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   281485篇
  免费   3706篇
  国内免费   1298篇
电工技术   4807篇
综合类   530篇
化学工业   40448篇
金属工艺   11487篇
机械仪表   8486篇
建筑科学   6510篇
矿业工程   1584篇
能源动力   7177篇
轻工业   22682篇
水利工程   3059篇
石油天然气   5787篇
武器工业   44篇
无线电   33711篇
一般工业技术   57224篇
冶金工业   51627篇
原子能技术   7551篇
自动化技术   23775篇
  2021年   2265篇
  2019年   2136篇
  2018年   3807篇
  2017年   3901篇
  2016年   4139篇
  2015年   2695篇
  2014年   4524篇
  2013年   12326篇
  2012年   7354篇
  2011年   10531篇
  2010年   7787篇
  2009年   9027篇
  2008年   9312篇
  2007年   9307篇
  2006年   7970篇
  2005年   7377篇
  2004年   7294篇
  2003年   7081篇
  2002年   6791篇
  2001年   6901篇
  2000年   6528篇
  1999年   6809篇
  1998年   16485篇
  1997年   11699篇
  1996年   8662篇
  1995年   6856篇
  1994年   6017篇
  1993年   6072篇
  1992年   4389篇
  1991年   4159篇
  1990年   4070篇
  1989年   4016篇
  1988年   3725篇
  1987年   3361篇
  1986年   3372篇
  1985年   3716篇
  1984年   3458篇
  1983年   3193篇
  1982年   3020篇
  1981年   3039篇
  1980年   3011篇
  1979年   2826篇
  1978年   2856篇
  1977年   3157篇
  1976年   4127篇
  1975年   2420篇
  1974年   2377篇
  1973年   2398篇
  1972年   2018篇
  1971年   1777篇
排序方式: 共有10000条查询结果,搜索用时 375 毫秒
21.

Sampling or task jitter affects the performance of digital control systems but realistic simulation of this effect has not been possible to date. Our previous work has developed a novel method to simulate sampling jitter in MATLAB/Simulink simulation software where the jitter is generated randomly. What has been missing is a way to capture sampling jitter from a target platform and then feed this timing information into the simulation. This paper presents a low-cost and novel solution to these problems. The method uses an Arduino board to capture task jitter from two different hardware platforms with multiple stressing conditions. Then the recorded performance data is used to drive realistic simulations of a control system. Measurement shows that the task jitter data does not follow any specific random distribution such as Gaussian or Uniform. Furthermore, very occasional timing patterns, which may not be picked up while testing a real system, can result in extreme controller responses. This novel method allows comparisons of different platforms and reduces the effort required to choose the most appropriate platform for full implementation.

  相似文献   
22.
Glass and Ceramics - An analysis of the specific mechanisms of the influence of the state of the grain structure on the thermoelectric properties (electrical resistivity and total thermal...  相似文献   
23.
This work presents the dielectric properties of YNbO4 (YNO)–TiO2 composites in the microwave range. X-ray diffraction analysis demonstrates that the addition of TiO2 to YNO results in the formation of a Y(Nb0.5Ti0.5)2O6 phase. In the microwave range, the values of permittivity and dielectric loss did not present major changes with the increment of TiO2. Moreover, the addition of TiO2 results in an improvement in the thermal stability of YNO, with YNO63 demonstrating a resonant frequency of ?8.96 ppm.°C?1. We utilised numerical simulations to evaluate the behaviour of these materials as dielectric resonator antennae and it is found that they exhibit a reflection coefficient below ?10 dB at the resonant frequency, with a realised gain of 4.94 – 5.76 dBi, a bandwidth of 665–1050 MHz and a radiation efficiency above 84%. Our results indicate that YNO–TiO2 composites are interesting candidates for microwave operating devices.  相似文献   
24.
Journal of Engineering Physics and Thermophysics - A numerical investigation has been made into the interaction of slender (5–20 calibers) steel cylinder strikers with orthotropic compost...  相似文献   
25.
Journal of Engineering Physics and Thermophysics - Results of investigation into the influence of a corrosion process on thermotechnical characteristics of heat pipes of low-temperature range are...  相似文献   
26.
Deshmukh  P.  Sar  S. K.  Smječanin  N.  Nuhanović  M.  Lalwani  R. 《Radiochemistry》2022,64(4):532-542
Radiochemistry - Magnetically modified waste bark of the Aegle marmelos tree was prepared by using green synthesis method and was used in a batch system for U(VI) removal from aqueous solution. The...  相似文献   
27.
Extracellular vesicles (EVs) are membranous structures, which are secreted by almost every cell type analyzed so far. In addition to their importance for cell-cell communication under physiological conditions, EVs are also released during pathogenesis and mechanistically contribute to this process. Here we summarize their functional relevance in asthma, one of the most common chronic non-communicable diseases. Asthma is a complex persistent inflammatory disorder of the airways characterized by reversible airflow obstruction and, from a long-term perspective, airway remodeling. Overall, mechanistic studies summarized here indicate the importance of different subtypes of EVs and their variable cargoes in the functioning of the pathways underlying asthma, and show some interesting potential for the development of future therapeutic interventions. Association studies in turn demonstrate a good diagnostic potential of EVs in asthma.  相似文献   
28.
29.
Mobile Networks and Applications - 5G/6G communication are first generation high speed wireless communication network which integrates the aerial data, terrestrial data and maritime data via...  相似文献   
30.
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