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71.
The present paper shows how a standard volumetric adsorption device can be used to measure solvent desorption isotherms on
gels. As gels are very soft materials, they shrink significantly during the measurement, and the data have to be analyzed
in terms of the mechanical properties of the gel’s skeleton. Methanol desorption isotherms are measured on a series of silica
gels, and the results are compared with independent characterizations, notably beam bending. 相似文献
72.
Elementary growth processes such as kink initiation, adding a molecule to a kink, and adding a molecule between two neighboring kinks and between two grains are theoretically studied in pentacene films by adding one molecule at a time to a predefined aggregate. For each molecule, the potential energy surface is calculated using the MM3 molecular mechanics force field, which allowed one to identify useful parameters like the energy barrier for diffusion and the energy to create kinks, as well as defect configurations. Depending on the properties of the potential energy surface and the resulting growth-condition-dependent probabilities of initiating defect configurations in the film, three types of pentacene defects are identified: a thermally activated defect, an intrinsic defect, and a kinetic defect. Upon film growth, most defects relax into the ideal crystal configuration. Bulk defects that resist relaxation have densities lower than 10(16) defects/cm3 at typical growth conditions. Grain boundary defects, on the other hand, are very stable. Moreover, interstitial molecules at grain boundaries are identified as a source of compressive stress. 相似文献
73.
Dr. Bhavana Gupta Mariana C. Afonso Dr. Lin Zhang Dr. Cedric Ayela Patrick Garrigue Dr. Bertrand Goudeau Prof. Alexander Kuhn 《Chemphyschem》2019,20(7):941-945
Combining the actuation of conducting polymers with additional functionalities is an interesting fundamental scientific challenge and increases their application potential. Herein we demonstrate the possibility of direct integration of a miniaturized light emitting diode (LED) in a polypyrrole (PPy) matrix in order to achieve simultaneous wireless actuation and light emission. A light emitting diode is used as a part of an electroactive surface on which electrochemical polymerization allows direct incorporation of the electronic device into the polymer. The resulting free-standing polymer/LED hybrid can be addressed by bipolar electrochemistry to trigger simultaneously oxidation and reduction reactions at its opposite extremities, leading to a controlled deformation and an electron flow through the integrated LED. Such a dual response in the form of actuation and light emission opens up interesting perspectives in the field of microrobotics. 相似文献
74.
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76.
Mezzenga R Grigorov M Zhang Z Servais C Sagalowicz L Romoscanu AI Khanna V Meyer C 《Langmuir : the ACS journal of surfaces and colloids》2005,21(14):6165-6169
We report on the order-to-order transitions of lyotropic liquid crystals formed by self-assembled monogylcerides and water in the presence of polysaccharides of various molecular weights. The phase diagram of monoglyceride-water-polysaccharide systems, their morphology, and the topology of liquid crystalline structures were determined by combining optical cross-polarization, oscillatory shear rheometry, and small-angle X-ray scattering. The presence of hydrophilic mono-, oligo-, and polysaccharides in the water domains of liquid crystalline phases resulted in a general decrease of the cubic-to-hexagonal transition temperature. Provided that the sugar could fit within the water channels, the decrease was observed to be dependent on the polysaccharide concentration but independent of its molecular weight. For isotropic bicontinuous cubic phases, monomeric sugars such as glucose were reported to shrink the lattice parameter of the structure without inducing phase transitions. However, when a polymeric form of glucose was used, such as dextran, transitions from the gyroidal Ia3d cubic phase to double diamond Pn3m cubic phases were observed at well-defined molecular weights of polysaccharide. These results were interpreted in terms of size exclusions of polymer sugars by the water domains of the liquid crystal phases as well as the different topologies of water channels. Molecular dynamics simulations of polysaccharides in the water environment were performed to support these findings. 相似文献
77.
Lubda D Lindner W Quaglia M du Fresne von Hohenesche C Unger KK 《Journal of chromatography. A》2005,1083(1-2):14-22
The porosity of monolithic silica columns is measured by using different analytical methods. Two sets of monoliths were prepared with a given mesopore diameter of 10 and 25 nm, respectively and with gradated macropore diameters between 1.8 and 7.5 microm. After preparing the two sets of monolithic silica columns with different macro- and mesopores the internal, external and total porosity of these columns are determined by inverse size-exclusion chromatography (ISEC) using polystyrene samples of narrow molecular size distribution and known average molecular weight. The ISEC data from the 4.6 mm analytical monolithic silica columns are used to determine the structural properties of monolithic silica capillaries (100 microm I.D.) prepared as a third set of samples. The ISEC results illustrate a multimodal mesopore structure (mesopores are pores with stagnant zones) of the monoliths. It is found by ISEC that the ratio of the different types of pores is dependent on the change in diameter of the macropores (serve as flow-through pores). The porosity data achieved from the mercury penetration measurement and nitrogen adsorption as well of scanning electron microscopy (SEM) and transmission electron microscopy (TEM) pictures are correlated with the results we calculated from the ISEC measurements. The ISEC results, namely the multimodal pore structure of the monoliths, reported in several publications, are not confirmed analyzing the pore structures of the different silica monoliths using all other analytical methods. 相似文献
78.
Dr. Cedric Tassel Yoshinori Goto Daichi Watabe Ya Tang Dr. Honcheng Lu Yoshinori Kuno Fumitaka Takeiri Dr. Takafumi Yamamoto Dr. Craig M. Brown Dr. James Hester Dr. Yoji Kobayashi Prof. Hiroshi Kageyama 《Angewandte Chemie (International ed. in English)》2016,55(33):9667-9670
The high‐pressure synthesis of a manganese oxyhydride LaSrMnO3.3H0.7 is reported. Neutron and X‐ray Rietveld analyses showed that this compound adopts the K2NiF4 structure with hydride ions positioned exclusively at the equatorial site. This result makes a striking contrast to topochemical reductions of LaSrMnO4 that result in only oxygen‐deficient phases down to LaSrMnO3.5. This suggests that high H2 pressure plays a key role in stabilizing the oxyhydride phase, offering an opportunity to synthesize other transition‐metal oxyhydrides. Magnetic susceptibility revealed a spin‐glass transition at 24 K that is due to competing ferromagnetic (Mn2+–Mn3+) and antiferromagnetic (Mn2+–Mn2, Mn3+–Mn3+) interactions. 相似文献
79.
Copper bromide complexed by fluorinated macroligands: towards microspheres by ATRP of vinyl monomers in scCO2 总被引:1,自引:0,他引:1
Grignard B Jérôme C Calberg C Jérôme R Wang W Howdle SM Detrembleur C 《Chemical communications (Cambridge, England)》2008,(3):314-316
We report the successful synthesis of poly(methyl methacrylate) (PMMA) by atom transfer radical polymerization using a catalyst ligated to a polymeric ligand having a dual role, i.e., the complexation of the copper salt and the stabilization of the growing PMMA particles; at the end of the polymerization, the catalyst is removed by supercritical fluid extraction leading to PMMA microspheres with low residual catalyst content. 相似文献
80.
Celine Marie Leroy Thierry Cardinal Veronique Jubera Dr. Mona Treguer‐Delapierre Dr. Jerome Majimel Jean Pierre Manaud Renal Backov Dr. Cedric Boissière Dr. David Grosso Prof. Clement Sanchez Dr. Bruno Viana Dr. Fabienne Pellé 《Chemphyschem》2008,9(14):2077-2084
Herein, EuIII‐doped 3D mesoscopically ordered arrays of mesoporous and nanocrystalline titania are prepared and studied. The rare‐earth‐doped titania thin films—synthesized via evaporation‐induced self‐assembly (EISA)—are characterized by using environmental ellipsoporosimetry, electronic microscopy (i.e. high‐resolution scanning electron microscopy, HR‐SEM, and transmission electron microscopy, HR‐TEM), X‐ray diffraction, and luminescence spectroscopy. Structural characterizations show that high europium‐ion loadings can be incorporated into the titanium‐dioxide walls without destroying the mesoporous arrangement. The luminescence properties of EuIII are investigated by using steady‐state and time‐resolved spectroscopy via excitation of the EuIII ions through the titania host. Using EuIII luminescence as a probe, the europium‐ion sites can be addressed with at least two different environments within the mesoporous framework, namely, a nanocrystalline environment and a glasslike one. Emission fluctuations (5D0→7F2) are observed upon continuous UV excitation in the host matrix. These fluctuations are attributed to charge trapping and appear to be strongly dependent on the amount of europium and the level of crystallinity. 相似文献