全文获取类型
收费全文 | 87602篇 |
免费 | 7355篇 |
国内免费 | 5504篇 |
专业分类
化学 | 24230篇 |
晶体学 | 1848篇 |
力学 | 7309篇 |
综合类 | 425篇 |
数学 | 21939篇 |
物理学 | 44710篇 |
出版年
2023年 | 236篇 |
2022年 | 324篇 |
2021年 | 470篇 |
2020年 | 848篇 |
2019年 | 1125篇 |
2018年 | 1106篇 |
2017年 | 841篇 |
2016年 | 722篇 |
2015年 | 600篇 |
2014年 | 1377篇 |
2013年 | 2237篇 |
2012年 | 1528篇 |
2011年 | 2135篇 |
2010年 | 2678篇 |
2009年 | 7244篇 |
2008年 | 8265篇 |
2007年 | 6777篇 |
2006年 | 6226篇 |
2005年 | 4401篇 |
2004年 | 4136篇 |
2003年 | 4342篇 |
2002年 | 5536篇 |
2001年 | 4046篇 |
2000年 | 3791篇 |
1999年 | 3599篇 |
1998年 | 3020篇 |
1997年 | 2119篇 |
1996年 | 1898篇 |
1995年 | 2324篇 |
1994年 | 2243篇 |
1993年 | 1671篇 |
1992年 | 1205篇 |
1991年 | 911篇 |
1990年 | 737篇 |
1989年 | 637篇 |
1988年 | 590篇 |
1987年 | 432篇 |
1985年 | 974篇 |
1984年 | 638篇 |
1983年 | 512篇 |
1982年 | 650篇 |
1981年 | 799篇 |
1980年 | 725篇 |
1979年 | 563篇 |
1978年 | 583篇 |
1977年 | 542篇 |
1976年 | 541篇 |
1975年 | 319篇 |
1974年 | 355篇 |
1973年 | 464篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
111.
We reveal that for a realistic system, interference effects are obtained such as the suppression of central line and inner sidebands and the narrowing of the outer fluorescence sidebands. For this purpose, we consider a spontaneous decay from an excited state to a metastable state when the excited and metastable states are resonantly coupled to an auxiliary metastable state by a laser field and a microwave field, respectively. The fluorescence spectrum evolves from a five-peaked structure into a doublet of ultrasharp lines as the ratio of the laser field Rabi frequency to the microwave Rabi frequency is decreased. The physical origin is presented in terms of dressed states. 相似文献
112.
Faisal A.A. El-Orany 《Optics Communications》2006,263(2):235-238
We prove that the revival-collapse phenomenon occurring in the atomic inversion of the two-photon Jaynes-Cummings model, when the mode is initially prepared in the coherent state and the atom is in the excited state, can be obtained from the evolution of the quadrature squeezing of the four-photon Jaynes-Cummings model. 相似文献
113.
We have applied Engel-Vosko exchange energy within density functional theory, to calculate the electronic structure and the optical properties of BaX (X = Te, Se, and S) compounds via full potential linearized augmented plane wave method. We have found that this improves the band gap results comparing to our previous work in which we had made use of Perdew et al. exchange energy functional. We have also calculated the dielectric constant of these compounds, using both Perdew et al. and Engel-Vosko schemes. It is shown that Engel-Vosko exchange energy functional leads to a better result. We have also reported the effect of spin-orbit coupling on the results. 相似文献
114.
Sub(L)中的五边形格特征及其数量不等式 总被引:1,自引:0,他引:1
五边形结构在刻画格的特征方面具有十分重要作用,应用格论及组合数学的方法讨论了格L与其子格格Sub(L)中所含五边形格之间的数量关系,给出了有限格L的子格格中三个元生成五边形格的充要条件,同时给出了Sub(L)所含不同五边形格数量的一个下界。 相似文献
115.
本文给出了一个关联图为圈的非负、半正定矩阵A为完全正的一个充要条件.我们还证明了这样的矩阵A(当A为完全正时)的分解指数即为A的阶数. 相似文献
116.
Laurent Gosse. 《Mathematics of Computation》2002,71(238):553-582
This paper investigates the behavior of numerical schemes for nonlinear conservation laws with source terms. We concentrate on two significant examples: relaxation approximations and genuinely nonhomogeneous scalar laws. The main tool in our analysis is the extensive use of weak limits and nonconservative products which allow us to describe accurately the operations achieved in practice when using Riemann-based numerical schemes. Some illustrative and relevant computational results are provided.
117.
考虑约束最优化问题:minx∈Ωf(x)其中:f:R^n→R是连续可微函数,Ω是一闭凸集。本文研究了解决此问题的梯度投影方法,在步长的选取时采用了一种新的策略,在较弱的条件下,证明了梯度投影响方法的全局收敛性。 相似文献
118.
We construct the complex simple Lie algebras using elementary algebraic geometry. We use our construction to obtain a new
proof of the classification of complex simple Lie algebras that does not appeal to the classification of root systems. 相似文献
119.
The dielectric responses (i.e. the refractive indices and the second order nonlinear susceptibilities) of all orthorhombic rare earth molybdates have been studied on the basis of the relationship between dielectric responses and the average atomic number of constituent atoms of crystals. Both the linear and second order nonlinear optical responses at 1.064 μm decrease with increasing atomic number from La to Lu. 相似文献
120.
Bond covalency and valence of elements in HgBa2Can−1CunO2n+2+δ (n=1, 2, 3, 4) were calculated and their relationship with Tc was discussed. For both oxygen and argon annealed samples, the results indicated that with the increase of n, the trend of bond covalency of Hg-O and Cu-O was the same or opposite compared with that of superconducting temperature. This may suggest that the magnitudes of Cu-O and Hg-O bond covalency are important in governing the superconducting temperature. For the highest Tc sample, Hg had the lowest valence, implying that lower valence of Hg was preferred in order to produce higher Tc. For fixed n, the valence of Cu in oxygen annealed samples was larger than that in argon annealed samples, indicating that oxygen annealed samples produced more carriers than argon annealed samples. 相似文献