【正文】 ynthetic fiber A39。這篇文章旨在就當(dāng)前科技，利用流程圖示程序，數(shù)據(jù)擷取，地理信息系統(tǒng)，圖形用戶界面，實時相關(guān)性數(shù)據(jù)庫，虛擬工具分析出一具體可行的環(huán)境安全監(jiān)控系統(tǒng)。s reading level, limiting the general readers‘ reading speed, so often used in possessing higher reading ability peopleoriented articles. In the third, the author introduces antecedent ―it‖ structure. In essence, this kind of structure is the impersonality one. ―It‖ is a kind of placeholder in the sentence that is not doing its job .Using―it‖, the form of the subject , guides the sentence, the real 福建師范大學(xué)碩士論文 6 subject with long sentences to the other end, which makes the sentence to avoid topheavy and impresses the readers a kind of harmonious beauty. Example 1:It follows from Maxwell‘s hypothesis that whenever there is a change in an electric field, a magic field is produced .Chinese meaning is ―由麥克斯假設(shè)可知，每當(dāng)電場發(fā)生變化時就產(chǎn)生磁場 ‖. Example 2: It is a familiar fact that atmospheric pressure decreases with increasing altitude .Chinese meaning is ―大家熟悉的是，大氣壓隨高度的增加而下降 ‖. This impersonality structure is often applied in articles on English for science and technology, since in English for science and technology the authors major in researching scientific phenomena and objective laws of science and technology, which does not stress by who. Using the ―it‖ structure can stress the predicate part and the sentence structure is relatively perfect, let the readers at the first sight to find out the sentence structure. (《科技英語演講》古德萊德（ Goodlad S） ,梁玲 35) In the last, periodic sentence structure .This structure is easy to understand. Periodic sentence is a rhetorical perspective, which puts the key meaning at the end of the sentence ,the secondary in the sentence first .It is a relatively rigorous sentence anization .The readers can not understand the full meaning of the sentence structure until they read the plete sentences. It has no fixed pattern in the structure, its characteristic is mainly advance the longer adverbial in much of the situation, and puts the short main clause in the end, which increases the difficulty in understanding sentences for the readers. For example: (1) We assumed that there were forces of attraction between molecules which varied rapidly with the distance so that the attraction between molecules that were more than a few tenmillions of millimeter apart was very small but became considerable when the molecules approached more closely . (2) Owing to the fact that electricity and be transmitted from where it is generated to where it is needed by means of power lines and transformers .Large power stations and be built in remote places far from industrial centers or large cities, as is often the case with hydroelectric power stations that are inspirable from water sources. (《科技翻譯》傅勇林，唐躍勤， 98) Frequent Use of Passive Voice A prominent feature on syntax in English for science and technology is the frequent use of passive voice. According to the survey of some linguists, pared with general English and literature English, in the textbooks on physics, chemistry and engineering, the use of passive voice can be accounted for at least 1/3 of the total verbs.(陳治業(yè)， 1994（ 2） )This helps to focus the readers‘ attentions on the thing ,phenomenon or process described in EST articles .That is because the passive voice is more objective thus readers‘ attention is easily paid to stated objects and facts. Zhang Zhenbang put forward :―Sentences or clauses using the passive word phrase as the predicate verb are called passive sentences .‖(章振邦， 1999) In explaining the reasons of the extensive use of the passive voice in English of science and technology, many linguists are based on the expatiation of the objectivity of what EST is related to .For example, Wang Zuoliang et al. think: Characteristics of the passive sentences Chapter One Syntax and Grammar of English for Science and Technology focusing on the passives happen to meet the needs of the objective description of English for science and technology ,which makes the description more accurate.(王佐良 丁往道， 1987) For example： (1) As noted previously ,the Q point may be located anywhere on dc load line by properly choosing bias resistors R1 and R2. The dc bias circuit can be used to advantage as an aid in visualization during this design process. Once Rb has been chosen to provide the desired bias stability, all the information required can be obtained from the dc bias circuit. 如前所述，通過適當(dāng)選擇偏置電阻 R1 和 R2， Q 點可以位于直流負(fù)載線上的任何位置。while with munications systems the primary objective is to convey, exact and process information, in which process considerable amounts of power may be consumed. （ The sentences marked in bold are the passive voice.） Through the example above and bined with mon sense, we can easily find out the frequent use of the passive voice in an article about English for science and technology .In a word ,the main purpose of EST is to describe the existed objective things and phenomenon, the scientific researches and the technological process, etc. The passive voice pay more attention to objective facts than the active voice, almost not influenced by any emotional color, which makes the article more convincing. As J .Perlmutter says ―it‘s traditional among technical writers to keep themselves in the background, to exclude personal pronouns and emphasize their work instead .‖ Impersonal Sentences In English for science and technology ,the writers often use impersonal sentences to better indicate the objective facts .EST writings describe the existed objective things and phenomenon, the scientific researches and the technological process, etc .What EST writings mainly discuss are the results and natural phenomenon of science but not the person who discovers or acplishes them, therefore, in English for science and technology the writers often use impersonal sentences .