全文获取类型
收费全文 | 423篇 |
免费 | 8篇 |
国内免费 | 3篇 |
专业分类
化学 | 254篇 |
力学 | 9篇 |
数学 | 45篇 |
物理学 | 126篇 |
出版年
2016年 | 3篇 |
2015年 | 5篇 |
2014年 | 6篇 |
2013年 | 19篇 |
2012年 | 18篇 |
2011年 | 11篇 |
2010年 | 8篇 |
2009年 | 9篇 |
2008年 | 23篇 |
2007年 | 23篇 |
2006年 | 18篇 |
2005年 | 20篇 |
2004年 | 18篇 |
2003年 | 11篇 |
2002年 | 12篇 |
2001年 | 5篇 |
2000年 | 11篇 |
1999年 | 14篇 |
1998年 | 2篇 |
1997年 | 5篇 |
1996年 | 7篇 |
1995年 | 12篇 |
1994年 | 10篇 |
1993年 | 4篇 |
1992年 | 19篇 |
1991年 | 10篇 |
1990年 | 16篇 |
1989年 | 11篇 |
1988年 | 8篇 |
1987年 | 2篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1982年 | 9篇 |
1981年 | 2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 | 5篇 |
1973年 | 3篇 |
1972年 | 9篇 |
1971年 | 4篇 |
1969年 | 4篇 |
1968年 | 4篇 |
1966年 | 5篇 |
1965年 | 2篇 |
1880年 | 2篇 |
1875年 | 2篇 |
排序方式: 共有434条查询结果,搜索用时 31 毫秒
11.
[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
12.
13.
14.
15.
16.
The molecular conformations and packing of [(tBuCO2)3M2(mu-X)M2(O2CtBu)3], where M = Mo and W, and X = oxalate and perfluoroterephthalate, determined in the solid-state from powder X-ray diffraction analysis, reveal one-dimensional coordination polymers involving pivalate-oxygen to metal interactions (X = perfluoroterephthalate), and oxalate--as well as pivalate-oxygen to metal bonds (X = oxalate), and allows explanation of the unusual state-dependent chromic properties of these compounds. 相似文献
17.
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
18.
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
19.
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
20.
Non-linear dielectric spectroscopy: antifouling and stabilisation of electrodes by a polymer coating
Woodward AM Davies EA Denyer S Olliff C Kell DB 《Bioelectrochemistry (Amsterdam, Netherlands)》2000,51(1):13-20
Non-linear dielectric spectroscopy (NLDS) has previously been shown to produce quantitative information that is indicative of the metabolic state of various organisms, by modeling the non-linear effects of their membranous enzymes on an applied oscillating electromagnetic field using supervised multivariate analysis methods. However, the instability of the characteristics of the measuring apparatus rendered the process temperamental at best in the laboratory and impractical for field use. The main practical problem, of the non-stationarity of the electrode-solution interface and the ease with which the electrode surfaces are subject to protein fouling. It is addressed by applying a thin, electrically transparent antifouling coat to the electrodes. This reduces the interminable cleaning procedures previously required to prepare the electrodes for use, increases their usable lifetime before recleaning, and also improves the precision and linearity of multivariate models on NLDS data. 相似文献