全文获取类型
收费全文 | 102061篇 |
免费 | 7876篇 |
国内免费 | 12855篇 |
专业分类
化学 | 78731篇 |
晶体学 | 1454篇 |
力学 | 2493篇 |
综合类 | 893篇 |
数学 | 12745篇 |
物理学 | 26476篇 |
出版年
2024年 | 88篇 |
2023年 | 740篇 |
2022年 | 1406篇 |
2021年 | 2133篇 |
2020年 | 2659篇 |
2019年 | 2480篇 |
2018年 | 2210篇 |
2017年 | 3048篇 |
2016年 | 3418篇 |
2015年 | 2997篇 |
2014年 | 4025篇 |
2013年 | 7812篇 |
2012年 | 6976篇 |
2011年 | 5890篇 |
2010年 | 4948篇 |
2009年 | 6646篇 |
2008年 | 6797篇 |
2007年 | 7190篇 |
2006年 | 6565篇 |
2005年 | 5472篇 |
2004年 | 5077篇 |
2003年 | 4224篇 |
2002年 | 5321篇 |
2001年 | 3205篇 |
2000年 | 2951篇 |
1999年 | 2785篇 |
1998年 | 2398篇 |
1997年 | 1952篇 |
1996年 | 1636篇 |
1995年 | 1525篇 |
1994年 | 1355篇 |
1993年 | 1126篇 |
1992年 | 1030篇 |
1991年 | 684篇 |
1990年 | 584篇 |
1989年 | 535篇 |
1988年 | 407篇 |
1987年 | 322篇 |
1986年 | 305篇 |
1985年 | 236篇 |
1984年 | 258篇 |
1983年 | 132篇 |
1982年 | 211篇 |
1981年 | 176篇 |
1980年 | 194篇 |
1979年 | 167篇 |
1978年 | 151篇 |
1977年 | 89篇 |
1976年 | 73篇 |
1973年 | 47篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Unconventional antiferromagnetic correlations of the doped Haldane gapsystem Y 2 BaNi 1 - x Zn x O 5
V. Villar R. Mélin C. Paulsen J. Souletie E. Janod C. Payen 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,25(1):39-51
We make a new proposal to describe the very low temperature susceptibility of the doped Haldane gap compound Y2BaNi1-xZnxO5. We propose a new mean field model relevant for this compound. The ground state of this mean field model is unconventional
because antiferromagnetism coexists with random dimers. We present new susceptibility experiments at very low temperature.
We obtain a Curie-Weiss susceptibility χ(
T
) ∼
C
/(Θ +
T
) as expected for antiferromagnetic correlations but we do not obtain a direct signature of antiferromagnetic long range order.
We explain how to obtain the “impurity” susceptibility
(
T
) by subtracting the Haldane gap contribution to the total susceptibility. In the temperature range [1 K, 300 K] the experimental
data are well fitted by T
(
T
) =
C
imp
1 +
T
imp
/
T
. In the temperature range [100 mK, 1 K] the experimental data are well fitted by T
(
T
) =
A
ln(
T
/
T
c
), where T
c
increases with x. This fit suggests the existence of a finite Néel temperature which is however too small to be probed directly in our experiments.
We also obtain a maximum in the temperature dependence of the ac-susceptibility
(
T
) which suggests the existence of antiferromagnetic correlations at very low temperature.
Received 17 July 2001 相似文献
992.
T. González-Lezana G. Delgado-Barrio P. Villarreal F.X. Gadéa 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,20(2):227-232
The stabilization method is applied to the case of interacting resonances in the photo-dissociation of van der Waals clusters
composed by a rare gas atom bound to a dihalogen molecule. The study of an illustrative two-dimensional model consisting in
a T-shaped NeI2 molecule shows the adequacy of the method whenever the projection of the stabilization wave functions on the assumed prepared
initial state is accounted for. The agreement of the fragmentation cross-sections with some previous results using the effective
resolvent method and accurate close-coupling calculations is excellent. The method reveals its utility as a complementary
tool since allows, through the analysis of the stabilization wave function in terms of zero-order levels, a precise characterization
of the resonant states involved.
Received 5 April 2002 / Received in final form 24 May 2002 Published online 19 July 2002 相似文献
993.
L. Stoyanov 《Mathematische Annalen》2002,324(4):743-771
In this paper we consider properties of obstacles satisfying some non-degeneracy conditions that can be recovered from the
scattering length spectrum (SLS). Clearly the latter tells us whether the obstacle K is trapping or non-trapping. If the set of trapped points is relatively small, then the SLS also determines the volume of
the obstacle, the number of its connected components, and whether its boundary is convex everywhere or it has non-trivial
concavities. Under the additional assumption that the curvature of the obstacle does not vanish of infinite order, it is proved
that from the SLS one can recover certain information about the number of reflection points of any simply reflecting ray in
the exterior of the obstacle. Finally, for some special classes of obstacles (e.g. star-shaped ones), it is shown that the
SLS completely determines the obstacle.
Received: 2 March 1999 / Revised version: 16 January 2001 / Published online: 5 September 2002 相似文献
994.
Let be a bounded, connected linearly convex set in with boundary. We show that the maximal ideal (both in ) and ) consisting of all functions vanishing at is generated by the coordinate functions .
Received: 2 July 2001; in final form: 26 September 2001 / Published online: 28 February 2002 相似文献
995.
Let (X,0) be the germ of a normal space of dimension n+1 and let f be the germ at 0 of a holomorphic function on X. Assume both X and f have an isolated singularity at 0. Denote by J the image of the restriction map , where F is the Milnor fibre of f at 0. We prove that the canonical Hermitian form on , given by poles of order at in the meromorphic extension of , passes to the quotient by J and is non-degenerate on . We show that any non-zero element in J produces a “mass concentration” at the singularity which is related to a simple pole concentrated at for (in a non-na?ve sense). We conclude with an application to the asymptotic expansion of oscillatory integrals , for , when .
Received: 28 May 2001 / Published online: 26 April 2002 相似文献
996.
由三羟甲基丙烷三丙烯酸酯(TMPTA)和乙二胺(EDA)直接进行M ichael加成反应,合成端基为3个NH2的树枝状大分子G(NH2)3,用硬脂酰氯将其端氨基进行酰胺化得到端基为3个硬脂酰基的树枝状大分子GS(R)3,产率为82.4%。GS(R)3进一步与碘甲烷反应,其分子中的3个仲氨基被季铵化,生成树枝状季铵盐GI(R)3,产率为82.0%。讨论了反应温度、反应时间和原料配比对GS(R)3和GI(R)3产率的影响,并用红外、核磁和元素分析对GS(R)3和GI(R)3的结构进行表征。 相似文献
997.
《Surface and interface analysis : SIA》2006,38(9):1257-1265
Four vanadium oxide layers on mineral TiO2(001)‐anatase supports with different thickness (3–33 Å) were prepared with reactive d.c. magnetron sputtering and were extensively studied with photoelectron spectroscopy. Al Kα radiation and 150 eV synchrotron radiation were used as excitation sources. The evolution of the 2p, 3s and 3p core level line shapes of V and Ti as a function of the vanadium oxide thickness was studied, as well as the O1s and O2s core lines and the valence band. All the V2p spectra of the deposited vanadium oxide layers consist of at least 60% V5+, the rest being V4+. The V3p region is complicated by multiplet splitting, which prevents the determination of the vanadium oxidation state. The V3p multiplet splitting is different for the two excitation energies. No reduction of the titania support surface due to the vanadium oxide deposition was observed. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
998.
L. Sauguet B. Ameduri B. Boutevin 《Journal of polymer science. Part A, Polymer chemistry》2006,44(15):4566-4578
The radical terpolymerization of 8‐bromo‐1H,1H,2H‐perfluorooct‐1‐ene with vinylidene fluoride (VDF) and perfluoro(4‐methyl‐3,6‐dioxaoct‐7‐ene) sulfonyl fluoride is presented. Changing the feed compositions of these three fluorinated comonomers enabled us to obtain different random‐type poly[vinylidene fluoride‐ter‐perfluoro(4‐methyl‐3,6‐dioxaoct‐7‐ene) sulfonyl fluoride‐ter‐8‐bromo‐1H,1H,2H‐perfluorooct‐1‐ene] terpolymers containing various sulfonyl fluoride and brominated side groups. Yields higher than 70% were reached in all cases. The hydrolysis of the sulfonyl fluoride group into the ? SO3Li function in the presence of lithium carbonate was quantitatively achieved without the content of VDF being affected, and so dehydrofluorination of the VDF base unit was avoided. These original terpolymers were then crosslinked via dangling bromine atoms in the presence of a peroxide/triallyl isocyanurate system, which produced films insoluble in organic solvents such as acetone and dimethylformamide (which totally dissolved uncured terpolymers). The acidification of ? SO3Li into the ? SO3H function enabled protonic membranes to be obtained. The thermal stabilities of the crosslinked materials were higher than those of the uncured terpolymers, and their electrochemical performances were investigated. According to the contents of the sulfonic acid side functions, the ion‐exchange capacities ranged from 0.6 to 1.5 mequiv of H+/g, whereas the water uptake and conductivities ranged from 5–26% (±11%) and from 0.5 to 6.0 mS/cm, respectively. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4566–4578, 2006 相似文献
999.
We present a new linearized model for the zero-one quadratic programming problem, whose size is linear in terms of the number of variables in the original nonlinear problem. Our derivation yields three alternative reformulations, each varying in model size and tightness. We show that our models are at least as tight as the one recently proposed in [7], and examine the theoretical relationship of our models to a standard linearization of the zero-one quadratic programming problem. Finally, we demonstrate the efficacy of solving each of these models on a set of randomly generated test instances. 相似文献
1000.