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51.
The synthesis of molecules bearing (trifluoromethylselenyl)methylchalcogenyl groups is described via an efficient two-step strategy based on a metal-free photoredox catalyzed decarboxylative trifluoromethylselenolation with good yields up to 88 %, which raised to 98 % in flow chemistry conditions. The flow methods allowed also to scale up the reaction. The mechanism of this key reaction was studied. The physicochemical characterization of these emerging groups was performed by determining their Hansch–Leo lipophilicity parameters with high values up to 2.24. This reaction was also extended to perfluoroalkylselenolation with yields up to 95 %. Finally, this method was successfully applied to the functionalization of relevant bioactive molecules such as tocopherol or estrone derivatives.  相似文献   
52.
J. Pouget 《Phase Transitions》2013,86(1-4):251-260
On the basis of a lattice model the domain structure for ferroelastic transformations is examined. The model accounts for both strongly nonlinear and competing interactions which allow for, in some situations, the propagation of nonlinear excitations. The model can be mostly applied to proper ferroelastic transformations of which In-Tl, Ti-Ni, etc.… are good prototypes. The phonon dispersion of the transverse acoustic waves obtained in the linearized case is discussed and the results show first a phonon softening at nonzero wave-number and next an upwards convexity of the phonon branch near the long-wavelength limit. This can be seen as pre-transitional effects. In a fully nonlinear case we consider vanishing dilatation transformations and the continuum approximation is applied to the one-dimensional version. Then, we investigate nonlinear excitations; three main classes of solution are found: i) quasi-harmonic solutions corresponding to periodically modulated structures in space which is a precursor effect of the elastic transformation, ii) an array of solitons made of periodic arrangements of parent-elastic domains and iii) a moving strain soliton. All the significant results are numerically illustrated by means of the microscopic model. Finally, the similarity to martensitic transformations and some extensions of the model are outlined.  相似文献   
53.
Hypoxia is an important contributing factor to the development of drug‐resistant cancer, yet few nonperturbative tools exist for studying oxygenation in tissues. While progress has been made in the development of chemical probes for optical oxygen mapping, penetration of such molecules into poorly perfused or avascular tumor regions remains problematic. A click‐assembled oxygen‐sensing (CAOS) nanoconjugate is reported and its properties demonstrated in an in vitro 3D spheroid cancer model. The synthesis relies on the sequential click‐based ligation of poly(amidoamine)‐like subunits for rapid assembly. Near‐infrared confocal phosphorescence microscopy was used to demonstrate the ability of the CAOS nanoconjugates to penetrate hundreds of micrometers into spheroids within hours and to show their sensitivity to oxygen changes throughout the nodule. This proof‐of‐concept study demonstrates a modular approach that is readily extensible to a wide variety of oxygen and cellular sensors for depth‐resolved imaging in tissue and tissue models.  相似文献   
54.
This article presents the utilization of “molecular amplification” to visualize the molecular architecture of “arborescent” (tree‐like) polystyrenes (arbPSs) using atomic force microscopy (AFM). arbPSs with Mn > 80,000 g/mol were synthesized via initiator‐monomer‐type (inimer) RAFT polymerization of styrene mediated by 4‐vinylbenzyl dithiobenzoate in bulk. These arbPS were then used as macrochain transfer agents for polymerization of vinylbenzyl chloride (VBCl) to give arborescent poly(styrene‐block‐vinylbenzyl chloride) (arbPS‐b‐VBCl). Poly(styryl) diphenylethyl lithium (Mn = 11,000 g/mol) was then grafted onto the VBCl units of the arbPS‐b‐VBCl. The Mn of the amplified arbPSs increased over >10 million g/mol, exceeding the exclusion limit of our size exclusion chromatography equipment. AFM confirmed the proposed branches on branches architecture in the samples, together with lesser branched species. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012  相似文献   
55.
There has been a growing interest in the utilization of sisal fibres as reinforcement in the production of polymeric composite materials. Natural fibres have gained recognition as reinforcements in fibre polymer–matrix composites because of their mechanical properties and environmental friendliness. The mechanical properties of sisal fibre-reinforced polymer composites have been studied by many researchers and a few of them are discussed in this article. Various fibre treatments, which are carried out in order to improve adhesion, leading to improved mechanical properties, are also discussed in this review paper. This review also focuses on the influence of fibre content and fabrication methods, which can significantly affect the mechanical properties of sisal fibre-reinforced polymer composites.  相似文献   
56.
The literature on oxidation kinetics of polyamides and model compounds has been reviewed in order to try to extract suitable information for non-empirical kinetic modeling. Polyamide characteristics are systematically compared to polyolefin ones, these latter being more extensively studied. From kinetic analysis point of view, it is shown that oxidation attacks predominantly α amino methylenes of which C–H bond is considerably weaker than the other methylenes. As a result, propagation by H abstraction is considerably faster in polyamides than in polyethylene for instance. Termination by radical combination is also very fast. Another cause of PA oxidizability is the instability of α amino hydroperoxides linked to the inductive effect of nitrogen. This instability is responsible for many key features of oxidation kinetics especially the absence of induction period.  相似文献   
57.
The synthesis and reactivity of mono‐ and bis‐S‐xanthyl NHC‐boranes is reported. The new NHC‐boranes are prepared through nucleophilic exchange at boron from either mono‐ or bis‐triflyl NHC‐boranes, themselves obtained by protolysis of the NHC‐BH3 starting compounds. The B?H bond of the S‐xanthyl NHC‐boranes can be cleaved both homolytically and heterolytically, albeit the latter is more synthetically useful. The S‐xanthyl NHC‐boranes can reduce both aldehydes and imines. The B?S bond can also be cleaved homolytically. Under UV irradiation, the S‐xanthyl NHC‐boranes generate NHC‐boryl radicals that can initiate radical polymerizations of acrylates.  相似文献   
58.
In this work, we prove the existence and the uniqueness of the strong solution of a low‐Mach model, for which the dynamic viscosity of the fluid is a given function of its temperature. The method is based on the convergence study of a sequence towards the solution, for which the rates are also given. The originality of the approach is to consider the system in terms of the temperature and the velocity, leading to a nonlinear temperature equation and the development of some specific tools and results.  相似文献   
59.
A one-pot methodology to synthesize metastable bicyclic 2,5-dihydrooxepines from cyclic 1,3-diketones and 1,4-dibromo-2-butenes through the retro-Claisen rearrangement of syn-2-vinylcyclopropyl diketone intermediates is reported. DFT calculations were performed to understand the reaction selectivity and mechanisms towards [1,3]- or [3,3]-sigmatropic rearrangements, highlighting the crucial influence of the temperature. The reaction was successfully applied to a short protecting group-free total synthesis of radulanin A, a natural 2,5-dihydrobenzoxepine. Moreover, the strong herbicidal potential of this natural product is demonstrated for the first time.  相似文献   
60.
We study the mechanical response, and tearing features of crêpe paper, a two-dimensional, very anisotropic material, with one direction much less stiff than the other one. Depending on how the soft direction has been pre-stretched or not, the apparent Young modulus of the material can be varied over a broad range, while its fracture energy remains unaltered. The classical tearing concertina problem shows that a macroscopic measurement (the shape of the teared region) provides a direct access to the fracture properties of the material (effective Young's modulus, and fracture energy). The overall discussion is conducted in the frame of Griffith's theory of fracture.  相似文献   
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