全文获取类型
收费全文 | 750篇 |
免费 | 62篇 |
国内免费 | 44篇 |
专业分类
化学 | 134篇 |
晶体学 | 2篇 |
力学 | 49篇 |
综合类 | 32篇 |
数学 | 512篇 |
物理学 | 127篇 |
出版年
2024年 | 1篇 |
2023年 | 14篇 |
2022年 | 8篇 |
2021年 | 23篇 |
2020年 | 24篇 |
2019年 | 24篇 |
2018年 | 30篇 |
2017年 | 24篇 |
2016年 | 30篇 |
2015年 | 21篇 |
2014年 | 32篇 |
2013年 | 57篇 |
2012年 | 29篇 |
2011年 | 41篇 |
2010年 | 34篇 |
2009年 | 34篇 |
2008年 | 46篇 |
2007年 | 40篇 |
2006年 | 44篇 |
2005年 | 44篇 |
2004年 | 30篇 |
2003年 | 25篇 |
2002年 | 27篇 |
2001年 | 21篇 |
2000年 | 25篇 |
1999年 | 12篇 |
1998年 | 18篇 |
1997年 | 20篇 |
1996年 | 9篇 |
1995年 | 20篇 |
1994年 | 4篇 |
1993年 | 3篇 |
1992年 | 4篇 |
1991年 | 3篇 |
1990年 | 3篇 |
1989年 | 3篇 |
1988年 | 2篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1985年 | 6篇 |
1984年 | 2篇 |
1982年 | 3篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1975年 | 1篇 |
1974年 | 2篇 |
1973年 | 1篇 |
排序方式: 共有856条查询结果,搜索用时 31 毫秒
1.
Victor García Jesús Sánchez-Márquez Estefanía Torres David Zorrilla Manuel Fernández 《International journal of quantum chemistry》2020,120(6):e26129
As part of previous studies, we introduced a new type of basis function named Simplified Box Orbitals (SBOs) that belong to a class of spatially restricted functions which allow the zero differential overlap (ZDO) approximation to be applied with complete accuracy. The original SBOs and their Gaussian expansions SBO-3G form a minimal basis set, which was compared to the standard Slater-type orbital basis set (STO-3G). In the present paper, we have developed the SBO basis functions at double-zeta (DZ) level, and we have assessed the option of expanding the SBO-DZ as a combination of Gaussian functions. Finally, we have determined the quality of the new basis set by comparing the molecular properties calculated with SBO-nG with those achieved with some standard basis sets. 相似文献
2.
Maurício Collares Yoshiharu Kohayakawa Robert Morris Guilherme O. Mota 《Random Structures and Algorithms》2020,56(4):1016-1030
We count orientations of avoiding certain classes of oriented graphs. In particular, we study , the number of orientations of the binomial random graph in which every copy of is transitive, and , the number of orientations of containing no strongly connected copy of . We give the correct order of growth of and up to polylogarithmic factors; for orientations with no cyclic triangle, this significantly improves a result of Allen, Kohayakawa, Mota, and Parente. We also discuss the problem for a single forbidden oriented graph, and state a number of open problems and conjectures. 相似文献
3.
4.
Abayomi Samuel Oke Oluwafemi Isaac Bada Ganiyu Rasaq Victoria Adodo 《Mathematical Methods in the Applied Sciences》2022,45(1):137-149
Coronavirus pandemic (COVID-19) hit the world in December 2019, and only less than 5% of the 15 million cases were recorded in Africa. A major call for concern was the significant rise from 2% in May 2020 to 4.67% by the end of July 15, 2020. This drastic increase calls for quick intervention in the transmission and control strategy of COVID-19 in Africa. A mathematical model to theoretically investigate the consequence of ignoring asymptomatic cases on COVID-19 spread in Africa is proposed in this study. A qualitative analysis of the model is carried out with and without re-infection, and the reproduction number is obtained under re-infection. The results indicate that increasing case detection to detect asymptomatically infected individuals will be very effective in containing and reducing the burden of COVID-19 in Africa. In addition, the fact that it has not been confirmed whether a recovered individual can be re-infected or not, then enforcing a living condition where recovered individuals are not allowed to mix with the susceptible or exposed individuals will help in containing the spread of COVID-19. 相似文献
5.
6.
7.
This paper is concerned with the classification of non-self-adjoint second-order difference equations. The relationship between the number of summable solutions of non-self-adjoint difference equations and that of the discrete linear Hamiltonian system is discussed. A classification for non-self-adjoint second-order difference equations is established, which is independent of the choice of the rotated half plane and the fixed point. 相似文献
8.
9.
It is considered the class of Riemann surfaces with dimT1 = 0, where T1 is a subclass of exact harmonic forms which is one of the factors in the orthogonal decomposition of the spaceΩH of harmonic forms of the surface, namely The surfaces in the class OHD and the class of planar surfaces satisfy dimT1 = 0. A.Pfluger posed the question whether there might exist other surfaces outside those two classes. Here it is shown that in the case of finite genus g, we should look for a surface S with dimT1 = 0 among the surfaces of the form Sg\K , where Sg is a closed surface of genus g and K a compact set of positive harmonic measure with perfect components and very irregular boundary. 相似文献
10.
Observation time-dependent self-diffusion coefficients can be used to obtain microstructural information of porous media. This paper presents two different kinds of Monte Carlo simulations of the self diffusion process of fluids like water in porous systems, a lattice-free method and a lattice-based method. The results for simple porous media model geometries agree well with each other and with published analytical as well as semi-analytical equations. The use of these equations, which are important for the interpretation of Pulsed Field Gradient-Nuclear Magnetic Resonance (PFG-NMR) time-dependent diffusion data with respect to properties of porous media, is discussed. 相似文献