全文获取类型
收费全文 | 491篇 |
免费 | 14篇 |
国内免费 | 44篇 |
专业分类
化学 | 539篇 |
晶体学 | 1篇 |
综合类 | 3篇 |
物理学 | 6篇 |
出版年
2023年 | 14篇 |
2022年 | 4篇 |
2021年 | 3篇 |
2020年 | 4篇 |
2019年 | 18篇 |
2018年 | 21篇 |
2017年 | 11篇 |
2016年 | 4篇 |
2015年 | 6篇 |
2014年 | 22篇 |
2013年 | 50篇 |
2012年 | 16篇 |
2011年 | 25篇 |
2010年 | 31篇 |
2009年 | 22篇 |
2008年 | 30篇 |
2007年 | 38篇 |
2006年 | 35篇 |
2005年 | 34篇 |
2004年 | 32篇 |
2003年 | 23篇 |
2002年 | 14篇 |
2001年 | 16篇 |
2000年 | 11篇 |
1999年 | 10篇 |
1998年 | 5篇 |
1997年 | 4篇 |
1996年 | 4篇 |
1995年 | 7篇 |
1994年 | 5篇 |
1993年 | 5篇 |
1992年 | 4篇 |
1991年 | 2篇 |
1990年 | 3篇 |
1989年 | 1篇 |
1988年 | 3篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1984年 | 2篇 |
1980年 | 1篇 |
1977年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1968年 | 1篇 |
1967年 | 1篇 |
排序方式: 共有549条查询结果,搜索用时 15 毫秒
541.
The reaction of 1,n-dichloroalkanes 3a (n=2-6) with an excess of lithium powder and a catalytic amount of 4,4′-di-tert-butylbiphenyl (DTBB; 2.5 mol %) in the presence of different carbonyl compounds [ButCHO, PhCHO, Et2CO, (CH2)4CO, (CH2)5CO, (CH2)7CO, (−)-menthone], in THF at −78 °C leads, after hydrolysis with water, to the expected 1,(n+2)-diols 4, yields being <25% for n=2, 3 and in the range of 45-79% for n=4-6. When the same protocol is applied to 1,n-bromochloroalkanes 3b and 1,n-dibromoalkanes 3c (n=2-6), diols 4 are obtained in general with lower yields. 相似文献
542.
Bartosz Zambroń 《Tetrahedron》2010,66(46):8974-8981
The acyliminium cations derived from 4-vinyloxy- or 4-acyloxy-azetidin-2-ones in the presence of Lewis acids can alkylate nucleophilic arenes bound to the β-lactam nitrogen atom through methyloxy, or methylthio tethers. The reactions smoothly proceed to afford the corresponding 3-oxa- or 3-thia-4,5-benzocephams in a good yield. The sulfur atom can be easily removed by Raney nickel reduction to provide the title compounds. 相似文献
543.
溴苄类化合物在医药、农药和染料等领域有广泛的应用, 在以往的报道中由甲基芳烃制备溴苄类化合物的方法都是采用自由基的历程进行的. 报道了一种以甲基芳烃与三溴化硼直接反应采用非自由基的历程制备系列溴甲基芳烃的新方法. 该方法反应条件温和、收率高、选择性好. 在考察电子效应和位阻效应时发现: 该方法对不同取代基的底物适应范围广, 带推电子取代基对反应有利; 取代基位阻有一定影响但是没有吸电子基团显著, 吸电子基团降低产率. 同时, 在研究溶剂、温度、三溴化硼用量和时间对反应的影响时找到了最佳反应条件. 相似文献
544.
545.
Bromination and thiocyanation of 2-amino- and 2-acetylamino-4-(2-furyl)thiazoles when 1 mol of reagent is used at 10°C are directed to the 5 position. Formation of 5'-bromo-substituted derivatives when the reaction temperature is raised is the result of a secondary, thermodynamically controlled process. Monohalogenation and mononitration of 4-(2-furyl)-2-methylthiazole are directed to the 5' position. Nitration of 2-acetylamino-4-(5-nitro-2-furyl)thiazole by a nitrating mixture is accompanied by oxidative cleavage of the 5-nitrofuran moiety and leads to formation of 5,5'- and 3',5'-dinitro derivatives. 相似文献
546.
Bromination of 4‐dichloromethyl‐4‐methylcyclohexa‐2,5‐dien‐1‐one and 4‐dichloromethyl‐3,4‐dimethylcyclohexa‐2,5‐dien‐1‐one has been studied. The reaction conditions required for the formation of mono‐, di‐, and tribrominated products have been optimized. 相似文献
547.
R. I. Yurchenko A. D. Ponomarenko N. N. Svarovskaya A. A. Tolmachev 《Chemistry of Heterocyclic Compounds》2005,41(5):656-661
A series of 1-adamantylimidazo[1,2-a]pyridines has been synthesized. The negative influence of electron-acceptor substituents in the pyridine ring on the alkylation of substituted 2-aminopyridines with bromomethyl (adamantan-1-yl) ketone has been demonstrated. Bromination of adamantylimidazo-[1,2-a]pyridines on boiling in liquid bromine or in the presence of a Lewis acid resulted in insertion of a bromine atom in the imidazole ring without affecting the adamantane nucleus. The compounds studied take part in the Ritter reaction despite the absence of an easily removed groups in the adamantane nucleus.__________Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, 761–766, May, 2005. 相似文献
548.
Liudmyla M. Grishchenko Galyna G. Tsapyuk Natalia S. Novichenko Oleksandr V. Mischanchuk Andrii V. Yatsymyrskiy Olga Yu. Boldyrieva 《Molecular Crystals and Liquid Crystals》2020,699(1):20-33
AbstractNanoporous activated carbon (NAC) beads that prepared by carbonization of microporous polymer 2,6-di-tert-butyl pyridine beads were subjected to bromination followed by amination to synthesize the NAC derivatives carrying amino groups. Grafted bromine groups, 0.41?mmol of Br per 1?g of NAC, are hydrolytic stable at 100 °С and can be successfully substituted by amino groups. SEM, TEM, and texture studies were shown a nanoporosity decrease. However, the aminated NAC beads maintained a narrow nanopore size distribution and high specific surface area, retaining a spherical shape. These beads were evaluated for capturing CO2 and showed good reversible adsorption capacity. The preparation method can easily be scaled up, and the NAC beads can be used for other adsorption applications where shaped carbon solids with developed nanoporosity are required. 相似文献
549.
Hanyang Bao Dr. Yunrong Chen Prof. Dr. Xiaoyu Yang 《Angewandte Chemie (International ed. in English)》2023,62(14):e202300481
Axially chiral diaryl ethers are a type of unique atropisomers bearing two potential axes, which have potential applications in a variety of research fields. However, the catalytic enantioselective synthesis of these diaryl ether atropisomers is largely underexplored when compared to the catalytic asymmetric synthesis of biaryl or other types of atropisomers. Herein, we report a highly efficient catalytic asymmetric synthesis of diaryl ether atropisomers through an organocatalyzed enantioselective desymmetrization protocol. The chiral phosphoric acid-catalyzed asymmetric electrophilic aromatic aminations of the symmetrical 1,3-benzenediamine type substrates afforded a series of diaryl ether atropisomers in excellent yields and enantioselectivities. The facile construction of heterocycles by the utilizations of the 1,2-benzenediamine moiety in the products provided access to a variety of structurally diverse and novel azaarene-containing diaryl ether atropisomers. 相似文献