全文获取类型
收费全文 | 220934篇 |
免费 | 2698篇 |
国内免费 | 1324篇 |
专业分类
化学 | 122727篇 |
晶体学 | 3228篇 |
力学 | 8888篇 |
综合类 | 61篇 |
数学 | 24367篇 |
物理学 | 65685篇 |
出版年
2020年 | 1754篇 |
2019年 | 1896篇 |
2018年 | 2483篇 |
2017年 | 2531篇 |
2016年 | 3645篇 |
2015年 | 2424篇 |
2014年 | 3537篇 |
2013年 | 8872篇 |
2012年 | 7686篇 |
2011年 | 9395篇 |
2010年 | 6649篇 |
2009年 | 6451篇 |
2008年 | 8792篇 |
2007年 | 8900篇 |
2006年 | 8384篇 |
2005年 | 7705篇 |
2004年 | 6870篇 |
2003年 | 6053篇 |
2002年 | 5985篇 |
2001年 | 6703篇 |
2000年 | 5067篇 |
1999年 | 3669篇 |
1998年 | 3038篇 |
1997年 | 3008篇 |
1996年 | 3014篇 |
1995年 | 2620篇 |
1994年 | 2718篇 |
1993年 | 2583篇 |
1992年 | 2831篇 |
1991年 | 2895篇 |
1990年 | 2706篇 |
1989年 | 2617篇 |
1988年 | 2558篇 |
1987年 | 2497篇 |
1986年 | 2520篇 |
1985年 | 3300篇 |
1984年 | 3359篇 |
1983年 | 2804篇 |
1982年 | 3046篇 |
1981年 | 2811篇 |
1980年 | 2607篇 |
1979年 | 2790篇 |
1978年 | 2996篇 |
1977年 | 3032篇 |
1976年 | 3059篇 |
1975年 | 2793篇 |
1974年 | 2906篇 |
1973年 | 2956篇 |
1972年 | 2318篇 |
1971年 | 1845篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
421.
Ya. L. Gol'dfarb G. P. Gromova L. I. Belen'kii 《Chemistry of Heterocyclic Compounds》1986,22(6):663-666
Bromination of thiazole by bromine in the presence of aluminum chloride in neutral solvent or without solvent takes place at the 2-position. Such an orientation contradicts the traditional addition-cleavage mechanism, and agrees with the ylid mechanism of electrophilic substitution. 2-Methylthiazole brominates at the 5-position, and the reaction is impeded in the presence of aluminum chloride; this is due to heterocycle deactivation by complexation with the Lewis acid at the nitrogen atom.Deceased.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 837–840, June, 1986. 相似文献
422.
423.
A. V. Bulatov I. M. Sosonkin A. T. Nikitaev G. A. Kalb M. L. Khidekel' 《Russian Chemical Bulletin》1985,34(5):895-899
Conclusions In the electroreduction of alizarin in an aprotic medium the stepwise formation of the anion-radical and subsequently of the dianion has been observed; under conditions of the prolonged process the anion-radical disproportionates and through intermediate stages of deprotonation and reduction is converted into the stable dianion-radical.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 983–988, May, 1985. 相似文献
424.
425.
A. V. Bobylev N. E. Buyanova A. P. Karnaukhov V. L. Khudyakov N. P. Manyakin 《Reaction Kinetics and Catalysis Letters》1976,5(4):389-394
The systematic and random errors in the determination of the surface area of adsorbents and catalysts by argon thermodesorption chromatography are analyzed.
.相似文献
426.
427.
428.
G. A. Sokol'skii V. M. Pavlov S. A. Agafonov I. L. Knunyants 《Chemistry of Heterocyclic Compounds》1973,9(2):164-167
Hexafluoroisobutenylidene sulfate is a sulfotrioxidizing agent with respect to various olefins; methylenemethionic acid is formed in the case of ethylene, while the corresponding-sulfones are formed in the case of tetrafluoroethylene and vinylidene fluoride. 2,2-Difluoro-2-hydroxy-ethanesulfonic acid sultone is characterized by a capacity for anionotropic transformations; a number of sulfoacetic acid derivatives were obtained on the basis of this sultone.See [1] for communication III.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 178–182, February, 1973. 相似文献
429.
The hydrogen-deuterium exchange of H-2 in 4-pyrimidone, a number of 1- and 3-alkyl-4-pyrimidones and several of their thione analogs in deuterium oxide at moderate temperatures is reported. This reaction is apparently not susceptible to acid or base catalysis. Cations of the 4-pyrimidones were found not to exchange H-2 at all in acid media. Catalytic amounts of bases do not alter the exchange rates whereas more concentrated alkali decompose the pyrimidone. However, 1,4(3,4)-dihydro-1,3-dimethyl-4-oxopyrimidinium iodide (and its 6-methyl analog) exchange H-2 quite rapidly in neutral deuterium oxide, almost instantly when triethylamine is added as a catalyst, and very slowly in dilute solutions of deuterium chloride in deuterium oxide. Mechanisms are proposed to account for these phenomena. 相似文献
430.