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   1524篇
  免费   92篇
  国内免费   3篇
电工技术   15篇
综合类   1篇
化学工业   369篇
金属工艺   32篇
机械仪表   42篇
建筑科学   63篇
矿业工程   3篇
能源动力   67篇
轻工业   195篇
水利工程   15篇
石油天然气   6篇
武器工业   1篇
无线电   154篇
一般工业技术   292篇
冶金工业   67篇
原子能技术   9篇
自动化技术   288篇
  2023年   23篇
  2022年   44篇
  2021年   65篇
  2020年   55篇
  2019年   60篇
  2018年   57篇
  2017年   56篇
  2016年   50篇
  2015年   53篇
  2014年   66篇
  2013年   129篇
  2012年   97篇
  2011年   138篇
  2010年   94篇
  2009年   75篇
  2008年   100篇
  2007年   68篇
  2006年   59篇
  2005年   41篇
  2004年   43篇
  2003年   46篇
  2002年   32篇
  2001年   15篇
  2000年   8篇
  1999年   8篇
  1998年   17篇
  1997年   11篇
  1996年   14篇
  1995年   13篇
  1994年   10篇
  1993年   11篇
  1992年   4篇
  1991年   4篇
  1990年   5篇
  1989年   2篇
  1988年   5篇
  1987年   6篇
  1985年   11篇
  1984年   3篇
  1983年   3篇
  1980年   1篇
  1979年   2篇
  1978年   1篇
  1976年   3篇
  1975年   1篇
  1973年   1篇
  1972年   1篇
  1971年   1篇
  1970年   2篇
  1969年   1篇
排序方式: 共有1619条查询结果,搜索用时 93 毫秒
101.
Controlling an approximation model of a controllable infinite dimensional linear control system does not necessarily yield a good approximation of the control needed for the continuous model. In the present paper, under the main assumptions that the discretized semigroup is uniformly analytic, and that the control operator is mildly unbounded, we prove that the semidiscrete approximation models are uniformly controllable. Moreover, we provide a computationally efficient way to compute the approximation controls. An example of application is implemented for the one- and two-dimensional heat equation with Neumann boundary control.  相似文献   
102.
Decisions about using addictive substances are influenced by distractions by addiction-related stimuli, of which the user might be unaware. The addiction-Stroop task is a paradigm used to assess this distraction. The empirical evidence for the addiction-Stroop effect is critically reviewed, and meta-analyses of alcohol-related and smoking-related studies are presented. Studies finding the strongest effects were those in which participants had strong current concerns about an addictive substance or such concerns were highlighted through experimental manipulations, especially those depriving participants of the substance. Theories to account for addiction-related attentional bias are discussed, of which the motivational theory of current concerns appears to provide the most complete account of the phenomenon. Recommendations are made for maximizing the precision of the addiction-Stroop test in future research. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
103.
The zeroth order plate mode shear wave velocity has been measured in thin strip specimens of Oriented Electrical Steel, Elinvar-Extra, and RMI 464 titanium alloy as a function of the angle between the propagation direction and the rolling direction. Also, the plane wave shear and longitudinal velocities have been measured along the normal to the rolling plane. The results in the Oriented Electrical Steel agree with the known (110)[001] texture. In the Elinvar-Extra there is a texture indistinguishable elastically from (100)[Oil], or partial (100)[011] superimposed on a random background. Different annealing temperatures following cold-rolling yield different degrees of anisotropy and different dependences (1/G)(dG/dT) of the shear modulus upon ambient temperature. At an annealing temperature of about 850‡C, (1/G)(dG/dT) evaluated near room temperature changes from positive to negative, and anisotropy becomes minimum. In the RMI 464 titanium alloy, the shear velocity anisotropy was only 1 pct in the rolling plane. Formerly with Bell Telephone Laboratories, Allen town, Pa.  相似文献   
104.
Goal-oriented methods are increasingly popular for elaborating software requirements. They offer systematic support for incrementally building intentional, structural and operational models of the software and its environment. They also provide various techniques for early analysis, notably, to manage conflicting goals or to anticipate abnormal environment behaviours that prevent goals from being achieved. On the other hand, tabular event-based methods are well-established for specifying operational requirements for control software. They provide sophisticated techniques and tools for late analysis of software behaviour models through simulation, model checking or table exhaustiveness checks. The paper proposes to take the best out of these two worlds to engineer requirements for control software. It presents a technique for deriving event-based specifications, written in the SCR tabular language, from operational specifications built according to the KAOS goal-oriented method. The technique consists of a series of transformation steps each of which resolves semantic, structural or syntactic differences between the KAOS source language and the SCR target language. Some of these steps need human intervention and illustrate the kind of semantic subtleties that need to be taken into account when integrating multiple formalisms. As a result of our technique SCR specifiers may use upstream goal-based processes à la KAOS for the incremental elaboration, early analysis, organization and documentation of their tables, while KAOS modelers may use downstream tables à la SCR for later analysis of the behaviour models derived from goal specifications.  相似文献   
105.
106.
TOSQAN is an experimental program undertaken by the Institut de Radioprotection et de Sûreté Nucléaire (IRSN) in order to perform thermal hydraulic containment studies. The TOSQAN facility is a large enclosure devoted to simulate typical accidental thermal hydraulic flow conditions in nuclear-pressurized water reactor (PWR) containment. The TOSQAN facility which is highly instrumented with non-intrusive optical diagnostics is particularly adapted to nuclear safety CFD code validation. The present work is devoted to studying the interaction of a water spray injection used as a mitigation means in order to reduce the gas pressure and temperature in the containment, to produce gases mixing and washout of fission products. In order to have a better understanding of heat and mass transfers between spray droplets and the gas mixture, and to analyze mixing effects due to spray activation, we perform detailed characterization of the two-phase flow.  相似文献   
107.
This paper describes realization and characterization of SrTiO3 (STO) high K MIM capacitors above BiCMOS integrated circuit (IC). These capacitances are connected to IC and are used as coupling capacitors in order to realize a high pass filter. Surface capacitance achieved is 10 nF/mm2 with capacitance value of 1.2 nF. The process for STO MIM fabrication does not exceed 400 °C, which is compatible with interconnections. Typical K and dielectric losses values obtained are, respectively 110% and 2%. Yield obtained reaches 83% for capacitors. A functional high pass filter using these STO capacitors was realized in this study. It exhibits a cut-off frequency at 6.5 kHz and a constant gain at higher frequencies of −1.3 dB.  相似文献   
108.
This article aims to provide information on the effects of the mobile phone on the socio-economic life of the rural dwellers in the Niger Delta region of Nigeria. The study adopted a semi-structured interview method. The study covered nine villages selected from Delta and Bayelsa States in the Niger Delta region of Nigeria. Convenience sampling technique was used to select 129 respondents who voluntarily agreed to participate in the study. The interview was tape recorded and the information collected from the tape recordings were transcribed and coded. Similar viewpoints toward the same question were put together for the analysis. The study revealed that the mobile phone has brought immerse socio-economic impact on the rural dwellers in the Niger Delta region of Nigeria. The study revealed that mobile phone use enable the rural dwellers to communicate with family members and friends in urban areas; relatives in urban areas send recharge cards for them to sell for money instead of traveling to meet them, and Call Center Operators become self-employed and through that make a living. Finally, the frequent recharging of mobile phones leads to indebtedness. The participants mentioned challenges such as network failure, non-availability of recharge cards, unreliable or complete absence of power supply to charge batteries, high charges by Network Service Providers, stealing of mobile phones, and unskilled persons repairing phones in rural areas. The introduction of mobile phones has lead to reduction of rural–urban migration by many jobless youths.  相似文献   
109.
The simplicity principle—an updating of Ockham's razor to take into account modern information theory—states that the preferred theory for a set of data is the one that allows for the most efficient encoding of the data. We consider this in the context of classification, or clustering, as a data reduction technique that helps describe a set of objects by dividing the objects into groups. The simplicity model we present favors clusters such that the similarity of the items in the clusters is maximal, while the similarity of items between clusters is minimal. Several novel features of our clustering criterion make it especially appropriate for clustering of data derived from, psychological procedures (e.g., similarity ratings): It is non-parametric, and may be applied in situations where the metric axioms are violated without requiring (information-forgetting) transformation procedures. We illustrate the use of the criterion with a selection of data sets. A distinctive aspect of this research is that it motivates a clustering algorithm from psychological principles.  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