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141.
Waste tire powder subjected to allylamine modification in the presence of ultraviolet (UV) radiation has been used to prepare polypropylene based thermoplastic vulcanizates with maleic anhydride polypropylene (MA‐PP) as compatibilizer. The effect of increasing the concentration of MA‐PP on performance characteristics like tensile strength, elongation and rheological properties have been investigated. X‐ray diffraction studies of the PP/waste tire powder blend indicate the disappearance of β crystalline peaks on addition of waste tire powder in the PP, whereas it is observed in the allylamine modified rubber powder loaded PP. Differential scanning calorimetry results further supported the above fact. The improvement in mechanical properties of the PP/allylamine modified rubber powder loaded thermoplastic vulcanizates has been explained in terms of βα transformation of PP crystals during straining of the samples and uniform dispersion of allylamine coated rubber powder in the PP matrix. The melt rheological properties of the thermoplastic vulcanizates loaded with modified rubber powder are higher than its counterpart due to the higher dispersion as a result of chemical interaction between the rubber powder surface with the MA‐PP. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   
142.
[reaction: see text] An efficient protocol has been developed using D-(2R)-Oppolzer sultam as a chiral auxiliary for generating anti/syn diastereomers with high enantiopurity and utilized in the efficient synthesis of natural product belactosin C and their synthetic congeners. It has been observed that a variation in the stoichiometry of the Lewis acid led to a difference in anti/syn selectivity.  相似文献   
143.
The development of devices made of micro- and nano-structured thin film materials has resulted in the need for advanced measurement techniques to characterize their mechanical properties. Photoacoustic techniques, which use pulsed laser irradiation to nondestructively induce very high frequency ultrasound in a test object via rapid thermal expansion, are suitable for nondestructive and non-contact evaluation of thin films. In this paper, we compare two photoacoustic techniques to characterize the mechanical parameters of edge-supported aluminum and silicon nitride double-layer thin films. The elastic properties and residual stresses in such films affect their mechanical performance. In a first set of experiments, a femtosecond transient pump–probe technique is used to investigate the Young’s moduli of the aluminum and silicon nitride layers by launching ultra-high frequency bulk acoustic waves in the films. The measured transient signals are compared with simulated transient thermoelastic signals in multi-layer structures, and the elastic moduli are determined. Independent pump–probe tests on silicon substrate-supported region and unsupported region are in good agreement. In a second set of experiments, dispersion curves of the A0 mode of the Lamb waves that propagate along the unsupported films are measured using a broadband photoacoustic guided-wave method. The residual stresses and flexural rigidities for the same set of double-layer membranes are determined from these dispersion curves. Comparisons of the results obtained by the two photoacoustic techniques are made and discussed.  相似文献   
144.
We demonstrate a hybrid Doppler-free/Doppler-sliced ion imaging approach that is well-suited for detection of H or D atoms. The method relies on 2 + 1 resonant ionization with identical, nearly counterpropagating beams that are coplanar but directed at a small angle relative to the detector face. This results in Doppler selection of the velocity component along the time of flight axis but Doppler-free detection in the plane perpendicular to this axis. The results show high signal level and excellent slicing ( approximately 5%), yielding velocity resolution completely determined by cation recoil in the ionization step.  相似文献   
145.
Ti(III)-mediated radical cyclization of β-aminoacrylate containing 2,3-epoxy alcohol moieties led to the formation of highly substituted piperidine and pyrrolidine rings. The pyrrolidine ring system was then transformed into an indolizidine framework present in many natural products.  相似文献   
146.
Kinetics and equilibria of the axial ligation of alkyl(aquo)cobaloximes by imidazole and cyanide have been measured spectrophotometrically in aqueous solutions of ionic strength 1.0 M at 25°C as a function of pH. Comparison of KIMD and KCN- of CH3, C2H5 and BrCH2cobaloximes indicates that their stability is in the order BrCH2>CH3>C2H2. As the electron-withdrawing capacity of the alkyl grouptrans to water increases, the electron density of the cobalt(III) decreases and thus it becomes a stronger Lewis acid and binds more strongly to imidazole and cyanide. The association and dissociation rate constants are better correlated to the relative softness of the ligand showing that cyanide binds 30 times faster than imidazole. These complexes are isolated and are characterized by IR and1H NMR spectra.  相似文献   
147.
Fundamental challenges in molecular biology can be addressed by using simple models on a lattice, where statistical mechanics and combinatoric techniques can be employed. The basic premise is that it is sensible to test any proposed method on the simplest of models in order to assess their validity before launching a full-scale attack on realistic problems. In this paper we follow this strategy and we present different efficient schemes to perform protein design and to extract effective amino acid interaction potentials.This work was supported in part by INFM, INFN sez. di Trieste, NASA and NATO.  相似文献   
148.
A highly stereoselective synthesis of (+)-cryptocarya diacetate is achieved through our recently developed strategy for the construction of 1,3-diols via Prins cyclisation. The route relies mainly on the reductive cleavage of allylic ethers, ozonolysis and Wittig olefination along with Prins cyclisation.  相似文献   
149.
R. Sridhar 《Tetrahedron letters》2005,46(51):8837-8839
A simple and efficient method for the synthesis of β-hydroxy selenides is reported at room temperature in impressive yields for the first time by the highly the regioselective ring-opening of oxiranes with benzeneselenol in water under supramolecular catalysis in the presence of β-cyclodextrin. This is a direct one-pot synthesis of β-hydroxy selenides under mild conditions using water as solvent and has many advantages over the existing methodologies. β-Cyclodextrin can also be recovered and reused.  相似文献   
150.
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