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31.
Ye X Yu A Georgiev GY Gruia F Ionascu D Cao W Sage JT Champion PM 《Journal of the American Chemical Society》2005,127(16):5854-5861
The rebinding kinetics of CO to protoheme (FePPIX) in the presence and absence of a proximal imidazole ligand reveals the magnitude of the rebinding barrier associated with proximal histidine ligation. The ligation states of the heme under different solvent conditions are also investigated using both equilibrium and transient spectroscopy. In the absence of imidazole, a weak ligand (probably water) is bound on the proximal side of the FePPIX-CO adduct. When the heme is encapsulated in micelles of cetyltrimethylammonium bromide (CTAB), photolysis of FePPIX-CO induces a complicated set of proximal ligation changes. In contrast, the use of glycerol-water solutions leads to a simple two-state geminate kinetic response with rapid (10-100 ps) CO recombination and a geminate amplitude that can be controlled by adjusting the solvent viscosity. By comparing the rate of CO rebinding to protoheme in glycerol solution with and without a bound proximal imidazole ligand, we find the enthalpic contribution to the proximal rebinding barrier, H(p), to be 11 +/- 2 kJ/mol. Further comparison of the CO rebinding rate of the imidazole bound protoheme with the analogous rate in myoglobin (Mb) leads to a determination of the difference in their distal free energy barriers: DeltaG(D) approximately 12 +/- 1 kJ/mol. Estimates of the entropic contributions, due to the ligand accessible volumes in the distal pocket and the xenon-4 cavity of myoglobin ( approximately 3 kJ/mol), then lead to a distal pocket enthalpic barrier of H(D) approximately 9 +/- 2 kJ/mol. These results agree well with the predictions of a simple model and with previous independent room-temperature measurements of the enthalpic MbCO rebinding barrier (18 +/- 2 kJ/mol). 相似文献
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34.
A. Meftah J.-F. Wyart N. Champion L. Tchang-Brillet 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,44(1):35-45
The emission spectrum of thulium produced by a vacuum spark source was observed in
the wavelength range from 700 to 2320 ? on the 10.7 m normal-incidence vacuum ultraviolet spectrograph
at the Paris-Meudon observatory. In the unknown spectrum of Tm IV, more than 760 lines have been identified for the first
time as transitions
between 157 levels of 4f115d, 33 levels of 4f116p, 9 levels of 4f116s and 10 levels of the 4f12 ground
configuration. A parametric interpretation of the levels has been carried out using the Cowan codes.
Configuration interaction effects are discussed, in particular with the core-excited configurations 5p54f13 and 5p54f125d.
Radial Slater parameters derived from 4f12 levels are larger than those pertaining to trivalent Tm ions
in compounds. A selection of 105 prominent lines is given. 相似文献
35.
M. LoBue F. Mazaleyrat M. Ammar R. Barrué Y. Champion S. Faure M. H?tch E. Snoeck J. Steiner F. Alouges 《Journal of magnetism and magnetic materials》2010,322(9-12):1290-1292
We use an approximate micromagnetic model, based on geometrical simplifications of the problem, to describe the vortex core structure observed in spherical Permalloy nanoparticles using off-axis electron holography. The magnetisation distribution inside the vortex core is directly calculated by minimising the micromagnetic energy functional and is compared with the experimental results. The symmetry constraints underlying the model are discussed envisaging possible generalisation to the case of vortex cores with structure strongly dependent on the coordinate directed along the axis of the vortex. Moreover the many-body effect associated with the presence of two small satellite particles is described by rescaling the size of the particle. 相似文献
36.
Geiser F Schultz M Betz L Shaimi M Lee J Champion W 《Journal of chromatography. A》1999,865(1-2):227-233
In this paper, we describe the direct, preparative enantioselective chromatography of racemic (rac)-propranolol hydrochloride (HCI) and rac-thioridazine.HCl using Chiralpak AD chiral stationary phase and mobile phase systems containing carbon dioxide and methanol without the use of basic or acidic additives. Isolated fractions of propranolol.HCl were positively identified by mass spectrometry, Beilstein flame test, melting point, and chemical analysis to be HCI enantiomers of propranolol-HCl salts exhibited characteristic mass spectra peaks at 36 and 38 mass-to-charge ratio in the expected 3:1 isotopic ratio for the solute that were absent in the mass spectra for the free-base forms. To our knowledge, the direct, preparative enantioselective isolation of HCI enantiomeric salts of rac-propranolol and of rac-thioridazine have not been previously demonstrated and published. 相似文献
37.
The functional Ito formula, in the form df() = f( + d ) f(),is formulated and proved in the context of a Lie algebra L associatedwith a quantum (non-commutative) stochastic calculus. Here fis an element of the universal enveloping algebra U of L, andf() + d() f() is given a meaning using the coproductstructure of U even though the individual terms of this expressionhave no meaning. The Ito formula is equivalent to a chaoticexpansion formula for f() which is found explicitly. 1991 MathematicsSubject Classification: primary 81S25; secondary 60H05; tertiary18B25. 相似文献
38.
The (t approximately 0) photodissociation quantum yields (Y(0)) of MbNO and MbO(2) are measured to be 50 +/- 5 and 28 +/- 6%, respectively, using MbCO (Y(0) = 100%) as a reference. When photolysis does not take place, we find that a significant portion of the photon energy contributes to heating of the residual six-coordinate heme (MbNO and MbO(2)). The time constant for vibrational relaxation of the six-coordinate ligand-bound heme is found to be close to 1 ps for both samples. The MbO(2) sample also shows a approximately 4-ps optical response that is assigned to a rapid phase (25-30% amplitude) of O(2) geminate rebinding. We observe no additional geminate recombination in the MbO(2) sample out to 120 ps. In contrast, the MbNO sample displays significant geminate recombination over the first 120 ps, which can be adequately fit with two exponentials whose amplitudes and time constants appear to depend weakly on the pump wavelength. This more complex kinetic behavior conceivably arises due to heating of the photodissociated heme and its effect on the geminate recombination as the system cools. Overall, the data are consistent with a hypothesis that distortions along the iron-ligand bending coordinate play a key role in the photodissociation process. The transient formation of an unphotolyzable FeO(2) side-on binding geometry is suggested to be responsible for the lowered quantum yield of MbO(2) relative to MbNO. 相似文献
39.
Mark T. Holtzapple Richard R. Davison M. Kyle Ross Salvador Aldrett-Lee Murlidhar Nagwani Chang-Ming Lee Champion Lee Seth Adelson William Kaar David Gaskin Hiroshi Shirage Nan-Sheng Chang Vincent S. Chang Mitchell E. Loescher 《Applied biochemistry and biotechnology》1999,79(1-3):609-631
The MixAlco process is a patented technology that converts any biodegradable material (e.g., sorted municipal solid waste,
sewage sludge, industrial biosludge, manure, agricultural residues, energy crops) into mixed alcohol fuels containing predominantly
2-propanol, but also higher alcohols up to 7-tridecanol. The feed stock is treated with lime to increase its digestibility.
then, it is fed to a fermentor in which a mixed culture of acid-forming microorganisms produces carboxylic acids. Calcium
carbonate is added to the fermentor to neutralize the acids to their corresponding carboxylate salt. The dilute (−3%) carboxylate
salts are concentrated to 19% using an amine solvent that selectively extracts water. Drying is completed using multi-effect
evaporators. Finally, the dry salts are thermally converted to ketones which subsequently are hydrogenated to alcohols. All
the steps in the MixAlco process have been proven at the laboratory scale. A techno-economic model of the process indicates
that with the tipping fees available in New York ($126/dry tonne), mixed alcohol fuels may be sold for $0.04/L ($0.16/gal)
with a 60% return on investment (ROI). With the average tipping fee in the United States rates ($63/dry tonne), mixed alcohol
fuels may be sold for $0.18/L ($0.69/gal) with a 15% ROI. In the case of sugarcane bagasse, which may be obtained for about
$26/dry ton, mixed alcohol fuels may be sold for $0.29/L ($1.09/gal) with a 15% ROI. 相似文献
40.