首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   23543篇
  免费   2146篇
  国内免费   1962篇
电工技术   1883篇
技术理论   3篇
综合类   2700篇
化学工业   731篇
金属工艺   780篇
机械仪表   1683篇
建筑科学   1118篇
矿业工程   693篇
能源动力   346篇
轻工业   346篇
水利工程   575篇
石油天然气   789篇
武器工业   358篇
无线电   3132篇
一般工业技术   814篇
冶金工业   582篇
原子能技术   169篇
自动化技术   10949篇
  2024年   59篇
  2023年   155篇
  2022年   350篇
  2021年   453篇
  2020年   517篇
  2019年   407篇
  2018年   365篇
  2017年   527篇
  2016年   631篇
  2015年   831篇
  2014年   1448篇
  2013年   1248篇
  2012年   1683篇
  2011年   2007篇
  2010年   1544篇
  2009年   1501篇
  2008年   1634篇
  2007年   1966篇
  2006年   1698篇
  2005年   1540篇
  2004年   1256篇
  2003年   1215篇
  2002年   951篇
  2001年   803篇
  2000年   620篇
  1999年   439篇
  1998年   350篇
  1997年   293篇
  1996年   255篇
  1995年   198篇
  1994年   152篇
  1993年   131篇
  1992年   82篇
  1991年   64篇
  1990年   34篇
  1989年   41篇
  1988年   30篇
  1987年   26篇
  1986年   18篇
  1985年   14篇
  1984年   20篇
  1983年   34篇
  1982年   13篇
  1981年   9篇
  1980年   6篇
  1979年   9篇
  1977年   8篇
  1976年   4篇
  1974年   3篇
  1959年   3篇
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
991.
The vocational schools in Taiwan regard professional certifications as a badge of skills achievement. The teaching in this context usually focuses on how to help students enhance their professional skills and pass the certificate examinations, particularly for computing courses. However, due to national education policy, pure online courses are not permitted here and in some other nations. In order to provide an appropriate design and arrangement of blended learning (BL) courses, the authors redesigned a course, integrating web-enabled self-regulated learning (SRL) with variations in online class frequency, and explored their effects on enhancing students' skills of deploying database management system (DBMS) and their thoughts regarding blended course and interventions concerning SRL. Three class sections with a total of 112 students were taken as three distinct groups. The results indicated that students in the group of SRL and BL with five online classes had the highest grades for using DBMS among the three groups, and had very positive thoughts regarding the interventions concerning BL and SRL. The authors also provide suggestions and implications for teachers and schools to adopt innovative teaching methods and technologies, and redesign their courses to help students learn.  相似文献   
992.
Today, software piracy is an issue of global importance. Computer science students are the future information and communication technologies professionals and it is important to study the way they approach this issue. In this article, we attempt to study attitudes, behaviours and the corresponding reasoning of computer science students in Greece regarding software piracy. The statements taken in 56 semi-structured interviews with students indicate that computer science students in Greece make intensive use of pirated software, mention as main reason for their practice the cost of genuine software, and blame the academic environment, coincidental stereotypes and their student status for this behaviour. They acknowledge the immoral character of their actions, as well as the fact that others are affected by software piracy, but they pay little attention to this action and they practically don't care. While keeping distance from software development companies, when specifically asked, they easily adopt the role of a software developer and attempt to substantiate their current and eventually future attitude out of hand. They consider software copyright laws to be inapplicable and unrealistic and fail to argue against intellectual property rights for mere digital products, such as software.  相似文献   
993.
Software modernization is critical for organizations that need cost-effective solutions to deal with the rapid obsolescence of software and the increasing demand for new functionality. This paper presents the XIRUP modernization methodology, which proposes a highly iterative process, structured into four phases: preliminary evaluation, understanding, building and migration. This modernization process is feature-driven, component-based, focused on the early elicitation of key information, and relies on a model-driven approach with extensive use of experience from the previous projects. XIRUP has been defined in the European IST project MOMOCS, which has also built a suite of support tools. This paper introduces the process using a case study that illustrates its activities, related tools and results. The discussion highlights the specific characteristics of modernization projects and how a customized methodology can take advantage of them.  相似文献   
994.

Context

Several metrics have been proposed to measure the extent to which class members are related. Connectivity-based class cohesion metrics measure the degree of connectivity among the class members.

Objective

We propose a new class cohesion metric that has higher discriminative power than any of the existing cohesion metrics. In addition, we empirically compare the connectivity and non-connectivity-based cohesion metrics.

Method

The proposed class cohesion metric is based on counting the number of possible paths in a graph that represents the connectivity pattern of the class members. We theoretically and empirically validate this path connectivity class cohesion (PCCC) metric. The empirical validation compares seven connectivity-based metrics, including PCCC, and 11 non-connectivity-based metrics in terms of discriminative and fault detection powers. The discriminative-power study explores the probability that a cohesion metric will incorrectly determine classes to be cohesively equal when they have different connectivity patterns. The fault detection study investigates whether connectivity-based metrics, including PCCC, better explain the presence of faults from a statistical standpoint in comparison to other non-connectivity-based cohesion metrics, considered individually or in combination.

Results

The theoretical validation demonstrates that PCCC satisfies the key cohesion properties. The results of the empirical studies indicate that, in contrast to other connectivity-based cohesion metrics, PCCC is much better than any comparable cohesion metric in terms of its discriminative power. In addition, the results also indicate that PCCC measures cohesion aspects that are not captured by other metrics, wherein it is considerably better than other connectivity-based metrics but slightly worse than some other non-connectivity-based cohesion metrics in terms of its ability to predict faulty classes.

Conclusion

PCCC is more useful in practice for the applications in which practitioners need to distinguish between the quality of different classes or the quality of different implementations of the same class.  相似文献   
995.

Context

Practitioners may use design patterns to organize program code. Various empirical studies have investigated the effects of pattern deployment and work experience on the effectiveness and efficiency of program maintenance. However, results from these studies are not all consistent. Moreover, these studies have not considered some interesting factors, such as a maintainer’s prior exposure to the program under maintenance.

Objective

This paper aims at identifying what factors may contribute to the productivity of maintainers in the context of making correct software changes when they work on programs with deployed design patterns.

Method

We performed an empirical study involving 118 human subjects with three change tasks on a medium-sized program to explore the possible effects of a suite of six human and program factors on the productivity of maintainers, measured by the time taken to produce a correctly revised program in a course-based setting. The factors we studied include the deployment of design patterns and the presence of pattern-unaware solutions, as well as the maintainer’s prior exposure to design patterns, the subject program and the programming language, and prior work experience.

Results

Among the factors under examination, we find that the deployment of design patterns, prior exposure to the program and the presence of pattern-unaware solutions are strongly correlated with the time taken to correctly complete maintenance tasks. We also report some interesting observations from the experiment.

Conclusion

A new factor, namely, the presence of pattern-unaware solutions, contributes to the efficient completion of maintenance tasks of programs with deployed design patterns. Moreover, we conclude from the study that neither prior exposure to design patterns nor prior exposure to the programming language is supported by sufficient evidences to be significant factors, whereas the subjects’ exposure to the program under maintenance is notably more important.  相似文献   
996.
为描述分布式开发环境中的软件可靠性增长情况,提出一种分布式开发环境下软件系统的可靠性模型。在实际的软件可靠性数据集上,通过使用适应性度量和AIC准则,对所提模型进行验证和评价。实验结果证明,该模型能捕获大量的可靠性成长曲线,具备较强的适用性和灵活性,且使用该模型所描述的分布式软件开发环境更符合实际情况。  相似文献   
997.
作为现代三大统计方法之一的聚类分析法目前已经广泛的应用于经济、生物、地理等领域。将聚类分析方法应用于大庆师范学院数学科学学院07级数学与应用数学专业本科2班全体学生的所有所学科目的成绩中,利用SPSSl6.0统计软件对学生进行分类,结合教育科学知识和多元统计的相关理论,分析了不同类型学生的特点并提出相应的培养意见,为高校有针对性的培养学生提供了一定依据。  相似文献   
998.
研究了响应面法在聚氯乙烯(PVC)热稳定剂配方研究中的使用价值.依据Box-Benhnken的中心组合实验设计原理,设计了响应面分析中的3因素3水平分析表及热稳定实验方案.使用SAS软件对实验数据进行了处理,得到了硬脂酸锌、硬脂酸钙和硬脂酸钡之间相互作用对热稳定时间影响的响应面曲面图.分析图表可知,硬脂酸锌对热稳定时间产生了负作用,硬脂酸锌和硬脂酸钙之间及硬脂酸锌与硬脂酸钡之间产生了交互作用.  相似文献   
999.
风险管理在软件质量管理体系中有着非常重要的作用.风险的起因来自于软件项目和产品研发过程中的不确定性,而这种不确定性就很可能给整个软件产品的质量带来各种各样的隐患.通过在软件测试过程中进行风险识别、风险分析和风险控制,从而进一步提高软件质量.该文从3个方面对软件测试风险管理进行阐述,并对软件测试常见风险进行分析,提出应对措施.  相似文献   
1000.
介绍了Mathematica软件中二元函数图形绘制的基本方法,进而研究了曲面相交所围成的空间立体图形的绘制方法和技巧,利用Mathematica软件绘制出了牟合方盖、球面与圆柱面相交、马鞍面与平面相交的立体图形.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号