全文获取类型
收费全文 | 291篇 |
免费 | 5篇 |
国内免费 | 37篇 |
专业分类
化学 | 316篇 |
晶体学 | 1篇 |
力学 | 2篇 |
综合类 | 1篇 |
数学 | 8篇 |
物理学 | 5篇 |
出版年
2023年 | 5篇 |
2022年 | 2篇 |
2021年 | 7篇 |
2020年 | 15篇 |
2019年 | 12篇 |
2018年 | 10篇 |
2017年 | 14篇 |
2016年 | 10篇 |
2015年 | 5篇 |
2014年 | 8篇 |
2013年 | 12篇 |
2012年 | 6篇 |
2011年 | 32篇 |
2010年 | 14篇 |
2009年 | 26篇 |
2008年 | 25篇 |
2007年 | 27篇 |
2006年 | 20篇 |
2005年 | 22篇 |
2004年 | 21篇 |
2003年 | 11篇 |
2002年 | 7篇 |
2000年 | 1篇 |
1999年 | 1篇 |
1998年 | 1篇 |
1996年 | 2篇 |
1995年 | 1篇 |
1994年 | 3篇 |
1993年 | 1篇 |
1992年 | 3篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1985年 | 1篇 |
1980年 | 1篇 |
1977年 | 1篇 |
排序方式: 共有333条查询结果,搜索用时 15 毫秒
11.
Arun K. Sinha Vinod Kumar Abhishek Sharma Anuj Sharma Rakesh Kumar 《Tetrahedron》2007,63(45):11070-11077
A mild and convenient one-pot two-step synthesis of hydroxystilbenes with trans selectivity has been developed through a modified Perkin reaction between benzaldehydes and phenylacetic acids bearing 4- or 2-hydroxy substitution at the aromatic ring, in the presence of piperidine-methylimidazole and polyethylene glycol under microwave irradiation. The observation of a simultaneous condensation-decarboxylation leading to the unusual formation of hydroxystilbenes in lieu of α-phenylcinnamic acid reveals an interesting facet to the classical Perkin reaction. The developed protocol provides a green alternative to the prevalent methods employing a toxic decarboxylating agent in the form of quinoline/Cu salt, and the requirement for harsh protection-deprotection steps for the synthesis of hydroxylated stilbenes. 相似文献
12.
An improved synthesis of the anti-cancer agent DMU-212 (trans-3,4,5,4′-tetramethoxystilbene) is described. The methodology involves the use of a Pd-oxazoline catalyst as a mediator of a regio-selective (Heck) C-C bond formation reaction. A simple isolation step is then used to obtain the title material. The compound has been further characterised in the solid-state by X-ray diffraction methods. 相似文献
13.
The effect of an electron attracting substituent in the Lewis acid catalyzed oligomerization of flavanols was investigated. The results showed that the presence of a COCF3, at the 8 position of a (+)-catechin unit strongly influenced the attack of the 6 free nucleophile flavanol position by the electrophile generated from a 4-O-alkyloxy protected catechin unit. This was observed either with TiCl4 or TMSOTf as Lewis acids in which the carbon-carbon bond formation was inhibited and the corresponding dimer was detected in small amount. On the contrary, the formation of a carbon-oxygen bond was observed and the corresponding C-4→O→C-3 ether linked procyanidin dimer was isolated in a good yield. In order to avoid the participation of the C-3 hydroxyl group in the dimerization reaction, the two flavanol units were forced into C-4→C-8 coupling by use of an internal link. The structural elucidation of the isolated compounds was achieved through MS and NMR spectroscopy. 相似文献
14.
15.
Maria Helena Araujo Maria D. Vargas Anthony G. Avent Fabrizia Grepioni 《Journal of organometallic chemistry》2004,689(22):3513-3519
The reactions of [HIr4(CO)9(Ph2PCCPh)(μ-PPh2)] (1) or [Ir4(CO)8(μ3-η2-HCCPh)(μ-PPh2)2] (2) with HCCPh gave two isomeric forms of [Ir4(CO)6(μ3-η2-HCCPh)(μ2-η4-C4H2Ph2)(μ-PPh2)2] (3 and 4) in good yields as the only products. These compounds were characterized with analytical and spectroscopic data including 1H, 13C and 31P NMR (1 and 2D) spectroscopy and their molecular structures were established by X-ray diffraction studies. Compounds 3 and 4 exhibit the same distorted butterfly metal polyhedral arrangement of metal atoms with two μ-PPh2 that occupy different positions in the structures of the two isomers. Both molecules contain a HCCPh ligand bonded in a μ3-η2-// mode to one of the wings of the butterfly and a metallacyclic ring, which resulted from head-to-tail coupling, in the case of [Ir4(CO)6(μ3-η2-HCCPh){μ2-η4-(H)CC(Ph)C(H)C(Ph)}(μ-PPh2)2] (3) and tail-to-tail coupling, in that of [Ir4(CO)6(μ3-η2-HCCPh){μ2-η4-(H)CC(Ph)C(Ph)C(H)}(μ-PPh2)2] (4), and which is linked to two metal atoms of the second wing of the butterfly. 相似文献
16.
Mecheril V. Nandakumar 《Tetrahedron》2005,61(41):9775-9782
A Pd2dba3/P(i-BuNCH2CH2)3N catalyzed one-pot synthesis of unsymmetrically substituted trans-4-N,N-diarylaminostilbenes and both symmetrically and unsymmetrically substituted N,N-diarylaminostyrene derivatives is reported. The procedure involves two or more palladium catalyzed sequential coupling reactions (an amination and an inter-molecular Heck reaction) in one-pot using the same catalyst system with two different aryl halides, including aryl chlorides and hetero aryl halides as the coupling partners. 相似文献
17.
A series of 3-(N-substituted)-aminoquinolin-2(1H)-ones have been synthesized by the palladium-catalyzed C-N coupling reaction starting from 3-bromoquinolin-2-(1H)-ones. Various nucleophiles including amines, amides, sulfonamides, carbamates and ureas have been used successfully. In all the cases, the reactions take place rapidly in 1,4-dioxane and proceed in good to excellent yield using palladium acetate as a catalyst, Xantphos as a ligand and Cs2CO3 as a base. 相似文献
18.
The distribution of hydrodesulfurization (HDS) products of thiophene was compared on 9 different catalysts at different degrees
of sulfidation and at aging in H2/thiophene mixtures. The main products of HDS were C4 and Cl-C3 hydrocarbons. The effect of sulfur uptake on the productsmin distribution was similar for Co and Ni promoted, and reverse
to that on Pd and Pt promoted samples. The effect of aging was similar for all samples.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
19.
Chong Han Sean M. Kelly Theresa Cravillion Scott J. Savage Tina Nguyen Francis Gosselin 《Tetrahedron》2019,75(32):4351-4357
An efficient synthesis of PI3K inhibitor GDC-0077, featuring two consecutive Cu-catalyzed CN coupling reactions, is reported. The described synthetic route involves a chemoselective Ullmann-type coupling of a chiral difluoromethyl-substituted oxazolidinone, a Cu-catalyzed N-arylation of l-alanine with high stereochemical integrity, and a high-yielding final amide bond formation step to produce GDC-0077 in >99.5 area % HPLC purity. 相似文献
20.
Suzuki-Miyaura coupling was achieved on a variety of aryl chlorides by using di(2,6-dimethylmorpholino)phenylphosphine (L1) as a bulky electron-rich monoaryl phosphine ligand. We report the couplings of various chlorobenzenes and heteroaryl chlorides. 相似文献