全文获取类型
收费全文 | 459篇 |
免费 | 9篇 |
国内免费 | 2篇 |
专业分类
化学 | 283篇 |
力学 | 12篇 |
数学 | 62篇 |
物理学 | 113篇 |
出版年
2016年 | 4篇 |
2015年 | 5篇 |
2014年 | 6篇 |
2013年 | 54篇 |
2012年 | 18篇 |
2011年 | 11篇 |
2010年 | 9篇 |
2009年 | 9篇 |
2008年 | 23篇 |
2007年 | 24篇 |
2006年 | 18篇 |
2005年 | 20篇 |
2004年 | 17篇 |
2003年 | 11篇 |
2002年 | 14篇 |
2001年 | 4篇 |
2000年 | 13篇 |
1999年 | 12篇 |
1997年 | 4篇 |
1996年 | 14篇 |
1995年 | 8篇 |
1994年 | 6篇 |
1993年 | 5篇 |
1992年 | 14篇 |
1991年 | 9篇 |
1990年 | 7篇 |
1989年 | 9篇 |
1988年 | 7篇 |
1986年 | 4篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1982年 | 9篇 |
1981年 | 3篇 |
1980年 | 6篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1977年 | 6篇 |
1976年 | 3篇 |
1975年 | 3篇 |
1974年 | 4篇 |
1973年 | 4篇 |
1972年 | 11篇 |
1971年 | 6篇 |
1970年 | 2篇 |
1969年 | 4篇 |
1968年 | 6篇 |
1966年 | 5篇 |
1965年 | 2篇 |
1880年 | 2篇 |
1875年 | 2篇 |
排序方式: 共有470条查询结果,搜索用时 0 毫秒
1.
Introduction to the proceedings of the thirteenth symposium on biotechnology for fuels and chemicals
Applied Biochemistry and Biotechnology - 相似文献
2.
Scott Charles D. Woodward Charlene A. Thompson James E. Blankinship Stephen L. 《Applied biochemistry and biotechnology》1990,24(1):799-815
Applied Biochemistry and Biotechnology - Both oxidative and reductive enzymes can be utilized to enhance coal solubilization in aqueous and organic media. Aerobic solubilization was carried out... 相似文献
3.
Cerium(III) ions in dilute sulphuric acid medium exhibit a characteristic fluorescence which has its excitation maximum at 260 nm and its fluorescence emission maximum at 350 nm. By utilising the osmium-catalysed redox reaction between cerium(IV) and arsenic(III), microgram amounts of arsenic (7.5–37.5 μg) may be determined by spectrofluorimetric measurement of the ceriurm(III) produced. The principle may be applied to the determination of several other ions which cannot yet be determined by direct spectrofluorimetry, e.g.. Fe(II) (5.6–28 μg), oxalate (8.8–44μg). Osmium(VIII) (0.05–0.2 μg) and iodide (0.6–2.5 μg) may be determined by their catalytic action. 相似文献
4.
Woodward C. A. Macinnis J. M. Lewis S. N. Greenbaum E. 《Applied biochemistry and biotechnology》1992,34(1):819-826
Applied Biochemistry and Biotechnology - Normal photosynthesis byCyanidium results in O2 evolution, suggesting that the uptake and subsequent reduction of CO2 also occur. This process, therefore,... 相似文献
5.
Spies MA Woodward JJ Watnik MR Toney MD 《Journal of the American Chemical Society》2004,126(24):7464-7475
Free energy profiles for alanine racemase from Bacillus stearothermophilus have been determined at pH 6.9 and 8.9 from global analysis of racemization progress curves. This required a careful statistical design due to the problems in finding the global minimum in mean square for a system with eight adjustable parameters (i.e., the eight rate constants that describe the stepwise chemical mechanism). The free energy profiles obtained through these procedures are supported by independent experimental evidence: (1). steady-state kinetic constants, (2). solvent viscosity dependence, (3). spectral analysis of reaction intermediates, (4). equilibrium overshoots for progress curves measured in D(2)O, and (5). the magnitudes of calculated intrinsic kinetic isotope effects. The free energy profiles for the enzyme are compared to those of the uncatalyzed and the PLP catalyzed reactions. At pH 6.9, PLP lowers the free energy of activation for deprotonation by 8.4 kcal/mol, while the inclusion of apoenzyme along with PLP additionally lowers it by 11 kcal/mol. 相似文献
6.
[structure: see text] A series of ruthenium(II) complexes containing BINOL-based monodonor phosphorus ligands have been prepared and applied to the asymmetric catalysis of the hydrogenation of aryl/alkyl ketones. The best ligands for this application are those which contain an aromatic groups with either a methoxide or bromide on the ortho position. Using these ligands, alcohols with ee's of up to 99% are formed. 相似文献
7.
8.
Hodgson P Lloyd-Jones GC Murray M Peakman TM Woodward RL 《Chemistry (Weinheim an der Bergstrasse, Germany)》2000,6(24):4451-4460
The C2-symmetric ("[DL]") and achiral ("[meso]") diastereoisomers of the hydrogen iodide salt of 1,8-bis-(N-benzyl-N-methylamino)naphthalene ([2H]-[I] ) interconvert in solution. Direct interconversion of the diastereoisomers of [2H]+ must involve hydrogen bond fission (to give "[nonHB-2H+]") and rotation-inversion of the non-protonated nitrogen centre. The global activation parameters (deltaH++ and deltaS++) for diastereoisomer interconversion in [D7]DMF have been determined from rate data obtained by temperature-drop and magnetisation-transfer 13C NMR spectroscopy over a temperature range of 170 degrees C. The process is found to have a high entropy of activation in both directions (deltaS++=163(+/-4) and 169(+/-4) JK(-1)mol(-1)) and this is suggested to arise through hydrogen bonding of the ammonium centre in [nonHB-2H+] with the solvent ([D7]DMF). Comparison of the enthalpy of activation (deltaH++) with that earlier found for diastereoisomer interconversion of the free-base form 2 suggests that the intramolecular hydrogen bond in [2H]+ is roughly equal in enthalpic strength (deltaH) with that made with the solvent ([D7]DMF) in the non-hydrogen-bonded intermediate [nonHB-2H+]. As such, the hydrogen bonding in [2H]+ may be considered as predominantly an entropically driven process, without any unusual enthalpic strength. 相似文献
9.
Ruthenium(II) complexes of monodonor ligands: efficient reagents for asymmetric ketone hydrogenation
Xu YA Clarkson GC Docherty G North CL Woodward G Wills M 《The Journal of organic chemistry》2005,70(20):8079-8087
[Chemical reaction: See text] A series of BINOL-derived ligands have been prepared and incorporated into ruthenium(II) complexes containing a diamine ligand. The complexes have proven to be excellent catalysts for the asymmetric hydrogenation of ketones, giving reduction products with enantiomeric excesses of up to 99%. 相似文献
10.
Chelated acyl rhodium hydrides, generated from the addition of [Rh(dppe)]ClO4 to beta-sulfide-substituted aldehydes, can function as the stoichiometric reductants in reductive aldol processes. Unsaturated nitriles, esters, and ketones can be used as enolate equivalents, and a variety of simple alpha- and beta-substituted aldehydes can be employed. The use of a second, more electrophilic, aldehyde allows three-component reactions to be performed. 相似文献