全文获取类型
收费全文 | 143篇 |
免费 | 5篇 |
专业分类
化学 | 93篇 |
晶体学 | 1篇 |
数学 | 11篇 |
物理学 | 43篇 |
出版年
2020年 | 1篇 |
2016年 | 4篇 |
2015年 | 1篇 |
2014年 | 3篇 |
2013年 | 6篇 |
2012年 | 6篇 |
2011年 | 6篇 |
2010年 | 4篇 |
2009年 | 4篇 |
2008年 | 13篇 |
2007年 | 5篇 |
2006年 | 7篇 |
2005年 | 15篇 |
2004年 | 10篇 |
2003年 | 9篇 |
2002年 | 5篇 |
2001年 | 2篇 |
2000年 | 4篇 |
1996年 | 3篇 |
1995年 | 2篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1990年 | 3篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1987年 | 3篇 |
1986年 | 1篇 |
1985年 | 3篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1976年 | 2篇 |
1974年 | 1篇 |
1972年 | 1篇 |
1971年 | 1篇 |
1968年 | 2篇 |
1967年 | 1篇 |
1939年 | 1篇 |
1871年 | 1篇 |
排序方式: 共有148条查询结果,搜索用时 115 毫秒
1.
Oxidative Addition to Palladium(0) Diphosphine Complexes: Observations of Mechanistic Complexity with Iodobenzene as Reactant 下载免费PDF全文
Dr. Almira Kurbangalieva Dr. Duncan Carmichael Dr. K. K. Hii Dr. Anny Jutand Dr. John M. Brown 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(4):1116-1125
Using a combination of electrochemical and NMR techniques, the oxidative addition of PhX to three closely related bis‐diphosphine P2Pd0 complexes, where the steric bulk of just one substituent was varied, has been analysed quantitatively. For the complex derived from MetBu2P, a rapid reaction ensued with PhI following an associative mechanism, and data was also obtained by cyclic voltammetry for PhOTs, PhBr and PhCl, revealing distinct relative reactivities from the related (PCx3)2Pd complex (Cx=cyclohexyl) previously studied. The corresponding EttBu2P complex reacted more slowly with PhI and was studied by NMR spectroscopy. The reaction course indicated a mixture of pathways, with contribution from a component that was [PhI] independent. For the CxtBu2P complex, reaction was again monitored by NMR spectroscopy, and was even slower. At high PhI concentrations reaction was predominantly linear in [PhI], but at lower concentrations the [PhI] independent pathway was again observed, and an accelerating influence of the reaction product was observed over the concentration range. The NMR spectra of the EttBu2P and CxtBu2P complexes conducted in C6D6 shows some line broadening that was augmented on addition of PhI. NMR experiments carried out in parallel show that there is rapid ligand exchange between free phosphine and the Pd2Pd complex and also a slow ligand crossover between different P2Pd complexes. DFT calculations were carried out to further test the feasibility of C6D6 involvement in the oxidative addition process, and located Van der Waals complexes for association of the P2Pd0 complexes with either PhI or benzene. PhI or solvent‐assisted pathways for ligand loss are both lower in energy than direct ligand dissociation. Taken all together, these results provide a consistent explanation for the surprising complexity of an apparently simple reaction step. The clear dividing line between reactions that give a di‐ or monophosphine palladium complex after oxidative addition clarifies the participation of the ligand in coupling catalysis. 相似文献
2.
Nam T. Nguyen Edward Greenhalgh Mohd J. Kamaruddin Jaouad El harfi Kim Carmichael Georgios Dimitrakis Samuel W. Kingman John P. Robinson Derek J. Irvine 《Tetrahedron》2014
This paper reports the first detailed study focussed upon identifying the influence that microwave heating (MWH) has upon the mechanic steps involved in the tin catalysed ring-opening of lactones such as ?-caprolactone (CL). Direct comparison of conventional (CH) and microwave (MWH) heated kinetic studies showed that a key factor in the reduction of the polymerisation cycle time with MWH was the elimination of the induction period associated with in situ catalyst manufacture and initiation. NMR studies demonstrated that the most significant mechanistic change contributing to the observed induction time reduction/elimination was faster initiation (i.e., reaction of the initiatior/catalyst complex with the first monomer unit). Consequently, analysis of the dielectric properties of the reaction components predicted that this MWH induced change was related to the selective volumetric heating of both the catalyst and the monomer. Furthermore, this indication of the greater significance of the initiation step in defining the length of the induction period suggests that this is the rate determining step of the process, whether conducted by CH or MWH. Increasing the catalyst concentration was demonstrated to produce significant reductions in reaction heat-up time and to induce a significant (up to 30 °C) overshoot in reaction mixture bulk temperature in with MWH only. Thus supporting the conclusion that selective heating of the organometallic species in the system contributes directly to differences in the reaction conditions and which need to be taken into account when drawing comparisons with CH systems. Consequently, both effects were concluded to be thermally generated from selective volumetric heating. 相似文献
3.
A Complex Adaptive System is a collection of autonomous, heterogeneous agents, whose behavior is defined with a limited number of rules. A Game Theory is a mathematical construct that assumes a small number of rational players who have a limited number of actions or strategies available to them. The CAS method has the potential to alleviate some of the shortcomings of GT. On the other hand, CAS researchers are always looking for a realistic way to define interactions among agents. GT offers an attractive option for defining the rules of such interactions in a way that is both potentially consistent with observed real‐world behavior and subject to mathematical interpretation. This article reports on the results of an effort to build a CAS system that utilizes GT for determining the actions of individual agents. © 2009 Wiley Periodicals, Inc. Complexity, 16,24–42, 2010 相似文献
4.
5.
J A Meriluoto J E Eriksson K Harada A M Dahlem K Sivonen W W Carmichael 《Journal of chromatography. A》1990,509(2):390-395
6.
Gregory R. Carmichael Adrian Sandu Tianfeng Chai Dacian N. Daescu Emil M. Constantinescu Youhua Tang 《Journal of computational physics》2008,227(7):3540-3571
Air quality prediction plays an important role in the management of our environment. Computational power and efficiencies have advanced to the point where chemical transport models can predict pollution in an urban air shed with spatial resolution less than a kilometer, and cover the globe with a horizontal resolution of less than 50 km. Predicting air quality remains a challenge due to the complexity of the governing processes and the strong coupling across scales. While air quality prediction is closely aligned with weather prediction, there are important differences, including the role of pollution emissions and their associated large uncertainties. Improvements in air quality prediction require a close integration of observations. As more atmospheric chemical observations become available chemical data assimilation is expected to play an essential role in air quality forecasting. In this paper advances in air quality forecasting are discussed with an emphasis on data assimilation. Applications of the four-dimensional variational method (4D-Var) and the ensemble Kalman filter (EnKF) approach are presented and the computation challenges are discussed. 相似文献
7.
Grazyna Strzelczak Edyta Janeba-Bartoszewicz Ian Carmichael Bronislaw Marciniak Krzysztof Bobrowski 《Research on Chemical Intermediates》2009,35(4):507-517
Radicals formed in γ-irradiated 1,3,5-trithiane (TT) and its three derivatives, α- and β-2,4,6-trimethyl-1,3,5-trithiane (α-TMT
and β-TMT), and 2,4,6-trimethyl-2,4,6-triphenyl-1,3,5-trithiane (TMTPT), were studied by the electron paramagnetic resonance
(EPR) method in the solid state. The sulfur radical cations (>S+•) were identified in all compounds at 77 K. In TT and its two derivatives, α-TMT and β-TMT, the >S+• decay via deprotonation-forming C-centered radicals. Further increase of temperature up to 293 K results in the appearance
of thiyl-type radicals (RS•). In TMTPT, the >S+• are stable up to 250 K. They formed the intermolecularly three-electron-bonded dimeric radical cations (S∴S)+ while RS• radicals were not observed. Some of the radical assignments and their EPR parameters (g and a hyperfine splittings) obtained support from the DFT calculations. 相似文献
8.
D. G. Carmichael 《Mathematical Methods of Operations Research》1986,30(6):B127-B134
Service operations involving an intermediate store are modelled using an extended definition of the system state which is a conventional definition of state supplemented with an indicator of the live capacity in the store. Additional to the parameters of mean service rate and mean arrival rate, a mean discharge rate of the store is introduced and the steady state probabilities are calculated in terms of these three quantities. Both finite source and infinite source cases are considered under the assumption of exponential distributions. The models permit production comparisons for systems with and for systems without storage devices. 相似文献
9.
Squeezing of the intracavity field in a degenerate parametric oscillator is calculated above threshold neglecting pump depletion. Arbitrary squeezing is in principle obtainable. We conclude that above threshold squeezing in the steady-state parametric oscillator is limited primarily by pump depletion rather than degradation by vacuum fluctuations at the mirrors. The squeezing predicted by the present calculation should be observable in an oscillator operated in a transient or pulsed mode 相似文献
10.
A two-level model for absorptive and dispersive bistability in a Fabry-Perot is described. Doppler broadening and the effects of atomic motion through the standing wave field are included. Numerical results illustrating saturation of the Doppler line are presented and bistable transmission characteristics are obtained for systems with varying degrees of Doppler broadening. 相似文献