全文获取类型
收费全文 | 681900篇 |
免费 | 6102篇 |
国内免费 | 1671篇 |
专业分类
化学 | 328604篇 |
晶体学 | 8857篇 |
力学 | 36878篇 |
综合类 | 17篇 |
数学 | 116820篇 |
物理学 | 198497篇 |
出版年
2021年 | 5505篇 |
2020年 | 6113篇 |
2019年 | 6845篇 |
2018年 | 21462篇 |
2017年 | 21445篇 |
2016年 | 19719篇 |
2015年 | 8581篇 |
2014年 | 12123篇 |
2013年 | 26628篇 |
2012年 | 26497篇 |
2011年 | 39180篇 |
2010年 | 26286篇 |
2009年 | 26233篇 |
2008年 | 33798篇 |
2007年 | 37169篇 |
2006年 | 21350篇 |
2005年 | 23159篇 |
2004年 | 20231篇 |
2003年 | 19102篇 |
2002年 | 16923篇 |
2001年 | 15631篇 |
2000年 | 12343篇 |
1999年 | 9311篇 |
1998年 | 8064篇 |
1997年 | 7875篇 |
1996年 | 7597篇 |
1995年 | 6685篇 |
1994年 | 6680篇 |
1993年 | 6468篇 |
1992年 | 6787篇 |
1991年 | 7239篇 |
1990年 | 6911篇 |
1989年 | 6818篇 |
1988年 | 6638篇 |
1987年 | 6432篇 |
1986年 | 6160篇 |
1985年 | 7848篇 |
1984年 | 8173篇 |
1983年 | 6832篇 |
1982年 | 7204篇 |
1981年 | 6691篇 |
1980年 | 6352篇 |
1979年 | 6821篇 |
1978年 | 7071篇 |
1977年 | 6831篇 |
1976年 | 6853篇 |
1975年 | 6544篇 |
1974年 | 6363篇 |
1973年 | 6706篇 |
1972年 | 4834篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
A new singular integral equation is obtained that describes the elastic equilibrium of a strip with both an inner and an edge slit (crack) and has a considerable advantage over existing equations /1–9/, etc.) from the viewpoint of a numerical realization and clarification of the analytical relationship with an analogous equation for a half-plane. Numerical results are given of a computation of the stress intensity coefficients at the tips of the inner and edge cracks that refine data in the literature. 相似文献
992.
993.
A. A. Ilyin 《Proceedings of the Steklov Institute of Mathematics》2006,255(1):136-149
A two-dimensional Navier-Stokes system with friction is considered in a large rect-angular periodic domain with area on the order of α?1, α → 0. Bounds for the dimension of the attractor are obtained, which are sharp both as α → 0 and v → 0, where v is the viscosity coefficient. 相似文献
994.
995.
Characterizations of the containment of a convex set either in an arbitrary convex set or in the complement of a finite union
of convex sets (i.e., the set, described by reverse-convex inequalities) are given. These characterizations provide ways of
verifying the containments either by comparing their corresponding dual cones or by checking the consistency of suitable associated
systems. The convex sets considered in this paper are the solution sets of an arbitrary number of convex inequalities, which
can be either weak or strict inequalities. Particular cases of dual characterizations of set containments have played key
roles in solving large scale knowledge-based data classification problems where they are used to describe the containments
as inequality constraints in optimization problems. The idea of evenly convex set (intersection of open half spaces), which
was introduced by W. Fenchel in 1952, is used to derive the dual conditions, characterizing the set containments. 相似文献
996.
A. I. Khachaturov 《Technical Physics》2006,51(2):226-230
The contribution of electrons moving at large angles to the barrier junction plane to the tunnel current is calculated. This contribution turns out to be small only if the Fermi energy of the electrons equals several electron volts. Otherwise, specifically, when the Fermi energy is no higher than 1–2 eV, this contribution dominates in high and thin potential barriers. It is found that the tunnel magnetic resistance in ferromagnet-insulator-ferromagnet contacts correlates with this contribution. It is this correlation that is responsible for a decrease in this contribution as the potential barriers get lower and thicker. 相似文献
997.
The theory of dielectric space-charge polarization losses describes well both the model of an inhomogeneous dielectric [1]
and the polarization resulting from mosaic blocks of alkali-halide crystals [2]. The Debye frequency dependences ε*(ω) and
tan δ(ω) with non-Arrhenius relaxation time are calculated in the first approximation of perturbation theory [3, 4] with the
use of a nonlinear system of the Fokker-Planck and Poisson equations for the interlayer polarization with allowance for tunnel
transitions of relaxation oscillators. For the Maxwell mechanism of space-charge relaxation, tan δ(ω) also has the Debye form
[5]. It should be noted that in studies cited above the electric field was considered uniform, and the nonlinearity of the
initial system of equations was not investigated. This paper removes these restrictions and elaborates a theory of relaxation
mechanism.
__________
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 28–34, November, 2006. 相似文献
998.
A. P. Avdeenko S. A. Konovalova O. N. Ludchenko 《Russian Journal of Organic Chemistry》2006,42(5):683-688
Reactions of halogens with N-arylsulfonyl-1,4-benzoquinone monoimines occur with the formation of a halogenonium ion that either transforms into a carbocation where the first halogen atom adds to the carbon in the ortho-position relative to the carbonyl carbon, or the halogenonium ion adds directly the second halogen atom. 相似文献
999.
In this paper we propose a general integration scheme for a Multi-Criteria Decision Making model of the Multi-Attribute Utility
Theory in Constraint Programming. We introduce the Choquet integral as a general aggregation function for multi-criteria optimization
problems and define the Choquet global constraint that propagates this function during the Branch-and-Bound search. Finally the benefits of the propagation
of the Choquet constraint are evaluated on the examination timetabling problem. 相似文献
1000.
Morphological and chemical properties of both the surface and interface of poly(vinylidene fluoride)/poly(methyl methacrylate)-co-poly(ethyl acrylate) (PVDF/PMMA-co-PEA) blend films have been investigated before and after the samples were exposed to ultraviolet (UV) irradiation using a xenon arc lamp at 50 °C and 9% relative humidity (RH) for 7 months. Surface and interfacial morphologies were studied by atomic force microscopy (AFM). Chemical composition information was obtained by confocal Raman microscopy, attenuated total reflection-FTIR spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS), and contact angle measurements. Results show an enrichment of the PVDF material at the air surface, while the acrylic copolymer enriches the interface. Blends having greater than 50% mass fraction of PVDF show little change in the surface morphology after UV exposure for 7 months. However, for a lower PVDF content, blends exhibit significant degradation of PMMA-co-PEA copolymer and a much rougher surface after UV exposure. Microstructural changes in the PVDF spherulites are also observed after UV degradation. It is found that the surface and interfacial morphologies are correlated with the chemical properties. 相似文献