全文获取类型
收费全文 | 603827篇 |
免费 | 5095篇 |
国内免费 | 1862篇 |
专业分类
化学 | 294965篇 |
晶体学 | 9052篇 |
力学 | 31536篇 |
综合类 | 16篇 |
数学 | 94305篇 |
物理学 | 180910篇 |
出版年
2021年 | 4284篇 |
2020年 | 4724篇 |
2019年 | 5313篇 |
2018年 | 16934篇 |
2017年 | 16892篇 |
2016年 | 16060篇 |
2015年 | 6837篇 |
2014年 | 10257篇 |
2013年 | 24079篇 |
2012年 | 21505篇 |
2011年 | 31423篇 |
2010年 | 21132篇 |
2009年 | 21421篇 |
2008年 | 26016篇 |
2007年 | 27970篇 |
2006年 | 18772篇 |
2005年 | 17546篇 |
2004年 | 16550篇 |
2003年 | 15379篇 |
2002年 | 14412篇 |
2001年 | 15683篇 |
2000年 | 12005篇 |
1999年 | 9292篇 |
1998年 | 7979篇 |
1997年 | 7835篇 |
1996年 | 7414篇 |
1995年 | 6591篇 |
1994年 | 6643篇 |
1993年 | 6312篇 |
1992年 | 6990篇 |
1991年 | 7169篇 |
1990年 | 6929篇 |
1989年 | 6722篇 |
1988年 | 6599篇 |
1987年 | 6668篇 |
1986年 | 6330篇 |
1985年 | 8123篇 |
1984年 | 8411篇 |
1983年 | 7028篇 |
1982年 | 7203篇 |
1981年 | 6886篇 |
1980年 | 6844篇 |
1979年 | 7063篇 |
1978年 | 7392篇 |
1977年 | 7251篇 |
1976年 | 7280篇 |
1975年 | 6741篇 |
1974年 | 6799篇 |
1973年 | 7007篇 |
1972年 | 4973篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
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
72.
73.
This paper examines the non-linear dynamic behaviour of a flexible shaft. The shaft is mounted on two journal bearings and the axial load is supported by a defective hydrodynamic thrust bearing at one end. The defect is a levelness defect of the rotor. The thrust bearing behaviour must be considered to be non-linear because of the effects of the defect. The shaft is modelled with typical beam finite elements including effects such as the gyroscopic effects. A modal technique is used to reduce the number of degrees of freedom. Results show that the thrust bearing defects introduce supplementary critical speeds. The linear approach is unable to show the supplementary critical speeds which are obtained only by using non-linear analysis. 相似文献
74.
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
75.
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
76.
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
77.
It is proved that the variety of relevant disjunction lattices has the finite embeddability property. It follows that Avron's relevance logic RMI min has a strong form of the finite model property, so it has a solvable deducibility problem. This strengthens Avron's result that RMI min is decidable. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
78.
The drawbacks of our earlier report of preparing fuel cell catalyst arrays by borohydride reduction of inkjet prepared arrays of metal salts are discussed along with the need for inclusion of state-of-the-art metrics in all array screening. An alternative method for screening of hydrogen/air cathode catalysts, direct methanol fuel cell (DMFC) anode catalysts, and catalyst loading studies is provided. State-of-the-art Johnson Matthey catalysts were used in control experiments to demonstrate the utility of the array fuel cell for high throughput screening of fuel cell catalysts in the 3-4 mg/cm2 range. This report lays out hard learned rules for high throughput screening and demonstrates that the array fuel cell can be used for very precise screening of libraries of membrane electrode assembly (MEA) components without the pitfalls discussed in the introduction. 相似文献
79.
We consider front solutions of the Swift–Hohenberg equation ∂
t
u= -(1+ ∂
x
2)2
u + ɛ2
u -u
3. These are traveling waves which leave in their wake a periodic pattern in the laboratory frame. Using renormalization techniques
and a decomposition into Bloch waves, we show the non-linear stability of these solutions. It turns out that this problem
is closely related to the question of stability of the trivial solution for the model problem ∂
t
u(x,t) = ∂
x
2
u (x,t)+(1+tanh(x-ct))u(x,t)+u(x,t)
p
with p>3. In particular, we show that the instability of the perturbation ahead of the front is entirely compensated by a diffusive
stabilization which sets in once the perturbation has hit the bulk behind the front.
Received: 23 February 2001 / Accepted: 27 August 2001 相似文献
80.
K. E. Mochalov O. A. Ustinova S. A. Strel’tsov S. L. Grokhovskii A. L. Zhuze I. R. Nabiev A. V. Sukhanova V. A. Oleinikov 《Optics and Spectroscopy》2002,93(4):493-500
Topotecan (TPT), a water-soluble derivative of camptothecin (inhibitor of human DNA topoiomerase I), has found wide application in cancer chemotherapy. The central problem in using topotecan is the presence of lactone rings in its molecules, which undergo hydrolysis at a physiological pH yielding an inactive and even toxic form of the drug. The analysis of Raman spectra of TPT in H2O and D2O solutions made it possible to assign the spectral bands to the vibrations of particular molecular groups. Spectral features indicative of the opening of the lactone rings of the TPT molecules, deprotonation of the hydroxyl groups in their quinoline fragments, and of possible participation of the hydroxyl and carbonyl groups in H bonding are found. The data obtained are necessary to study the molecular mechanisms of TPT-DNA interaction and the formation of ternary complexes between TPT, DNA, and DNA topoisomerase I. 相似文献