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   115038篇
  免费   13479篇
  国内免费   15285篇
化学   79327篇
晶体学   1228篇
力学   6244篇
综合类   1395篇
数学   14616篇
物理学   40992篇
  2024年   208篇
  2023年   1109篇
  2022年   2449篇
  2021年   3706篇
  2020年   3417篇
  2019年   3272篇
  2018年   2926篇
  2017年   3455篇
  2016年   4180篇
  2015年   3847篇
  2014年   5266篇
  2013年   9146篇
  2012年   6591篇
  2011年   6569篇
  2010年   5749篇
  2009年   6957篇
  2008年   7229篇
  2007年   7588篇
  2006年   6764篇
  2005年   5599篇
  2004年   5104篇
  2003年   4685篇
  2002年   6456篇
  2001年   3750篇
  2000年   3267篇
  1999年   2719篇
  1998年   2493篇
  1997年   2114篇
  1996年   2015篇
  1995年   1767篇
  1994年   1630篇
  1993年   1424篇
  1992年   1371篇
  1991年   985篇
  1990年   797篇
  1989年   745篇
  1988年   696篇
  1987年   508篇
  1986年   440篇
  1985年   519篇
  1984年   427篇
  1983年   237篇
  1982年   440篇
  1981年   567篇
  1980年   516篇
  1979年   552篇
  1978年   417篇
  1977年   324篇
  1976年   270篇
  1973年   193篇
排序方式: 共有10000条查询结果,搜索用时 171 毫秒
991.
We give a verification theorem by employing Arrow's generalization of the Mangasarian sufficient condition to a general jump diffusion setting and show the connections of adjoint processes to dynamic programming. The result is applied to financial optimization problems.  相似文献   
992.
15N isotopic enrichment was necessary for the unequivocal assignment of the 1H NMR lines to the protons in the NH–OH fragment of benzohydroxamic acid, BHXA, C6H5CONHOH, in dry dimethyl sulfoxide solutions. The assignment [δ(NH) = 11.21, δ(OH) = 9.01, 1J(15N,1H) = 102.2 Hz, 2J(15N,1H) <1.5 Hz], which is opposite to that used by other authors, confirms the assignment extended to BHXA by Brown and co‐workers from the spectra of acetohydroxamic acid. The enrichment allowed also assignment of the 29Si lines in the spectra of disilylated benzohydroxamic acid, (Z)‐tert‐butyldimethylsilyl Ntert‐butyldimethylsilyloxybenzoimidate (2) and (Z)‐tert‐butyldiphenylsilyl Ntert‐butyldiphenylsilyloxybenzoimidate (3), and confirmed structure of the monosilylated products, Ntert‐butyldiphenylsilyloxybenzamide (4) and Ntert‐butyldiphenylsilyloxy benzoimidic acid (5). Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   
993.
由于腔模与激子对压力的依赖关系不同,所以可以选择不同的压力使激子和光场处于不同的耦合状态,从而实现对耦合的调谐。利用这种办法,我们观测到了代表激子与光场强耦合作用的Rabi分裂。由于在我们现有样品结构中压力对激子本征行为的影响很小,与以前报道的温度、电场等调谐方式相比,这种调谐方法不仅可以有效地调谐半导体微腔内激子与腔模的耦合程度,而且能够保持激子的本征性质在整个调谐过程中基本不变。这有助于研究在强耦合过程中激子极化激元的本征性质。将实验结果与压力下激子与腔模耦合理论进行拟合,得出了正确的Rabi分裂值。  相似文献   
994.
The selfconsistent diagram approximation (SCDA) is generalized for three-dimensional lattice gases with nearest neighbor repulsive interactions. The free energy is represented in a closed form through elementary functions. Thermodynamical (phase diagrams, chemical potential and mean square fluctuations), structural (order parameter, distribution functions) as well as diffusional characteristics are investigated. The calculation results are compared with the Monte Carlo simulation data to demonstrate high precision of the SCDA in reproducing the equilibrium lattice gas characteristics. It is shown that similarly to two-dimensional systems the specific statistical memory effects strongly influence the lattice gas diffusion in the ordered states. Received 7 August 2002 / Received in final form 22 January 2003 Published online 24 April 2003  相似文献   
995.
We compute particle creation for a real massive scalar field conformally coupled to a spatially closed Robertson–Walker space-time background, with time-dependent scale factor. This is a dynamical Casimir effect with moving boundaries.  相似文献   
996.
激发对相干态的等阶Y压缩效应   总被引:16,自引:0,他引:16  
沈华嘉 《光子学报》2003,32(7):879-881
用数值计算法研究了激发对相干态|ζ;m〉=a+mb+m|ζ〉的等阶Y压缩效应.结果表明:对于态a+mb+m|ζ〉,光场存在着等阶K(=2,3,4,5,…)次方Y压缩效应,但是随着场模上光子增加数m的增大,等阶K次方Y压缩效应减弱.  相似文献   
997.
We use methods of nonequilibrium statistical thermodynamics to investigate two dissipative processes in solids. We find the electron energy losses of a particle moving in a planar channeling regime and the sound absorption coefficient in metals under electron impurity scattering. The oscillator model is used to analyze the contribution from the effect of electron entrainment by a moving scattering center to the total dissipated energy. We investigate the frequency and temperature dependence of energy losses and also the dependence of the absorption coefficient on the sound wave vector.  相似文献   
998.
Phenethylammonium-based perovskites, which can be regarded as a semiconductor/insulator multiple quantum well consisting of lead halide semiconductor layers sandwiched between phenethylammonium insulator layers were prepared. To investigate the effects of the electronic state and the orientation of organic insulator layers on the optical properties of layered perovskites, fluorine substituted analogues were also prepared. The structure and optical properties were investigated by the XRD, UV–Vis absorption, and fluorescence measurements. The exciton absorption peak was shifted by the substitution of fluorine atoms in organic ammonium compounds. It became clear that the optical properties of two-dimensional perovskite compounds were controlled by the substitution of fluorine atoms.  相似文献   
999.
1000.
In this paper, we consider approximation to derivatives of a function by using radial basis function interpolation. Most of well-known theories for this problem provide error analysis in terms of the so-called native space, say Cφ. However, if a basis function φ is smooth, the space Cφ is extremely small. Thus, the purpose of this study is to extend this result to functions in the homogenous Sobolev space.  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