全文获取类型
收费全文 | 196877篇 |
免费 | 3036篇 |
国内免费 | 934篇 |
专业分类
化学 | 109328篇 |
晶体学 | 2578篇 |
力学 | 8225篇 |
综合类 | 8篇 |
数学 | 22926篇 |
物理学 | 57782篇 |
出版年
2021年 | 1254篇 |
2020年 | 1431篇 |
2019年 | 1411篇 |
2018年 | 1416篇 |
2017年 | 1448篇 |
2016年 | 2888篇 |
2015年 | 2484篇 |
2014年 | 3103篇 |
2013年 | 9010篇 |
2012年 | 7540篇 |
2011年 | 9475篇 |
2010年 | 5762篇 |
2009年 | 5797篇 |
2008年 | 8632篇 |
2007年 | 8592篇 |
2006年 | 8388篇 |
2005年 | 7799篇 |
2004年 | 7056篇 |
2003年 | 6053篇 |
2002年 | 5913篇 |
2001年 | 6471篇 |
2000年 | 4951篇 |
1999年 | 3848篇 |
1998年 | 2994篇 |
1997年 | 3017篇 |
1996年 | 2943篇 |
1995年 | 2610篇 |
1994年 | 2527篇 |
1993年 | 2359篇 |
1992年 | 2639篇 |
1991年 | 2611篇 |
1990年 | 2292篇 |
1989年 | 2273篇 |
1988年 | 2277篇 |
1987年 | 2159篇 |
1986年 | 2103篇 |
1985年 | 3111篇 |
1984年 | 3108篇 |
1983年 | 2501篇 |
1982年 | 2706篇 |
1981年 | 2571篇 |
1980年 | 2549篇 |
1979年 | 2429篇 |
1978年 | 2528篇 |
1977年 | 2461篇 |
1976年 | 2344篇 |
1975年 | 2303篇 |
1974年 | 2216篇 |
1973年 | 2267篇 |
1972年 | 1314篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
L. Pillier C. Moreau X. Mercier J.F. Pauwels P. Desgroux 《Applied physics. B, Lasers and optics》2002,74(4-5):427-434
Cavity ring-down spectroscopy (CRDS) is used to measure the NO mole fraction formed in the burnt gases of low-pressure premixed
flames. It is shown that the line-of-sight absorption is greatly increased by the contribution of the NO molecules surrounding
the burner. This contribution has been quantified by developing a mathematical procedure taking into account the spatial and
spectral features of the CRDS measurement. Calculations have been undertaken in the general case of a stable species not consumed
in the flame. The most sensitive parameter is the temperature both in the flame and outside the flame. Simulations allow the
selection of the best spectroscopic transitions for a given flame (i.e. a given temperature profile), ensuring the weakest
influence of the inaccuracy affecting the temperature determination. High quantum states belonging to the A–X (0–1) band of
NO have been found to be the most valuable and have led to a NO mole fraction determination with an accuracy of ±13%. NO absorption
in the flame was completely masked using the A–X (0–0) band. Finally, the prompt-NO mole fraction formed in a methane/air
flame stabilized at 33 Torr is obtained by combining CRDS and laser induced fluorescence techniques.
Received: 12 October / Revised version: 1 February 2002 / Published online: 14 March 2002 相似文献
993.
994.
The algebra dual to Woronowicz's deformation of the two-dimensional Euclidean group is constructed. The same algebra is obtained from SU
q
(2) via contraction on both the group and algebra levels. 相似文献
995.
Paul C. Bressloff 《Physica D: Nonlinear Phenomena》1997,110(3-4):195-208
We prove the existence of spatially localized ground states of the diffusive Haken model. This model describes a self-organizing network whose elements are arranged on a d-dimensional lattice with short-range diffusive coupling. The network evolves according to a competitive gradient dynamics in which the effects of diffusion are counteracted by a localizing potential that incorporates an additional global coupling term. In the absence of diffusive coupling, the ground states of the system are strictly localized, i.e. only one lattice site is excited. For sufficiently small non-zero diffusive coupling , it is shown analytically that localized ground states persist in the network with the excitations exponentially decaying in space. Numerical results establish that localization occurs for arbitrary values of in one dimension but vanishes beyond a critical coupling c(d), when d> 1. The one-dimensional localized states are interpreted in terms of instanton solutions of a continuum version of the model. 相似文献
996.
997.
Phil Diamond Peter Kloeden Victor Kozyakin Alexei Pokrovskii 《Mathematische Nachrichten》1998,191(1):59-81
The finiteness of computer arithmetic can lead to some dramatic differences between the behaviour of a continuous dynamical system and a computer simulation. A thorough rigorous theoretical analysis of what may or what does happen is usually extremely difficult and to date little has been done even in relatively simple contexts. The comparative behaviour of a rotation mapping in the plane and on a uniform lattice in the plane is one such example. Simulations show that the rounding operator applied to a planar rotation mapping more or less preserves the qualitative behaviour of the original mapping, whereas the application of the truncation operator to a planar rotation can lead to quite different dynamical features. In this paper a theoretical justification of the properties of the planar rotation mappings under truncation to a, uniform integer lattice is provided, in particular properties of boundedness and dissipativity are investigated. 相似文献
998.
A. A. Collyer D. W. Clegg M. Morris D. G. Parker G. W. Wheatley G. C. Corfield 《Journal of polymer science. Part A, Polymer chemistry》1991,29(2):193-200
High molecular weight alternating block copolymers of polyethesulphone (PES) and polydimethylsiloxane (PDMS) were prepared by the condensation of dimethylamino-terminated PDMS oligomers and hydroxy-terminated PES oligomers in 1,2-dichlorobenzene. Microphase separation of the block copolymers at exceptionally short block lengths was observed by differential scanning calorimetry (DSC) and transmission electron microscopy (TEM). The Si? O? C intersegment linkage in these materials appeared to display poor hydrolytic stability which is contrary to results obtained for other block copolymers. 相似文献
999.
A mean-field model of nonlinearly coupled oscillators with randomly distributed frequencies and subject to independent external white noises is analyzed in the thermodynamic limit. When the frequency distribution isbimodal, new results include subcritical spontaneous stationary synchronization of the oscillators, supercritical time-periodic synchronization, bistability, and hysteretic phenomena. Bifurcating synchronized states are asymptotically constructed near bifurcation values of the coupling strength, and theirnonlinear stability properties ascertained. 相似文献
1000.
In this paper we define the vertex-cover polynomial Ψ(G,τ) for a graph G. The coefficient of τr in this polynomial is the number of vertex covers V′ of G with |V′|=r. We develop a method to calculate Ψ(G,τ). Motivated by a problem in biological systematics, we also consider the mappings f from {1, 2,…,m} into the vertex set V(G) of a graph G, subject to f−1(x)f−1(y)≠ for every edge xy in G. Let F(G,m) be the number of such mappings f. We show that F(G,m) can be determined from Ψ(G,τ). 相似文献