have(has)+过去分词
1.现在完成时用来表示现在之前已发生活或完成的动作或状态,但其结果却和现在有联系,也就是说,动作或状态发生在过去但它的影响现在还存在. I have lost my wallet.(含义是:现在我没有钱花了.)
改性环氧树脂Jane has laid the table.(含义是:已可以吃饭了.)
Michael has been ill.(含义是:现在仍然很虚弱)
He has returned from abroad. (含义是:现在已在此地)
2. 现在完成时可以用来表示发生在过去某一时刻的,持续到现在的情况,常与for,since连用.
Mary has been ill for three days.
I have lived here since 1998.
3. 现在完成时往往同表示不确定的过去时间状语连用,如already, yet, just, before, recently, lately等:
He has already obtained a scholarship.
I haven't seen much of him recently (lately).
We have seen that film before. 科学时代杂志
Have they found the missing child yet
4. 现在完成时常常与表示频度的时间状语连用,如often, sometimes, ever, never, twice, on several occasion等:
Have you ever been to Beijing
I have never heard Bunny say anything against her. 罗丹明b
I have used this pen only three times. It is still good.
George has met that gentleman on several occasions.
自发功5. 现在完成时还往往可以同包括现在时间在内的时间状语连用,如now, up to these few days/weeks/months/years, this morning/week/month/year, now, just, today, up to present, so far等:
Peter has written six papers so far.
Man has now learned to release energy from the nucleus of the atom.
There has bee too much rain in San Francisco this year.
The friendly relations and cooperation between our two countries have been enhanced in the past few years.
Up to the present everything has been successful.
6. 现在完成时表示现在之前业已完成的动作,虽然其效果或影响仍然存在但已不再继续,但是有一些现在完成时的句子,在后面加上for+一段时间,则现在完成时的动作就表示延续性.
Thomas has studied Russian. (现在不再学俄语)
Thomas has studied Russian for three years. (=Thomas began to study Russian three years ago, and is still studying it now.(同第2点用法第一个例句)
7. 现在完成时还可以用来表示过去的一个时间到现在这段时间内重复发生的动作.
We have had four texts this semester.
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现在完成时的“完成用法”和“未完成用法”
1.现在完成时的"完成用法"
现在完成时的"完成用法"指的是动作发生在过去某一时刻并已结束，但该动作对现在产生了影响，与现在情况具有因果关系。
例如：He has turned off the light.他已把灯关了。(动作结束于过去，但说明的是现在的情况--灯现在不亮了。)
现在完成时"完成用法"的特点是动作不延续，因此，该时态只能与表示不定的过去时间状语(如：already，yet，before，recently等)、频度时间状语(如：never，ever，once等)、包括现在时刻在内的时间状语(如：this morning ／ month ／，today等)连用。
例如： Have you found your pen yet？你已到你的钢笔了吗？
2.现在完成时的"未完成用法"
现在完成时的"未完成用法"指的是动作开始于过去某一时刻，一直延续到现在，或可能还要继续下去。
例如：He has lived here since 1978.自从1978年以来，他一直住在这儿。(动作起始于1978年，一直住到现在，可能还要继续住下去。)
I have been in the army for more than 5 years.我在部队已经呆了五年多了。(动作开始于5年前，一直延续至今，有可能还要继续下去。)
此种用法的句中常需一个表示一段时间的状语(由since或for引导)，或表示与现在时刻相连的时间状语(如：up to now，so far)等。
例如：I have heard nothing from him up to now.到目前为止我没有他的任何消息。
注意：(1)现在完成时的未完成用法只适用于延续性动词，不可用于终止性动词，即瞬间完成或延续时间很短的动词。如：come，go，arrive，leave，join，become，die等。 (2)现在完成时常见两种句型： 第一部落
①主语＋have / has been＋for短语
②It is＋一段时间＋ since从句
例如：He has been in the League for three years.或It is three years since he joined the League. 他入团已三年了
现在完成时用法解析
1.构成
现在完成时是由助动词 have(has)+动词的过去分词构成。助动词说明该谓语是属于现在
时范围。它和主语的人称、数要保持一致。过去分词是主要的谓语动词，说明句子的意义。
2.用法
(1)表示动作发生在过去某个不确定的时间，但对现在留下了某种影响和结果。常被just、already、yet 等副词修饰。如：
-Have you had lunch yet? -Yes,I have. I've just had it.
你(已经)吃午饭了吗？ 我刚刚吃过。(现在我不饿了)
(2)表示从过去某一时刻开始一直持续到现在的动作或状态。这个动作可能刚停止，可能仍然在进行。常带有for和since等表示一段时间的状语。 如：He has taught here since 1981
他自1981年就在这儿教书。(可能还要继续教)
I have't seen her for four years.
我有四年没见到她了。
乌昌 (3)表示说话前发生过一次或多次的动作，现在成为一种经验，一般译为汉语“过”，常带有twice,ever,never,three times等时间状语。
如： I have been to Beijing twice.我去过北京二次。
3.现在完成时的时间状语
(1)现在完成时属于现在时范围，故不能和过去的时间状语连用。如：yesterday,last Sunday,in1990,three years ago等。但是，在强调动作产生的后果和影响时，可以和一些表示不确定的时间状语连用。
a. 用副词already和yet。already一般用于肯定句中，yet一般用于否定句和 疑问句中。如：We have already finished our homework.我们已完成作业了。
They haven't finished their homework yet.他们还没有完成作业。
b.用ever 和never。多用于否定或疑问句中，表示“曾经”或“从未“等。 如：-Have you ever
been to the Great Wall?你曾经去过长城吗？
-I have never been to the Great Wall.我从未去过长城。
c.用表示到说话为止的过去时间状语，如just,before,up to now,the past few years等。例如：I have seen her before,but I can not remember where.
我以前见过她，但记不起在哪里见过。
He has been there three times the last few days.
近几年他去过那里三次了。
d.用包括“现在”在内的时间状语，如：now,today,this morning(month,year,term)等。例如：-Have you met him today?-No,I haven't.
今天你见过他吗？我 没有。
How many times have you been there this year?
今年你去过那里多少次？
(2)现在完成时可以和带有since或for等表示“一段时间”的状语连用,表示动作或状态从某一时刻开始，一直持续到现在。如：I haven't seen him for two years. 但是，像come,arrive,buy等终止性动词不能与表示“一段时间”的状语连用。要用，必须改为“be(在)”等延续性动词来表述。现归纳总结一下由非延续性动词到延续性动词的转换：
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