全文获取类型
收费全文 | 706599篇 |
免费 | 6955篇 |
国内免费 | 2189篇 |
专业分类
化学 | 360563篇 |
晶体学 | 10009篇 |
力学 | 34745篇 |
综合类 | 29篇 |
数学 | 106614篇 |
物理学 | 203783篇 |
出版年
2021年 | 5140篇 |
2020年 | 5781篇 |
2019年 | 6247篇 |
2018年 | 17606篇 |
2017年 | 17256篇 |
2016年 | 17740篇 |
2015年 | 8484篇 |
2014年 | 12009篇 |
2013年 | 28561篇 |
2012年 | 25079篇 |
2011年 | 35756篇 |
2010年 | 23698篇 |
2009年 | 23735篇 |
2008年 | 30319篇 |
2007年 | 32125篇 |
2006年 | 22894篇 |
2005年 | 21934篇 |
2004年 | 20679篇 |
2003年 | 18827篇 |
2002年 | 17491篇 |
2001年 | 18412篇 |
2000年 | 14311篇 |
1999年 | 11123篇 |
1998年 | 9440篇 |
1997年 | 9194篇 |
1996年 | 8999篇 |
1995年 | 8116篇 |
1994年 | 8090篇 |
1993年 | 7748篇 |
1992年 | 8719篇 |
1991年 | 8679篇 |
1990年 | 8323篇 |
1989年 | 7980篇 |
1988年 | 8156篇 |
1987年 | 7934篇 |
1986年 | 7535篇 |
1985年 | 9795篇 |
1984年 | 10069篇 |
1983年 | 8266篇 |
1982年 | 8428篇 |
1981年 | 8333篇 |
1980年 | 7961篇 |
1979年 | 8273篇 |
1978年 | 8680篇 |
1977年 | 8473篇 |
1976年 | 8493篇 |
1975年 | 7775篇 |
1974年 | 7911篇 |
1973年 | 8060篇 |
1972年 | 5669篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
992.
993.
von Eynatten G. Ritter T. Bömmel H. E. Dransfeld K. 《Zeitschrift für Physik B Condensed Matter》1987,65(3):341-345
A new model is presented which explains well the dramatic decrease of the Mössbauer line intensities with raising temperatures for freely dispersed iron microscrystals. In contrast to other theories which consider mainly vibration to be responsible we discuss here the decrease in terms of large amplitude diffusive rotational or translational jumps of the particles. Such diffusive jumps lead — in agreement with the observation — to a strong reduction of the Mössbauer-intensity without broadening the line width in a noticeable way. The typical potential well for a diffusing particle in an equilibrium position is derived quantitatively to be 13 meV. The model might be important also for a new understanding of the dynamics of catalytic clusters either in contact with each other or with larger solid surfaces.Part of this work was supported by the DFG Sonderforschungsbereich 306, Konstanz 相似文献
994.
Luca Lambertini Raimondello Orsini 《Central European Journal of Operations Research》2007,15(1):105-117
We reconsider the role of network externalities in a dynamic spatial monopoly where the firm must invest in order to accumulate
capacity, while consumers may have either linear or quadratic preferences. We (1) characterise saddle point equilibria, (2)
prove that the extent of market coverage is increasing in the network effect and (3) unlike the existing static literature
on the same problem, the monopolist may not make introductory price offers. Then, we briefly deal with the socially optimal
solution, showing that, in general, a planner would serve more consumers than a profit-seeking monopolist.
相似文献
995.
In this paper, we study an evasion problem in systems described by equations of parabolic type. We consider four versions of constraints on the control parameters. 相似文献
996.
997.
Experimental data is presented for the interaction between a propagating flame and a simple vortex flow field structure generated
in the wake of solid obstacles. The interaction between gas movement and obstacles creates vortex shedding forming a simple
flow field recirculation. The presence of the simple turbulent structure within the gas mixture curls the flame front increasing
curvature and enhancing burning rate. A novel twin camera Particle Image Velocimetry, PIV, was employed to characterise the
flow field recirculation and the interaction with the flame front. The technique allowed the quantification of the flame/vortex
interaction. The twin camera technique provides data to define the spatial variation of both the velocity of the flow field
and flame front. Experimentally obtained values of local flame displacement speed and flame stretch rate are presented for
simple flame/vortex interactions. 相似文献
998.
G. S. Bisnovatyi-Kogan 《Physics of Particles and Nuclei》2006,37(5):647-676
It is now commonly accepted that cosmic γ-ray bursts (GRBs) are of cosmological origin. This conclusion is based on the statistical analysis of GRBs and the measurements of line redshifts in GRB optical afterglows, i.e., in the so-called long GRBs. In this review, the models of radiation and models of GRB sources are considered. In most of these models, if not in all of them, the isotropic radiation cannot provide the energy release necessary for the appearance of a cosmological GRB. No correlation is noted between the redshift, the GRB-spectrum shape, and the total detected energy. The comparison between data obtained in the Soviet experiment KONUS and the American experiment BATSE shows that they substantially differ in statistical properties and the detection of hard x-ray lines. The investigation of hard gamma (0.1–10 GeV) afterglows, the measurement of prompt optical spectra during the GRB detection, and the further investigation of hard x-ray lines is of obvious importance for gaining insight into the GRB origin. Observations of two bright optical GRB afterglows point to the fact that an initially bright optical flare is directly related to the GRB itself, and the subsequent weak and much more continuous optical radiation is of a different nature. The results of observations of optical GRB afterglows are discussed. They point to the fact that the GRBs originate in distant galaxies with a high matter density, where intense star formation takes place. The interaction of the cosmological GRB radiation with a dense surrounding molecular cloud results in the appearance of long-duration (up to 10 years) weak optical afterglows associated with the heating and reradiation of gas. Results of 2D numerical simulation of the heating and reradiation of gas in various variants of the relative disposition of GRB and molecular clouds are presented. In conclusion, the possible relation between the so-called short GRBs and recurrent sources of soft γ rays in our Galaxy, the so-called “soft gamma repeaters,” is discussed. 相似文献
999.
G. S. Patrin V. V. Beletskiĭ D. A. Velikanov O. A. Bayukov V. V. Vershinin O. V. Zakieva T. N. Isaeva 《Physics of the Solid State》2006,48(4):700-704
The results of experimental and theoretical studies of the low-temperature properties of FeSi crystals are presented. The specific features of the magnetic susceptibility are shown to be related to the superparamagnetic behavior of impurity clusters. The thermomagnetic hysteresis phenomena observed are explained using the model of exchange-coupled clusters. 相似文献
1000.
N. G. Rachkova I. I. Shuktomova A. I. Taskaev 《Russian Journal of Applied Chemistry》2006,79(5):715-721
Sorption of U, Ra, and Th from multicomponent aqueous salt solutions on hydrolyzed wood lignin is studied. The mechanism of radionuclide sorption from saline solutions is suggested on the basis of the results of sequential extraction. 相似文献