英语句子中作谓语的动词发生的时间和存在状态不同，其表达形式亦不同，谓语动词的这种不同的形式称作时态。在写句子的时候，准确地把握句子的时态是科技论文写作中的关键之一。英语句子中的谓语动词虽然有16个时态，但在科技论文中常用的只有5种，即一般现在时，一般过去时，一般将来时、过去完成时和现在完成时。而用得最为频繁的只有一般过去时和一般现在时。
(1)一般现在时态
用于正式发表的内容。
Optically active amines bearing the stereogenic center as the position areimportant compounds because of their broad range of applications and theirpharmacological properties.
用于前言中的一般性背景叙述。
In most cases, the pharmacological activities of these amines are relatedto the configuration of the stereogenic center.
用于图或表的引出。
Fig.2 representsthe binding mode of the substituents of R-amines 1~6.
The results are collected in Table 1.
用于对实验结果的讨论。
Amphetamine shows a lower E value than those of its methoxy analogous,which is due to the fact that (R)-methoxyamphetamines react faster than(R)-amphetamine and that (S)-amphetamine is transformed more quickly than(S)-methoxyamphetamines. In the same way, the higher E value for mexile- tineis mainly a consequence of the slower reactivity of its (S)-enantiomer. Theseresults can be explained to a large extent on the basis of the size of thesubstituents attached to the stereocenter and size of the small pocket.
用于一般性真理的描述。
Streptomycin inbibits the growth of tuberculosis.
(2)一般过去时态
用于描述论文实验部分中有关试剂和材料的使用。
Lipase was from C.Antarctica , Novozym 435 was a gift Novo Nordisk Co and was employed without any further treatment.solvent were of spectrophotometric grade and they were stored with 4 A molecular sieves under nitrogen prior to use.(±)-Mexiletine waspurchased as its chlorohydree from Aldrich. The other racemic amines were obtainedby reductive amination the corresponding ketone.
用于描述测试仪器的使用。
Melting pointswere determined on a Kofler hot-stage apparatus. Ultra-violet spectra wererecorded by using pye-unicam SP 800 and Philips PU 8720 spectrometers.Infra-red spectra were recorded on a Perkin-Elmer FE 1710 Fourier Transformspectrometer 1H NMR spectra were recorded Bruker WH 360 (360 MHz)spectrometer and tetramethylsilane was used as the internal standard. Massspectra were recorded on Kratos MS 80 or MS 25 spectrometers.
用于实验过程的描述。
Imprintingmolecules were added to the combined eluates , ASTM printers were used, theracemic substrates, (R)-enantiomer of the substrate, or the (S)-enantiomer ofthe substrate The samples were mixed and kept at room temperature for 20 min,then put on ice for 5 min. The imprinted proeteins were precipitated with 30%isopropanol. After mixing for 10 min, the samples were put on ice for 60 min.After centrifugation, the precipitates were washed once with ice-coldisopropanol and after a second centrifugation step the precipitates werelyophilized.
用于实验结果和讨论的描述。
The parameters k1 , k2 and α1 in eq.(2) weredetermined by nonlinear regression program. Values of immobilized lipases weresimilar and greater than those of free lipase. The solid curves in Figs. 1 and2 were calculated by using the parameters estimated.
用于结论中的描述。
Theoctadecyl-sepabeads preparation was the most efficient among those examined.This preparation presented the highest enantioselectivity, good activity andhigh stability under the harsh reaction conditions.
The thermostability of lipase was enhanced by immobilization. Deactivation of the lipases followed a two-step series model. When incubation temperature was below 60℃. lipase immobilized in alginate gels was found to have very high thermostability compared with free and the immobilized lipases. This was because of the strong affinity between lipase and alginate. Likewise, thermostabilization was loand for the lipase immobilized in inorganic microcapsules when incubation temperature was above 60℃. This was due to thestabilization of the intermediate state of the lipase.
(3)一般将来时
用于打算要做的工作和预期的结果的描述。
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We will nextuse the conversion values obtained after a reaction time of 7h.
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In some areas ofthe world, cancer has become or shortly will become the leading disease-relatedcause of death of the human population.
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Studies on genetherapy will be carried out in the near future.
(4)现在完成时态
用于到写论文时为止的一段时间内从结果上看与现在有联系的情况的描述。
Though immobilization does not necessarily lead to stabilization, there have been manyreports on enzyme stabilization by immobilization In most cases, including thepresent study it has not been possible to clearly elucidate the nature of theinteraction between the enzyme and the support.
Although fewchemotherapeutic regimens have yielded lasting remissions or cures, it is clearthat new therapeutic options are necessary.
用于论文结论中对全文的概括性总结的描述,强调动作到现在所产生的结果。
The effectof enzyme immobilization on the catalytic properties of different CAL-Bpreparations in the resolution of several cyclopyrrolone compounds in aqueousmedia has been studied. This work has demonstrated the strong influence of theenzyme preparation and the nature of the substrate.
(5)过去完成时态
用来追叙或补叙相对于过去某一时间之前所发生的动作。
When the genetic information could betranslated into therapeutics that could selectively ablate tumors without the systemicside effect often associated with cancer druge , some of the first oncogenedefects had been discovered.
时态是科技英语论文表述中的一个关键性语法问题。在论文的各个不同章节中，尽管表述的重点是不同的，但谓语动词的使用却是有规律的。通常描述作者自己的研究工作应该用一般过去时态,如论文的摘要，研究方法和过程,所得到的研究结果等因为这些章节中主要描述作者自己在写论文之前所做的工作、所发生的现象所得到的数据和结果。通常在前言中叙述已经公开发表了的内容和作者在论文中对自己所得结果进行讨论时使用一般现在时态,因为这些内容都是被确认了的知识。
学习来源：《中英文科技论文写作教程》