还没有完成他希望完成的课题。 3）As the storm is close at hand, many ships began to sail back to the port。
   眼看风暴即将来临，许多船只开始驶回港口。   4）Realizing that his retirement was near at hand, he looked for some additional income。
   意识到即将退休，他寻了些事可有些额外收入。、 on hand 有三种基本用法：① “在手头”、“在手边”；② “即将来临”、“在眼 前”； ③“在场”、“到场”。
     ●“在手头”、“在手边”，侧重强调手头“现有的”或“已备的”，随时可用之。含 something is already available to you or in stock and able to be used if needed 的意思。
     1）I always like to keep a certain amount of money on hand。 我总爱在手头保留一定数量的钱。
   2）The shop has a large stock of the new types of mobile phones on hand。   该商店现有大批新型手机出售。
   3）Berkshire always keeps at least $20 billion cash on hand for unforeseen events or investment opportunities。
     伯克郡公司总是在手上保持200亿美金已备突发事件或投资之需。 4）He has too much work on hand to go picnicking with us。
   他手头的工作太多了，不能跟我们去野餐。 5）We have nobody on hand to repair your car。   我们现在没有人能修你的车。
   6）We will have some experts on hand to give you any help you need at all times。 我们将有一些专家随时能给你们所需要的帮助。
     ●“即将来临”、“在眼前”， 含义与at hand有些贴近，但用法不同，at hand 常同连 系动词be 的一般式连用，而 on hand 则需用于将来时态。
   1）Soon school will end and summer vacation will be on hand。   学校不久就要放假了，暑假快要来临了。
   2）Recent economic performance suggests that a major crisis will be on hand。 最近的经济情况表明一场大的危机就在眼前。
     3）They felt that the total destruction of the scheme would be on hand。 他们感到这一计划彻底失败的时候就将到来。
   ●“在场”、“到场”。 1）Worldwide English broadcasters were on hand to describe the event as it happened。
     国际英语广播员到现场直播了这一事件的始末。 2）More than 100 police and 120 civil protection volunteers were on hand in case of incidents。
     为防止发生事故，活动现场安排了100多名警察和120名民防志愿者。 3）Blake's secretary is always on hand when he appears in public。
   布莱克出现在公众面前时，他的秘书总在场。   4）Be sure to be on hand early at the party so that you can make the acquiantance with other guests。
   晚会你一定要早点来，以便结识一些其他来宾。   5）He had sweated over every innovation ever made there, and had always been on hand at the most critical times。
   那里每一项技术革新都有他的汗水，每个关键时刻都有他在场。   in hand 侧重强调手中掌控的的物或事，随时可用，随时可做（in one's possession ; ready to be used or done）， 也可表示手头正在进行的事。
  所以in hand 除了表示“在 手头”、“在手边”的意思外，还可表示“控制中”或“在进行中”。   ●“在手头”、“在手边”。 1）After I paid the bill, I had only 10 dollars in hand。
   付完帐单后，我手头只有10美元了。 2）Keep your attention on the matter in hand。   把注意力集中在手头的事情上。
   3）The matter in hand is urgent and we must deal with in right now。 手头的这件事很紧迫，我们必须马上处理。
   ●“控制中”，相当于under control 的意思。   1）Don’t worry about it。 The situation has been well in hand。
   不用担心，局势已经控制住了。 2）Can you have the situation well in hand? 你能完全控制住这种形势吗？ 3）The matter seems to be subtle, and is hard to have it in hand。
     这件事似乎很微妙的，现在还很难掌控。 ●“在进行中”。相当于 under way 的意思。 1）He reported that a sudden breakout of fighting was in hand on the border。
     他报告说，边境上突然爆发的战斗在进行中。 2）We should finish the work we have in hand before we begin something new。
   我们在开始新工作之前，必须完成我们手头正在进行的工作。   3）The judge would not admit the testimony, ruling that it was extrinsic to the matter in hand。
   法官不接受此项证词，裁定它与正在审议的事无关。   4）While a play was still seek, other preparations were already in hand。
   剧本虽还没有确定，但其它准备工作就已经着手进行。