全文获取类型
收费全文 | 168篇 |
免费 | 2篇 |
国内免费 | 1篇 |
专业分类
化学 | 109篇 |
晶体学 | 1篇 |
力学 | 3篇 |
数学 | 24篇 |
物理学 | 34篇 |
出版年
2023年 | 1篇 |
2021年 | 1篇 |
2020年 | 2篇 |
2019年 | 1篇 |
2018年 | 1篇 |
2017年 | 4篇 |
2016年 | 5篇 |
2015年 | 2篇 |
2014年 | 3篇 |
2013年 | 11篇 |
2012年 | 9篇 |
2011年 | 6篇 |
2010年 | 2篇 |
2009年 | 6篇 |
2008年 | 11篇 |
2007年 | 13篇 |
2006年 | 9篇 |
2005年 | 5篇 |
2004年 | 2篇 |
2003年 | 7篇 |
2002年 | 5篇 |
2001年 | 6篇 |
2000年 | 4篇 |
1999年 | 1篇 |
1998年 | 2篇 |
1997年 | 2篇 |
1996年 | 2篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1989年 | 1篇 |
1987年 | 1篇 |
1985年 | 5篇 |
1984年 | 2篇 |
1982年 | 4篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 4篇 |
1977年 | 5篇 |
1976年 | 1篇 |
1975年 | 2篇 |
1974年 | 4篇 |
1973年 | 2篇 |
1972年 | 3篇 |
1971年 | 1篇 |
1969年 | 1篇 |
1965年 | 1篇 |
1958年 | 1篇 |
1928年 | 1篇 |
1923年 | 1篇 |
排序方式: 共有171条查询结果,搜索用时 437 毫秒
1.
L.J. Vanmaele P.J. De Clercq M. Vandewalle S.J. Halkes W.R.M. Overbeek 《Tetrahedron》1984,40(7):1179-1182
An efficient method for the preparation of crystalline α-hydroxy previtamin D3 is described. Also the stereoselective reduction of 1-keto previtamin is discussed; it was observed that with aluminum hydride is the most abundant product. This stands in contrast with previously reported LiAlH4 and NaBH4 mediated reductions. 相似文献
2.
Carla M. Bossu Edilene C. Ferreira Fernanda S. Chaves Eveline A. Menezes Ana Rita A. Nogueira 《Microchemical Journal》2006,84(1-2):88-92
A flow injection system was proposed to evaluate the transient product of a colorimetric reaction between hydrolysable tannin and potassium iodate (KIO3) solution. The system optimization was accomplished by using statistical methods based on experimental design. Flow rate of KIO3 solution, sample volume, carrier flow rate, and reaction coil were the selected factors for evaluation. On screening step, complete factorial 24 was used and two levels for each selected factor were studied. For the optimization phase, a centered face composite design 22 + star was employed to evaluate sample volume and flow rate of KIO3 solution, which were the factors identified in the screening phase as having more influence on the absorbance signal. After optimization, the proposed system was compared with batch determination. Some characteristics, such as analytical frequency, reagent consumption and chemical residues generation presented better results by the use of the proposed system if compared with batch method. The system presented good repeatability with standard deviation lower than 3%, for n = 10, linearity (R2 = 0.9974) for tannic acid standard, analytical frequency of 15 injections h− 1 and limit of quantification of 24 mg L− 1 of tannic acid. Good results were obtained when the proposed system was applied to hydrolysable tannin determination in Stryphnodendron barbatimão, Eucalyptus citriodora and Phyllanthus niruri, samples of plants commonly used in popular medicine. 相似文献
3.
4.
Recently, structure has been assigned to the iridoid specionin. In the present letter the total synthesis of is described. Comparison of spectral data reveals that the final product is not identical with natural specionin. Therefore the original structural assignment of specionin must be revised. 相似文献
5.
The total synthesis of (±) dihydroreynosin and of (±) 1-oxocostic acid (R = H) are illustrative examples for a short entry into 1-oxygenated eudesmanes via an easily accessible key intermediate . 相似文献
6.
A number of polyfunctionalized cis-bicycio ¦3.3.0¦octanes have been synthesized starting from the tricyclic key intermediate which was obtained by the intramolecular cyclopropanation reaction of the diazo keto ester . Selected stereocontrolled transformations of using nucleophiles and electrophiles have been studied for the preparation of the title compounds. 相似文献
7.
The hydroxylation and the epoxidation of the cis and trans isomers of 3,4-dimethylcyclopentene and 4-t-butyl-3-methylcyclopentene have been studied. The stereoselectivity was studied as a function of the basic conformation of the individual cyclopentenes; the conformations were determined by 1H NMR spectroscopy. 相似文献
8.
Vitamin D analogues, characterized by a decalin CD-ring fragment are described. 相似文献
9.
L. D'Haenens C. C. Van De Sande M. Schelfaut M. Vandewalle 《Journal of mass spectrometry : JMS》1987,22(6):330-333
The chemical ionization (CI) mass spectra of the 2-tert-butyl-substituted 1,3-cyclopentane- and 1,3-cyclohexanediol diacetates and dimethyl ethers have been determined using isobutane and methane as reagent gases. From the differences in the spectra of these compounds, it clearly follows that steric and conformational effects are expresssed in the CI mass spectra. The relative impact of these effects, however, is strongly dependent on diol derivatization and 2-alkyl substitution. 相似文献
10.
The retroaldol-aldol isomerization of the epimeric hydroxyketones and was found to yield predominantly and , respectively, under kinetic conditions in the presence of chelating lithium cations. In hydroxylic medium is the preferred kinetic product. Under equilibration conditions and predominate. 相似文献