全文获取类型
收费全文 | 116篇 |
免费 | 2篇 |
专业分类
化学 | 67篇 |
晶体学 | 2篇 |
力学 | 1篇 |
数学 | 10篇 |
物理学 | 38篇 |
出版年
2023年 | 3篇 |
2022年 | 1篇 |
2018年 | 1篇 |
2017年 | 3篇 |
2016年 | 3篇 |
2015年 | 1篇 |
2014年 | 5篇 |
2013年 | 7篇 |
2012年 | 3篇 |
2011年 | 4篇 |
2010年 | 4篇 |
2009年 | 3篇 |
2008年 | 4篇 |
2007年 | 8篇 |
2006年 | 4篇 |
2005年 | 4篇 |
2004年 | 4篇 |
2003年 | 5篇 |
2002年 | 3篇 |
2001年 | 1篇 |
2000年 | 2篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1990年 | 2篇 |
1985年 | 3篇 |
1984年 | 6篇 |
1983年 | 7篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1960年 | 2篇 |
1956年 | 1篇 |
1955年 | 1篇 |
1954年 | 2篇 |
1941年 | 2篇 |
1923年 | 1篇 |
排序方式: 共有118条查询结果,搜索用时 328 毫秒
101.
This study describes the first synthesis of a fjord-region tetrahydroepoxide (11), derived from the carcinogenic hydrocarbon benzo[g]chrysene. This compound is a more potent DNA alkylating agent than the corresponding 3,4-diol 1,2-epoxide. 相似文献
102.
Okazaki T Laali KK Zajc B Lakshman MK Kumar S Baird WM Dashwood WM 《Organic & biomolecular chemistry》2003,1(9):1509-1516
A stable ion study of a series of BaP derivatives is reported. 7,8-Dihydro-BaP 1 gives a persistent bay-region benzyliclike carbocation which shows extensive charge delocalization into the pyrene moiety. In contrast, a "benzylic" carbocation can not be generated from 9,10-dihydro-BaP 2. Introduction of bulky substituents at peri C-6 of 9,10-dihydro-BaP (as in 4 and 5) prevents side reactions (dimerization) to the extent that the initially formed carbocation undergoes rearrangement to generate the corresponding bay-region "benzylic" carbocation as a persistent species. Introduction of methoxy substituents into the 1- or 3-positions of 9,10-dihydro-BaP-7(8H)-one (6,7) increases its electrophilic reactivity to the extent that stable carboxonium-arenium dications are produced in FSO3H-SO2ClF. A detailed NMR study (at 500 MHz) of the resulting mono- and dications is reported, and charge delocalization mode (as well as conformational aspects) are addressed. Other oxidized derivatives of BaP such as the 7,8-dihydrodiol 9 and the 7,8-dihydrodibenzoate 8 are not suitable models for stable ion study because of competing O-protonation (and elimination). Energies for various possible arenium ions and regioisomeric "benzylic" cations were computed by the DFT method at the B3LYP/6-31G(d)//B3LYP/6-31G(d) level or by AM1 for comparison with the experimental results. These findings provide further evidence in support of the stability sequence: 1-pyrenyl > 4-pyrenyl > 2-pyrenyl in alpha-pyrene-substituted carbocations as models for the intermediates arising from BaP-epoxide ring opening. In an effort to provide a parallel, a series of alpha-pyrenylcarbinols were subjected to a DNA binding study using human MCF-7 cells. The results/trends are discussed and compared with the stable ion data. 相似文献
103.
[reaction: see text] Palladium catalyzed cross coupling of nucleoside arylsulfonates and arylboronic acids has been accomplished under mild conditions and at room temperature. Among three structurally similar ligands that differ in their steric and electronic properties, one yielded an effective catalyst in conjunction with Pd(OAc)2. Of the nucleoside arylsulfonates evaluated, the O6-(2,4,6-trimethylphenyl)sulfonate proved optimal, but other alkyl and alkoxy derivatives were also reasonably reactive. On the other hand, a 2-nitrophenyl and a 2-thienyl derivative were ineffective substrates. PhMe and THP were suitable as solvents, yielding good results in several cases, although reactions of some arylboronic acids were faster in PhMe. In contrast, reactions of arylboronic acids bearing strongly electron-withdrawing groups proceeded more successfully in THP. Interplay between several factors that include substituents on the nucleoside arylsulfonate, ligand substituents, and solvent is responsible for successful cross coupling. Using 31P NMR, an initial investigation has been conducted to study the interaction of Pd(OAc)2 with the ligand. At a 1:1 stoichiometry of ligand and Pd(OAc)2, a predominant species, likely a cyclopalladation product, was obtained. At a 2:1 ratio of ligand and Pd(OAc)2, a different species bearing chemically distinct phosphine ligands was observed. Both complexes display catalytic activity, although the 2:1 species may be superior. 相似文献
104.
Lakshman MK Hilmer JH Martin JQ Keeler JC Dinh YQ Ngassa FN Russon LM 《Journal of the American Chemical Society》2001,123(32):7779-7787
Suzuki-Miyaura cross-coupling of haloaromatic compounds with arylboronic acids provides a simple entry to biaryl systems. Despite its ease, to date, there are no detailed investigations of this procedure for deoxynucleoside modification. As shown in this study, a wide variety of C-6 arylpurine 2'-deoxyriboside (C-6 aryl 2'-deoxynebularine analogues) and C-2 aryl 2'-deoxyinosine analogues can be conveniently prepared via the Pd-mediated cross-coupling of arylboronic acids with the C-6 halonucleosides, 6-bromo- or 6-chloro-9[2-deoxy-3,5-bis-O-(tert-butyldimethylsilyl)-beta-D-erythro-pentofuranosyl]purine (1 and 2), and the C-2 halonucleoside, 2-bromo-O(6)-benzyl-3',5'-bis-O-(tert-butyldimethylsilyl)-2'-deoxyinosine (3). Although bromonucleoside 1 proved to be a good substrate for the Pd-catalyzed Suzuki-Miyaura cross-couplings, we have noted that for several C-6 arylations, the chloronucleoside 2 provides superior coupling yields. Also described in this study is a detailed evaluation of catalytic systems that led to optimal product recoveries. Finally, a comparison of the C-C and C-N bond-forming reactions of deoxynucleosides is also reported. On the basis of this comparison, we provide evidence that C-N bond formation at the C-6 position, leading to N-aryl 2'-deoxyadenosine analogues, is more sensitive to the ligand used, whereas C-C bond-forming reactions at the same position are not. In contrast to the ligand dependency exhibited in C-N bond formation at the C-6 position, comparable reactions at the C-2 position of purine deoxynucleosides proceed with less sensitivity to the ligand used. 相似文献
105.
106.
107.
108.
109.
110.