全文获取类型
收费全文 | 12574篇 |
免费 | 1568篇 |
国内免费 | 1612篇 |
专业分类
化学 | 5259篇 |
晶体学 | 97篇 |
力学 | 2002篇 |
综合类 | 200篇 |
数学 | 5865篇 |
物理学 | 2331篇 |
出版年
2024年 | 19篇 |
2023年 | 149篇 |
2022年 | 197篇 |
2021年 | 346篇 |
2020年 | 469篇 |
2019年 | 412篇 |
2018年 | 407篇 |
2017年 | 485篇 |
2016年 | 576篇 |
2015年 | 384篇 |
2014年 | 597篇 |
2013年 | 1164篇 |
2012年 | 718篇 |
2011年 | 713篇 |
2010年 | 623篇 |
2009年 | 779篇 |
2008年 | 811篇 |
2007年 | 861篇 |
2006年 | 702篇 |
2005年 | 613篇 |
2004年 | 578篇 |
2003年 | 502篇 |
2002年 | 496篇 |
2001年 | 400篇 |
2000年 | 370篇 |
1999年 | 355篇 |
1998年 | 282篇 |
1997年 | 240篇 |
1996年 | 211篇 |
1995年 | 222篇 |
1994年 | 178篇 |
1993年 | 157篇 |
1992年 | 109篇 |
1991年 | 116篇 |
1990年 | 78篇 |
1989年 | 62篇 |
1988年 | 49篇 |
1987年 | 46篇 |
1986年 | 37篇 |
1985年 | 42篇 |
1984年 | 39篇 |
1983年 | 23篇 |
1982年 | 27篇 |
1981年 | 23篇 |
1980年 | 23篇 |
1979年 | 21篇 |
1978年 | 8篇 |
1977年 | 15篇 |
1976年 | 7篇 |
1957年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 224 毫秒
991.
To avoid the unstable phenomena caused by time delays and perturbations, we investigate the sufficient conditions to ensure the global exponential robust stability with a convergence rate for the reaction-diffusion neural networks with S-type distributed delays. Because S-type distributed delays lead to some difficulty, we also introduce a new generalized Halanay inequality and a novel method-system-approximation method into the qualitative research of neural networks. Moreover, the sufficient criteria provided here, which are rather accessible and feasible, have wider adaptive range. 相似文献
992.
Considered herein is the Ostrovsky equation which is widely used to describe the effect of rotation on the surface and internal solitary waves in shallow water or the capillary waves in a plasma. It is shown that the solitary-wave solutions are orbitally stable for certain wave speeds.
993.
We study Hilbert spaces expanded with a unitary operator with a countable spectrum. We show that the theory of such a structure is ω ‐stable and admits quantifier elimination. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
994.
It has been recently shown that large growth factors might occur in Gaussian Elimination with Partial Pivoting (GEPP) also when solving some plausibly natural systems. In this note we argue that this potential problem could be easily solved, with much smaller risk of failure, by very small (and low cost) modifications of the basic algorithm, thus confirming its inherent robustness. To this end, we first propose an informal model with the goal of providing further support to the comprehension of the stability properties of GEPP. We then report the results of numerical experiments that confirm the viewpoint embedded in the model. Basing on the previous observations, we finally propose a simple scheme that could be turned into (even more) accurate software for the solution of linear systems. 相似文献
995.
Thin viscous fluid film flows over rotating curvilinear surfaces are considered. The steady-state flow is studied for large and finite Ekman numbers. The possibility of obtaining a film of given thickness is considered. The wave formation on the surface of an inhomogeneous film and the development of nonlinear waves are also investigated. The film flow parameters in the cases of flow over a plane disk and a curvilinear surface are compared. 相似文献
996.
我们设计了包含准平面四配位碳原子的Fullerene[51]及其八个包含准平面四配位碳原子的衍生物,而且采用B3LYP方法研究了它们的结构、稳定性和成键性质。结果表明:这九种新型化合物是稳定的,它们的垂直电离能很大,而垂直电子亲和势相对较小。这些结构都包含五员环和六员环、以及更大的十员环。 相似文献
997.
Bernardi M. Inês B. Araújo Vinícius D. Mesquita Alexandre Frigo Geraldo J. M. Maia Lauro J. Q. 《Journal of Thermal Analysis and Calorimetry》2009,95(3):923-928
Novel zinc(II) complex compounds of general formula Zn(C6H5COO)2·L2 (where L=caffeine (caf) and urea (u)) were synthesized and characterized by elemental analysis and IR spectroscopy. The thermal behaviour
of the complexes was studied during heating in air by thermogravimetry. It was found that the thermal decomposition of the
anhydrous Zn(II) benzoate compounds with bioactive ligands was initiated by the release of organic ligands at various temperatures.
On further heating of the compounds up to 400°C the thermal degradation of the benzoate anions took place. Zinc oxide was
found as the final product of the thermal decomposition of all zinc(II) benzoate complex compounds heated to 600°C. Results
of elemental analysis, infrared spectroscopy, mass spectroscopy and thermogravimetry are presented. 相似文献
998.
999.
Based on the Floquet theory on ordinary differential equations with periodically variable coefficients and the bifurcation
approach to nonlinear equations, a numerical approach to determining the stability region of control parameters is established
for a dynamic control system composed of a moving body levitated magnetically over flexible guideways. The system is nonlinearly
coupled among the elastic deformation of guideways, disturbance the levitation position of the body and electromagnetic control
forces. The numerical simulation is given for the system in the case in which the control parameters are taken within and
out of the stability region respectively. Results show that this approach is reliable.
This project is supported by NSFC(No. 19725207), the Pre-research Project of the Committee of Science and Technology for Defence
of China and the Science Foundation of Education Ministry of China for Ph. D. Programmes. 相似文献
1000.
In this paper, hybrid bidirectional associative memory neural networks with discrete delays is considered. By ingeniously importing real parameters di > 0(i = 1,2,···,n) which can be adjusted, we establish some new sufficient conditions for the dynamical characteristics of hybrid bidirectional associative memory neural networks with discrete delays by the method of variation of parameters and some analysis techniques. Our results generalize and improve the related results in [10,11]. Our work is significant... 相似文献