全文获取类型
收费全文 | 26938篇 |
免费 | 3868篇 |
国内免费 | 2848篇 |
专业分类
化学 | 8859篇 |
晶体学 | 202篇 |
力学 | 2084篇 |
综合类 | 527篇 |
数学 | 9542篇 |
物理学 | 12440篇 |
出版年
2024年 | 27篇 |
2023年 | 237篇 |
2022年 | 390篇 |
2021年 | 543篇 |
2020年 | 683篇 |
2019年 | 601篇 |
2018年 | 599篇 |
2017年 | 711篇 |
2016年 | 827篇 |
2015年 | 779篇 |
2014年 | 1202篇 |
2013年 | 2061篇 |
2012年 | 1340篇 |
2011年 | 1725篇 |
2010年 | 1594篇 |
2009年 | 1933篇 |
2008年 | 1973篇 |
2007年 | 2014篇 |
2006年 | 1792篇 |
2005年 | 1535篇 |
2004年 | 1304篇 |
2003年 | 1306篇 |
2002年 | 1145篇 |
2001年 | 965篇 |
2000年 | 832篇 |
1999年 | 766篇 |
1998年 | 637篇 |
1997年 | 574篇 |
1996年 | 469篇 |
1995年 | 410篇 |
1994年 | 381篇 |
1993年 | 301篇 |
1992年 | 296篇 |
1991年 | 242篇 |
1990年 | 156篇 |
1989年 | 164篇 |
1988年 | 126篇 |
1987年 | 121篇 |
1986年 | 75篇 |
1985年 | 138篇 |
1984年 | 97篇 |
1983年 | 61篇 |
1982年 | 107篇 |
1981年 | 70篇 |
1980年 | 58篇 |
1979年 | 81篇 |
1978年 | 40篇 |
1977年 | 44篇 |
1976年 | 31篇 |
1973年 | 36篇 |
排序方式: 共有10000条查询结果,搜索用时 19 毫秒
991.
带二次修正项的Dirac方程在拓扑绝缘体、石墨烯、超导等新材料电磁光特性分析中有着十分广泛的应用.本文工作的创新点有:一是首次提出了矩阵形式带有二次修正项的Dirac方程,它是比较一般的数学框架,涵盖了上述材料体系很多重要的物理模型,具体见附录A;二是针对上述材料体系的电磁响应问题,提出了有界区域Weyl规范下具有周期间断系数矩阵形式带二次修正项Maxwell-Dirac系统的多尺度渐近方法,结合Crank-Nicolson有限差分方法和自适应棱单元方法,发展了一类多尺度算法.数值试验结果验证了多尺度渐近方法的正确性和算法的有效性. 相似文献
992.
The excited state intramolecular proton transfer (ESIPT) processes in 3‐methylsalicyclic acid (3‐MeSA) and 3‐methoxysalicyclic acid (3‐MeOSA) have been investigated in cyclohexane medium by emission spectroscopic techniques. The ESIPT process was characterized in 3‐MeSA from the large Stokes fluorescent band (455 nm), but it was suppressed by 3‐MeOSA in cyclohexane. The ESIPT process was found to be accelerated both in 3‐MeSA and 3‐MeOSA in the presence of a hydrogen bond accepting agent, triethylamine (TEA). Further, theoretical calculations were carried out at the ground and excited states to complement the experimental evidences. 相似文献
993.
《Stochastic Processes and their Applications》2019,129(11):4239-4268
We prove that loop-erased random walks on the finite pre-Sierpiński gaskets can be extended to a loop-erased random walk on the infinite pre-Sierpiński gasket by using the ‘erasing-larger-loops-first’ method, and obtain the asymptotic behavior of the walk as the number of steps increases, in particular, the displacement exponent and a law of the iterated logarithm. 相似文献
994.
Bingquan Ji Luming Zhang Xuanxuan Zhou 《Numerical Methods for Partial Differential Equations》2019,35(3):1056-1079
In this article, a compact finite difference method is developed for the periodic initial value problem of the N‐coupled nonlinear Klein–Gordon equations. The present scheme is proved to preserve the total energy in the discrete sense. Due to the difficulty in obtaining the priori estimate from the discrete energy conservation law, the cut‐off function technique is employed to prove the convergence, which shows the new scheme possesses second order accuracy in time and fourth order accuracy in space, respectively. Additionally, several numerical results are reported to confirm our theoretical analysis. Lastly, we apply the reliable method to simulate and study the collisions of solitary waves numerically. 相似文献
995.
In this study, a strong competition model was considered between two species in a heterogeneous environment. For a system with two different constant diffusion rates for each competitor, the fast diffuser can be selected evolutionally under suitable assumptions if the competing interaction between the species is strong. We also claim that a strongly interacting competition leads to a more evolutionary selection than that with the same population dynamics if a species moves with a certain non-uniform dispersal. Furthermore, species with a certain non-uniform dispersal have a competitive advantage over linear random diffusers. In addition, a species with highly sensitive dispersal response to the environment may survive. These strongly competitive advantages were demonstrated by investigating the stability of semi-trivial solutions of the system with non-uniform dispersal and comparing it to the conditions of the model with constant diffusion. 相似文献
996.
We study uniqueness of a solution for an inverse source problem arising in linear time-fractional diffusion equations with time dependent coefficients. New uniqueness results are formulated in Theorem 3.1. We also show optimality of the conditions under which uniqueness holds by explicitly constructing counterexamples, that is by constructing more than one solution in the case when the conditions for uniqueness are violated. 相似文献
997.
Goran Radojev Torsten Linß 《Numerical Methods for Partial Differential Equations》2019,35(6):2305-2317
Collocation with triquadratic C1‐splines for a singularly perturbed reaction–diffusion problem in three dimension is studied. A posteriori error bound in the maximum norm is derived for the collocation method on arbitrary tensor‐product meshes which is robust in the perturbation parameter. Numerical results are presented that support our theoretical estimate. 相似文献
998.
This paper investigates the blow-up of solutions for a time fractional nonlinear reaction–diffusion equation with weakly spatial source. We first derive two sufficient conditions under which the solutions may blow up in finite time. Then, we prove the existence of global solution when the initial data are small enough. Moreover, the long time behavior of bounded solutions will be analyzed. 相似文献
999.
In this article, a singularly perturbed convection–diffusion equation is solved by a linear finite element method on a Shishkin mesh. By means of an analysis exploiting symmetries in the convective term of the bilinear form, a new superconvergence rate, which improves the existing result, is obtained. 相似文献
1000.
本文利用正整数模q的正则数的定义以及解析方法研究一类与Dedekind和有关的和式的计算问题,并给出这个和式在一些特殊点上有趣的恒等式. 相似文献