ems can cause loss of important travel information and misunderstanding of vital instructions during an emergency. An outstanding feature of long spaces is that classical room acoustic theory is not applicable since the assumption of a diffuse field does not hold with the extreme dimension condition. Consequently, works required for an understanding of the behavior of sound in long spaces and for an acoustic prediction which takes into account the relevant characteristics.
(3)衔接手段
如果综述中多处需要引用同一个作者或同一篇文章，那么，需要用一些连接手段使上下文衔接，让意思流畅、连贯，并起到提醒读者的作用。
例2l
a. The author goes on to say that…
b. The article further states that…　
c. The author also states / argues / believes that …
d. The author concludes that …
8.4 如何写研究动机与目的
在介绍了他人在某领域的工作和成果之后，下一步便介绍作者自己的研究动机、目的与内容。介绍研究动机可以从两个角度人手，一是指出前人尚未解决的问题或知识的空白，二是说明解决这一问题，或填补知识空白的重要意义。
主要句型有：
句型1：用表示否定意义的词例little，few，no或none of+名词作主语。如：
例22
a．Little information／attention／work／research…
b．Few studies／investigations／researchers／attempts…
C．No studies／data／calculations…
d．None　of　these studies／findings／calculations…
注意：
(1)little后面的名词是不可数名词，而few后面是可数名词，而且是复数形式。
(2)no后面直接用名词(可数或不可数名词)，表示泛指，“到目前为止还没有……”的意思，而none of后用指示代词these，those(或定冠词the)+名词，表示“在特定的范围中还没有……”的意思。也就是说，在上文所提到过的那些研究中，还没有解决某一问题，由此来暗示知识的空白部分。
下面举几个表示否定意义的例子。
例23
a. Unfortunately, few educational opportunities exit to teach farmers and rural homeowners effective water supply management.
b. There have been few specific reports in the literature of oak and hickory decline.
c. There is, however, little qualitative information regarding purple loosestrife vegetative reproduction.
d. However, there exists little research on science fair projects.
句型2:里表示对照的句型。如:
例24
a. The research has tended to focus on…, rather than on…
b. These studies have emphasized…, as opposed to…
c. Although considerable research has been devoted to…, rather less attention has been paid to…
d. Although there is much hope that three-dimensional coupled models will lead to better understanding of the factors that control hurricane intensity and to increased reliability of hurricane intensity forecasts, the present generation of models may not have enough horizontal resolution to capture the full intensity of extreme storms.
句型3：提出问题或假设。如：
例25
a. However, it remains unclear whether…
b. It would thus be of interest to learn how…
c. If these results could be confirmed, they would provide strong evidence for …
d. These findings suggest that this treatment might not be so effective when applied to…
e. It would seem, therefore, that further investigations are needed in order to…
指出或暗示了知识领域里的空白，或提出了问题或假设之后，下一步理所当然应该告诉读者本研究的目的和内容，要解决哪些问题，以填补上述空白，或者证明所提出的假设。
此部分常见的句型请参见7.3.1节，如何写摘要中的目的部分。这里只略举几例。
例26
a. The aim of the present paper is to give …
b. This paper reports on the results obtained…
c. In this paper we give preliminary results for…
d. The main purpose of the experiment reported here was to…
e. This study was designed to evaluate…
f. The present work extends the use of the last model by…
g. We now report the interaction between…
h. The primary focus of this paper is on…
i．The aim of this investigation was to test…
j．It　is　the purpose　of the present paper to provide…
从暗示知识的空白到本研究的目的与内容一般需要用一些过度词，以提示一下读者。如上面这些例句中，用了this paper，here，the　present　work，now，this investigation，the present paper等词或词组。
为了引起读者的注意，这些词或词组一般放在句首。
例27
…The fate of these sect

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