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   1276篇
  免费   68篇
电工技术   15篇
综合类   1篇
化学工业   384篇
金属工艺   27篇
机械仪表   27篇
建筑科学   129篇
矿业工程   6篇
能源动力   46篇
轻工业   167篇
水利工程   20篇
石油天然气   3篇
无线电   79篇
一般工业技术   150篇
冶金工业   73篇
原子能技术   15篇
自动化技术   202篇
  2023年   14篇
  2022年   42篇
  2021年   52篇
  2020年   38篇
  2019年   43篇
  2018年   58篇
  2017年   50篇
  2016年   54篇
  2015年   37篇
  2014年   63篇
  2013年   87篇
  2012年   69篇
  2011年   83篇
  2010年   66篇
  2009年   63篇
  2008年   48篇
  2007年   61篇
  2006年   42篇
  2005年   29篇
  2004年   30篇
  2003年   14篇
  2002年   17篇
  2001年   18篇
  2000年   20篇
  1999年   27篇
  1998年   20篇
  1997年   11篇
  1996年   12篇
  1995年   12篇
  1994年   15篇
  1993年   10篇
  1992年   9篇
  1991年   7篇
  1990年   8篇
  1989年   5篇
  1988年   8篇
  1987年   9篇
  1985年   6篇
  1983年   7篇
  1982年   5篇
  1981年   5篇
  1979年   5篇
  1978年   6篇
  1977年   4篇
  1975年   4篇
  1974年   3篇
  1966年   3篇
  1954年   3篇
  1940年   4篇
  1934年   3篇
排序方式: 共有1344条查询结果,搜索用时 0 毫秒
61.
62.
63.
Facial autonomic responses may contribute to emotional communication and reveal individual affective style. In this study, the authors examined how observed pupillary size modulates processing of facial expression, extending the finding that incidentally perceived pupils influence ratings of sadness but not those of happy, angry, or neutral facial expressions. Healthy subjects rated the valence and arousal of photographs depicting facial muscular expressions of sadness, surprise, fear, and disgust. Pupil sizes within the stimuli were experimentally manipulated. Subjects themselves were scored with an empathy questionnaire. Diminishing pupil size linearly enhanced intensity and valence judgments of sad expressions (but not fear, surprise, or disgust). At debriefing, subjects were unaware of differences in pupil size across stimuli. These observations complement an earlier study showing that pupil size directly influences processing of sadness but not other basic emotional facial expressions. Furthermore, across subjects, the degree to which pupil size influenced sadness processing correlated with individual differences in empathy score. Together, these data demonstrate a central role of sadness processing in empathetic emotion and highlight the salience of implicit autonomic signals in affective communication. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
64.
This paper discusses the simulation of bubbling gas-solid flows by using the Eulerian two-fluid approach. Predictions of particle motion, bed expansion, bubble size and bubble velocity in bubbling beds containing Geldart B particles are compared with experimental results and correlations found in the literature. In addition, gas mixing in a bed of Geldart A particles is investigated.An in-house code has been developed based on the finite-volume method and the time-splitting approach using a staggered grid arrangement. The velocities in both phases are obtained by solving the 2D Reynolds-averaged Navier/Stokes equations using a partial elimination algorithm (PEA) and a coupled solver. The k-ε turbulence model is used to describe the turbulent quantities in the continuous phase.In general, the model predictions are in good agreement with experimental data found in the literature. Most important observations are: the level of the restitution coefficient was found to be crucial in order to obtain successful results from 2D axisymmetric simulations of a system containing Geldart B particles. Bubble size and bubble rise velocities are not as sensitive to the restitution coefficient. The turbulence model is of outmost importance concerning gas mixing in a fluidized bed of Geldart A particles.From these numerical analyzes an optimized granular flow two-fluid model can be designed for the purpose of simulating reactive systems in fluidized bed reactors.  相似文献   
65.
During last few decades, emerging environmental regulations worldwide, more notably in Europe and Japan, have targeted the elimination of Pb usage in electronic assemblies due to the inherent toxicity of this element. This situation drives to the replacement of the Sn–Pb solder alloy of eutectic composition commonly used as joining material to suitable lead-free solders for microelectronic assembly. Sn-based alloys containing Ag, Cu, Bi, and Zn are potential lead-free solders, usually close to the binary or ternary eutectic composition. For this reason a great effort was directed to establish reliable thermophysical data fundamental to interpret the solidification process and fluidity of alloys belonging to these systems. In this work, an analysis of the solidification process of pure Sn, binary Sn–Ag, Sn–Cu, Sn–Bi, Sn–Zn, Sn–Pb and ternary Sn–Ag–Cu eutectic alloys was carried out using computer aided-cooling curve analysis and differential scanning calorimetry.  相似文献   
66.
Regional innovation systems (RSI) concept is an important theoretical framework to analyse regional profiles of regions when trying to understand Innovation but it has also been used by practioners to design and implement policies. This study hopes to contribute to the understanding of the Algarve RSI, a peripheral Portuguese region in the National and European framework, where an economic growth is supported by Tourism, which leaves it out of the group of poorest regions when the GDPpc indicator is taken in account. The regional profile, the comparison with the other European regions and the characterisation of RSI following developed typologies are discussed in this paper. Through the analysis of 175 regions of the EU 15 the study seeks to find the dimensions underlying the innovative phenomena and to create homogeneous groups of regions that display similar profiles. Factorial Analysis was used to reduce the dimension of data from a barrage of regional indicators such as: Critical Mass of Territories, Economic Performance, Level of Wealth, Employment Market, Sectoral Structure of the Economy, Age Group Structure, Education and Training, Technological Employment, R&D and Patents. Having determined the four main factors with significant results (Technological Innovation, Human Capital, Economic Structure and Availability of the Employment Market) what followed was a hierarchical analysis of Clusters, resulting in five groupings of regions: Disadvantaged Regions, Average Regions, Central Regions, Large Economic Centres and Innovating Regions. A synthesis of the recent Regional Innovation Strategies for the Algarve is presented including previous experiences (Ettirse and INOVAlgarve) and the Algarve’s Regional Innovation Plan, which will try to create a pathway for regional development supported by knowledge-based activities for a more diversified regional economy.  相似文献   
67.
The influence of the temperature and precursor pressure on the defect density of single-walled carbon nanotubes (SWCNTs) grown by catalytic chemical vapor deposition was studied for several catalyst–precursor couples. The SWCNT defect density was assessed by studying the Raman D band. In situ Raman monitoring was used to determine experimental conditions allowing the preparation of samples free of pyrolytic carbon and not altered by air exposure. The most striking feature is that the Arrhenius plots of the IG/ID ratio systematically display a convex shape, i.e. the apparent activation energy decreases with increasing temperature. From HRTEM observations and oxidation experiments, this evolution of the D band features is ascribed to the catalytic growth of long SWCNTs with few defects at high temperature and of short and defective SWCNTs and carbon structures at low temperature. The convex Arrhenius behavior is well accounted by two kinetic models: (i) a model considering a change of intermediate states as a function of the temperature (for instance due to a phase transition of the catalyst particle or a change of intermediate carbon species) and (ii) a model considering a high-temperature process of defect creation (for instance by reaction with reactive gas species).  相似文献   
68.
Reachability, joinability and confluence properties are known to be undecidable for flat term rewrite systems (TRS). We give shorter and conceptually simpler proofs of these results. We also prove undecidability of weak normalization and unique normalization properties for flat TRS. The first author was supported by Spanish Ministry of Education and Science by the FORMALISM project (TIN2007-66523) and by the LOGICTOOLS-2 project (TIN2007-68093-C02-01). The second author was supported by Spanish Ministry of Education and Science by the FORMALISM project (TIN2007-66523).  相似文献   
69.
70.
The biogenicity of ancient morphological microfossil-like objects can be established by linking morphological (e.g. cell remnants and extracellular polymeric matrix) and chemical (e.g. isotopes, biomarkers and biominerals) evidence indicative of microorganisms or microbial activity. We have developed a non-destructive micro-analytical ion beam system capable of measuring with high spatial resolution the stable carbon isotope ratios of thin samples used for transmission electron microscopy. The technique is based on elastic scattering of alpha particles with an energy of 2.751 MeV. At this energy the 13C cross section is enhanced relative to the pure Rutherford cross section for 13C, whereas the 12C cross section is reduced relative to its pure Rutherford cross section. Here we report the initial results of this experimental approach used to characterize ultramicrotomed sections of sulfur-embedded graphite and microbial cells.  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