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   1966篇
  免费   112篇
  国内免费   3篇
电工技术   36篇
综合类   2篇
化学工业   519篇
金属工艺   20篇
机械仪表   51篇
建筑科学   75篇
矿业工程   1篇
能源动力   70篇
轻工业   230篇
水利工程   19篇
石油天然气   4篇
无线电   190篇
一般工业技术   300篇
冶金工业   211篇
原子能技术   4篇
自动化技术   349篇
  2024年   4篇
  2023年   22篇
  2022年   90篇
  2021年   112篇
  2020年   54篇
  2019年   62篇
  2018年   75篇
  2017年   56篇
  2016年   87篇
  2015年   64篇
  2014年   85篇
  2013年   132篇
  2012年   111篇
  2011年   124篇
  2010年   119篇
  2009年   119篇
  2008年   109篇
  2007年   77篇
  2006年   67篇
  2005年   68篇
  2004年   41篇
  2003年   57篇
  2002年   54篇
  2001年   30篇
  2000年   17篇
  1999年   29篇
  1998年   30篇
  1997年   21篇
  1996年   14篇
  1995年   23篇
  1994年   19篇
  1993年   10篇
  1992年   9篇
  1991年   7篇
  1990年   4篇
  1989年   9篇
  1988年   7篇
  1987年   4篇
  1986年   4篇
  1985年   5篇
  1984年   7篇
  1983年   6篇
  1982年   5篇
  1981年   11篇
  1980年   4篇
  1978年   3篇
  1976年   2篇
  1975年   3篇
  1964年   2篇
  1946年   1篇
排序方式: 共有2081条查询结果,搜索用时 15 毫秒
101.
The aim of this paper is to present a picture of student experience of a collaborative e-learning module in an asynchronous e-learning environment. A distance learning module on music education worth five credit points for a bachelor online degree for primary school educating teachers was assessed using a self-evaluation questionnaire that gathered quantitative and qualitative data about student satisfaction of the collaborative e-learning activity. The quantitative part of the questionnaire consisted of 27 closed questions on a 10-point Likert scale and offered data about satisfaction with the module. The qualitative part of the questionnaire provided an insight into the participant perspective of the online collaborative experience. General open questions on satisfaction and dissatisfaction were analyzed with an inductive analysis which showed the evaluation criteria used by 92 students. Results of the analysis showed five themes of the participants’ perspectives, which were interpreted by the researcher as: teamwork, cognitive, operating, organizing, and emotive/ethic for the positive aspects and teamwork, operating, organizing, and emotive/ethic for the aspects to be improved. The aspects that were associated with satisfaction include: collaborating, comparing ideas, sharing knowledge and skills to support each other, peer learning, analyzing and integrating different points of view, the usability of the platform, group planning and workload management. Aspects of the student learning experience that should inform the improvements of e-learning include: more collaboration between students since some students engage differently; more coordination and organization, the workload management in the group activities, some technical problems such as updating modifications. The participants’ results in the module increased their didactic potential as primary school teachers. The findings are discussed in relation to their potential impact on developing collaborative activities addressed to teacher education in distance learning. Implications for future research are also considered.  相似文献   
102.
There are many abandoned underground mines beneath the city of Rome, created in the Pleistocene pyroclastic deposits over thousands of years. These pose a serious public safety risk hence the study was undertaken to better assess the stability of the underground workings. The Villa de Sanctis public park was selected as a suitable test site, as in this area the cavity network can be inspected and the different steps of the progressive migration of voids toward the surface can be identified. In addition to an underground geological survey, geophysical investigations were undertaken to elucidate some key characteristics of the involved lithological units, including elastic stiffness and layer thickness. Recommendations are made for further studies of the accessible and inaccessible areas.  相似文献   
103.
A modeling method aimed at eliminating the need of explicit crack representation in bi-dimensional structures is presented for the simulation of the initiation and subsequent propagation within composite materials. This is achieved by combining a meshless method with a physical stress–displacement based criterion known as Cohesive Model. This model consents to apply a penalty-based approach to delamination modeling where a variable penalty factor along the crack segment allows to loosen or tight the two parts according to their relative displacements. Results are showed for classical single mode loading benchmark cases and compared to experimental results taken from the literature.  相似文献   
104.
We show that human observers strongly underestimate a linear or circular trajectory that a luminous spot follows in the dark. At slow speeds, observers are relatively accurate, but, as the speed increases, the size of the path is progressively underestimated, by up to 35%. The underestimation imposes little memory load and does not require tracking of the trajectory. Most importantly, we found that underestimation occurred only when successive motion vectors changed in direction. This suggests a perceptual rather than representational origin of the illusion, related to vector-sum integration over time of neural motion signals in different directions. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
105.
Professional geropsychology is a growing area of practice and training. To meet the mental health needs of an aging population, increasing numbers of psychologists need to develop competence to work with older adults, their families, and related care systems. The Pikes Peak model for geropsychology training (Knight, Karel, Hinrichsen, Qualls, & Duffy, 2009) delineates attitude, knowledge, and skill competencies for professional geropsychology practice and makes recommendations for training. In this paper, we define and illustrate the Pikes Peak geropsychology practice competencies through a case example. In the case, an older man with complex needs seeks care through a generalist psychologist in an outpatient setting. The attitudes, knowledge, and skills that the psychologist needs to consider, and implications for training, are reviewed. Training recommendations and resources are provided, with a focus on the training needs of psychologists who wish to expand their practices to include older adults. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
106.
The authors discuss a semantic-mediation architecture to advance traditional approaches for standards-based business-to-business (B2B) interoperability. The architecture is supported by the Athena Knowledge Representation and Semantics Mediation tool suite. Initial experimentations with the architecture and the toolset offer discussions of key architectural and functional aspects and suggest directions for future tools enhancements.  相似文献   
107.
A compact voltage controlled CMOS current divider is presented. Differently from previous implementations, exploiting the MOSFET translinear characteristics in subthreshold region, the proposed circuit is based on devices operating from moderate to strong inversion. An input current linearity range of nearly a decade is obtained by compensating for the deviations from the ideal drain current square-law approximation through an original empirical approach. The circuit is suitable for use as a building block in analog multipliers and for transconductor continuous tuning. The effectiveness of the proposed configuration is demonstrated by means of electrical simulations, performed on a prototype designed with a commercial process. The robustness of the linearization algorithm with respect to temperature variations is proven.  相似文献   
108.
The time reversal of a completely-positive, nonequilibrium discrete-time quantum Markov evolution is derived in a general framework via a suitable adjointness relation. Space-time harmonic processes are then introduced for the forward and reverse-time transition mechanisms, and their role in the study of quantum dynamics is illustrated by discussing (operator and scalar) relative entropy dynamics.  相似文献   
109.
A homo-tetrameric approximately 160-kDa cystathionine gamma-lyase was purified to homogeneity from Lactobacillus reuteri DSM 20016 by four chromatographic steps. The activity was pyridoxal-5'-phosphate dependent and the enzyme catalyzed the alpha,gamma-elimination reaction of L-cystathionine, producing L-cysteine, ammonia and alpha-ketobutyrate. The enzyme was active towards a range of amino acids and amino acid derivatives, including methionine. The pH and temperature optima were found to be 8.0 and 35 degrees C. respectively. Isoelectric pH (pI) was approximately 5.0 as determined by two-dimensional electrophoresis. Sensitivity to chemical inhibitors was typical of lactococcal cystathionine gamma- and beta-lyases, except it was inhibited by sulphydryl reagents. The N-terminal sequence was MKFNTQLIHGGNSED, which had 100% homology with cystathionine beta-lyase of Lb. reuteri 104R (Accession Number (CAC05298). Lb. reuteri DSM 20016. together with 10 other strains of non-starter lactic acid bacteria, was used as adjunct starter in the production of miniature ('anestrato Pugliese-like cheeses. After 40 d ripening, the water-soluble extract of the cheeses with added Lactobacillus fermentum DT41 and Lb. reuteri DSM 20016 contained the highest enzyme activities on cystathionine and methionine substrates. Determinations of methanethiol, dimethyl sulphide, dimethyl disulphide and dimethyl trisulphide in the miniature cheeses confirmed the findings of enzyme activities.  相似文献   
110.
We have built a fiber-optic confocal reflectance microscope capable of imaging human tissues in near real time. Miniaturization of the objective lens and the mechanical components for positioning and axially scanning the objective enables the device to be used in inner organs of the human body. The lateral resolution is 2 micrometers and axial resolution is 10 micrometers. Confocal images of fixed tissue biopsies and the human lip in vivo have been obtained at 15 frames/s without any fluorescent stains. Both cell morphology and tissue architecture can be appreciated from images obtained with this microscope.  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