全文获取类型
收费全文 | 296篇 |
免费 | 6篇 |
国内免费 | 1篇 |
专业分类
化学 | 238篇 |
力学 | 7篇 |
数学 | 19篇 |
物理学 | 39篇 |
出版年
2023年 | 2篇 |
2022年 | 2篇 |
2021年 | 4篇 |
2020年 | 3篇 |
2019年 | 2篇 |
2017年 | 2篇 |
2016年 | 3篇 |
2015年 | 3篇 |
2014年 | 3篇 |
2013年 | 11篇 |
2012年 | 4篇 |
2011年 | 13篇 |
2010年 | 9篇 |
2009年 | 6篇 |
2008年 | 15篇 |
2007年 | 10篇 |
2006年 | 20篇 |
2005年 | 18篇 |
2004年 | 23篇 |
2003年 | 19篇 |
2002年 | 17篇 |
2001年 | 14篇 |
2000年 | 7篇 |
1999年 | 3篇 |
1998年 | 4篇 |
1997年 | 3篇 |
1996年 | 9篇 |
1995年 | 4篇 |
1994年 | 9篇 |
1993年 | 2篇 |
1992年 | 3篇 |
1991年 | 2篇 |
1990年 | 11篇 |
1989年 | 2篇 |
1988年 | 5篇 |
1987年 | 3篇 |
1986年 | 1篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 6篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1977年 | 2篇 |
1976年 | 4篇 |
1975年 | 1篇 |
1974年 | 3篇 |
1971年 | 1篇 |
1955年 | 1篇 |
排序方式: 共有303条查询结果,搜索用时 15 毫秒
231.
Amatore C Bahsoun AA Jutand A Meyer G Ndedi Ntepe A Ricard L 《Journal of the American Chemical Society》2003,125(14):4212-4222
The kinetics of the reaction of PhPdI(AsPh(3))(2) (formed via the fast oxidative addition of PhI with Pd(0)(AsPh(3))(2)) with a vinyl stannane CH(2)[double bond]CH[bond]Sn(n-Bu)(3) has been investigated in DMF. This reaction (usually called transmetalation step) is the prototype of the rate determining second step of the catalytic cycle of Stille reactions. It is established here that the transmetalation proceeds through PhPdI(AsPh(3))(DMF), generated by the dissociation of one ligand AsPh(3) from PhPdI(AsPh(3))(2). PhPdI(AsPh(3))(DMF) is the reactive species, which leads to styrene through its reaction with CH(2)[double bond]CH[bond]SnBu(3). Consequently, in DMF, the overall nucleophilic attack mainly proceeds via a mechanism involving PhPdI(AsPh(3))(DMF) as the central reactive complex and not PhPdI(AsPh(3))(2). The dimer [Ph(2)Pd(2)(mu(2)-I)(2)(AsPh(3))(2)] has been independently synthesized and characterized by its X-ray structure. In DMF, this dimer dissociates quantitatively into PhPdI(AsPh(3))(DMF), which reacts with CH(2)[double bond]CH[bond]SnBu(3). The rate constant for the reaction of PhPdI(AsPh(3))(DMF) with CH(2)[double bond]CH[bond]SnBu(3) has been determined in DMF for each situation and was found to be comparable. 相似文献
232.
[reaction: see text] An efficient entry to the fully elaborated skeleton of vinigrol is described. The installation of the desired stereochemistry at C(12) and the construction of the eight-membered ring were achieved in one operation by a remarkably facile anionic oxy-Cope rearrangement of Z-isopropenyl isomer 24. 相似文献
233.
J. F. Grunstein P. Dizabo M. Ricard J. P. Brun 《Journal of mass spectrometry : JMS》1974,9(12):1166-1172
Under electron-impact, two ‘retro’ Diels-Alder fragmentation paths are observed in the spectra of 2,4- substituted 1,3-benzodioxan; one with normal ‘retro’ Diels-Alder reaction and the other with hydrogen transfer. 相似文献
234.
Doux M Mézailles N Ricard L Le Floch P Adkine P Berclaz T Geoffroy M 《Inorganic chemistry》2005,44(4):1147-1152
Oxidation of the square planar Rh(I) complex [Rh(SPS(Me))(PPh3)] (SPS(Me) = 1-methyl-1-P-2.6-bis(diphenylphosphinosulfide)-3,5-(bisphenyl)-phosphinine) (1) based on mixed SPS-pincer ligand with hexachloroethane yielded the Rh(III) dichloride complex [Rh(SPS(Me))(PPh3)Cl2] (2), which was structurally characterized. The homoleptic Rh(III) complex [Rh(SPS(Me))2][Cl] (4) was obtained via the stoichiometric reaction of SPS(Me) anion (3) with [Rh(tht)3Cl3] (tht = tetrahydrothiophene). Complex 4, which was characterized by X-ray diffraction, was also studied by cyclic voltammetry. Complex 4 can be reversibly reduced at E = -1.16 V (vs SCE) to give the neutral 19-electron Rh(II) complex [Rh(SPS(Me))2] (5). Accordingly, complex 5 could be synthesized via chemical reduction of 4 with zinc dust. EPR spectra of complex 5 were obtained after electrochemical or chemical reduction of 4 in THF or CH2Cl2. Hyperfine interaction with two equivalent 31P nuclei was observed in liquid solution, while an additional coupling with a spin 1/2 nucleus, probably 103Rh, was detected in frozen solution. The 31P couplings are consistent with DFT calculations that predict a drastic increase in the axial P-S bond lengths when reducing (SPS(Me))2Rh(III). In the reduced complex, the unpaired electron is mainly localized in a rhodium d(z2) orbital, consistent with the g-anisotropy measured at 100 K. 相似文献
235.
Dimethyl-1,5-cyclooctadiene (DMCOD) is synthesized by the Ni-catalyzed dimerization of isoprene and consists of 80% 1,5-dimethyl-1,5-cyclooctadiene (1,5-DMCOD) and 20% 1,6-dimethyl-1,5-cyclooctadiene (1,6-DMCOD). Reaction of Hhfac (1,1,1,5,5,5-hexafluoro-2,4-pentanedione) with Ag(2)O in the presence of DMCOD results in the formation of isomeric Ag(I) species. Repeated recrystallizations yield an isomerically pure compound ((1,5-DMCOD)Ag(hfac))(2) that was characterized by X-ray crystallography and (1)H and (13)C NMR and IR spectroscopy. X-ray crystallography revealed a dinuclear complex with a short Ag-Ag spacing (3.0134(3) ? at -150 degrees C and 3.0278(5) ? at -20 degrees C) and bridging hfac ligands (&mgr;(2) bonding). The overall geometry around the Ag atoms is a deformed tetrahedron with two short Ag-O bonds (2.375 ? average) and two Ag-diene bonds. The methyl groups of the 1,5-DMCOD ligand are pointed toward the center of the molecule. Decomposition of the silver complex in a biphasic HCl (1 M)/CH(2)Cl(2) mixture liberates isomerially pure 1,5-DMCOD; this diene is subsequently used to synthesize isomerically pure (1,5-DMCOD)Cu(hfac). The latter compound was characterized by (1)H and (13)C NMR and IR spectroscopy and is a useful liquid precursor for Cu CVD. Crystallographic data: C(30)H(34)Ag(2)F(12)O(4), monoclinic, P2(1)/c (No. 14), Z = 4; at -150 degrees C, a = 12.428(1) ?, b = 11.071(1) ?, c = 24.520(2) ?, beta = 101.98(1) degrees; at -20 degrees C, a = 12.597(1) ?, b = 11.191(1) ?, c = 24.641(2) ?, beta = 102.08(1) degrees. 相似文献
236.
A straightforward synthesis of enantiopure (S)- and (R)-α-Tfm-pyroglutamic acid is reported. The strategy is based on the use of a chiral CF3-hydroxymorpholinone intermediate conveniently obtained from ethyl trifluoropyruvate-based chiral CF3-oxazolidines (Fox). The key step is an oxidative cyclization followed by a reductive cleavage of the (R)-phenylglycinol chiral auxiliary. 相似文献
237.
Theoretical Computer‐Aided Mutagenic Study on the Triple Green Fluorescent Protein Mutant S65T/H148D/Y145F
下载免费PDF全文
![点击此处可从《Chemphyschem》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Pau Armengol Dr. Ricard Gelabert Prof. Miquel Moreno Prof. José M. Lluch 《Chemphyschem》2015,16(10):2134-2139
Green fluorescent protein (GFP) mutant S65T/H148D has been proposed to host a photocycle that involves an excited‐state proton transfer between the chromophore (Cro) and the Asp148 residue and takes place in less than 50 fs without a measurable kinetic isotope effect. It has been suggested that the interaction between the unsuspected Tyr145 residue and the chromophore is needed for the ultrafast sub‐50 fs rise in fluorescence. To verify this, we have performed a computer‐aided mutagenic study to introduce the additional mutation Y145F, which eliminates this interaction. By means of QM/MM molecular dynamics simulations and time‐dependent density functional theory studies, we have assessed the importance of the Cro–Tyr145 interaction and the solvation of Asp148 and shown that in the triple mutant S65T/H148D/Y145F a significant loss in the ultrafast rise of the Stokes‐shifted fluorescence should be expected. 相似文献
238.
239.
240.