全文获取类型
收费全文 | 672篇 |
免费 | 16篇 |
国内免费 | 2篇 |
专业分类
化学 | 512篇 |
晶体学 | 6篇 |
力学 | 20篇 |
数学 | 100篇 |
物理学 | 52篇 |
出版年
2023年 | 2篇 |
2022年 | 10篇 |
2021年 | 8篇 |
2020年 | 12篇 |
2019年 | 14篇 |
2018年 | 6篇 |
2017年 | 9篇 |
2016年 | 9篇 |
2015年 | 16篇 |
2014年 | 15篇 |
2013年 | 30篇 |
2012年 | 33篇 |
2011年 | 45篇 |
2010年 | 26篇 |
2009年 | 25篇 |
2008年 | 40篇 |
2007年 | 40篇 |
2006年 | 33篇 |
2005年 | 37篇 |
2004年 | 27篇 |
2003年 | 30篇 |
2002年 | 34篇 |
2001年 | 11篇 |
2000年 | 15篇 |
1999年 | 5篇 |
1998年 | 9篇 |
1997年 | 10篇 |
1996年 | 18篇 |
1995年 | 5篇 |
1994年 | 4篇 |
1993年 | 9篇 |
1992年 | 6篇 |
1991年 | 5篇 |
1990年 | 6篇 |
1989年 | 6篇 |
1987年 | 5篇 |
1986年 | 7篇 |
1985年 | 9篇 |
1984年 | 2篇 |
1983年 | 4篇 |
1982年 | 7篇 |
1981年 | 9篇 |
1980年 | 8篇 |
1979年 | 2篇 |
1978年 | 6篇 |
1977年 | 6篇 |
1976年 | 6篇 |
1973年 | 4篇 |
1970年 | 1篇 |
1927年 | 1篇 |
排序方式: 共有690条查询结果,搜索用时 15 毫秒
621.
Rousset S Nocentini S Rouillard D Baroche C Moustacchi E 《Photochemistry and photobiology》2002,75(2):159-166
The genetic disease Fanconi anemia (FA), generally considered to be a DNA repair defect, has also been related to a deficiency in cellular defense against reactive oxygen species (ROS). Results show that mitochondrial matrix densification occurs rapidly and transiently in FA fibroblasts following 8-methoxypsoralen (8-MOP) photoreaction or ultraviolet A (320 to 380 nm) (UVA) irradiation. This effect is oxygen dependent because it is more important under 20 than under 5% oxygen tension. In contrast, in normal fibroblasts very little, if any, densification of mitochondrial matrix is induced by treatments even at the highest oxygen tension. The changes in matrix density in FA cells are accompanied by some modifications in transmembrane potential, linked to a Fenton-like reaction, and in mitochondrial cardiolipin content, differing from the responses of normal cells. These data are indicative of some sort of membrane damage induced by 8-MOP photoreaction and UVA irradiation, to which FA cells appear to be particularly sensitive. 相似文献
622.
Neureiter Markus Danner Herbert Thomasser Christiane Saidi Bamusi Braun Rudolf 《Applied biochemistry and biotechnology》2002,98(1-9):49-58
Sugarcane bagasse, a byproduct of the cane sugar industry, is an abundant source of hemicellulose that could be hydrolyzed
to yield a fermentation feedstock for the production of fuel ethanol and chemicals. The effects of sulfuric acid concentration,
temperature, time, and dry matter concentration on hemicellulose hydrolysis were studied with a 20-L batch hydrolysis reactor
using a statistical experimental design. Even at less severe conditions considerable amounts (>29%) of the hemicellulose fraction
could be extracted. The percentage of soluble oligosaccharides becomes very low in experiments with high yields in monosaccharides,
which indicates that the cellulose fraction is only slightly affected. For the sugar yields, acid concentration appears to
be the most important parameter, while for the formation of sugar degradation products, temperature shows the highest impact.
It could be demonstrated that the dry matter concentration in the reaction slurry has a negative effect on the xylose yield
that can be compensated by higher concentrations of sulfuric acid owing to a positive interaction between acid concentration
and dry matter contents. 相似文献
623.
The complex formation of uranyl UO(2)(2+) with chloride ions in acetonitrile was studied by UV-vis and U L(III) EXAFS spectroscopy. The investigations unambiguously point to the existence of a [UO(2)Cl(4)](2-) species in solution with D(4)(h)() symmetry. The distances in the U(VI) coordination sphere are U-O(ax) = 1.77 +/- 0.01 Angstroms and U-Cl = 2.68 +/- 0.01 Angstroms. 相似文献
624.
We report the synthesis of novel anticancer compounds based on bioreductive and DNA-alkylating properties. The strategy was to combine a benzoquinone annelated pyrrole with bioreductive properties with a set
of DNA-alkylating functionalities, thus resulting in bifunctional anticancer compounds. The biological activity of all compounds
was evaluated against a number of cancer cell lines. One of the compounds should be emphasized. 相似文献
625.
Victoire Djean Marcin Konowalczyk Jamie Gravell Matthew J. Golesworthy Catlin Gunn Nils Pompe Olivia Foster Vander Elst Ke-Jie Tan Mark Oxborrow Dirk G. A. L. Aarts Stuart R. Mackenzie Christiane R. Timmel 《Chemical science》2020,11(30):7772
Certain pairs of paramagnetic species generated under conservation of total spin angular momentum are known to undergo magnetosensitive processes. Two prominent examples of systems exhibiting these so-called magnetic field effects (MFEs) are photogenerated radical pairs created from either singlet or triplet molecular precursors, and pairs of triplet states generated by singlet fission. Here, we showcase confocal microscopy as a powerful technique for the investigation of such phenomena. We first characterise the instrument by studying the field-sensitive chemistry of two systems in solution: radical pairs formed in a cryptochrome protein and the flavin mononucleotide/hen egg-white lysozyme model system. We then extend these studies to single crystals. Firstly, we report temporally and spatially resolved MFEs in flavin-doped lysozyme single crystals. Anisotropic magnetic field effects are then reported in tetracene single crystals. Finally, we discuss the future applications of confocal microscopy for the study of magnetosensitive processes with a particular focus on the cryptochrome-based chemical compass believed to lie at the heart of animal magnetoreception.Confocal microscopy is showcased as a powerful technique for the measurement of spatiotemporally-resolved magnetic field effects in both solutions and single crystals. 相似文献
626.
Marc Lang Alain Lacroix Christiane Pont Jean-Pierre Fleury 《Helvetica chimica acta》1986,69(5):1025-1033
2-Aza-1,3-dienes. Synthesis and Properties of 1-Alkylpyrazone-imines and their Tautomers Treatment of 5-dialkylamino-1,1-dicyano-2-aza-1,3-dienes (or their 1-methoxycarbonyl analogoues) with primary amines gives substituted 1-alkyl-3-cyano-(or methoxycarbonyl-)pyrazoneimines. Tautomeric behaviour, nucleophilic addition to imino function and spectroscopic data of these isomers are examined. 相似文献
627.
Ulic SE Kosma A Leibold C Della Védova CO Willner H Oberhammer H 《The journal of physical chemistry. A》2005,109(16):3739-3744
Structural and conformational properties of two sulfenyl derivatives, trifluoromethanesulfenyl acetate, CF3S-OC(O)CH3 (1), and trifluoromethanesulfenyl trifluoroacetate, CF3S-OC(O)CF3 (2), were determined by gas electron diffraction, vibrational spectroscopy, in particular with IR (matrix) spectroscopy, which includes photochemical studies, and by quantum chemical calculations. Both compounds exist in the gas phase as a mixture of two conformers, with the prevailing component possessing a gauche structure around the S-O bond. The minor form, 15(5)% in 1 and 11(5)% in 2 according to IR(matrix) spectra, possesses an unexpected trans structure around the S-O bond. The C=O bond of the acetyl group is oriented syn with respect to the S-O bond in both conformers. UV-visible broad band irradiation of 1 and 2 isolated in inert gas matrixes causes various changes to occur. Conformational randomization clearly takes place in 2 with simultaneous formation of CF3SCF3. For 1 the only reaction channel detected leads to the formation of CH3SCF3 with the consequent extrusion of CO2. Quantum chemical calculations (B3LYP/6-31G and MP2 with 6-31G and 6-311G(2df,pd) basis sets) confirm the existence of a stable trans conformer. The calculations reproduce the conformational properties for both compounds qualitatively correct with the exception of the B3LYP method for compound 2 which predicts the trans form to be prevailing, in contrast to the experiment. 相似文献
628.
Erben MF Della Védova CO Boese R Willner H Leibold C Oberhammer H 《Inorganic chemistry》2003,42(22):7297-7303
The geometric structure and conformational properties of trifluoromethyl chlorosulfonate (chlorosulfuric acid trifluoromethyl ester), CF(3)OSO(2)Cl, have been determined by X-ray crystallography, gas electron diffraction (GED), and vibrational spectroscopy (IR(gas), IR(matrix), and Raman(liquid)). These experimental investigations were supplemented by quantum chemical calculations (B3LYP with 6-311G* and 6-311+G(3df) basis sets). All experimental methods result in a single conformer with gauche orientation of the CF(3) group relative to the S[bond]Cl. The dihedral angle delta(COSCl) is determined to be 91.7(3) degrees in the crystal and 94(3) degrees in the gas phase. This dihedral angle corresponds to a near-eclipsed orientation of the O[bond]C relative to one of the S[double bond]O bonds (delta(CO[bond]SO) = -23.0(3) degrees and -21(3) degrees in the crystal and gas phase, respectively). 相似文献
629.
Michel Legraverend Emile Bisagni Christiane Huel 《Journal of heterocyclic chemistry》1989,26(6):1881-1881
Epoxidation of 2-azabicyclo[2.2.1]hept-5-en-3-one has been performed in high yield with potassium hydrogen persulfate at pH 6, 1H nmr data indicate an exo stereoconfiguration of the epoxide. 相似文献
630.
We present a neutron scattering analysis of the density and the static structure factor of confined methanol at various temperatures. Confinement is performed in the cylindrical pores of MCM-41 silicates with pore diameters D=24 and 35 A. A change of the thermal expansivity of confined methanol at low temperature is the signature of a glass transition, which occurs at higher temperature for the smallest pore. This is evidence of a surface induced slowing down of the dynamics of the fluid. The structure factor presents a systematic evolution with the pore diameter, which has been analyzed in terms of excluded volume effects and fluid-matrix cross correlation. Conversely to the case of Van der Waals fluids, it shows that stronger fluid-matrix correlations must be invoked most probably in relation with the H-bonding character of both methanol and silicate surface. 相似文献