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   1559084篇
  免费   32203篇
  国内免费   8278篇
化学   682713篇
晶体学   20459篇
力学   75302篇
综合类   104篇
数学   243161篇
物理学   379826篇
无线电   198000篇
  2021年   14784篇
  2020年   17413篇
  2019年   17568篇
  2018年   14678篇
  2016年   30327篇
  2015年   21983篇
  2014年   32902篇
  2013年   78841篇
  2012年   41811篇
  2011年   40103篇
  2010年   40936篇
  2009年   45570篇
  2008年   42737篇
  2007年   40251篇
  2006年   45843篇
  2005年   38725篇
  2004年   39595篇
  2003年   36920篇
  2002年   37483篇
  2001年   37011篇
  2000年   32586篇
  1999年   29455篇
  1998年   27656篇
  1997年   27505篇
  1996年   27013篇
  1995年   24789篇
  1994年   24242篇
  1993年   23657篇
  1992年   23488篇
  1991年   23740篇
  1990年   22467篇
  1989年   22057篇
  1988年   21201篇
  1987年   19940篇
  1986年   18756篇
  1985年   25309篇
  1984年   26399篇
  1983年   22313篇
  1982年   23739篇
  1981年   22903篇
  1980年   22159篇
  1979年   22090篇
  1978年   23311篇
  1977年   22894篇
  1976年   22532篇
  1975年   21228篇
  1974年   20842篇
  1973年   21384篇
  1972年   15556篇
  1967年   13275篇
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
81.
Journal of Communications Technology and Electronics - In recent years, there has been a rapid improvement in photonics products due to the use of multilayer heterostructures grown on the basis of...  相似文献   
82.
Mobile Networks and Applications - Project MindCatcher is an art/research project which has the intention to explore the potential of interactive artistic environments for measuring and a better...  相似文献   
83.
Sohrabi  M. 《Analysis Mathematica》2021,47(2):421-435
Analysis Mathematica - In this paper, we discuss measure theoretic characterizations for Moore-Penrose inverse of Lambert conditional operators, denoted by (MwEMu)?, in some operator classes...  相似文献   
84.
Surface passivation treatment is a widely used strategy to resolve trap-mediated nonradiative recombination toward high-efficiency metal-halide perovskite photovoltaics. However, a lack of passivation with mixture treatment has been investigated, as well as an in-depth understanding of its passivation mechanism. Here, a systematic study on a mixed-salt passivation strategy of formamidinium bromide (FABr) coupled with different F-substituted alkyl lengths of ammonium iodide is demonstrated. It is obtained better device performance with decreasing chain length of the F-substituted alkyl ammonium iodide in the presence of FABr. Moreover, they unraveled a synergistic passivation mechanism of the mixed-salt treatment through surface reconstruction engineering, where FABr dominates the reformation of the perovskite surface via reacting with the excess PbI2. Meanwhile, ammonium iodide passivates the perovskite grain boundaries both on the surface and top perovskite bulk through penetration. This synergistic passivation engineer results in a high-quality perovskite surface with fewer defects and suppressed ion migration, leading to a champion efficiency of 23.5% with mixed-salt treatment. In addition, the introduction of the moisture resisted F-substituted groups presents a more hydrophobic perovskite surface, thus enabling the decorated devices with excellent long-term stability under a high humid atmosphere as well as operational conditions.  相似文献   
85.
86.
Sun  J.  Yuan  H. 《Experimental Mechanics》2021,61(3):565-580
Experimental Mechanics - Temperature gradients significantly affect the material fatigue process. A reliable and robust test procedure is needed for quantifying the effects of temperature gradients...  相似文献   
87.
Journal of Optimization Theory and Applications - Direct optimization of many-revolution spacecraft trajectories is performed using an unconstrained formulation with many short-arc, embedded...  相似文献   
88.
Russian Physics Journal - The temperature dependences of the linear dielectric permittivity ε′ and the third harmonic coefficient γ3ω for nanocomposites obtained by embedding a...  相似文献   
89.

In this work we analysed the stepwise charging technique to find the limits from which it is beneficial in terms of load capacitance and charge–discharge frequency. We included in the analysis practical limitations such as the consumption of auxiliary logic needed to implement the technique and the minimum size of auxiliary switches imposed by the technology. We proposed an ultra-low-power logic block to push these limits and to obtain benefits from this technique in small capacitances. Finally, we proposed to use a stepwise driver in the driving of the gate capacitance of power switches in switched-capacitor (SC) DC–DC converters. We designed and manufactured, in a 130 nm process, a SC DC–DC converter and measured a 29% energy reduction in the gate-drive losses of the converter. This accounts for an improvement of 4% (from 69 to 73%) in the overall converter efficiency.

  相似文献   
90.
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