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   413108篇
  免费   5041篇
  国内免费   1743篇
化学   227528篇
晶体学   6502篇
力学   16994篇
综合类   36篇
数学   45234篇
物理学   123598篇
  2019年   3158篇
  2018年   3677篇
  2017年   3528篇
  2016年   5983篇
  2015年   4288篇
  2014年   6209篇
  2013年   18301篇
  2012年   12912篇
  2011年   15994篇
  2010年   10635篇
  2009年   10548篇
  2008年   14408篇
  2007年   14636篇
  2006年   13561篇
  2005年   12625篇
  2004年   11470篇
  2003年   10270篇
  2002年   10100篇
  2001年   12090篇
  2000年   9187篇
  1999年   7256篇
  1998年   5870篇
  1997年   5893篇
  1996年   5654篇
  1995年   5306篇
  1994年   5069篇
  1993年   5003篇
  1992年   5689篇
  1991年   5525篇
  1990年   5316篇
  1989年   5334篇
  1988年   5318篇
  1987年   5240篇
  1986年   4910篇
  1985年   6760篇
  1984年   6978篇
  1983年   5699篇
  1982年   6181篇
  1981年   6005篇
  1980年   5802篇
  1979年   5993篇
  1978年   6360篇
  1977年   6130篇
  1976年   6232篇
  1975年   5706篇
  1974年   5720篇
  1973年   6044篇
  1972年   3843篇
  1968年   3291篇
  1967年   3238篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
A general theory of the phenomenon of recovered voltage in polymers was considered on the basis of representation of an actual poling process by a discrete set of Debye relaxators. Examples of numerical solution of the direct and inverse problems are given. A correlation expression between intentionally aged polymer specimens and recovered-voltage curves was proposed for use in the assessment of the material state of a polymer under actual service conditions. It was shown that it is sufficient to restrict consideration to three relaxation processes in analysis of the phenomenon.  相似文献   
992.
In this paper we present spectroscopic properties of doped and undoped titanium dioxide (TiO2) as nanofilms prepared by the sol-gel process with rhodamine 6G doping and studied by photoacoustic absorption, excitation and emission spectroscopy. The absorption spectra of TiO2 thin films doped with rhodamine 6G at very low concentration during their preparation show two absorption bands, one at 2.3 eV attributed to molecular dimmer formation, which is responsible for the fluorescence quenching of the sample and the other at 3.0 eV attributed to TiO2 absorption, which subsequently yields a strong emission band at 600 nm. The electronic band structure and optical properties of the rutile phase of TiO2 are calculated employing a fully relativistic, full-potential, linearized, augmented plane-wave (FPLAPW) method within the local density approximation (LDA). Comparison of this calculation with experimental data for TiO2 films prepared for undoped sol-gels and by sputtering is performed.  相似文献   
993.
994.
995.
996.
The black-body radiation is considered in a theory with noncommutative electromagnetic fields; that is noncommutativity is introduced in field space, rather than in real space. A direct implication of the result on cosmic microwave background map is argued.  相似文献   
997.
Synchronization of Genesio chaotic system via backstepping approach   总被引:9,自引:0,他引:9  
Backstepping design is proposed for synchronization of Genesio chaotic system. Firstly, the control problem for the chaos synchronization of nominal Genesio systems without unknown parameters is considered. Next, an adaptive backstepping control law is derived to make the error signals between drive Genesio system and response Genesio system with an uncertain parameter asymptotically synchronized. Finally, the approach is extended to the synchronization problem for the system with three unknown parameters. The stability analysis in this article is proved by using a well-known Lyapunov stability theorem. Note that the approach provided here needs only a single controller to realize the synchronization. Two numerical simulations are presented to show the effectiveness of the proposed chaos synchronization scheme.  相似文献   
998.
The general problem of finding a distribution in hyperfine interaction parameters from experimental Mössbauer spectra is outlined. Existing methods may lack flexibility to be easily applicable to simple problems. A line shape for hyperfine parameter distributions is given, which is based on linear segments in the probability function. This method is applied in the analysis of samples containing iron in a silicate glass.  相似文献   
999.
We have investigated the magnetic, electrical transport and electron spin resonance (ESR) properties of polycrystalline Nd0.85Na0.15MnO3 prepared by sol–gel method. A ferromagnetic–paramagnetic (FM–PM) transition is observed around 110 K, which is not accompanied by a metal–insulator transition. The sample displays the complete PM state associated with the ESR spectra fitted by single Lorentzian line shape above 130 K. Below 130 K, ESR spectra become distorted and then linewidth increases rapidly, where short-range magnetic order develops and coexists with PM phase due to the inhomogeneous magnetic state. In addition, the large difference between the activation energies obtained from the resistivity and ESR parameters (peak-to-peak linewidth and line intensity) at the frame of adiabatic small polaron hopping model is pointed out for Nd0.85Na0.15MnO3.  相似文献   
1000.
Recently, S. Reich and S. Simons provided a novel proof of the Kirszbraun-Valentine extension theorem using Fenchel duality and Fitzpatrick functions. In the same spirit, we provide a new proof of an extension result for firmly nonexpansive mappings with an optimally localized range.

  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