全文获取类型
收费全文 | 2395篇 |
免费 | 51篇 |
国内免费 | 10篇 |
专业分类
化学 | 1361篇 |
晶体学 | 15篇 |
力学 | 44篇 |
数学 | 233篇 |
物理学 | 803篇 |
出版年
2022年 | 23篇 |
2021年 | 32篇 |
2020年 | 36篇 |
2019年 | 23篇 |
2018年 | 17篇 |
2017年 | 29篇 |
2016年 | 52篇 |
2015年 | 44篇 |
2014年 | 45篇 |
2013年 | 81篇 |
2012年 | 122篇 |
2011年 | 131篇 |
2010年 | 81篇 |
2009年 | 75篇 |
2008年 | 122篇 |
2007年 | 110篇 |
2006年 | 105篇 |
2005年 | 113篇 |
2004年 | 103篇 |
2003年 | 72篇 |
2002年 | 97篇 |
2001年 | 38篇 |
2000年 | 58篇 |
1999年 | 19篇 |
1998年 | 22篇 |
1997年 | 20篇 |
1996年 | 39篇 |
1995年 | 35篇 |
1994年 | 47篇 |
1993年 | 49篇 |
1992年 | 44篇 |
1991年 | 29篇 |
1990年 | 36篇 |
1989年 | 29篇 |
1988年 | 25篇 |
1987年 | 36篇 |
1986年 | 24篇 |
1985年 | 50篇 |
1984年 | 33篇 |
1983年 | 21篇 |
1982年 | 24篇 |
1981年 | 15篇 |
1980年 | 19篇 |
1979年 | 34篇 |
1978年 | 24篇 |
1977年 | 19篇 |
1976年 | 18篇 |
1975年 | 17篇 |
1974年 | 27篇 |
1973年 | 16篇 |
排序方式: 共有2456条查询结果,搜索用时 46 毫秒
101.
Maurí cio Braga de Araú jo Nelson Moreira Pinhal Ney Vernon Vugman 《Radiation Physics and Chemistry》2002,64(5-6):389-393
The kinetics of oxidized and reduced Ni2+ complexes produced by X-ray irradiation on single crystals of NaCl doped with [Ni(CN)4]2− is studied by Electron Paramagnetic Resonance at room temperature. The interdependent generation of these two complexes is attributed to migration of the charge compensating vacancy from the reduced to the oxidized complex in a reversible reaction. At higher X-ray doses, there is a predominant formation of the reduced complex. 相似文献
102.
LONG-RANGE TRIPLET-SINGLET ENERGY TRANSFER FROM ENZYME GENERATED TRIPLET ACETONE TO XANTHENE DYES 总被引:1,自引:0,他引:1
Enzyme-generated and protected acetone transfers its energy to xanthene dyes by a nontrivial process. The relative populations of the S1 state are indicative of the operation of a heavy atom effect, being 1:15:100 for fluorescein, eosine and Rose Bengal. On the other hand Stern-Volmer constants and k ET 0 values are similar for the three dyes and are remarkably higher than for collisional processes.
It is tentatively suggested that at least for eosine and Rose Bengal, a triplet-triplet cxciton transfer may occur to populate an upper triplet state of the dye followed by heavy-atom enhanced intersystem crossing to the S1 state. 相似文献
It is tentatively suggested that at least for eosine and Rose Bengal, a triplet-triplet cxciton transfer may occur to populate an upper triplet state of the dye followed by heavy-atom enhanced intersystem crossing to the S
103.
Light-induced metastable linkage isomers of trans-[Ru(NH(3))(4)Cl(SO(2))]Cl and trans-[Ru(NH(3))(4)(H(2)O)(SO(2))](C(6)H(5)SO(3))(2) have been identified for the first time using photocrystallographic methods. In both linkage isomers the SO(2) ligand is side bound, but the Ru-O and Ru-S distances are considerably longer and almost equal in the trans-H(2)O isomer. DFT calculations confirm that both isomers correspond to minima on the ground-state potential energy surface and also predict the existence of a second oxygen-bound isomer for both compounds. The decay of the light-induced species has been studied by both DSC and IR. Activation energies for the thermal back-reaction, as derived from the temperature-dependent disappearance of light-induced IR bands, are 50.0 and 58.4 kJ/mol for the two isomers, which is larger than the corresponding numbers for photoinduced side-bound nitrosyl linkage isomers. 相似文献
104.
The reactive Kr+F2− potential energy surface is probed by two-photon, laser-induced chemical bond formation during a Kr+F2 collision. This is compared with the pulsed laser excitation (two-photon) of Kr(2p9) followed by collision with F2 leading to the formation of KrF(B, C). In addition to reporting the excitation spectrum for the two-phonon-induced collision process, these techniques were used to determine quenching rate constants of Kr2F*. Quenching by Xe gives XeF(B, C) with rate constant (1.5±0.2)×10−10 cm3 s−1; the quenching rate constant for F2 is (1.5±0.2)×10−10 cm3 s−1, and the radiative lifetime of Kr2F* is 240±35 ns. The quenching rate constant for the coupled Kr(2p8) and Kr(2p9) levels by F2 is (13±2)×10−10 cm3 s−1. 相似文献
105.
Determination of tea catechins 总被引:5,自引:0,他引:5
An overview of analytical methods for the measurement of biologically important tea catechins is presented. Liquid chromatography and capillary electrophoresis are the most cited techniques for catechin separation, identification and quantitation. Liquid chromatography with ultraviolet detection is frequently used; however, mass spectrometry, electrochemical, fluorescence and chemiluminescence detection are also utilized in cases where more sensitive or selective detection is needed. Two modes of capillary electrophoresis, capillary zone electrophoresis and micellar electrokinetic capillary chromatography, have been employed for the determination of catechins. Both modes of capillary electrophoresis are based on ultraviolet detection. Additional analytical techniques, such as gas chromatography, thin-layer chromatography, paper chromatography, spectrophotometry, biosensing, chemiluminescence and nuclear magnetic resonance spectroscopy have also been utilized for the determination of catechins and are reviewed herein. 相似文献
106.
Catalyzed asymmetric acyl halide-aldehyde cyclocondensation (AAC) reactions afford highly enantiomerically enriched 3,4-disubstituted-2-oxetanones. These reactions constitute catalytic asymmetric propionate aldol additions. An optically active Al(III)-triamine complex (10 mol %) catalyzes the di(isopropyl)ethylamine-mediated cyclocondensation of propionyl bromide and a variety of aldehydes to afford beta-lactone adducts with uniformly high enantioselection (90 --> 98% ee), diastereoselection (74 --> 98% de), and chemical yields (78-90%). Lactone ring opening reveals that the enantiomerically enriched beta-lactones act as surrogates for syn propionate aldol adducts. 相似文献
107.
[reaction: see text] Optically active 4-substituted 2-oxetanones provide conduits for preparing 2,3-dihydro-4H-pyrone heterocycles. Enantioenriched beta-lactones are prepared by asymmetric catalytic acyl halide-aldehyde cyclocondensation reactions. Hydrazone anion-mediated beta-lactone ring opening and ensuing cyclization-dehydroamination of the derived beta-ketohydrazone afford the desired dihydropyrones (68-81%). Optimized lactone ring-opening-cyclization reaction conditions render a variety of optically active 4-substituted-2-oxetanones as effective precursors to enantioenriched 2,3-dihydro-4H-pyrones. 相似文献
108.
109.
110.