全文获取类型
收费全文 | 976篇 |
免费 | 29篇 |
国内免费 | 5篇 |
专业分类
化学 | 747篇 |
晶体学 | 10篇 |
力学 | 11篇 |
数学 | 59篇 |
物理学 | 183篇 |
出版年
2023年 | 6篇 |
2022年 | 8篇 |
2021年 | 7篇 |
2020年 | 13篇 |
2019年 | 12篇 |
2018年 | 15篇 |
2017年 | 12篇 |
2016年 | 16篇 |
2015年 | 15篇 |
2014年 | 22篇 |
2013年 | 46篇 |
2012年 | 53篇 |
2011年 | 47篇 |
2010年 | 30篇 |
2009年 | 33篇 |
2008年 | 52篇 |
2007年 | 38篇 |
2006年 | 55篇 |
2005年 | 73篇 |
2004年 | 55篇 |
2003年 | 46篇 |
2002年 | 53篇 |
2001年 | 18篇 |
2000年 | 19篇 |
1999年 | 14篇 |
1998年 | 11篇 |
1997年 | 12篇 |
1996年 | 15篇 |
1995年 | 9篇 |
1994年 | 11篇 |
1993年 | 7篇 |
1992年 | 14篇 |
1991年 | 8篇 |
1990年 | 9篇 |
1989年 | 12篇 |
1988年 | 5篇 |
1987年 | 10篇 |
1986年 | 12篇 |
1985年 | 16篇 |
1984年 | 13篇 |
1983年 | 10篇 |
1982年 | 14篇 |
1981年 | 10篇 |
1979年 | 6篇 |
1978年 | 12篇 |
1976年 | 5篇 |
1974年 | 4篇 |
1973年 | 5篇 |
1968年 | 4篇 |
1967年 | 5篇 |
排序方式: 共有1010条查询结果,搜索用时 15 毫秒
101.
Hayashi M Sasano Y Nagasawa S Shibuya M Iwabuchi Y 《Chemical & pharmaceutical bulletin》2011,59(12):1570-1573
A highly active organocatalyst for alcohol oxidation has been developed. 9-Azanoradamantane N-oxyl (Nor-AZADO 4), constituting an unhindered, stable nitroxyl radical, exhibits superior catalytic activity to 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) and AZADOs in the oxidation of alcohols to their corresponding carbonyl compounds. 相似文献
102.
The collision complex formed from a vibrationally excited reactant undergoes redissociation to the reactant, intramolecular vibrational relaxation (randomization of vibrational energy), or chemical reaction to the products. If attractive interaction between the reactants is large, efficient vibrational relaxation in the complex prevents redissociation to the reactants with the initial vibrational energy, and the complex decomposes to the reactants with low vibrational energy or converts to the products. In this paper, we have studied the branching ratios between the intramolecular vibrational relaxation and chemical reaction of an adduct HO(v)-CO formed from OH(X(2)Π(i)) in different vibrational levels v = 0-4 and CO. OH(v = 0-4) generated in a gaseous mixture of O(3)/H(2)/CO/He irradiated at 266 nm was detected with laser-induced fluorescence (LIF) via the A(2)Σ(+)-X(2)Π(i) transition, and H atoms were probed by the two-photon excited LIF technique. From the kinetic analysis of the time-resolved LIF intensities of OH(v) and H, we have found that the intramolecular vibrational relaxation is mainly governed by a single quantum change, HO(v)-CO → HO(v-1)-CO, followed by redissociation to OH(v-1) and CO. With the vibrational quantum number v, chemical process from the adduct to H + CO(2) is accelerated, and vibrational relaxation is decelerated. The countertrend is elucidated by the competition between chemical reaction and vibrational relaxation in the adduct HOCO. 相似文献
103.
Okada T Yamanaka K Hirose Y Goto Y Tani T Inagaki S 《Physical chemistry chemical physics : PCCP》2011,13(17):7961-7967
The excited state characteristics of phenylene (Ph)-bridged periodic mesoporous organosilica (PMO) powders with crystal-like and amorphous wall structures are investigated. Crystal-like Ph-PMO has a molecular ordering of the bridging organic moieties with intervals of 0.76 and 0.44 nm parallel and perpendicular to the mesochannel direction, respectively, whereas amorphous Ph-PMO has no molecular-level periodicity in the wall. Fluorescence from the exciton and excimer of the Ph moieties and the defect center in the silicate network were detected at room temperature, but fluorescence from the excimer and the defect center were not detected at 77 K for crystal-like Ph-PMO dispersed in a methanol/ethanol mixed solvent. The decay curve of the exciton fluorescence of crystal-like Ph-PMO at room temperature was analyzed successfully using a one-dimensional diffusion model quenched by the defect center and the excimer site. The results were discussed in comparison with those for the crystal-like biphenylene-bridged PMO reported in the preceding paper (Yamanaka et al., Phys. Chem. Chem. Phys., 2010, 12, 11688-11696). The existence of excited states with various conformations including ground state dimers or aggregates of the Ph moieties was suggested for amorphous Ph-PMO. It was clearly apparent that the differences in the excited state dynamics reflected the differences in the molecular-level structure in the wall. 相似文献
104.
The optically active (R)- and (S)-flavanones were prepared by an enzymatically enantioselective hydrolysis of (±)-flavanone oxime O-acylates employing lipases, followed by hydrolysis with acid. 相似文献
105.
Shuzo Izumi 《Journal d'Analyse Mathématique》2002,86(1):235-246
The vanishing order of the value of a smooth function at a point along a subset is related to the order of its Taylor expansion
there. To compare these vanishing orders the Spallek function is introduced. A number of properties of this function are developed. 相似文献
106.
Two possible enolate anions of trimethylsilylmethyl ketones have been prepared regioselectively by the appropriate choice of base. The one directed to the silylmethyl site behaves as a highly reactive and (E)-selective condensation reagent to aldehydes. 相似文献
107.
Satoru Nakashima Yuichi Masuda Izumi Motoyama Hirotoshi Sano 《Hyperfine Interactions》1988,40(1-4):319-322
It was found that the packing of cations and anions influences the electronic structures of mixed-valence binuclear ferrocene derivatives. Temperature-dependence of the mixed-valence state of 11, 1111-diisobutylbiferrocenium triiodide was observed in a crystalline state, whereas only a trapped-valence state was found in a dispersed state. The packing effect was also observed for a series of 11, 1111-dialkyl- and 11, 1111-bis(methylbenzyl)biferrocenium triiodides by means of ESR spectroscopy. 相似文献
108.
Izumi Ojima 《Nuclear Physics B》1978,143(2):340-352
A concise criterion for observables in Yang-Mills theory is presented in the framework of covariant canonical field theory. As an example, the symmetric energy-momentum tensor θøν is proved to be an observable and its physically meaningful form is clarified. The validity of the “Maxwell-type” equation of motion is established in the physical subspace phys defined by the subsidiary condition (QB: BRS charge). Its meaning and consequences are discussed in connection with the notion of observables: especially, all (quasi-) local observables in QCD are shown to be colour singlets and this fact paves the way to quark confinement. 相似文献
109.
α,β-Unsaturated carbonyl compounds and butenolides are readily prepared by the rhodium(I) catalyzed isomerization of 1,3-diene monoepoxides and α-alkylidene-γ-butyrolactones, respectively. The former transformation is formally regarded as the equivalent of a regiospecific aldol condensation of an unsymmetrical ketone. 相似文献
110.
The transfer hydrogenation of β-trimethylsilyl alcohols catalyzed by HRh(PPh3)4 has been successfully applied to the efficient synthesis of α-trimethylsilyl ketones. 相似文献