全文获取类型
收费全文 | 1591篇 |
免费 | 95篇 |
国内免费 | 3篇 |
专业分类
化学 | 1394篇 |
晶体学 | 10篇 |
力学 | 16篇 |
数学 | 62篇 |
物理学 | 207篇 |
出版年
2023年 | 15篇 |
2022年 | 11篇 |
2021年 | 25篇 |
2020年 | 47篇 |
2019年 | 36篇 |
2018年 | 28篇 |
2017年 | 16篇 |
2016年 | 42篇 |
2015年 | 55篇 |
2014年 | 68篇 |
2013年 | 83篇 |
2012年 | 150篇 |
2011年 | 138篇 |
2010年 | 74篇 |
2009年 | 87篇 |
2008年 | 151篇 |
2007年 | 137篇 |
2006年 | 137篇 |
2005年 | 129篇 |
2004年 | 95篇 |
2003年 | 55篇 |
2002年 | 40篇 |
2001年 | 13篇 |
2000年 | 8篇 |
1999年 | 6篇 |
1998年 | 6篇 |
1997年 | 5篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1994年 | 2篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1991年 | 2篇 |
1985年 | 4篇 |
1984年 | 1篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1978年 | 5篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 3篇 |
1974年 | 3篇 |
1973年 | 1篇 |
排序方式: 共有1689条查询结果,搜索用时 437 毫秒
141.
142.
Kourist R Miyauchi Y Uemura D Miyamoto K 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(2):557-563
Variant G74C of arylmalonate decarboxylase (AMDase) from Bordatella bronchoseptica has a unique racemising activity towards profens. By protein engineering, variant G74C/V43A with a 20-fold shift towards promiscuous racemisation was obtained, based on a reduced activity in the decarboxylation reaction and a two-fold increase in the racemisation activity. The mutant showed an extended substrate range, with a 30-fold increase in the reaction rate towards ketoprofen. Molecular dynamics simulations and the substrate profile of the racemase indicate that the steric and polar effects of the substrate structure play a more dominant role on catalysis than mere kinetic α-proton acidity. The observation that the conversion of β,γ-unsaturated carboxylic acids does not lead to a rearrangement to form their α,β isomers indicates a concerted rather than a stepwise mechanism. Interestingly, a substrate bearing a nitro group instead of the carboxylic acid group on the α-carbon atom was also converted by the racemase. 相似文献
143.
We report an angle-resolved electron energy loss spectroscopy (EELS) study on the valence-shell electronic excitations in CF(4). Experimentally momentum-transfer-dependent generalized oscillator strengths (GOSs) or GOS profiles for low-lying electronic excitations at 12.6, 13.8, and 14.8 eV are derived from EELS spectra measured at an incident electron energy of 3 keV. We also calculate GOS profiles using theoretical wave functions at the equation-of-motion coupled cluster singles and doubles level. There are good agreements between experiment and theory except for a significant discrepancy at small momentum transfer for the 1t(l) → 3s Rydberg excitation at 12.6 eV. The experimental GOS profile for 1t(l) → 3s exhibits a shape that is typical of a dipole allowed transition, while the excitation is formally dipole forbidden. This symmetry breaking behavior is rationally accounted for by qualitatively analyzing the nature of vibronic coupling effects. For the excitation band at 13.8 eV, a shoulder and extrema are observed in the GOS profile and are then found to be mainly due to the 2(1)T(2) transition. Furthermore, the theoretical GOS profile for the 2(1)T(2) transition exhibits a remarkable oscillatory pattern; its origin is discussed by considering multicenter interference effects. For the 14.8 eV excitation band, the predominant nondipole nature of the underlying transitions are revealed and comparisons with the theoretical calculations show that major contributions to this band come from the 4t(2) → 3p excitation. 相似文献
144.
Suzuki D Kato H Ohkawa M Anzai K Tanaka H Limão-Vieira P Campbell L Brunger MJ 《The Journal of chemical physics》2011,134(6):064311
We report measurements of differential and integral cross sections for electron excitation of the Schumann-Runge continuum, longest band, and second band electronic states in molecular oxygen. The energy range of the present study is 15-200 eV, with the angular range of the differential cross section (DCS) measurements from 2 to 130°. A generalized oscillator strength analysis is then employed in order to derive integral cross sections (ICSs) from the corresponding DCSs, and these ICSs are compared with relevant energy and oscillator strength scaled Born cross section (BEf-scaling [Y.-K. Kim, J. Chem. Phys. 126, 064305 (2007)]) results determined as a part of this investigation. Interestingly, while the present Schumann-Runge continuum and second band ICSs were in reasonable agreement with the respective BEf-scaling results, agreement for the longest band was poor below 100 eV with a possible reason for this apparently anomalous behavior being canvassed here. Finally, where possible all present data are compared with the results from earlier measurements and calculations with the level of agreement found being very good in some cases and marginal in others. 相似文献
145.
A new homologous series of isoflavone-based ethers,7-(4-bromoalkyloxy)-3-(4’-decyloxyprienyl)-4H-1-benzopyran-4-ones were synthesized and characterized.The mesomorphic properties of all homologues were investigated by differential scanning calorimetry(DSC) and polarizing optical microscopy(POM).Enantiotropic smectic A(SmA) phase was observed for all homologues.The structure-property study was carried out by comparing the mesomorphic behavior of the homologues with those previously reported analogues.The bromine atom from the alkyloxy side chain of the benzene ring fused to the heterocyclic moiety was found to be capable of changing the mesomorphic properties. 相似文献
146.
Efficient and stereoselective synthesis of a disaccharide fragment, 2-deoxy-4-O-(N'-monodemethyl-D-forosaminyl)-2-methylamino-β-D-xylopyranoside, of a novel antibiotic, incednine (1), is described. The key β-stereoselective formation of a 2,3,4,6-tetradeoxy-4-methylamino glycoside bond was achieved by remote participation-assisted glycosylation. 相似文献
147.
Saigusa D Shibuya M Jinno D Yamakoshi H Iwabuchi Y Yokosuka A Mimaki Y Naganuma A Ohizumi Y Tomioka Y Yamakuni T 《Analytical and bioanalytical chemistry》2011,400(10):3635-3641
We recently demonstrated that nobiletin, a citrus flavonoid, exhibits anti-dementia action in animals. However, no determination methods for the content of nobiletin with beneficial action in the brain of nobiletin-administered animals have been developed, nor has its pharmacokinetics been revealed completely. Here, we established the high-performance liquid chromatography/photodiode array detection method for nobiletin determination using Bond Elut C18 SPE cartridges for extraction, where the calibration curve was linear over 0.025-10 ng, with coefficient of variation of less than 6.76%. This method enabled us to determine pharmacokinetic parameters of nobiletin given intraperitoneally or per os in the brain of mice. 相似文献
148.
149.
The present paper deals with the algebro-geometric aspects of the eigenvector mapping for a free rigid body. The eigenvector mapping is regarded as a rational mapping to the complex projective plane from the product of the elliptic curves, one of which is the integral curve and the other the spectral curve. This is the space of the necessary data to determine the eigenvectors. The eigenvector mapping admits a factorisation through a Kummer surface, which is a double covering of the projective plane branched along a sextic curve associated with the dynamics. The key of the argument is the Cremona transformation of the projective plane and some elliptic fibrations of the Kummer surface. 相似文献
150.
Takeuchi D 《Journal of the American Chemical Society》2011,133(29):11106-11109
Pd and Ni diimine complexes catalyze the isomerization polymerization of alkenylcyclohexanes to afford polymers composed of alternating trans-cyclohexane-1,4-diyl rings and oligomethylene spacers with high selectivity. The melting points of the polymers vary from 130 to 226 °C depending on length of the oligomethylene spacer. 相似文献