全文获取类型
收费全文 | 503875篇 |
免费 | 19895篇 |
国内免费 | 12903篇 |
专业分类
化学 | 282917篇 |
晶体学 | 7631篇 |
力学 | 23788篇 |
综合类 | 677篇 |
数学 | 59528篇 |
物理学 | 162132篇 |
出版年
2022年 | 5565篇 |
2021年 | 6610篇 |
2020年 | 7297篇 |
2019年 | 7475篇 |
2018年 | 8329篇 |
2017年 | 8033篇 |
2016年 | 12012篇 |
2015年 | 9051篇 |
2014年 | 12769篇 |
2013年 | 24730篇 |
2012年 | 21701篇 |
2011年 | 24468篇 |
2010年 | 17508篇 |
2009年 | 17024篇 |
2008年 | 20861篇 |
2007年 | 20289篇 |
2006年 | 19053篇 |
2005年 | 16854篇 |
2004年 | 14935篇 |
2003年 | 13185篇 |
2002年 | 12722篇 |
2001年 | 13409篇 |
2000年 | 10540篇 |
1999年 | 8704篇 |
1998年 | 7469篇 |
1997年 | 7198篇 |
1996年 | 6880篇 |
1995年 | 6373篇 |
1994年 | 6336篇 |
1993年 | 5789篇 |
1992年 | 6339篇 |
1991年 | 6197篇 |
1990年 | 5949篇 |
1989年 | 5646篇 |
1988年 | 5571篇 |
1987年 | 5424篇 |
1986年 | 5198篇 |
1985年 | 6669篇 |
1984年 | 6883篇 |
1983年 | 5931篇 |
1982年 | 6043篇 |
1981年 | 5815篇 |
1980年 | 5728篇 |
1979年 | 5798篇 |
1978年 | 6134篇 |
1977年 | 6000篇 |
1976年 | 6112篇 |
1975年 | 5727篇 |
1974年 | 5742篇 |
1973年 | 6021篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
92.
93.
The acoustic field inside a shell excited by a spatially inhomogeneous harmonic pressure field is studied. The shell is assumed
to have a finite length, a set of orthogonal stiffening ribs, two ends bounding the acoustic volume, and a sound-insulating
structure, which includes layers of sound-insulating material, resonant elements, and an interior panel. The shell is considered
to be orthotropic with boundary conditions corresponding to a free support. For the acoustic field in the closed volume, analytical
expressions are derived with allowance for the elastoacoustic interaction of the shell with the sound-insulating layers and
with the medium both inside the shell (with arbitrary impedance values at the ends) and outside it. These expressions are
used to investigate the effect of different types of resonant systems on the sound field inside the shell. 相似文献
94.
The effect of hydrogen on the photoluminescence and planar conductivity of GaAs/InGaAs quantum-well heterostructures with an island Pd layer at the anodically oxidized surface was studied. Unlike continuous deposited Pd layers, island layers do not cause the formation of defects in the GaAs surface region and yet the Pd layer maintains high catalytic activity with respect to hydrogen. It is found that the thermal treatment of such a structure in a hydrogen atmosphere causes atomic-hydrogen passivation of the defects in quantum wells. Studies of the characteristics of planar photoresistors with an island Pd layer acting as hydrogen sensors show that their hydrogen detectivity is approximately two orders of magnitude higher than that of diode structures with continuous Pd layers. 相似文献
95.
Fundamental processes in long air gap discharges 总被引:2,自引:0,他引:2
I. Gallimberti G. Bacchiega Anne Bondiou-Clergerie Philippe Lalande 《Comptes Rendus Physique》2002,3(10):854
The development of atmospheric lightning is initiated and sustained by the formation in virgin air of ‘streamer corona’ and ‘leader’ discharges, very similar to those observed in laboratory long sparks. Therefore, the experimental and theoretical investigations of these laboratory discharges have become of large interest to improve the physical knowledge of the lightning process and to develop self-consistent models that could be applied to new protection concepts.In the present paper the fundamental processes of the subsequent phases of long air gap discharges are analyzed, from the first corona inception and development to the leader channel formation and propagation. For all these processes simulations models are discussed that have been essentially derived and simplified by the authors, in order to develop sequential time-dependent simulation of the laboratory breakdown, with both positive and negative voltages. The possibility of extending these models to the case of natural lightning is discussed in the companion paper, presented in this same volume. To cite this article: I. Gallimberti et al., C. R. Physique 3 (2002) 1335–1359. 相似文献
96.
Gábor Dörnyei Marietta Bárczai-Beke Gábor Blaskó Péter Péchy Csaba Szántay 《Tetrahedron letters》1982,23(28):2913-2916
Regioselective demethylation of 3,4-dihydropapaveraldine (a) at 7 and 3' positions affords a properly substituted diphenolic key intermidiate (d) for the synthesis of reticuline and N-norreticuline. 相似文献
97.
F. G. Gerasimato 《Journal of Mathematical Sciences》1991,57(5):3381-3383
We propose a simplified method of determining the integral characteristics of the opening of a parachute which makes it possible to compute the maximal stress on a parachute and the trajectory parameters of the motion of the load in the region of the opening of the parachute, and to determine the size of the portion of the canopy at the time of maximal stress.Translated fromDinamicheskie Sistemy, No. 6, 1987, pp. 38–41. 相似文献
98.
E. G. Tarakanova 《Journal of Applied Spectroscopy》1991,54(4):357-362
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 54, No. 4, pp. 581–587, April, 1991. 相似文献
99.
The spin-1 Ising model, which is equivalent to the three-component lattice gas model, is used to study wetting transitions in three-component surfactant systems consisting of an oil, water, and a nonionic surfactant. Phase equilibria, interfacial profiles, and interfacial tensions for three-phase equilibrium are determined in mean field approximation, for a wide range of temperature and interaction parameters. Surfactant interaction parameters are found to strongly influence interfacial tensions, reducing them in some cases to ultralow values. Interfacial tensions are used to determine whether the middle phase, rich in surfactant, wets or does not wet the interface between the oil-rich and water-rich phases. By varying temperature and interaction parameters, a wetting transition is located and found to be of the first order. Comparison is made with recent experimental results on wetting transitions in ternary surfactant systems.This paper is dedicated to J. K. Percus in honor of his 65th birthday. 相似文献
100.
M. B. Wright 《The Journal of the Operational Research Society》1989,40(2):187-192
This paper addresses a problem common to all railway networks. Given a fixed train timetable and locomotives (or other forms of traction) of various types, each train must be allocated a locomotive. This paper examines the use of stochastic algorithms for such a problem. Two types of algorithm are used—a simple ‘local improvement’ method, performed successively from randomly chosen starting points, and a ‘simulated annealing’ approach. Both are found to give considerably better results than a deterministic method in current use, and the annealing approach is probably the better stochastic method. 相似文献