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   6763篇
  免费   336篇
  国内免费   132篇
电工技术   240篇
技术理论   2篇
综合类   725篇
化学工业   156篇
金属工艺   32篇
机械仪表   51篇
建筑科学   4091篇
矿业工程   232篇
能源动力   201篇
轻工业   124篇
水利工程   285篇
石油天然气   113篇
武器工业   3篇
无线电   135篇
一般工业技术   178篇
冶金工业   279篇
原子能技术   7篇
自动化技术   377篇
  2024年   28篇
  2023年   49篇
  2022年   103篇
  2021年   126篇
  2020年   136篇
  2019年   105篇
  2018年   81篇
  2017年   149篇
  2016年   169篇
  2015年   213篇
  2014年   566篇
  2013年   406篇
  2012年   517篇
  2011年   575篇
  2010年   605篇
  2009年   554篇
  2008年   464篇
  2007年   544篇
  2006年   364篇
  2005年   329篇
  2004年   252篇
  2003年   221篇
  2002年   201篇
  2001年   133篇
  2000年   91篇
  1999年   55篇
  1998年   41篇
  1997年   28篇
  1996年   25篇
  1995年   14篇
  1994年   6篇
  1993年   19篇
  1992年   5篇
  1991年   8篇
  1990年   4篇
  1989年   4篇
  1988年   6篇
  1987年   3篇
  1986年   4篇
  1984年   6篇
  1983年   4篇
  1977年   2篇
  1973年   2篇
  1964年   1篇
  1961年   1篇
  1960年   1篇
  1959年   2篇
  1958年   2篇
  1956年   2篇
  1954年   1篇
排序方式: 共有7231条查询结果,搜索用时 15 毫秒
51.
The explosive growth of the Internet has made the knowledge and skills for creating Web pages into general subjects that all students should learn. It is now common to teach the technical side of the production of Web pages and many teaching materials have been developed. However teaching the aesthetic side of Web page design has been neglected, and students not in art or design majors are normally confronted with difficulties when they do expressive design of Web pages.  相似文献   
52.
The widespread availability of digital learning resources in a variety of media formats offers the possibility to make a profound difference in education. This potential has not been fully realised for range of interrelated reasons. In this paper we study the key characteristics of learning resources that have proved effective in changing learning and teaching, and relate them to existing frameworks for understanding resources. We outline the relationships between resources, their users, and the way they are used, and explore issues that influence practitioners in choosing a particular resource. Our study is based on a review of resources for e-learning and chemistry in post-compulsory education, undertaken for the UK Joint Information Systems Committees (JISC), as part of a wider study examining ‘The Effectiveness of Resources, Tools and Support Services used by Tutors in Designing and Delivering E-Learning Activities’.  相似文献   
53.
在现代社会的发展中,世界经济全球化拉近了不同国家,不同民族之间的距离,全球文明一体化已经成为世界发展的必然趋势,世界越来越趋向于在各个领域方面相互依存,日益趋同的不可分割的整体。它一方面推动了社会的进步和发展,而另一方面却破坏了文化的多样性,导致建筑风格的雷同,地域特色文化的消失。如何在建筑的发展中创造出适应时代需求而又体现自身特色的建筑,本文针对广西玉林民居现存的状况,初探营造体现具"岭南都会"特色精神意义的场所,让玉林民居焕发新活力,新形象。  相似文献   
54.
在3维场景重构、运动估计、机器视觉等领域,不仅希望能检测出图像中的角点,而且还希望获得角点附近更多的信息,即能对角点进行进一步分类。为了能对图像中检测出的角点进行分类,提出了一种基于有向面积的角点分类方法,该方法首先采用基于协方差矩阵特征向量的小波变换角点检测原理检测出图像边缘上的角点;然后根据角点两侧的边缘信息定义了6种类型的角点;最后通过计算角点附近边缘上顺序排列的3个有向面积,实现对角点的分类。实验表明,基于有向面积的角点分类,具有较高的准确性。  相似文献   
55.
本研究以主体功能区划作为控制单元进行划分,以水功能区纳污能力作为环境容量基础数据,结合国家环境保护部污染物排放统计数据,分析京津冀和西北五省(自治区)的不同主体功能区的地表水环境容量超载情况。结果显示,在水资源缺乏的京津冀和西北五省(自治区)地区,其重点开发区的氨氮排放入河量均已超出水环境容量,城镇生活污水排放是水环境氨氮容量超载的主要贡献因子。对于农产品主产区和重点生态功能区,京津冀地区水环境的化学需氧量(COD)和氨氮排放量普遍超载,而西北五省(自治区)还有19%~73%的水环境容量剩余。不同主体功能区的环境和产业政策取决于主体功能区的类型和水环境容量的超载情况。  相似文献   
56.
A smart city incorporates infrastructure methods that are environmentally responsible, such as smart communications, smart grids, smart energy, and smart buildings. The city administration has prioritized the use of cutting-edge technology and informatics as the primary strategy for enhancing service quality, with energy resources taking precedence. To achieve optimal energy management in the multidimensional system of a city tribe, it is necessary not only to identify and study the vast majority of energy elements, but also to define their implicit interdependencies. This is because optimal energy management is required to reach this objective. The lighting index is an essential consideration when evaluating the comfort indicators. In order to realize the concept of a smart city, the primary objective of this research is to create a system for managing and monitoring the lighting index. It is possible to identify two distinct phases within the intelligent system. Once data collection concludes, the monitoring system will be activated. In the second step, the operation of the control system is analyzed and its effect on the performance of the numerical model is determined. This evaluation is based on the proposed methodology. The optimized results were deemed satisfactory because they maintained the brightness index value (79%) while consuming less energy. The intelligent implementation system generated satisfactory outcomes, which were observed 1.75 times on average.  相似文献   
57.
益农  肇义 《福建建筑》1996,(3):9-10
本文从介绍“自然回归论”和“城市化威胁论”引述到重视解决好城市化进程中出现的环境问题的重要性及其所涉及的方方面面的问题。  相似文献   
58.
A new method for retrieving soil moisture content over vegetated fields, employing multitemporal radar and optical images, is presented. It is based on the integration of the temporal series of radar data within an inversion scheme and on the correction of the vegetation effects. The retrieval algorithm uses the Bayesian maximum posterior probability and assumes the existence of a relation among the soil conditions at the different times of the series. The correction of the vegetation effects models the variation, with respect to the initial time of the series, of the component of the backscattering coefficient due to the soil characteristics as function of the variations of the measured backscattering coefficient and of the biomass. The method is tested on the data acquired throughout the SMEX02 experiment. The results show that measured and estimated soil moistures are fairly well correlated and that the performances of multitemporal retrieval algorithm are better than those obtained by employing one radar acquisition, especially in terms of capability to detect soil moisture changes. Although the approach to correct the vegetation effects on radar observations needs to be further assessed on different sets of data, this finding demonstrates that the proposed method has a potential to improve the quality of the soil moisture retrievals.  相似文献   
59.
The negative impact of online gaming on adolescents has received much attention. The question of how to reduce their pathological use of online gaming is a critical issue. Based on the concept of external justification in dissonance theory, this experimental study aimed to examine whether severity of threat and justification of effort would impact adolescent players’ attitude change toward online gaming and their subjective estimations of online gaming addiction. The results echoed predictions from classic studies in dissonance theory. When participants engaged in attitude–discrepant behavior, i.e., persuading other adolescents that an apparently interesting online game is not fun at all, their attitudes toward online gaming shifted more dramatically to the negative side in the context of a low level of threat rather than a high level of threat. Additionally, the magnitude of attitude change was more prominent when participants exerted more rather than less effort to engage in attitude–discrepant behavior. Moreover, a similar pattern of participants’ evaluations of the likelihood of online gaming addiction was also observed. The findings show that dissonance theory has the potential to be useful for inducing adolescent players to disengage in online gaming.  相似文献   
60.
This mixed-methods study investigates the effects of student attitudes and behaviours on the outcomes of learning mathematics with computer tools. A computer tool was used to help students develop the mathematical concept of function. In the whole sample (N = 521), student attitudes could account for a 3.4 point difference in test scores between individuals on a 10-point scale. General attitude towards mathematics positively predicted test scores. However, more able students who were well-disposed towards mathematical computer tools achieved lower scores. Self-reported behaviours were unrelated to test scores. Detailed observation of a small number of students (= 8) revealed that positive attitudes towards mathematics and mathematical computer tools augmented exhibited learning behaviours, and that both a positive attitude to mathematical computer tools and exhibited learning behaviours benefited tool mastery. Although tool mastery and test scores are intimately related, reflective processes appear to mediate this relationship. Promoting learning with mathematical computer tools needs to take several factors into account, including improving student attitudes, raising levels of learning behaviours, and giving sufficient opportunity for constructing new mathematical knowledge within meaningful mathematical discourse.  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