The main reason lies in that , in the field of l2 teaching , researchers and teachers have always tried to find out effective ways to improve their students " proficiency in a second language . but their efforts were greeted with unsatisfactory results 出现这一热点的主要原因是在过去的几十年里，虽然人们研究教学方法的热情高涨，但是却没有收到令人满意的教学效果。
For decades , one of the biggest criticisms of at & t , and more recently lucent , has been that the company did a great job of inventing new technologies but was sometimes slow to turn those technologies into revenue - producing , market - leading products 在过去的几十年里，对at & t （现在是对朗讯）的一个最严厉批评就是它在新技术的发明方面非常成功，但是有时在将那些技术转化为能够创造收益、在市场上领先的产品方面却步伐缓慢。
With this in minds , many researchers have proposed a variety of models for describing the nonlinear fracture of concrete for the past decades . amid them most take the critical stress intensity factor kic as the fracture toughness , a sign of ability to resist the crack extension 对此，在过去的几十年里，众多研究人员提出了很多描述混凝土非线性断裂的模型，而其中的大多数断裂模型都以临界应力强度因子k _ ( ic )作为抵抗裂缝扩展阻力的断裂韧度。
The past decades have found that linguists and educators have put out numerous articles and works on language teaching , which are helpful both in theoretical instructions and practical teaching . yet there are few articles on the topic of exemplification 在过去的几十年里，国内外的语言学家和教育家撰写了无数有关语言教育教学的文章和著作，这些文献也为英语教学中的举例提供了一定的理论指导和实践帮助，遗憾的是没有专门的举例研究方面的论文。
During the past several decades , in the research of automatic vehicle recognition , classical methods obtained gratifying results ; as well as encountered much difficulty . in this paper , we use artifical neural network to resolve the vehicle recognition problem and attain satisfactory results 在过去的几十年里对自动汽车识别的研究历程中，经典法取得了一定的可喜成果，但也遇到了许多困难本文将人工神经元网络用于解决汽车识别问题取得了较为满意成果。
During the last years , many investigators have researched the two problems and presented many significant results . however , there exist many important problems to be solved , such as the problems of resilient control for 2 - d systems ; filtering for interconnected systems , the problem of designing robust controllers and filters for singular systems and nonlinear systems 在过去的几十年里，许多学者对此问题做了研究，给出了大量有意义的结果，但是仍有很多问题没有解决，如2 - d系统的弹性控制问题，关联时滞系统的滤波问题，广义不确定系统的鲁棒控制器与滤波器的设计问题，以及非线性系统的滤波问题。
In the past several years , as the core department of the enterprise , design , process and product department adopted the leading informationization means : computer aided techniques ( cad , capp , cam ) continuously , and the result is good , it is proved that local informationization can improve the market competition power obviously 在过去的几十年里，作为企业核心的设计、工艺和制造部门相继采用了先进的信息化手段：计算机辅助技术( cad 、 capp 、 cam等) ，取得了良好的效果，证明局部的信息化可以明显提高市场竞争力。
Although the knowledge of wind effects on tall buildings has significantly improved over the last decades , an understanding of the mechanism that the atmospheric flow field to various wind include effects on structures has not been developed sufficiently for formulation of functional expressions . not only is the wind approaching a building complex , but the flow pattern generated around a building is complicated by the distortion of the mean flow field , the flow separation , the vortex formation , and the wake development 在过去的几十年里,虽然人们对高层建筑风效应的了解已有显著提高,但对大气流场与结构物各种风致响应的关系还不能用解析表达式加以描述。由于平均流场的奇变、流动分离、旋涡形成以及紊流的发展,不仅使得流向建筑物的风,而且使得绕建筑物的流谱变得十分复杂。
