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   20369篇
  免费   3606篇
  国内免费   1708篇
化学   4338篇
晶体学   53篇
力学   2721篇
综合类   555篇
数学   9668篇
物理学   8348篇
  2024年   23篇
  2023年   207篇
  2022年   316篇
  2021年   476篇
  2020年   522篇
  2019年   471篇
  2018年   480篇
  2017年   732篇
  2016年   834篇
  2015年   674篇
  2014年   1136篇
  2013年   1425篇
  2012年   1140篇
  2011年   1306篇
  2010年   1168篇
  2009年   1315篇
  2008年   1473篇
  2007年   1542篇
  2006年   1266篇
  2005年   1145篇
  2004年   1096篇
  2003年   913篇
  2002年   862篇
  2001年   701篇
  2000年   583篇
  1999年   569篇
  1998年   495篇
  1997年   431篇
  1996年   376篇
  1995年   382篇
  1994年   243篇
  1993年   222篇
  1992年   163篇
  1991年   197篇
  1990年   127篇
  1989年   83篇
  1988年   111篇
  1987年   74篇
  1986年   61篇
  1985年   68篇
  1984年   48篇
  1983年   31篇
  1982年   36篇
  1981年   38篇
  1980年   27篇
  1979年   27篇
  1978年   16篇
  1977年   11篇
  1976年   8篇
  1974年   7篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
91.
《中国物理 B》2021,30(10):104211-104211
The ideal optomechanically induced transparency effects of an output probe field are investigated in a cavity optoelectromechanical system, which is composed of an optical cavity, a charged mechanical resonator, and a charged object.Although the charged mechanical resonator damping rate is nonzero, the ideal optomechanically induced transparency can still appear due to the non-rotating wave approximation effect in the system. The location of optomechanically induced transparency dip can be controlled via the Coulomb coupling strength. In addition, we find that both the transparency window width and the maximum dispersion curve slope are closely related to the optical cavity decay rate.  相似文献   
92.
ABSTRACT

The scope of output-only/blind identification is restricted to stochastic/statistical processes, but for the first time in this study, the detectability conditions for general output-only subspace identification are investigated. This aids the range of input sources to be extended in a much realistic manner, beyond the only stochastic inputs. For this purpose, the subspace framework is assigned to make a connection between the output signal contents and the LTI system order. A few substantial hypotheses and algebraic statements are propounded affirming the sufficiency of the genuine output sequences for the identification purpose. This can be perceived as the cornerstone of state-space model reconstruction. In order to consolidate the notions according to reality, several examples are studied and examined for different input classes with stochastic disturbance.  相似文献   
93.
Combining the dual least action principle with Mountain-pass lemma,we obtain the existence of brake orbits for first-order convex Hamiltonian systems with particular anisotropic growth.  相似文献   
94.
王淦平  李春霞  金晓  黄华  刘振帮 《强激光与粒子束》2020,32(5):053003-1-053003-4
分析了采用单一同轴磁场时强流相对论多注阴极的侧端发射问题,研究了在不同磁场内半径和多注漂移管长度情况下多注电子束的传输效率。研究发现:由于引导磁场尺寸有限,高压下多注阴极杆及多注阴极柱的电子束发射是影响多注电子束传输效率的主要因素,且该部分电子束对多注漂移管入口管壁的轰击直接影响了多注速调管的重频能力。设计了采用永磁铁和同轴磁场组合工作的强流相对论多注二极管,理论分析和模拟计算证明:基于组合磁场的多注二极管可明显减弱甚至抑制多注阴极发射球头以外的电子束发射,并且组合磁场的磁场位形和强度可满足强流相对论多注电子束的高效、稳定传输。  相似文献   
95.
96.
97.
A photoredox catalytic ensemble consisting of CuO‐Fe2O3 nanocomposites and oligomeric derivative of phenazine has been developed. The prepared system acts as an efficient photoredox catalyst for C?N bond formation reaction via SET mechanism under ‘green’ conditions (aerial environment, mixed aqueous media, recyclable), requiring less equivalents of base and amine substrate. The present study demonstrates the significant role of supramolecular assemblies as photooxidants and reductants upon irradiation and their important contribution towards the activation of the metallic centre through energy transfer and electron transfer pathways. The potential of oligomer 4 : CuO‐Fe2O3 has also been explored for C?C bond formation reactions via the Sonogashira protocol.  相似文献   
98.
In the present study the cadmium (Cd) was determined in serum samples of psoriatic patients. The severity of psoriasis was evaluated according to criteria based on standard clinical diagnosis using Psoriasis Area Severity Index (PASI) score. In present study, an innovative tunable green solvent system based microextraction (TSS-ME) was applied for the enrichment of Cd in acid digested serum samples prior to determination with flame atomic absorption spectrometry. The hydrophobic complex of Cd-ammonium pyrrolidine thiocarbamate was extracted in a tunable solvent system which was prepared from a polybasic amine (N, N, N′, N′-tetramethyl-1, 4-diaminobutane), decanol and water system. The tunable green solvent system (TSS) which has zero ionic strength was converted to homogeneous monophasic polar hydrophilic phase via exposure to CO2 at different pressure and time duration. Then hydrophobic enriched Cd- ammonium pyrrolidine thiocarbamate was back extracted, using HNO3 (0.1 to 0.5 mol L−1) then the second round of TSS-ME was applied. The acidic aqueous phase enrich with analyte was separated from tunable solvent. The separated TSS was easily reused for up to 10 time for preconcentration purposes without loss of its enrichment character. The smoker and nonsmoker psoriatic patients at PASI >10, have two to three folds higher Cd levels in serum samples than healthy persons.  相似文献   
99.
王婧 《中国物理 B》2020,(3):245-250
We propose a scheme for realizing the optical nonreciprocal response based a four-mode optomechanical system,consisting of two charged mechanical modes and two linearly coupled optical modes. Two charged mechanical modes are coupled by Coulomb interaction, and two optical modes are coupled to one of mechanical modes by radiation pressure. We numerically evaluate the transmission probability of the probe field to obtain the optimum optical nonreciprocal response parameters. Also, we show that the optical nonreciprocal response is caused by the quantum interference between the optomechanical couplings and the linearly coupled interaction that breaks the time-reversal symmetry.  相似文献   
100.
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