全文获取类型
收费全文 | 461篇 |
免费 | 19篇 |
国内免费 | 2篇 |
专业分类
化学 | 365篇 |
晶体学 | 2篇 |
力学 | 6篇 |
数学 | 54篇 |
物理学 | 55篇 |
出版年
2024年 | 3篇 |
2023年 | 5篇 |
2022年 | 7篇 |
2021年 | 13篇 |
2020年 | 12篇 |
2019年 | 6篇 |
2018年 | 5篇 |
2017年 | 7篇 |
2016年 | 19篇 |
2015年 | 14篇 |
2014年 | 16篇 |
2013年 | 37篇 |
2012年 | 35篇 |
2011年 | 37篇 |
2010年 | 19篇 |
2009年 | 14篇 |
2008年 | 21篇 |
2007年 | 24篇 |
2006年 | 19篇 |
2005年 | 19篇 |
2004年 | 19篇 |
2003年 | 13篇 |
2002年 | 20篇 |
2001年 | 4篇 |
2000年 | 7篇 |
1999年 | 4篇 |
1998年 | 5篇 |
1997年 | 3篇 |
1996年 | 2篇 |
1995年 | 3篇 |
1994年 | 2篇 |
1993年 | 6篇 |
1992年 | 2篇 |
1991年 | 3篇 |
1989年 | 6篇 |
1988年 | 2篇 |
1987年 | 5篇 |
1985年 | 4篇 |
1984年 | 2篇 |
1982年 | 6篇 |
1981年 | 2篇 |
1980年 | 7篇 |
1979年 | 7篇 |
1978年 | 2篇 |
1975年 | 4篇 |
1974年 | 2篇 |
1973年 | 2篇 |
1972年 | 1篇 |
1970年 | 1篇 |
1966年 | 1篇 |
排序方式: 共有482条查询结果,搜索用时 15 毫秒
71.
Enolate Stabilization by Anion–π Interactions: Deuterium Exchange in Malonate Dilactones on π‐Acidic Surfaces 下载免费PDF全文
François N. Miros Dr. Yingjie Zhao Dr. Gevorg Sargsyan Marion Pupier Dr. Céline Besnard Dr. César Beuchat Dr. Jiri Mareda Dr. Naomi Sakai Prof. Stefan Matile 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(8):2648-2657
Of central importance in chemistry and biology, enolate chemistry is an attractive topic to elaborate on possible contributions of anion–π interactions to catalysis. To demonstrate the existence of such contributions, experimental evidence for the stabilization of not only anions but also anionic intermediates and transition states on π‐acidic aromatic surfaces is decisive. To tackle this challenge for enolate chemistry with maximal precision and minimal uncertainty, malonate dilactones are covalently positioned on the π‐acidic surface of naphthalenediimides (NDIs). Their presence is directly visible in the upfield shifts of the α‐protons in the 1H NMR spectra. The reactivity of these protons on π‐acidic surfaces is measured by hydrogen–deuterium (H–D) exchange for 11 different examples, excluding controls. The velocity of H–D exchange increases with π acidity (NDI core substituents: SO2R>SOR>H>OR>OR/NR2>SR>NR2). The H–D exchange kinetics vary with the structure of the enolate (malonates>methylmalonates, dilactones>dithiolactones). Moreover, they depend on the distance to the π surface (bridge length: 11–13 atoms). Most importantly, H–D exchange depends strongly on the chirality of the π surface (chiral sulfoxides as core substituents; the crystal structure of the enantiopure (R,R,P)‐macrocycle is reported). For maximal π acidity, transition‐state stabilizations up to ?18.8 kJ mol?1 are obtained for H–D exchange. The Brønsted acidity of the enols increases strongly with π acidity of the aromatic surface, the lowest measured pKa=10.9 calculates to a ΔpKa=?5.5. Corresponding to the deprotonation of arginine residues in neutral water, considered as “impossible” in biology, the found enolate–π interactions are very important. The strong dependence of enolate stabilization on the unprecedented seven‐component π‐acidity gradient over almost 1 eV demonstrates quantitatively that such important anion–π activities can be expected only from strong enough π acids. 相似文献
72.
Voltametric,Amperometric, and Chronopotentiometric Determination of Submicromolar Concentrations of Carboxin 下载免费PDF全文
New procedures for the determination of pesticide carboxin were developed using differential pulse voltammetry, HPLC with amperometric detection and chronopotentiometry at carbon paste electrode and reticulated vitreous carbon electrode, respectively. Developed procedures based on electrochemical oxidation of carboxin were successfully applied on the determination of carboxin in the model samples of drinking and river water. Limits of detection in samples of river water were in 10?7 mol L?1 concentration range for all procedures and electrodes used. All developed procedures proved to be sensitive, accurate and, due to the resistance of the electrode to the passivation, also simple to handle. 相似文献
73.
Tanaka H Bollot G Mareda J Litvinchuk S Tran DH Sakai N Matile S 《Organic & biomolecular chemistry》2007,5(9):1369-1380
In this report, we describe design, synthesis, evaluation and molecular dynamics simulations of synthetic multifunctional pores with pi-acidic naphthalenediimide clamps. Experimental evidence is provided for the formation of unstable but inert, heterogeneous and acid-insensitive dynamic tetrameric pores that are sensitive to base and ionic strength. Blockage experiments reveal that the introduction of aromatic electron donor-acceptor interactions provides access to the selective recognition of pi-basic intercalators within the pore. This breakthrough is important for the application of synthetic pores as multianalyte sensors. 相似文献
74.
Moakes G Daemen LL Gelbaum LT Leisen J Marecek V Janata J 《The journal of physical chemistry. B》2007,111(25):7312-7317
The effect of lithium ion on the ordering of water in water-saturated nitrobenzene has been probed by 2H NMR, diffusion ordered spectroscopy and neutron scattering. It was shown that increased water concentration in LiClO4/wet nitrobenzene results in the formation of a metastable solvatomer with mixed water and nitrobenzene character, Li+(W/NB). This species is shown to decay over hours to two solvatomers, one dominated by nitrobenzene Li+(NB) and the other dominated by water Li+(W). To confirm the assignment of these solvation states, diffusion ordered deuterium NMR spectroscopy has been used to elucidate the hydrodynamic radii of these solvatomers. Neutron scattering yields vibrational spectroscopy information that shows how addition of lithium to the nitrobenzene/water system results in relatively slow self-organization of the water environment (hours). 相似文献
75.
Voltammetric determination of aminobiphenyls at a boron-doped nanocrystalline diamond film electrode
Voltammetric behavior of 2-aminobiphenyl, 3-aminobiphenyl, and 4-aminobiphenyl at a boron-doped nanocrystalline diamond film electrode was investigated using cyclic voltammetry and differential pulse voltammetry. Optimum conditions have been found for the determination of those genotoxic substances by differential pulse voltammetry at the above given electrode in the concentration range of 2 × 10−7 to 1 × 10−5 mol/L. 相似文献
76.
Robert E. Bruccoleri Jiri Novotny Malcolm E. Davis Kim A. Sharp 《Journal of computational chemistry》1997,18(2):268-276
A common problem in the calculation of electrostatic potentials with the Poisson-Boltzmann equation using finite difference methods is the effect of molecular position relative to the grid. Previously a uniform charging method was shown to reduce the grid dependence substantially over the point charge model used in commercially available codes. In this article we demonstrate that smoothing the charge and dielectric values on the grid can improve the grid independence, as measured by the spread of calculated values, by another order of magnitude. Calculations of Born ion solvation energies, small molecule solvation energies, the electrostatic field of superoxide dismutase, and protein-protein binding energies are used to demonstrate that this method yields the same results as the point charge model while reducing the positional errors by several orders of magnitude. © 1997 by John Wiley & Sons, Inc. 相似文献
77.
78.
79.
Sarah Sulzer‐Mossé Alexandre Alexakis Prof. Jiri Mareda Dr. Guillaume Bollot Gerald Bernardinelli Dr. Yaroslav Filinchuk Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(13):3204-3220
Chiral framework : Chiral amines with pyrrolidine frameworks catalyze the enantioselective conjugate addition of a wide range of aldehydes to various vinyl sulfones and vinyl phosphonates in high yields and with enantioselectivities up to >99 % ee (see scheme). The high versatility of the Michael adducts is exemplified by various functionalizations with conservation of the optical purity.
80.
Gorteau V Bollot G Mareda J Perez-Velasco A Matile S 《Journal of the American Chemical Society》2006,128(46):14788-14789
We report the design, synthesis, and evaluation of rigid oligonaphthalenediimide (O-NDI) rods that are expected to act as transmembrane anion-pi slides. Studies in fluorogenic large unilamellar egg yolk phosphatidylcholine vesicles reveal that rigid O-NDI rods mediate anion-selective transport with a rare halide VI selectivity sequence (Cl- > F- > Br- > I-). This and decreasing activity, selectivity, and halide sequence with increasing positive charge of the rod termini support the occurrence of anion-pi interactions. A strong anomalous mole fraction effect in Cl-/I- mixtures is in agreement with the existence of multiple active sites along the anion-pi slide and multi-anion hopping as a mechanism of transport. The strong inverted NDI quadruple moment found by DFT calculations is in excellent agreement with these results. 相似文献