全文获取类型
收费全文 | 1191篇 |
免费 | 5篇 |
专业分类
化学 | 474篇 |
晶体学 | 13篇 |
力学 | 20篇 |
数学 | 161篇 |
物理学 | 528篇 |
出版年
2021年 | 12篇 |
2020年 | 16篇 |
2019年 | 20篇 |
2018年 | 30篇 |
2017年 | 41篇 |
2016年 | 29篇 |
2015年 | 21篇 |
2014年 | 45篇 |
2013年 | 38篇 |
2012年 | 37篇 |
2011年 | 50篇 |
2010年 | 49篇 |
2009年 | 35篇 |
2008年 | 32篇 |
2007年 | 43篇 |
2006年 | 39篇 |
2005年 | 28篇 |
2004年 | 25篇 |
2003年 | 32篇 |
2002年 | 28篇 |
2001年 | 37篇 |
2000年 | 19篇 |
1999年 | 19篇 |
1998年 | 16篇 |
1997年 | 16篇 |
1996年 | 17篇 |
1995年 | 13篇 |
1994年 | 14篇 |
1993年 | 17篇 |
1992年 | 13篇 |
1991年 | 19篇 |
1990年 | 12篇 |
1989年 | 12篇 |
1988年 | 18篇 |
1987年 | 15篇 |
1986年 | 13篇 |
1985年 | 14篇 |
1984年 | 14篇 |
1981年 | 20篇 |
1980年 | 14篇 |
1979年 | 11篇 |
1978年 | 12篇 |
1977年 | 16篇 |
1976年 | 18篇 |
1974年 | 20篇 |
1973年 | 14篇 |
1972年 | 17篇 |
1969年 | 13篇 |
1968年 | 11篇 |
1966年 | 10篇 |
排序方式: 共有1196条查询结果,搜索用时 31 毫秒
21.
The results of a kinetic study of model reactions between substituted phenols and bromobenzene in the presence of potassium carbonate and the copper(I) chloride–8-hydroxyquinoline catalytic complex in N,N-dimethylformamide are presented. The reactions were found to obey a first-order rate law. Both orbital and charge interactions should be taken into account in a consideration of the effect of the structural characteristics of reactants on the rate of reaction. The kinetics of substitution of the phenoxide anion for an aromatically bound halogen atom in activated and nonactivated systems with the formation of practically valuable aryl ethers were comparatively studied. The results presented provide an opportunity to distinguish the common features and regularities of activated and nonactivated aromatic substitution in the test systems. 相似文献
22.
23.
The enthalpies of formation (ΔH
f
o) for 23 halosubstituted radicals were determined from the published data on bond dissociation energies. The ΔH
f
o values of the corresponding molecules necessary for the calculation of ΔH
f
o of the radicals were taken from handbooks or calculated by the additive-group method. The conjugation energies of the radicals
are calculated, and the effect of substituents at the π-system on these values was shown. Errors of determination of the ΔH
f
o values of the radicals were estimated.
For Part 1, see Ref. 1.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 643–646, April, 1998. 相似文献
24.
Russian Chemical Bulletin - 相似文献
25.
The effect of the composition of a supporting electrolyte containing EDTA and H3PO4, the parameters of the analytical cycle, and the concentration of a depolarizer on the electrochemical behavior of arsenic(III) and copper(II) was studied by anodic stripping voltammetry at a gold-graphite electrode. The optimum conditions for determining these elements were found. Different techniques are proposed for the isolation of the analytical signals from the total voltammetric signal using postelectrolysis and subtracting voltammograms. It is shown that 0.007 µg/mL arsenic(III) can be determined in the presence of 30-fold amounts of copper(II) and 0.007 µg/mL copper(II) can be found in the presence of 40-fold amounts of arsenic(III).Translated from Zhurnal Analiticheskoi Khimii, Vol. 60, No. 2, 2005, pp. 179–186.Original Russian Text Copyright © 2005 by Kamenev, Lyakhov, Orlov.This revised version was published online in April 2005 with corrections to the author names and book review format. 相似文献
26.
N. N. Kolos V. D. Orlov E. K. Slobodina E. Yu. Yur'eva S. P. Korshunov Zyong van Tué 《Chemistry of Heterocyclic Compounds》1992,28(2):222-227
1,2,4-Triazolo[3,4-b]-1,3,4-thiadiazines, hydrazones, and -thio adducts were obtained by reactions of 4-amino-3-mercapto-1,2,4-triazole with -bromoacetophenones, aldehydes, and ,-unsaturated ketones. Conditions that promote the cyclocondensation of the -thio adducts to the previously undescribed 1,2,4-triazolo[3,4-b]-1,3,4-thiadiazepines were found. The chemical and spectral properties of the compounds obtained are discussed.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 267–272, February, 1992. 相似文献
27.
T. V. Beryozkina N. N. Kolos V. I. Musatov V. D. Orlov 《Russian Chemical Bulletin》2006,55(6):1056-1059
3,4-Dihydrobenzo-1,4-oxazin-2-ones were obtained from the corresponding β-aroylacrylic acids and 2-aminophenols. With 2-amino-4(5)-nitrophenols,
stable intermediate β-amino adducts (4-aryl-4-oxobutyric acid derivatives) were isolated.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1018–1021, June, 2006. 相似文献
28.
N. N. Veniaminov S. A. Khovavko S. A. Voronov S. L. Orlov L. A. Azarov S. Yu. Arkhipov T. N. Evdokimov 《Journal of Analytical Chemistry》2003,58(4):355-360
The elemental and isotopic composition of the core material of a hard-core projectile that had fallen onto the ground was studied by secondary-ion mass spectrometry, alpha and gamma spectrometry, X-ray photoelectron spectroscopy, and scanning electron microscopy with X-ray microanalysis. The environmental aspect of the use of depleted uranium ammunition in Yugoslavia is discussed. 相似文献
29.
S. V. Tsukerman V. M. Nikitchenko V. D. Orlov V. F. Lavrushin 《Chemistry of Heterocyclic Compounds》1967,3(4):173-177
The dipole moments of 25α, β unsaturated ketones of the thiophene series are measured in benzene at 25°, and their most probable coplanar conformations established. For the systems studied it is shown that, in the static state, the 2-thienyl group exhibits an electron-donating effect, greater than those of 2-furyl and phenyl. Introduction of electron-donating and electron-accepting substituents into the molecule of 1-(thienyl-2)-3-phenylpropenones as well as shift of the carbonyl group away from the aryl one towards the heterocyclic ring, leads in general to an increase in dipole moment. A linear relationship is found for the changes in dipole moment of isomeric thiophene ketones due to electron-donating substituents. Dipole moments of propen-3-ones correlate satisfactorily with Hammett σ parameters for substituents, and intermolecular distances. 相似文献
30.
S. M. Desenko V. D. Orlov V. V. Lipson O. V. Shishkin K. A. Potekhin Yu. T. Struchkov 《Chemistry of Heterocyclic Compounds》1993,29(1):95-99
Condensation of 5-amino-3-methylpyrazole with chalcone or dypnone gives aromatic substituted 6,7-dihydropyrazolo[1,5-a]pyrimidines which undergo air oxidation. An x-ray structure for 2-methyl-6-hydroxy-5,7-diphenyl-6,7-dihydropyrazolo[1,5-a]pyrimidine is reported.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 109–114, January, 1993. 相似文献