全文获取类型
收费全文 | 7561篇 |
免费 | 869篇 |
国内免费 | 741篇 |
专业分类
化学 | 2120篇 |
晶体学 | 149篇 |
力学 | 1235篇 |
综合类 | 90篇 |
数学 | 2584篇 |
物理学 | 2993篇 |
出版年
2024年 | 12篇 |
2023年 | 47篇 |
2022年 | 94篇 |
2021年 | 108篇 |
2020年 | 154篇 |
2019年 | 143篇 |
2018年 | 149篇 |
2017年 | 162篇 |
2016年 | 198篇 |
2015年 | 157篇 |
2014年 | 353篇 |
2013年 | 499篇 |
2012年 | 367篇 |
2011年 | 429篇 |
2010年 | 400篇 |
2009年 | 476篇 |
2008年 | 491篇 |
2007年 | 530篇 |
2006年 | 410篇 |
2005年 | 449篇 |
2004年 | 437篇 |
2003年 | 371篇 |
2002年 | 319篇 |
2001年 | 278篇 |
2000年 | 264篇 |
1999年 | 248篇 |
1998年 | 217篇 |
1997年 | 225篇 |
1996年 | 158篇 |
1995年 | 142篇 |
1994年 | 104篇 |
1993年 | 104篇 |
1992年 | 137篇 |
1991年 | 97篇 |
1990年 | 53篇 |
1989年 | 50篇 |
1988年 | 45篇 |
1987年 | 43篇 |
1986年 | 39篇 |
1985年 | 31篇 |
1984年 | 24篇 |
1983年 | 12篇 |
1982年 | 20篇 |
1981年 | 22篇 |
1980年 | 9篇 |
1979年 | 30篇 |
1978年 | 21篇 |
1977年 | 15篇 |
1976年 | 12篇 |
1974年 | 5篇 |
排序方式: 共有9171条查询结果,搜索用时 15 毫秒
91.
92.
The propagation of solitons through optical couplers is studied here in this paper. Both the twin-core couplers as well as the multiple-core couplers are considered here in this paper. The parameter dynamics of the solitons that are governed by the coupled generalized nonlinear Schrodinger's equation, due to non-Kerr law nonlinearity, has been obtained for such couplers. 相似文献
93.
本文研究了无界无限维商品空间上的生产经济均衡的存在性.虽然我们把商品空间看成是Riesz空间,但并没有在它的正锥上作任何内部假设.同时我们的结果也为现代企业或公司从事经济预测、制订生产计划、改善经营管理、提高劳动生产率以及优化经济机制提供了理论依据. 相似文献
94.
Ross W. Mair David G. Cory Sharon Peled Ching-Hua Tseng Samuel Patz Ronald L. Walsworth 《Journal of magnetic resonance (San Diego, Calif. : 1997)》1998,135(2):478-486
Pulsed-field-gradient NMR techniques are demonstrated for measurements of time-dependent gas diffusion. The standard PGSE technique and variants, applied to a free gas mixture of thermally polarized xenon and O2, are found to provide a reproducible measure of the xenon diffusion coefficient (5.71 × 10−6m2s−1for 1 atm of pure xenon), in excellent agreement with previous, non-NMR measurements. The utility of pulsed-field-gradient NMR techniques is demonstrated by the first measurement of time-dependent (i.e., restricted) gas diffusion inside a porous medium (a random pack of glass beads), with results that agree well with theory. Two modified NMR pulse sequences derived from the PGSE technique (named the Pulsed Gradient Echo, or PGE, and the Pulsed Gradient Multiple Spin Echo, or PGMSE) are also applied to measurements of time dependent diffusion of laser polarized xenon gas, with results in good agreement with previous measurements on thermally polarized gas. The PGMSE technique is found to be superior to the PGE method, and to standard PGSE techniques and variants, for efficiently measuring laser polarized noble gas diffusion over a wide range of diffusion times. 相似文献
95.
Heng-You Lan 《Journal of Mathematical Analysis and Applications》2007,327(1):481-493
In this paper, we introduce and study a new system of nonlinear A-monotone multivalued variational inclusions in Hilbert spaces. By using the concept and properties of A-monotone mappings, and the resolvent operator technique associated with A-monotone mappings due to Verma, we construct a new iterative algorithm for solving this system of nonlinear multivalued variational inclusions associated with A-monotone mappings in Hilbert spaces. We also prove the existence of solutions for the nonlinear multivalued variational inclusions and the convergence of iterative sequences generated by the algorithm. Our results improve and generalize many known corresponding results. 相似文献
96.
A. C. Orifici R. S. Thomson R. Degenhardt C. Bisagni J. Bayandor 《Mechanics of Composite Materials》2007,43(1):9-28
Analysing the collapse of skin-stiffened structures requires capturing the critical phenomenon of skin-stiffener separation,
which can be considered analogous to interlaminar cracking. This paper presents the development of a numerical approach for
simulating the propagation of interlaminar cracks in composite structures. A degradation methodology was introduced in MSC.Marc,
which involved the modelling of a structure with shell layers connected by user-defined multiple-point constraints (MPCs).
User subroutines were written that employ the virtual crack closure technique (VCCT) to determine the onset of crack growth
and modify the properties of the user-defined MPCs to simulate crack propagation. Methodologies for the release of failing
MPCs are presented and are discussed with reference to the VCCT assumption of self-similar crack growth. The numerical results
obtained by using the release methodologies are then compared with experimental data for a double-cantilever beam specimen.
Based on this comparison, recommendations for the future development of the degradation model are made, especially with reference
to developing an approach for the collapse analysis of fuselage-representative structures.
Russian translation published in Mekhanika Kompozitnykh Materialov, Vol. 43, No. 1, pp. 15–42, January–February, 2007. 相似文献
97.
在局部区域上的奇摄动反应扩散方程初始边值问题 总被引:2,自引:2,他引:0
本文是讨论一类在局部区域上的奇摄动反应扩散初始边值问题.利用算子理论和 不动点原理,得到了相应问题解的存在性和唯一性. 相似文献
98.
具有转向点超曲面的奇摄动椭圆型方程边值问题 总被引:5,自引:0,他引:5
本文利用多重尺度法和比较定理,研究了n维空间中一类具有转向点超曲面的奇摄动椭圆方程边值问题,研究了该值问题解的渐近性态。 相似文献
99.
We present a new linearized model for the zero-one quadratic programming problem, whose size is linear in terms of the number of variables in the original nonlinear problem. Our derivation yields three alternative reformulations, each varying in model size and tightness. We show that our models are at least as tight as the one recently proposed in [7], and examine the theoretical relationship of our models to a standard linearization of the zero-one quadratic programming problem. Finally, we demonstrate the efficacy of solving each of these models on a set of randomly generated test instances. 相似文献
100.
应用多尺度微扰理论到广义非简谐振子, 得到了一阶经典和量子微扰解. 特别是
我们的量子解在极限条件下能方便地转变为经典解, 并且坐标和动量算符的对易
关系的简化十分自然. 与Taylor级数解相比较, 无论是在经典还是在量子解
中频率移动都出现在各阶振动表达式中, 所以多尺度微扰解是弱耦合非简谐振动的较好解法. 相似文献