全文获取类型
收费全文 | 12589篇 |
免费 | 1272篇 |
国内免费 | 1026篇 |
专业分类
化学 | 2672篇 |
晶体学 | 100篇 |
力学 | 4428篇 |
综合类 | 262篇 |
数学 | 4032篇 |
物理学 | 3393篇 |
出版年
2024年 | 16篇 |
2023年 | 79篇 |
2022年 | 294篇 |
2021年 | 389篇 |
2020年 | 315篇 |
2019年 | 265篇 |
2018年 | 287篇 |
2017年 | 361篇 |
2016年 | 466篇 |
2015年 | 341篇 |
2014年 | 488篇 |
2013年 | 810篇 |
2012年 | 601篇 |
2011年 | 663篇 |
2010年 | 590篇 |
2009年 | 723篇 |
2008年 | 746篇 |
2007年 | 786篇 |
2006年 | 791篇 |
2005年 | 618篇 |
2004年 | 613篇 |
2003年 | 565篇 |
2002年 | 493篇 |
2001年 | 451篇 |
2000年 | 416篇 |
1999年 | 392篇 |
1998年 | 320篇 |
1997年 | 319篇 |
1996年 | 268篇 |
1995年 | 218篇 |
1994年 | 170篇 |
1993年 | 154篇 |
1992年 | 145篇 |
1991年 | 129篇 |
1990年 | 96篇 |
1989年 | 83篇 |
1988年 | 69篇 |
1987年 | 79篇 |
1986年 | 55篇 |
1985年 | 44篇 |
1984年 | 34篇 |
1983年 | 19篇 |
1982年 | 32篇 |
1981年 | 33篇 |
1980年 | 8篇 |
1979年 | 18篇 |
1978年 | 11篇 |
1977年 | 6篇 |
1976年 | 7篇 |
1975年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Marcus Carlsson 《Expositiones Mathematicae》2021,39(1):149-157
von Neumann’s inequality in matrix theory refers to the fact that the Frobenius scalar product of two matrices is less than or equal to the scalar product of the respective singular values. Moreover, equality can only happen if the two matrices share a joint set of singular vectors, and this latter part is hard to find in the literature. We extend these facts to the separable Hilbert space setting, and provide a self-contained proof of the “latter part”. 相似文献
2.
3.
In this work the results of the statistical topometric analysis of fracture surfaces of soda-lime-silica glass with and without ionic exchange treatment are reported. In this case, the mechanism of substitution is K+-Na+. atomic force microscopy (AFM) was employed to record the topometric data from the fracture surface. The roughness exponent (ζ) and the correlation length (ξ) were calculated by the variable bandwidth method. The analysis for both glasses (subjected and non-subjected to ionic exchange) for ζ shows a value ∼0.8, this value agrees well with that reported in the literature for rapid crack propagation in a variety of materials. The correlation length shows different values for each condition. These results, along with those of microhardness indentations suggest that the self-affine correlation length is influenced by the complex interactions of the stress field of microcracks with that resulting from the collective behavior of the point defects introduced by the strengthening mechanism of ionic exchange. 相似文献
4.
Sensitivity analysis is a mathematical tool, first developed for optimization methods, which aim is to characterize a system response through the variations of its output parameters following modifications imposed on the input parameters of the system. Such an analysis may quickly become laborious when the thermal model under consideration is complex or the number of input parameters is high. In this paper, we develop a mathematical model to analyse the heat exchanges in four different types of solar air collectors. When building this thermal model we show that for each collector, at quasi-steady state, the energy balance equations of the components of the collector cascade into a single first-order non-linear differential equation that is able to predict the thermal behaviour of the collector. Our heat transfer model clearly demonstrates the existence of an important dimensionless parameter, referred to as the thermal performance factor of the collector, that compares the useful thermal energy which can be extracted from the heater to the overall thermal losses of that collector for a given set of input parameters. A sensitivity analysis of our thermal model has been performed for the most significant input parameters such as the incident solar irradiation, the inlet fluid temperature, the air mass flow rate, the depth of the fluid channel, the number and nature of the transparent covers in order to measure the impact of each of these parameters on our model. An important result which can be drawn from this study is that the heat transfer model developed is robust enough to be used for thermal design studies of most known flat plate solar air heaters, but also of flat plate solar water collectors and linear solar concentrators. 相似文献
5.
Boundedness of commutators on homogeneous Herz spaces 总被引:9,自引:0,他引:9
The boundedness on homogeneous Herz spaces is established for a large class of linear commutators generated by BMO(R
n
) functions and linear operators of rough kernels which include the Calderón-Zygmund operators and the Ricci-Stein oRfiUatory
singular integrals with rough kernels.
Project supponed in pan by the National h’atural Science Foundation of China (Grant No. 19131080) and the NEDF of China. 相似文献
6.
We study spectral properties of discrete Schrödinger operators with potentials obtained via dimerization of a class of aperiodic sequences. It is shown that both the nature of the autocorrelation measure of a regular sequence and the presence of generic (full probability) singular continuous spectrum in the hull of primitive and palindromic (four block substitution) potentials are robust under dimerization. Generic results also hold for circle potentials. We illustrate these results with numerical studies of the quantum mean square displacement as a function of time. The numerical techniques provide a very fast algorithm for the time evolution of wave packets. 相似文献
7.
Lin Surong 《Annals of Differential Equations》2006,22(4):517-523
The singularly perturbed boundary value problem for nonlinear higher order ordinary differential equation involving two small parameters has been considered. Under appropriate assumptions, for the three cases:ε/μ2→0(μ→0),μ2/ε→0 (ε→0) andε=μ2, the uniformly valid asymptotic solution is obtained by using the expansion method of two small parameters and the theory of differential inequality. 相似文献
8.
9.
Milutin R. Dostanic 《Proceedings of the American Mathematical Society》2002,130(6):1755-1764
We prove a second order formula concerning distribution of singular values of Toeplitz matrices in some cases when conditions of the H. Widom Theorem are not satisfied.
10.
A FUNDAMENTAL SOLUTION FOR THE LAPLACE OPERATOR ON THE QUATERNIONIC HEISENBERG GROUP 总被引:2,自引:0,他引:2
朱理 《数学物理学报(B辑英文版)》2002,22(3)
In this paper, the author studies the Laplace operator on the quaternionic Heisenberg group, construct a fundamental solution for it and use this solution to prove the Lp-boundedness and the weak (1-1) boundedness of certain singular convolution operators on the quaternionic Heisenberg group. 相似文献