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   5936篇
  免费   151篇
  国内免费   206篇
电工技术   137篇
综合类   40篇
化学工业   754篇
金属工艺   288篇
机械仪表   88篇
建筑科学   141篇
矿业工程   17篇
能源动力   94篇
轻工业   312篇
水利工程   15篇
石油天然气   331篇
武器工业   13篇
无线电   351篇
一般工业技术   616篇
冶金工业   2497篇
原子能技术   42篇
自动化技术   557篇
  2022年   47篇
  2021年   85篇
  2020年   44篇
  2019年   60篇
  2018年   86篇
  2017年   83篇
  2016年   86篇
  2015年   91篇
  2014年   118篇
  2013年   178篇
  2012年   181篇
  2011年   290篇
  2010年   245篇
  2009年   245篇
  2008年   253篇
  2007年   226篇
  2006年   272篇
  2005年   230篇
  2004年   238篇
  2003年   189篇
  2002年   235篇
  2001年   195篇
  2000年   155篇
  1999年   179篇
  1998年   181篇
  1997年   172篇
  1996年   119篇
  1995年   130篇
  1994年   137篇
  1993年   144篇
  1992年   97篇
  1991年   52篇
  1990年   98篇
  1989年   100篇
  1988年   72篇
  1987年   60篇
  1986年   66篇
  1985年   54篇
  1984年   51篇
  1983年   45篇
  1981年   56篇
  1979年   40篇
  1978年   35篇
  1977年   37篇
  1976年   32篇
  1975年   41篇
  1974年   34篇
  1971年   79篇
  1970年   41篇
  1968年   35篇
排序方式: 共有6293条查询结果,搜索用时 15 毫秒
981.
The business of ICT (Information and Communications Technology) standards is more different in China than it is in Europe or in Japan.While it started out as a centralized effort over the millennia (yes,you read me right),in the past twenty years it has been driven equally by local government,state-owned enterprises and private enterprises either in standards organizations or trade associations.This has resulted in what meteorologists might call a turbulent situation.The current goals of standardization in China include:a push for quality and safety;encouraging home-grown innovation,whether regionally or nationally;influencing the direction of innovation internationally;and emphasizing market-driven approaches.Eventually China will be a formidable standards player.There is direct business value in helping Chinese companies master the art of participating in de jure and de facto standards bodies,in watching and analyzing their participation strategies - and in participating as a company or an organization because innovation is increasingly being shaped in standards.  相似文献   
982.
Gravitational-wave detectors such as Virgo and the laser interferometric gravitational-wave observatory (LIGO) use a long-baseline Michelson interferometer with Fabry-Perot cavities in the arms to search for gravitational waves. The symmetry between the two Fabry-Perot cavities is crucial to reduce the interferometer's sensitivity to the laser amplitude and frequency noise. To this purpose, the transmittance of the mirrors in both cavities should be as close as possible. This paper describes the realization and the characterization of the first twin large low-loss mirrors with transmissions differing by less than 0.01%.  相似文献   
983.
A method for matching dipole antennas to capacitive or inductive arbitrary complex impedances is proposed for ultra high frequency radio frequency identification (RFID) tag antenna designs. It can be applied to straight, capacitive-loaded, meander or any small high-Q dipole topology. For this purpose, design stages are provided with the corresponding formulas. The reflection coefficient simulations and measurements of four implemented prototypes show the expected output when the RFID frequency band, bandwidth, chip impedance and maximum tag size are required as inputs for the method. The eventual S11 < 10 dB bandwidth depends on the chip impedance Q factor and the antenna size. How this bandwidth is manifested in terms of the read range is also discussed. A length ratio of up to 31.1% regarding the standard Λ/2 dipole at resonance is obtained.  相似文献   
984.
Hybrid synthetic amphiphilic biomolecules are emerging as promising supramolecular materials for biomedical and technological applications. Herein, recent progress in the field of nucleic acid based lipids is highlighted with an emphasis on their molecular design, synthesis, supramolecular properties, physicochemical behaviors, and applications in the field of health science and technology. In the first section, the design and the study of nucleolipids are in focus and then the glyconucleolipid family is discussed. In the last section, recent contributions of responsive materials involving nucleolipids and their use as smart drug delivery systems are discussed. The supramolecular materials generated by nucleic acid based lipids open new challenges for biomedical applications, including the fields of medicinal chemistry, biosensors, biomaterials for tissue engineering, drug delivery, and the decontamination of nanoparticles.  相似文献   
985.
986.
987.
988.
A key, yet often neglected, component of digital evolution and evolutionary models is the ‘selection method’ which assigns fitness (number of offspring) to individuals based on their performance scores (efficiency in performing tasks). Here, we study with formal analysis and numerical experiments the evolution of cooperation under the five most common selection methods (proportionate, rank, truncation-proportionate, truncation-uniform and tournament). We consider related individuals engaging in a Prisoner''s Dilemma game where individuals can either cooperate or defect. A cooperator pays a cost, whereas its partner receives a benefit, which affect their performance scores. These performance scores are translated into fitness by one of the five selection methods. We show that cooperation is positively associated with the relatedness between individuals under all selection methods. By contrast, the change in the performance benefit of cooperation affects the populations’ average level of cooperation only under the proportionate methods. We also demonstrate that the truncation and tournament methods may introduce negative frequency-dependence and lead to the evolution of polymorphic populations. Using the example of the evolution of cooperation, we show that the choice of selection method, though it is often marginalized, can considerably affect the evolutionary dynamics.  相似文献   
989.
990.
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