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   23831篇
  免费   508篇
  国内免费   739篇
电工技术   451篇
综合类   48篇
化学工业   2678篇
金属工艺   2258篇
机械仪表   960篇
建筑科学   481篇
矿业工程   47篇
能源动力   887篇
轻工业   1180篇
水利工程   153篇
石油天然气   369篇
武器工业   5篇
无线电   2793篇
一般工业技术   6735篇
冶金工业   3881篇
原子能技术   311篇
自动化技术   1841篇
  2023年   53篇
  2022年   144篇
  2021年   205篇
  2020年   149篇
  2019年   257篇
  2018年   427篇
  2017年   411篇
  2016年   469篇
  2015年   363篇
  2014年   577篇
  2013年   1558篇
  2012年   933篇
  2011年   1430篇
  2010年   1123篇
  2009年   1306篇
  2008年   1304篇
  2007年   1310篇
  2006年   1147篇
  2005年   1044篇
  2004年   865篇
  2003年   802篇
  2002年   767篇
  2001年   738篇
  2000年   704篇
  1999年   735篇
  1998年   1478篇
  1997年   1050篇
  1996年   911篇
  1995年   565篇
  1994年   458篇
  1993年   376篇
  1992年   241篇
  1991年   247篇
  1990年   158篇
  1989年   170篇
  1988年   121篇
  1987年   87篇
  1986年   59篇
  1985年   59篇
  1984年   38篇
  1983年   32篇
  1982年   27篇
  1981年   30篇
  1980年   20篇
  1979年   9篇
  1978年   8篇
  1977年   9篇
  1976年   20篇
  1975年   17篇
  1973年   11篇
排序方式: 共有10000条查询结果,搜索用时 14 毫秒
11.
Sarcopenia is the loss of skeletal muscle mass and function with advancing age. It involves both complex genetic and modifiable risk factors, such as lack of exercise, malnutrition and reduced neurological drive. Cognitive decline refers to diminished or impaired mental and/or intellectual functioning. Contracting skeletal muscle is a major source of neurotrophic factors, including brain-derived neurotrophic factor, which regulate synapses in the brain. Furthermore, skeletal muscle activity has important immune and redox effects that modify brain function and reduce muscle catabolism. The identification of common risk factors and underlying mechanisms for sarcopenia and cognition may allow the development of targeted interventions that slow or reverse sarcopenia and also certain forms of cognitive decline. However, the links between cognition and skeletal muscle have not been elucidated fully. This review provides a critical appraisal of the literature on the relationship between skeletal muscle health and cognition. The literature suggests that sarcopenia and cognitive decline share pathophysiological pathways. Ageing plays a role in both skeletal muscle deterioration and cognitive decline. Furthermore, lifestyle risk factors, such as physical inactivity, poor diet and smoking, are common to both disorders, so their potential role in the muscle–brain relationship warrants investigation.  相似文献   
12.
13.
Research funding has been seen as one of the most important resource in the reward system of science. And usage of publications denotes an interesting perspective of user behavior in scientific communication. This study aims to address the relationship between funding and Usage Count, which is a new metrics item established on the platform of Web of Science. Full records of 300,010 articles published in 2013 were downloaded in October 2015, and divided into six disciplines, including information science library science, education educational research, economics, computer science, materials science, and chemistry. Seven indicators were proposed to measure the impact, including Funding rate, Citation per paper, Usage rate, Usage per paper, Citation difference, Usage difference, and Conversion rate. It concluded funding has impact on usage and citation, and funded papers attract more usage, but varying in different disciplines. Usage Count can be used in the extension of citation metrics but with limits. This study originally engages with usage metrics and detected that there is positive correlation between usage and funding.  相似文献   
14.
Based on the phase transformation theories, especially the T0 concept of bainite transformation, alloy optimisation of bainitic steel with carbides has been carried out aiming at the produce of plastic mould with large cross-section. The effect of manganese and silicon on proeutectoid ferrite and bainite transformation is explored by dilatometric analysis, XRD and different microscopy techniques. The results show that after the alloy optimisation, the transformation of proeutectoid ferrite is suppressed and when the cooling rate is lower than 0·1°C?s??1, the new lower bainite transformation appears by decreasing carbon capacity of austenite and promoting carbide precipitation. Industrial production proves that the optimised alloy SDP1 can meet the demand for the plastic mould with the thickness of 1050?mm.  相似文献   
15.
A new constitutive equation of thermoelasticity for crystals is presented based on the interatomic potential and solid mechanics at finite temperature. Using the new constitutive equation, the calculations for crystal copper and graphene are carried out under different loading paths at different temperatures. The calculated results are in good agreement with those of the previous thermoelasticity constitutive equation based on quantum mechanics, which clearly indicates that our new constitutive equation of thermoelasticity is correct. A lot of comparisons also show that the present theory is more concise and efficient than the previous thermal stress theory in the practical application.  相似文献   
16.
We report a general template strategy for rational fabrication of a new class of nanostructured materials consisting of multicore shell particles. Our approach is demonstrated by encapsulating Au or Pt nanoparticles in silica shells. Other superstructures of these hollow shells, like dimers, trimers, and tetramers can also be formed by nanoparticle‐mediated self‐assembly. We have also used the as‐prepared multicore Au–silica hollow particles to perform the first studies of Ostwald ripening in confined microspace, in which chloride was found to be an efficient mediating ligand. After treatment with aqua regia, Au–Cl complex is formed inside the shell, and is found to be very active under in situ transmission electron microscopy observations while confined in a microcell. This aspect of the work is expected to motivate further in situ studies of confined crystal growth.  相似文献   
17.
18.
19.
20.
We perform a systematic measurement of the degree-of-polarization (DOP) and eye-closure penalty for optical signals with orthogonal polarizations. We find that the symmetry of DOP is maintained for the orthogonal polarizations under both first and higher order polarization-mode dispersion (PMD), whereas the symmetry of eye-closure penalty is broken under second-order PMD. An orthogonal polarization pair can have large disparity of eye-closure penalty despite an identical DOP. We also demonstrate a novel approach to estimate the maximum eye-closure penalty asymmetry with three orthogonal polarizations on the Poincare/spl acute/ sphere.  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