全文获取类型
收费全文 | 315546篇 |
免费 | 2533篇 |
国内免费 | 807篇 |
专业分类
化学 | 167499篇 |
晶体学 | 4713篇 |
力学 | 14575篇 |
综合类 | 12篇 |
数学 | 35595篇 |
物理学 | 96492篇 |
出版年
2019年 | 3119篇 |
2018年 | 4137篇 |
2017年 | 4222篇 |
2016年 | 5719篇 |
2015年 | 3117篇 |
2014年 | 5233篇 |
2013年 | 12446篇 |
2012年 | 9566篇 |
2011年 | 11793篇 |
2010年 | 8643篇 |
2009年 | 8456篇 |
2008年 | 10895篇 |
2007年 | 10962篇 |
2006年 | 10294篇 |
2005年 | 9554篇 |
2004年 | 8790篇 |
2003年 | 7944篇 |
2002年 | 8021篇 |
2001年 | 8503篇 |
2000年 | 6420篇 |
1999年 | 5065篇 |
1998年 | 4581篇 |
1997年 | 4457篇 |
1996年 | 4195篇 |
1995年 | 3925篇 |
1994年 | 3659篇 |
1993年 | 3727篇 |
1992年 | 3928篇 |
1991年 | 4187篇 |
1990年 | 4067篇 |
1989年 | 4111篇 |
1988年 | 3996篇 |
1987年 | 4055篇 |
1986年 | 3762篇 |
1985年 | 4881篇 |
1984年 | 5063篇 |
1983年 | 4274篇 |
1982年 | 4688篇 |
1981年 | 4457篇 |
1980年 | 4226篇 |
1979年 | 4533篇 |
1978年 | 4848篇 |
1977年 | 4794篇 |
1976年 | 4902篇 |
1975年 | 4640篇 |
1974年 | 4462篇 |
1973年 | 4790篇 |
1972年 | 3475篇 |
1971年 | 2985篇 |
1970年 | 2778篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
A fast-frequency modulated (FM) diode laser has been optically narrowed using the technique of resonant optical feedback, to provide linewidths in each FM mode of ≈ 200 kHz peak-to-peak. With a drive frequency of 50 MHz and modulation index of 0.2, the FM laser has been used for the first time to obtain Doppler-free FM spectra of the Rb D1 line at 795 nm. The potential use of this system for laser frequency stabilisation is discussed. 相似文献
52.
V. K. Malyutenko A. I. Liptuga V. A. Botte V. I. Chernyakhovskii 《Journal of Applied Spectroscopy》1991,55(4):1024-1028
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 55, No. 4, pp. 624–629, October, 1991. 相似文献
53.
Under idealized conditions, electroconvection in a nematic liquid crystal sets in at a well-defined threshold of the driving ac voltage. Fluctuating convection rolls of a small amplitude below that threshold have been observed recently. The measurement of the amplitude of these fluctuations is described in detail in this paper. It is based on averaging the light intensity signals using the structure function and a quantitative analysis of the light deflection. 相似文献
54.
The determination of the past and the future of a physical system are complementary aims of measurements. An optimal determination of the past of a system can be achieved by an informationally complete set of physical quantities. Such a set is always strongly noncommutative. An optimal determination of the future of a physical system can be obtained by a Boolean complete set of quantities. The two aims can be reconciled to a reasonable degree with using unsharp measurements.This work was partly supported by the Bundesministerium für Forschung und Technologie, Bonn, the Research Institute for Theoretical Physics, Helsinki, and the University of Turku Foundation, Turku. 相似文献
55.
W. Richard Strark 《Mathematical Logic Quarterly》1989,35(4):311-320
56.
The occurrence and formation of black spots areas in PolyLED devices has been studied by time-of-flight SIMS (TOFSIMS). The composition, shape and position of the black spots is visualised by three-dimensional (3D)-TOFSIMS depth-profiling. It has been established that the formation of non-emissive spots is due to the growth of aluminium oxide clusters at the AlBa/polymer interface. Electron injection in the black spots is lost by the resulting local increase of the resistivity of the cathode. 相似文献
57.
Photoisomerization of provitamin D 3 (7-dehydrocholesterol) in a nematic liquid crystal (ZLI-1695, Merck) is investigated in detail by UV absorption spectroscopy. It is found that dissolution of chiral molecules of provitamin D 3 induces the cholesteric phase in a nematic. The spectral kinetics of photoisomerization in this phase changes significantly from that in an ethanol solution. A sharp nonmonotonic dependence of the increase in accumulation of trans isomer tachysterol in a liquid crystal matrix with a decrease in the induced cholesteric pitch from 2200 to 25 μm is revealed. 相似文献
58.
V. I. Korobov 《Few-Body Systems》2002,31(2-4):133-138
In this contribution we consider a phenomenon of metastable states in antiprotonic helium atoms, precise spectroscopy of
these states and a present-day study of the electromagnetic properties of antiprotons.
Received October 16, 2001; accepted for publication November 13, 2001 相似文献
59.
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
60.
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