第2个回答 2009-01-12
现在完成时
1.表示过去发生的但对现在有影响的动作，可以不用时间状语。也可以和一些表示不定过去的时间状语连用，比如already,yet,ever,never,just,once,recently
等。
1).
i
have
been
to
Peking
many
times.
我多次去过北京（现在对北京有所了解）
2).
he
has
bought
a
car.(现在他有车可以开了)
2.表示从过去某时间开始一直延续到现在的动作。一般要跟个表示一段时间的状语since,
so
far,
in
recently
years,
for
+时间段。
例如
1）.
he
has
lived
here
since
1949.
2)
he
has
lived
here
for
40
years.
过去完成时
表示过去某一时刻以前已经完成的动作，常由by，
before等。主要是宾语或定语从句中常见。状语从句也会用到
1）by
the
end
of
last
year,
i
had
worked
in
this
college
for
ten
years.去年年底是过去时间，而在大学工作十年是在去年年底之前，故用过去完成)
2）he
had
been
a
teacher
for
years
before
he
became
a
writer.(成为作家是过去式，而做老师是在成为作家之前，过去的过去就用过去完成式)
3）he
knew
that
he
had
made
a
mistaken
(他知道为过去式，而犯错是在知道之前，过去的过去)
不知清楚了没？
--------------------------------------------------------------------
has
是宾语,,
一句句字一定要有主,谓,宾结构饿,,
i
bought
a
car
更本就不是句子,,
has是修饰bought的,,
不然你可以说
i
want
buy
a
car.
我想买辆车,,
但是I
has
bought
a
car
是我买了一辆车,,
你说这句话的时候车已经买好了饿,,
所以是过去式,,
懂了挖.?
第4个回答 2008-03-18
过去完成时
1） 概念：表示过去的过去
----|-------|-----|---->其构成是had +过去分词构成。
那时以前 那时 现在
2） 用法
a. 在told, said, knew, heard, thought等动词后的宾语从句。
She said (that) she had never been to Paris.
b. 状语从句
在过去不同时间发生的两个动作中，发生在先，用过去完成时；发生在后，用一般过去时。
When the police arrived, the thieves had run away.
c. 表示意向的动词，如hope, wish, expect, think, intend, mean, suppose等，用过去完成时表示"原本…，未能…"
We had hoped that you would come, but you didn't.
3) 过去完成时的时间状语before, by, until , when, after, once, as soon as。
He said that he had learned some English before.
By the time he was twelve, Edison had began to make a living by himself.
Tom was disappointed that most of the guests had left when he arrived at the party.
典型例题
The students ___ busily when Miss Brown went to get a book she ___ in the office.
A. had written, left B，were writing, has left C. had written, had left D. were writing, had left
答案D. "把书忘在办公室"发生在"去取书"这一过去的动作之前，因此"忘了书"这一动作发生在过去的过去，用过去完成时。句中when表示的是时间的一点，表示在"同学们正忙于……"这一背景下，when所引导的动作发生。因此
前一句应用过去进行时。
注意： had no … when 还没等…… 就……
had no sooner… than 刚…… 就……
He had no sooner bought the car than he sold it.
过去完成时的用法（1）
表示过去某一时刻之前已经完成的动作，常与由by，before引导的时间状语连用。
We had learned 5000 words by the end of last month.
到上个月底为止我已经学了五千个单词。
I had finished the composition before supper.
晚饭前我就已经把作文写完了。
过去完成时的用法（2）
表示过去某一动作之前已经完成的动作，常与由when，before等连词引导的时间状语从句连用。
When I woke up it had already stopped raining.
我醒来的时候雨就已经停了。
I hadn't learned any English before I came here.
我来这儿之前没学过英语。
常用于引导这类状语从句的连词有：when当...的时候，as soon as一...就，
before在...之前，after在...之后，until直到，等。
过去完成时的用法（3）
用于宾语从句或间接引语中
I wondered who had taken the umbrella without permission.
我想知道谁不经允许就把雨伞拿去。
He told me that he had passed the exam.
他告诉我他已通过考试。
过去完成时的用法（4）
某些动词的过去完成时表示一个打算要做却没有做成的事。
I had intended to come over to see you last night, but someone called and I couldn't get away.
昨晚我本打算来看你，但有人来找，脱不开身。
We had hoped to catch the early bus, but found it was gone.
我们本希望搭早班车，却发现车已开了。
这类动词有：intend打算，hope希望，plan计划，mean预定，want想要，
think想要，等。
过去完成时的用法（5）
用于表示与过去事实相反的虚拟条件从句中
If you had come yesterday, you would have met him.
如果你昨天来的话，你就已经见到他的面了。
She would have come if she hadn’t been so busy.
要不是这么忙的话，她就已经来了。
现在完成时是英文时态的一种
现在完成时的用法
have(has)+过去分词(done)
1.现在完成时用来表示现在之前已发生过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.)
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.
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.
I have used this pen only three times. It is still good.
George has met that gentleman on several occasions.
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.
===================
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 ／year...，today等)连用。
例如： Have you found your pen yet？你已找到你的钢笔了吗？
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：
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