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181.
Kahr B  Arteaga O 《Chemphyschem》2012,13(1):79-88
The year 2011 is the bicentennial of François Arago’s discovery of optical rotation. The immediate usurpation of the study of optical activity by Jean‐Baptiste Biot led to the first well‐known judgments of the arrangements of atoms in space. Scientists are less aware that Arago achieved something far greater than his contributions to optics, by signing the 1848 decree that abolished slavery throughout the French Empire. Opposing attitudes of Arago and Biot toward abolition, foreshadowed in their early rift over optical rotation, were surprisingly exposed in mid‐century developments in chiroptics. As shown in a recent book by Levitt, Arago sought a reinvention of the whole colonial plantation system consistent with Republican principles, while Biot tried to place the cane sugar industry and slave‐based economy on the quantitative foundation of saccharimetry. A reevaluation of the circumstances of abolition can celebrate both societal evolution and optical rotation on the 200th birthday of the latter. Episodes from Arago’s life that arguably created his predisposition toward abolition are emphasized: He was imprisoned several times as a young man and knew the loss of liberty, his brother Jacques witnessed slavery in Brazil and advocated abolition in travel books prepared with François, and finally, in writing the biography of the Marquis de Condorcet, the spirit behind the first, albeit impermanent French abolition of slavery in 1794, Arago found proof of concept for his comparable challenge. Curiously, the measurement of the optical rotation of crystals and sugar, the foci of Arago and Biot, respectively, remain among the greatest challenges in polarimetry. Current developments are reviewed with respect to chiroptical anisotropy and in vivo glucose detection driven by the pandemic of diabetes, a disease diagnosed polarimetrically by Biot that claimed the life of Arago.  相似文献   
182.
We present an experimental study on the first stages of the thin film growth of the organic molecule F(16)CuPc (hexadecafluoro-copper-phthalocyanines) on SiO(2). By means of in situ X-ray reflectivity, in situ grazing incidence X-ray diffraction (GIXD), and ex situ atomic force microscopy (AFM), we provide a detailed picture of the film growth mode and its structural evolution at the nanometer scale. We discovered the formation of a low-density layer of molecular aggregates with heights between 5 and 10 A at the interface with the SiO(2) and show that, on top of this interfacial layer, the nucleation and two-dimensional growth of elongated islands of upright standing molecules take place. Structural changes are observed, pointing to significant relaxations of the lattice parameters within the first layers of standing molecules.  相似文献   
183.
We report the self-organization of organic nanodots with high crystallinity during the growth of organic heterostructures of Di-indenoperylene (DIP) onto copper-hexadecafluorophthalocyanine (F16CuPc), donor and acceptor molecules, respectively. The process is related to the Stranski-Krastanov growth mode, which is accompanied by a novel type of structural reconstruction of the underlying organic film. This reconstruction affects three monolayers adjacent to the organic interface. In spite of the close resemblance to the formation of semiconductor nanostructures for inorganic heteroepitaxy, the present results conclusively demonstrate a distinctly different growth mechanism for organic heteroepitaxy whose understanding demands further theoretical studies.  相似文献   
184.
We give tight lower bounds on the cardinality of the sumset of two finite, nonempty subsets A,BR2 in terms of the minimum number h1(A,B) of parallel lines covering each of A and B. We show that, if h1(A,B)?s and |A|?|B|?2s2−3s+2, then
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185.
The design, construction and evaluation of a low cost, cyclic olefin copolymer (COC)-based continuous flow microanalyzer, with optical detection, to monitor carbon dioxide in bottled wines and beers as well as in fermentation processes, is presented. The microsystem, constructed by computer numerically controlled (CNC) micromilling and using a multilayer approach, integrates microfluidics, gas-diffusion module and an optical flow-cell in a single polymeric substrate. Its size is slightly bigger than a credit card, exactly 45 × 60 × 4 mm in the microfluidic and diffusion module zone and 22.5 × 40 × 3 mm in the flow-cell zone. The gas-diffusion module is based on a hydrophobic polyvinylidene fluoride (PVDF) membrane, which allows the transfer of the carbon dioxide present in the sample to a bromothymol blue (BTB) pH-sensitive acceptor solution, where the color change is measured optically. The detection system consisted of a LED with an emission peak at 607 nm and a photodiode integrated in a printed circuit board (PCB). The obtained analytical features after the optimization of the microfluidic platform and hydrodynamic variables are a linear range from 255 to 10000 mg L−1 of CO2 and a detection limit of 83 mg L−1 with a sampling rate of 30 samples h−1.  相似文献   
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Combined high pressure single crystal X-ray diffraction experiments and ab initio simulations based on the density functional theory have been performed on a copper(I) iodide cluster formulated [Cu4I4{PPh2(CH2CH?=?CH2)}4] under high pressure up to 5?GPa. An exhaustive study of compressibility has been done by means of determination of isothermal equations of state and structural changes with pressure at 298?K taking advantage of the single crystal is more precise than powder X-ray diffraction for this type of experiments. It allows us to report the evidence of the existence of an isostructural phase transition of second order at 2.3?GPa not detected so far.  相似文献   
190.
The magnetic field and temperature dependencies of the magnetic moments of superconducting crystals of V3Si have been studied. In a constant magnetic field and at temperatures somewhat below the superconducting transition temperature, the moments are hysteretic in temperature. However, the magnetic moment–magnetic field isotherms are reversible and exhibit features that formally resemble the pressure–volume isotherms of the liquid–gas transition. This suggests the existence of a first-order phase transition, a two-phase regime, and a critical point in the superconducting phase diagram. The two phases are disordered vortex configurations with the same magnetization, but with different vortex densities. The entropy change, determined from the data using the Clausius–Clapeyron equation, is consistent with estimates based on the difference in the vortex densities of the two phases.  相似文献   
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