全文获取类型
收费全文 | 251814篇 |
免费 | 4237篇 |
国内免费 | 689篇 |
专业分类
化学 | 134901篇 |
晶体学 | 2929篇 |
力学 | 9896篇 |
综合类 | 14篇 |
数学 | 31166篇 |
物理学 | 77834篇 |
出版年
2021年 | 1889篇 |
2020年 | 2269篇 |
2019年 | 2127篇 |
2018年 | 2802篇 |
2017年 | 2720篇 |
2016年 | 4836篇 |
2015年 | 3414篇 |
2014年 | 4738篇 |
2013年 | 11235篇 |
2012年 | 9261篇 |
2011年 | 11256篇 |
2010年 | 7501篇 |
2009年 | 7147篇 |
2008年 | 10194篇 |
2007年 | 10174篇 |
2006年 | 9417篇 |
2005年 | 8555篇 |
2004年 | 7531篇 |
2003年 | 6498篇 |
2002年 | 6296篇 |
2001年 | 6795篇 |
2000年 | 5287篇 |
1999年 | 4077篇 |
1998年 | 3476篇 |
1997年 | 3370篇 |
1996年 | 3293篇 |
1995年 | 3092篇 |
1994年 | 3152篇 |
1993年 | 2984篇 |
1992年 | 3293篇 |
1991年 | 3132篇 |
1990年 | 2972篇 |
1989年 | 2878篇 |
1988年 | 2819篇 |
1987年 | 2724篇 |
1986年 | 2517篇 |
1985年 | 3415篇 |
1984年 | 3567篇 |
1983年 | 2910篇 |
1982年 | 3140篇 |
1981年 | 3023篇 |
1980年 | 2885篇 |
1979年 | 3053篇 |
1978年 | 3215篇 |
1977年 | 3103篇 |
1976年 | 3055篇 |
1975年 | 2904篇 |
1974年 | 2918篇 |
1973年 | 2895篇 |
1972年 | 1875篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
This paper presents the simulation of surface acoustic wave (SAW)-induced absorption coefficient and refractive index change in InGaAs-GaAs multiple quantum well (MQW) structures operating near 980 nm. The exciton problem is solved in two dimensional momentum space to include the non-axial effect due to strain induced valance band mixing and nonparabolicity. The optical absorption coefficient and refractive index changes near the band gap in the MQWs are calculated as a function of SAW power. 相似文献
992.
F. Farid 《Linear and Multilinear Algebra》2002,50(3):223-239
An upper bound for the number of components of the numerical range of matrix polynomials is established. We also establish a necessary condition and a sufficient condition for the connectedness of the numerical range of a quadratic selfadjoint matrix polynomial. The boundary of the numerical range of linear matrix polynomials is also considered. 相似文献
993.
V. F. Klimkin 《Technical Physics》2002,47(9):1106-1111
Methods for analyzing statistical distributions of the breakdown delay time are generalized. A statistical approach is used to study electric breakdown in n-hexane in a 2.1-MV/cm quasi-uniform electric field at a pulse duration of ∼5×10−8 s. Two different mechanisms for the anode breakdown are shown to coexist and compete with each other. One of them incorporates the “bubble” stage, whereas the other one is related to ionization in the liquid itself. It is found that the weaker influence of the external pressure on the pulsed electric strength of liquids in the nanosecond range is caused by a transition to the ionization mechanism for the anode breakdown at elevated pressures. 相似文献
994.
F. D. Saccone C. E. Rodrí guez Torres F. H. S nchez O. Gutfleisch 《Physica B: Condensed Matter》2002,320(1-4):312-315
In the present work, a quantitative analysis of the phase compositions by Mössbauer effect spectroscopy of solid and conventional hydrogen disproportionated Pr13.7Fe80.3B6.0 and Pr13.7Fe63.5Co16.7Zr0.1B6.0 alloys was carried out. Significant amounts of intermediate borides t-Fe3B and Pr(Fe, Co)12B6 were detected after solid hydrogen disproportionation treatment in Pr13.7Fe80.3B6.0 and Pr13.7Fe63.5Co16.7Zr0.1B6.0 alloys, respectively. After conventional hydrogenation–disproportionation–desorption–recombination treatment these phases were not detected and in no case residual Pr2Fe14B-phase was found. It was observed that the amount of intermediate borides after disproportionation can be correlated with the degree of texture after recombination at various temperatures. 相似文献
995.
F. Sibel Salman Jayant R. Kalagnanam Sesh Murthy Andrew Davenport 《Journal of Heuristics》2002,8(2):215-239
For hard optimization problems, it is difficult to design heuristic algorithms which exhibit uniformly superior performance for all problem instances. As a result it becomes necessary to tailor the algorithms based on the problem instance. In this paper, we introduce the use of a cooperative problem solving team of heuristics that evolves algorithms for a given problem instance. The efficacy of this method is examined by solving six difficult instances of a bicriteria sparse multiple knapsack problem. Results indicate that such tailored algorithms uniformly improve solutions as compared to using predesigned heuristic algorithms. 相似文献
996.
We have investigated the low-lying collective states and electromagnetic transitions in 94Mo within the framework of the interacting boson model. The influence of model parameters on the energy levels and electromagnetic properties has been investigated. The analysis of the obtained results and the parameter values predict that the 23+state is the lowest mixed symmetry state with pure F = Fmax - 1 in this nucleus. The calculated results predicate that the 25+ (two-Q-phonon) mixed symmetry state is closed to the J = 2+ at 2.870 MeV in the experimental data, and the 2.965 MeV state is the lowest mixed symmetry with J = 3+. 相似文献
997.
We have studied antimony and selenium atomization processes including a chemical matrix modifier (palladium-containing activated
carbon) during their determination by electrothermal atomic absorption spectrometry. We have developed and fine-tuned an experimental
setup for determining the kinetic characteristics (activation energy and frequency factor) for element atomization processes
from measurements in the initial section of the analytical signal. We provide a rationale for the most likely mechanism for
the interactions that occur. The results of the kinetic studies of the atomization processes showed that the modifier we developed
was highly effective, as a result of formation of a thermally stable condensed system C-Pd-A (where A is the analyte).
__________
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 4, pp. 530–534, July–August, 2006. 相似文献
998.
999.
1000.
A. F. Ivanov 《Ukrainian Mathematical Journal》1989,41(8):903-906
Translated from Ukrainskii Matematicheskii Zhurnal, Vol. 41, No. 8, pp. 1054–1058, August, 1989. 相似文献