isn't完整形式是is not。not是个副词，它的意思是“不，没有”。not可以与be动词、助动词及情态动词can等组合成其否定形式，也可以用于否定后面的词或短语，作否定的回答，也可以用于表示拒绝或否定某事的可能性。例句：I don't know if he's telling the truth or not.我不知道他是否说了真话。

not null.非空；非空约束；不为空；不能为空

Not see.不见；看不见；看不得；悠久不见

Not really.算不上；也不是；不完全是；不尽然

Not worth.不值；不足；不必

Not optimistic.不容乐观

Not unrelated.不无关系

Not only.不只；不仅；不仅仅；不仅是

if not.如果不；否则；如果不这样的话；如果没有

not good.次品；不良；不好；疵勒火差劲

1、BE is not I was too careless,Help!

是不是我太粗心了，救命！

2、It is not within my power to help you.

我是爱莫能助啊。

3、It is not clear what they want us to do.

我们不肯定他们要我们做什么。

4、As you're aware,this is not a new problem.

正如你所了解的，这不是一个新问题。

5、Her work is not up to standard.

她的工作不合格。

6、It is not often that you get such an opportunity.

你得到这样的机会，可不是常有的事。

7、The problem is not primarily a financial one.

这个问题基本上不是财政问题。

8、The success of the system is not in doubt.

这种制度的成功确定无疑。

9、The company's financial position is not certain.

这家公司的财务状况不明朗。

10、The house is not open to the public.

这所住宅不对外开放。

11、The medicine is not for internal use.

这种药不可内服。

12、Failing one exam is not the end of the world.

一次考试不及格并非世界末日。

13、The street is not safe for children to play in.

孩子在大街上玩不安全。

14、Sorry,my English is not very good.

对不起，我的英语不太好。

15、The painting is not representative of his work of the period.

这幅画不是他在那个时期的代表作。

16、The exhibition is not open to the general public.

这次展览不对公众开放。

17、Price is not always an accurate marker of quality.

价格并不总是质量的准确标志。

18、The college is not an officially recognized English language school.

那所学院不是官方认可的英语学校。

19、It is not merely a job,but a way of life.

这不仅仅是一份工作，而且是一种生活方式。

20、That question is not within the scope of this talk.

那个问题不在本次会谈范围之内。

1、There isn't nearly enough time to get there now.

现在根本没有足够的时间赶到那儿。

2、His work isn't up to much.

他的活儿做得不怎么样。

3、Life isn't like in the movies,you know.

你知道，生活不像在电影里那样。

4、In essence,your situation isn't so different from mine.

从本质上讲，你我的情况并非相差很远。

5、This idea isn't new.

这主意不新鲜。

6、He isn't here now─could you ring back later?

他现在不在——你过会儿再打电话来好吗？

7、Isn't it time you started to get organized?

你该提高点效率了吧？

8、This house isn't big enough for us.

这房子对我们来说不够大。

9、Isn't it time the government came clean about their plans for education?

这难道不是政府彻底说明教育计划的时候了吗？

10、I can't see him now─it isn't convenient.

我现在不便见他。

11、He isn't anything like my first boss.

他完全不像我的第一个老板。

12、Business isn't good but we're managing to hold our own.

生意不景气，但我们正设法坚持下去。

13、That isn't quite square with what you said yesterday.

这跟你昨天所讲的不大吻合。

14、Your car isn't fit to be on the road!

你的车子还不适合上马路！

15、This isn't very important─I don't want to make an issue of it.

这不太重要——我不想把它当回事儿。

16、It really isn't half bad,is it?

这的确很不错，对吗？

17、It's hot today,isn't it?

今天很热，对吗？

18、He isn't in the office much.

他不怎么待在办公室。

19、We need some more paint;there isn't any left.

我们还需要一些油漆，已经用光了。

20、This isn't as bad as I thought.

这没我原来所想的那么差。