全文获取类型
收费全文 | 916篇 |
免费 | 48篇 |
国内免费 | 9篇 |
专业分类
化学 | 589篇 |
晶体学 | 3篇 |
力学 | 15篇 |
数学 | 176篇 |
物理学 | 190篇 |
出版年
2023年 | 11篇 |
2022年 | 8篇 |
2021年 | 39篇 |
2020年 | 24篇 |
2019年 | 42篇 |
2018年 | 40篇 |
2017年 | 20篇 |
2016年 | 43篇 |
2015年 | 30篇 |
2014年 | 32篇 |
2013年 | 51篇 |
2012年 | 63篇 |
2011年 | 72篇 |
2010年 | 44篇 |
2009年 | 31篇 |
2008年 | 61篇 |
2007年 | 71篇 |
2006年 | 61篇 |
2005年 | 53篇 |
2004年 | 43篇 |
2003年 | 33篇 |
2002年 | 21篇 |
2001年 | 12篇 |
2000年 | 5篇 |
1999年 | 11篇 |
1998年 | 5篇 |
1997年 | 4篇 |
1996年 | 4篇 |
1995年 | 8篇 |
1994年 | 5篇 |
1993年 | 3篇 |
1992年 | 3篇 |
1991年 | 1篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 3篇 |
1984年 | 1篇 |
1981年 | 1篇 |
1979年 | 3篇 |
1978年 | 1篇 |
1975年 | 1篇 |
1973年 | 1篇 |
1965年 | 2篇 |
排序方式: 共有973条查询结果,搜索用时 31 毫秒
931.
We prove large deviation results for sums of heavy-tailed random elements in rather general convex cones being semigroups equipped with a rescaling operation by positive real numbers. In difference to previous results for the cone of convex sets, our technique does not use the embedding of cones in linear spaces. Examples include the cone of convex sets with the Minkowski addition, positive half-line with maximum operation and the family of square integrable functions with arithmetic addition and argument rescaling. 相似文献
932.
The separation factor is calculated for a binary gaseous mixture in two-layer membranes composed of nano- and microporous layers. The transfer in nanosized pores is described with regard to the diffusion in an adsorption layer. The mutual influence of components when they pass through the fine-pore layer is taken into account. The dependence of the diffusion coefficients in the adsorption layer on the degree of surface coverage is taken into account. It is shown that the mutual influence of the components on the transfer in the adsorption layer substantially affects the separation factor and its dependence on process parameters. The problem concerning the asymmetry of the separation factor at different membrane orientations with respect to the flow is discussed. 相似文献
933.
Mechanism of the Asymmetric Hydrogenation of Exocyclic α,β‐Unsaturated Carbonyl Compounds with an Iridium/BiphPhox Catalyst: NMR and DFT Studies 下载免费PDF全文
Yuanyuan Liu Prof. Ilya D. Gridnev Prof. Wanbin Zhang 《Angewandte Chemie (International ed. in English)》2014,53(7):1901-1905
The mechanism of the asymmetric hydrogenation of exocyclic α,β‐unsaturated carbonyl compounds with the (aS)‐Ir/iPr‐BiphPhox catalyst was studied by NMR experiments and DFT computational analyses. Computed optical yields of the asymmetric hydrogenation proceeding by an iridium(I)/iridium(III) mechanism involving a transition state stabilized through two intramolecular hydrogen bonds are in good accordance with the experimental ee values. 相似文献
934.
Alkali‐Metal Trichloroacetates for Dichloromethylenation of Fullerenes: Nucleophilic Addition‐Substitution Route 下载免费PDF全文
Marina G. Apenova Vladimir A. Akhmetov Nikita M. Belov Dr. Alexey A. Goryunkov Dr. Ilya N. Ioffe Dr. Natalia S. Lukonina Dr. Vitaliy Yu. Markov Prof. Dr. Lev N. Sidorov 《化学:亚洲杂志》2014,9(3):915-923
The first experimental evidence that fullerenes react with alkali‐metal trichloroacetates through a nucleophilic addition‐substitution route, yielding dichloromethylenefullerenes as the final products, is reported. The intermediates, C60(CCl3)? and C70(CCl3)? anions, have been isolated in their protonated forms as ortho‐C60(CCl3)H, as well as three ortho and one para isomer of C70(CCl3)H. The structures were unambiguously determined by means of 1H, 13C, and 1H–13C HMBC NMR spectroscopy along with UV/Vis spectroscopy. The observed regiochemistry was analyzed with the aid of quantum chemical calculations. Conversion of the protonated compounds into the [6,6]‐closed C60/70(CCl2) cycloadducts under basic conditions can be effected only for the ortho isomers, whereas para‐C70(CCl3)H decomposes back into pristine C70. 相似文献
935.
Li C Pobelov I Wandlowski T Bagrets A Arnold A Evers F 《Journal of the American Chemical Society》2008,130(1):318-326
Recent STM molecular break-junction experiments have revealed multiple series of peaks in the conductance histograms of alkanedithiols. To resolve a current controversy, we present here an in-depth study of charge transport properties of Au|alkanedithiol|Au junctions. Conductance histograms extracted from our STM measurements unambiguously confirm features showing more than one set of junction configurations. On the basis of quantum chemistry calculations, we propose that certain combinations of different sulfur-gold couplings and trans/gauche conformations act as the driving agents. The present study may have implications for experimental methodology: whenever conductances of different junction conformations are not statistically independent, the conductance histogram technique can exhibit a single series only, even though a much larger abundance of microscopic realizations exists. 相似文献
936.
Yudanov IV Matveev AV Neyman KM Rösch N 《Journal of the American Chemical Society》2008,130(29):9342-9352
Experimental findings imply that edge sites (and other defects) on Pd nanocrystallites exposing mainly (111) facets in supported model catalysts are crucial for catalyst modification via deposition of CH(x) (x = 0-3) byproducts of methanol decomposition. To explore this problem computationally, we applied our recently developed approach to model realistically metal catalyst particles as moderately large three-dimensional crystallites. We present here the first results of this advanced approach where we comprehensively quantify the reactivity of a metal catalyst in an important chemical process. In particular, to unravel the mechanism of how CH(x) species are formed, we carried out density functional calculations of C-O bond scission in methanol and various dehydrogenated intermediates (CH3O, CH2OH, CH2O, CHO, CO), deposited on the cuboctahedron model particle Pd79. We calculated the lowest activation barriers, approximately 130 kJ mol(-1), of C-O bond breaking and the most favorable thermodynamics for the adsorbed species CH3O and CH2OH which feature a C-O single bond. In contrast, dissociation of adsorbed CO was characterized as negligibly slow. From the computational result that the decomposition products CH3 and CH2 preferentially adsorb at edge sites of nanoparticles, we rationalize experimental data on catalyst poisoning. 相似文献
937.
Elles CG Shkrob IA Crowell RA Arms DA Landahl EC 《The Journal of chemical physics》2008,128(6):061102
Time-resolved x-ray absorption spectroscopy has been used to observe the transient species generated by one-photon detachment of an electron from aqueous bromide. The K-edge spectrum of the short-lived Br(0) atom exhibits a resonant 1s-4p transition that is absent for the Br(-) precursor. The strong 1s-4p resonance suggests that there is very little charge transfer from the solvent to the open-shell atom, whereas weak oscillations above the absorption edge indicate that the solvent shell around a neutral Br(0) atom is defined primarily by hydrophobic interactions. These conclusions are in agreement with Monte Carlo and quantum chemical simulations of the solvent structure. 相似文献
938.
Voskressensky LG Vorobiev IV Borisova TN Varlamov AV 《The Journal of organic chemistry》2008,73(12):4596-4601
Reaction of 10-cyanotetrahydrobenzo[b][1,6]naphthyridines (1-6) with activated alkynes affords stable benzo[b]pyrrolo[2,1-f][1,6]naphthyridine-4-ium ylides (7-14) in moderate yields. A proposed mechanism for their formation consists of a new tandem multistage process. 相似文献
939.
Dr. Ilya E. Kuznetsov Alexey A. Piryazev Azaliia F. Akhkiamova Maxim E. Sideltsev Dr. Denis V. Anokhin Alina V. Lolaeva Dr. Mikhail V. Gapanovich Davlad S. Zamoretskov Dr. Diana K. Sagdullina Prof. Dr. Mikhail V. Klyuev Dr. Dimitri A. Ivanov Dr. Alexander V. Akkuratov 《Chemphyschem》2023,24(21):e202300310
Conjugated small molecules are advanced semiconductor materials with attractive physicochemical and optoelectronic properties enabling the development of next-generation electronic devices. The charge carrier mobility of small molecules strongly influences the efficiency of organic and hybrid electronics based on them. Herein, we report the synthesis of four novel small molecules and their investigation with regard to the impact of molecular structure and thermal treatment of films on charge carriers’ mobility. The benzodithiophene-containing compounds (BDT) were shown to be more promising in terms of tuning the morphology upon thermal treatment. Impressive enhancement of hole mobilities by more than 50 times was found for annealed films based on a compound M4 comprising triisopropylsilyl-functionalized BDT core. The results provide a favorable experience and strategy for the rational design of state-of-the-art organic semiconductor materials (OSMs) and for improving their charge-transport characteristics. 相似文献
940.
Ilya Kuselman 《Journal of Analytical Chemistry》2008,63(4):405-406