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101.
DR. E. W. J. Mitchell 《Contemporary Physics》2013,54(3):217-222
The accurate measurement of the thermal conductivity of metals still poses considerable experimental difficulty. The reasons for this, and the main ways in which the problem has been approached, are summarized. A detailed examination of the development in technique and methods of measurement shows that while most of the steady-state methods introduced over 50 years ago are still being improved, the emphasis in the last few years has been on the development of methods which give more rapid results, particularly at high temperatures. 相似文献
102.
A. G. J. MacFarlane 《International Journal of Mathematical Education in Science & Technology》2013,44(4):359-366
The role played by the concepts of characteristic values and characteristic functions in modern control theory is briefly outlined. It is then shown that, by introducing the idea of a characteristic transfer function, the classical stability theorem of Nyquist can be extended to the general multivariable feedback system. 相似文献
103.
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105.
Juan Crugeiras Howard Maskill William MacFarlane Iain D. Menneer Ana Rios Miguel A. Rios 《Journal of Physical Organic Chemistry》2011,24(2):162-171
The effect of acidity upon the rate of nitrosation of N‐benzyl,O‐methylhydroxylamine ( 3 ) in 1:1 (v/v) H2O/MeOH at 25 °C has been investigated. The pseudo‐first‐order rate constant (kobs) for loss of HNO2 as the limiting reagent decreases as [H3O+] increases. This is compatible with two parallel reaction channels (Scheme 2 ). One involves the direct reaction of the free hydroxylamine with HNO2 (k1 = 1.4 × 102 dm3 mol?1 s?1, 25 °C) and the other involves the reaction of the free hydroxylamine with NO+ (k2 = 5.9 × 109 dm3 mol?1 s?1). In contrast, there is only a very slight increase in kobs with increasing [H3O+] for nitrosation of N,O‐dimethylhydroxylamine ( 4 ) in dilute aqueous solution at 25 °C to give N‐nitroso‐dimethylhydroxylamine, 5 . This also fits a two‐channel mechanism (Scheme 3 ). Again, one involves the nitrosation of the free base by NO+ (k2 = 8 × 109 dm3 mol?1 s?1, 25 °C) but the other channel now involves catalysis by chloride (k3 = 1.3 × 108 dm3 mol?1 s?1). Arising from these results, we propose an estimate of pKa ~ ?5 for protonated nitrous acid, (O = N? OH), which is appreciably different from the literature value of +1.7. The interconversion of cis and trans conformational isomers of 5 has been investigated by temperature‐dependent NMR spectroscopy in CDCl3, methanol‐d4, toluene‐d8 and dimethyl sulfoxide‐d6. Enthalpies and entropies of reaction and of activation have been determined and compared with computational values obtained at the B3LYP/6‐31G* level of theory. The cis form is slightly more stable at normal temperatures and no solvent effects upon the thermodynamics or kinetics of the conformational equilibrium were predicted computationally or detected experimentally. In addition, key geometric parameters and dipole moments have been calculated for the cis and trans forms, and for the lowest energy transition structure for their interconversion, in the gas phase and in chloroform. These results indicate electronic delocalisation in the ground states of 5 which is lost in the transition structure for their interconversion. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
106.
Somers AE Biddulph SM Howlett PC Sun J MacFarlane DR Forsyth M 《Physical chemistry chemical physics : PCCP》2012,14(22):8224-8231
Ionic liquids have been shown to be highly effective lubricants for a steel on aluminium system. This work shows that the chemistry of the anion and cation are critical in achieving maximum wear protection. The performance of the ILs containing a diphenylphosphate (DPP) anion all showed low wear, as did some of the tris(pentafluoroethyl)trifluorophosphate (FAP) and bis(trifluoromethanesulfonyl)amide (NTf(2)) anion containing ILs. However, in the case of the FAP and NTf(2) based systems, a cation dependence was observed, with relatively poor wear resistance obtained in the case of an imidazolium FAP and two pyrrolidinium NTf(2) salts, probably due to tribocorrosion caused by the fluorine reaction with the aluminium substrate. The systems exhibiting poor performance generally had a lower viscosity, which also impacts on their tribological properties. Those ILs that exhibited low wear were shown to have formed protective tribofilms on the aluminium alloy surface. 相似文献
107.
A few years ago, Strathclyde University's postgraduate course in OR was redesigned. A significant innovation was to introduce a short working placement part-way through the course-the ‘apprenticeship’ period - which students spend as temporary members of real-life OR (or directly-related) groups. This paper reports on two aspects of this apprenticeship scheme; how it has worked as an educational exercise, and what the students' experiences have told us about the general state of OR in the UK 相似文献
108.
Chakhalian JA Kiefl RF Miller R Brewer J Dunsiger SR Morris G MacFarlane WA Sonier JE Eggert S Affleck I Keren A Verdaguer M 《Physical review letters》2003,91(2):027202
We report muon spin rotation measurements of the local magnetic susceptibility around a positive muon in the paramagnetic state of the quasi-one-dimensional spin 1/2 antiferromagnet dichlorobis (pyridine) copper (II). Signals from three distinct sites are resolved and have a temperature dependent frequency shift which is significantly different than the magnetic susceptibility. This difference is attributed to a muon induced perturbation of the spin 1/2 chain. The obtained frequency shifts are compared with transfer matrix density-matrix renormalization-group numerical simulations. 相似文献
109.
Bobroff J Alloul H MacFarlane WA Mendels P Blanchard N Collin G Marucco JF 《Physical review letters》2001,86(18):4116-4119
Using 7Li NMR shift data, the anomalous local moment induced by spinless Li impurities persists below T(c) in YBa 2Cu 3O6+y. In the underdoped regime, the moments retain their Curie law below Tc. In contrast, near optimal doping, the large Kondo screening observed above Tc (TK = 135 K) is strongly reduced below Tc as expected theoretically when the superconducting gap develops. The limited spatial extent of the induced moment (on first near neighbor Cu) is not drastically modified below Tc, which allows a comparison with STM determination of the local density of states. Our results constrain theoretical models of the impurity electronic properties. 相似文献
110.