全文获取类型
收费全文 | 4674篇 |
免费 | 112篇 |
国内免费 | 22篇 |
专业分类
化学 | 3091篇 |
晶体学 | 20篇 |
力学 | 138篇 |
数学 | 652篇 |
物理学 | 907篇 |
出版年
2023年 | 29篇 |
2022年 | 100篇 |
2021年 | 119篇 |
2020年 | 69篇 |
2019年 | 89篇 |
2018年 | 60篇 |
2017年 | 71篇 |
2016年 | 187篇 |
2015年 | 106篇 |
2014年 | 152篇 |
2013年 | 252篇 |
2012年 | 293篇 |
2011年 | 334篇 |
2010年 | 202篇 |
2009年 | 200篇 |
2008年 | 287篇 |
2007年 | 298篇 |
2006年 | 243篇 |
2005年 | 256篇 |
2004年 | 213篇 |
2003年 | 186篇 |
2002年 | 158篇 |
2001年 | 54篇 |
2000年 | 59篇 |
1999年 | 48篇 |
1998年 | 41篇 |
1997年 | 44篇 |
1996年 | 66篇 |
1995年 | 53篇 |
1994年 | 52篇 |
1993年 | 33篇 |
1992年 | 21篇 |
1991年 | 28篇 |
1990年 | 30篇 |
1989年 | 35篇 |
1988年 | 23篇 |
1987年 | 22篇 |
1986年 | 18篇 |
1985年 | 27篇 |
1984年 | 39篇 |
1983年 | 18篇 |
1982年 | 24篇 |
1981年 | 30篇 |
1980年 | 23篇 |
1979年 | 19篇 |
1978年 | 19篇 |
1977年 | 12篇 |
1975年 | 13篇 |
1974年 | 7篇 |
1970年 | 7篇 |
排序方式: 共有4808条查询结果,搜索用时 15 毫秒
21.
Substrate relaxation is shown to play an important role in the 1 : 2 regular chemisorption of hydrogen atoms above alternate carbon atoms in a graphite monolayer. Binding energy, population analysis and electron density maps show that the direct HC bond is strengthened on relaxation. 相似文献
22.
Nelson Durán Klaus Zinner Roberto Casadei de Baptista Carmen C. C. Vidigal Giuseppe Cilento 《Photochemistry and photobiology》1976,24(4):383-388
Abstract— The thiophenyl ester of indole-3-acetic acid and indole-3-acetonitrile produce chemiluminescence in aerated dimethylsulfoxide in the presence of potassium t -butoxide. The emitter is the aromatic aldehyde. In the case of acetonitrile, the other product expected from the cleavage of an intermediate dioxetane, cyanate/isocyanate, has also been identified. Other auxins also chemiluminesce under similar conditions, but the emitters have not been properly identified.
These systems are models for the peroxidase catalyzed oxidation of indole-3-acetic acid to indole-3-carboxaldehyde and as such support the earlier inference (Vidigal et al , 1975) that the excited aldehyde is generated in the enzymic process.
An additional result is the observation of an exciplex between excited indole-3-carboxaldehyde and the thiophenylester of indole-3-acetic acid. This appears to be the first case of chemical generation of an exciplex by a route other than radical ion reaction, presumably by the dioxetane route. 相似文献
These systems are models for the peroxidase catalyzed oxidation of indole-3-acetic acid to indole-3-carboxaldehyde and as such support the earlier inference (Vidigal et al , 1975) that the excited aldehyde is generated in the enzymic process.
An additional result is the observation of an exciplex between excited indole-3-carboxaldehyde and the thiophenylester of indole-3-acetic acid. This appears to be the first case of chemical generation of an exciplex by a route other than radical ion reaction, presumably by the dioxetane route. 相似文献
23.
24.
Carlo Carlini Emo Chiellini Roberto Solaro 《Journal of polymer science. Part A, Polymer chemistry》1980,18(7):2129-2142
Homogeneous catalytic systems based on optically active low-molecular-weight and macromolecular titanium alcoholates and tri-isobutyl aluminum were used in the isomerization and hydrogenation of chiral and prochiral olefins. The reactions performed in a nitrogen and hydrogen atmosphere show a different behavior in regard to reaction rate, composition of reaction mixture, and stereochemical control. The catalyst based on macromolecular titanium alcoholate displays lower activity and a varying influence on the stereochemical pathway with respect to the catalysts based on low- molecular-weight alcoholates. The data obtained in both cases strongly support the absence of a stereocontrol by the growing chain in the stereoelective polymerization of racemic α-olefins by Ziegler-Natta catalysts based on optically active precursors. Finally evidence is provided in favor of the intermediate step responsible for asymmetric isomerization which does not occur via η-allyl complex. 相似文献
25.
Aringhieri Roberto Bigharaz Sara Duma Davide Guastalla Alberto 《Central European Journal of Operations Research》2022,30(1):189-211
Central European Journal of Operations Research - Disaster management generally includes the post-disaster stage, which consists of the actions taken in response to the disaster damages. These... 相似文献
26.
Some algebraic structures determined by the class (þ) of all effects of a Hilbert space þ and by some subclasses of (þ) are investigated, in particular de Morgan-Brouwer-Zadeh posets [it is proved that (þ
n
)(n<) has such a structure], Brouwer-Zadeh
*
posets (a quite trivial example consisting of suitable effects is given), and Brouwer-Zadeh
3
posets which are both de Morgan and
*.It is shown that a nontrivial class of effects of a Hilbert space exists which is a BZ
3
poset. An -preclusivity relation on the set of all vectors of þ is introduced, and it is shown that it satisfies the regularity condition also for [1/2, 1]. 相似文献
27.
Roberto Conti 《Letters in Mathematical Physics》1995,35(3):237-250
In a theory of local field algebras satisfying the split property, we introduce an algebra generated by the local energy-momentum operators obtained from the canonical local implementation of translations, and possibly by the local charges operators. We discuss the relations of this algebra to the given algebra of local observables and take some steps toward the characterization of theories where they coincide. In the presence of spontaneously broken symmetries, we present a no-go theorem. 相似文献
28.
Mohammad R. Ahmady Roberto R. Mendel 《Zeitschrift fur Physik C Particles and Fields》1995,65(2):263-265
The decay rates for the exclusiveB decaysBK
c
andBK*
c
are calculated in the context of the heavy quark effective theory. We obtain(BK
c
)/ (BK)=1.6±0.2 and(BK*
c
)/ (K*)=0.39±0.04. These results lead to estimates BR(BK
c
)=(0.11±0.02)% and BR(BK*
c
)=(0.05±0.01)% if we use the central current experimental values forB(K, K
*) branching ratios. 相似文献
29.
Roberto Zucchini 《Communications in Mathematical Physics》1996,181(3):529-568
A lagrangian euclidean model of Drinfeld-Sokolov (DS) reduction leading to generalW-algebras on a Riemann surface of any genus is presented. The background geometry is given by the DS principal bundleK associated to a complex Lie groupG and anSL(2,) subgroupS. The basic fields are a hermitian fiber metricH ofK and a (0, 1) Koszul gauge fieldA
* ofK valued in a certain negative graded subalgebrar ofg related tos. The action governing theH andA
* dynamics is the effective action of a DS field theory in the geometric background specified byH andA
*. Quantization ofH andA
* implements on one hand the DS reduction and on the other defines a novel model of 2d gravity, DS gravity. The gauge fixing of the DS gauge symmetry yields an integration on a moduli space of DS gauge equivalence classes ofA
* configurations, the DS moduli space. The model has a residual gauge symmetry associated to the DS gauge transformations leaving a given fieldA
* invariant. This is the DS counterpart of conformal symmetry. Conformal invariance and certain non-perturbative features of the model are discussed in detail. 相似文献
30.
Roberto Pignoni 《Geometriae Dedicata》1993,45(3):263-287
We study some global projective properties of real plane curves with cusps, beaks and normal crossings. Starting from Fabricius-Bjerre's formula on the singularities of a curve in an affine plane, we describe its extension to a projective setting. Given a curve RP2, by fixing a base point we associate some indices to its singularities and double tangents. We prove two global relations linking these entities together. 相似文献