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   3439篇
  免费   184篇
  国内免费   2篇
电工技术   23篇
综合类   4篇
化学工业   886篇
金属工艺   30篇
机械仪表   62篇
建筑科学   130篇
矿业工程   10篇
能源动力   134篇
轻工业   553篇
水利工程   35篇
石油天然气   10篇
无线电   280篇
一般工业技术   491篇
冶金工业   118篇
原子能技术   35篇
自动化技术   824篇
  2024年   4篇
  2023年   41篇
  2022年   127篇
  2021年   161篇
  2020年   90篇
  2019年   109篇
  2018年   126篇
  2017年   126篇
  2016年   157篇
  2015年   108篇
  2014年   203篇
  2013年   286篇
  2012年   275篇
  2011年   270篇
  2010年   208篇
  2009年   208篇
  2008年   191篇
  2007年   172篇
  2006年   103篇
  2005年   100篇
  2004年   75篇
  2003年   84篇
  2002年   59篇
  2001年   30篇
  2000年   30篇
  1999年   34篇
  1998年   50篇
  1997年   33篇
  1996年   36篇
  1995年   24篇
  1994年   20篇
  1993年   16篇
  1992年   12篇
  1991年   5篇
  1990年   11篇
  1989年   12篇
  1988年   3篇
  1987年   6篇
  1986年   4篇
  1985年   4篇
  1984年   1篇
  1983年   1篇
  1982年   2篇
  1981年   2篇
  1980年   1篇
  1978年   4篇
  1977年   1篇
排序方式: 共有3625条查询结果,搜索用时 0 毫秒
101.
In this paper we present WEEV (Writing Environment for Educational Video games), a methodology for educational point-and-click adventure game authoring. Our approach aims to allow educators to actively collaborate in the educational game development process, using a narrative-based representation. WEEV is based on a pragmatic reinterpretation of previous works on narrativity and video games, enhanced by the use of a novel visual language to represent the flow of the story or narrative. The WEEV methodology has been implemented into an actual tool based on the already established <e-Adventure> platform for educational games. This tool was improved with feedback gathered from formative evaluation, end-users testing (i.e. educators), and actual use in the development of an educational game. The system, still under development, presents some user-interaction problems along with a need for the educational effectiveness of the resulting games to be further analyzed. However, this paper highlights that, according to the qualitative results of evaluations, WEEV can indeed be successfully applied to simplify the game creation process and that by using representations of games that educators can understand, WEEV can help provide educational value to games.  相似文献   
102.
This paper presents a method for automatically producing optimal strut-and-tie models for the design of reinforced concrete beams. The optimal model is generated by means of an optimization problem solved by using genetic algorithms. The basic idea developed here is that from an initial random generation of possible configurations of the strut-and-tie model for the beam subjected to study, new populations of possible configurations may be generated in an iterative way by using genetic operators until reaching an optimum solution for the studied problem which corresponds to the strut-and-tie configuration which minimizes the total strain energy. In the optimal configuration, compressive struts are not enforced to be parallel, which allows representing more consistently the physical reality of the flow of forces. Furthermore, the method is more simple and easier to apply than the methods based on the concepts of evolutionary structural optimization.  相似文献   
103.
This study examined measurement invariance of the Gifted Rating Scales—School Form (GRS–S) across the United States, Puerto Rico, China, South Korea, and Turkey, using multigroup confirmatory factor analysis. A total of 1,817 students were rated by 287 teachers using either translated versions of GRS–S or the original English GRS–S. Results indicate a similar factor structure for the GRS–S across the five locations; six factors with each of the 72 items equivalently loaded to the same latent variable across groups. The metric invariance test and the factor variance and covariance invariance tests reveal that the patterns of factor loadings and the factor variances and covariances are invariant across the five groups. Moreover, the scalar invariance test indicates that item means are equivalent across the groups. These results suggest that the GRS–S has intercultural utility and can be similarly interpreted. Implications and limitations of the present research for gifted identification are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
104.
New solution processable 4‐(2‐hexyldecan)‐4H‐bisthieno[2,3‐d:3′,2′‐b]pyrrole and 4,4′‐dialkyl‐2,2′‐bithiazole‐based copolymers (PBTzDTPs) are synthesized with excellent FET performance. These novel copolymers have considerable potential in printable electronics as they have high charge carrier mobilities, excellent air stability, good solution processibility, and no requirement for post‐deposition thermal annealing, all requirements for this field of application. The thin film transistors fabricated from PBTzDTPs achieve field effect mobilities as high as 0.14 cm2 V?1 s?1 with current on/off ratios up to 106 without thermal annealing. In addition, the devices exhibit stable performance in air, showing no significant degradation over 60 days. Moreover, the polymers described here provide an excellent example of the systems in which higher mobility performance does not require higher crystalline, long‐range ordered structures. Such a system appears to be particularly promising for rapid fabrication techniques, where kinetic conditions usually prevent the development of long‐range order.  相似文献   
105.
Probabilistic harmonic load flow (HLF) is currently enjoying renewed popularity. This is not surprising since in the near future, thousands of photovoltaic (PV) systems will be integrated into distribution systems. However, as yet, there is no model capable of explaining PV harmonic current behaviour in probabilistic HLF studies. To fill this gap, the harmonic modelling of PV systems proposed in this paper has three key points. First, it provides an effective model of the relationship between PV harmonic current emission and background harmonic voltages. Second, it statistically characterises PV harmonic currents (relative magnitude and phase angle) at different fundamental‐frequency current output intervals using historical time‐series data. In this statistical characterisation, the first fifth moments of each PV harmonic current are used to accurately approximate the raw probability density function (PDF) by means of the Legendre series. Finally, the third key point of this harmonic modelling is a method capable of determining the distribution functions of PV harmonic currents (absolute magnitude and phase angle), based on the statistical characterisation and a fundamental‐frequency probabilistic PV model. The numerical results obtained confirm the effectiveness of this PV model. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   
106.
107.
108.
The development and characterization of biodegradable polymers deriving from renewable natural sources has attracted much attention. The aim of this work was to partially characterize a thermoplastic starch obtained from the starch of seeds from the ramon tree (TPS‐RS) as an option to substitute thermoplastic starch from corn (TPS‐CS), in some of its applications. At 55% of relative humidity (RH), TPS‐RS had higher tensile strength and deformation than TPS‐CS. X‐ray diffraction analysis showed similar values in residual crystallinity (percentage of crystallinity that remains after plasticization process) in both TPS. The SEM micrographs showed a few remnant granular structures in the TPS‐RS. The FTIR showed a greater intensity in band at 1016 cm?1 in the TPS‐CS and TPS‐RS in comparison with their corresponding native starch, indicating an increase in the amorphous region after plasticization. The TGA analysis showed greater thermal stability in TPS‐CS (340 °C) compared with TPS‐RS (327 °C). In addition, the glass transition temperature in both TPS was 24 °C. The results obtained represent a starting point to potentialize the use of TPS‐RS instead of TPS‐CS for the development of new biodegradable materials for practical applications in different areas. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44235.  相似文献   
109.
Oxidation of Metals - The oxidation characteristics of a roll-grade high-speed steel with different tempering heat treatments were studied under thermal cycling conditions at 650&nbsp;°C...  相似文献   
110.
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