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991.
Chantalle J. Krajewska Sen R. Kavanagh Lina Zhang Dominik J. Kubicki Krishanu Dey Krzysztof Gakowski Clare P. Grey Samuel D. Stranks Aron Walsh David O. Scanlon Robert G. Palgrave 《Chemical science》2021,12(44):14686
Lead-free halides with perovskite-related structures, such as the vacancy-ordered perovskite Cs3Bi2Br9, are of interest for photovoltaic and optoelectronic applications. We find that addition of SnBr2 to the solution-phase synthesis of Cs3Bi2Br9 leads to substitution of up to 7% of the Bi(iii) ions by equal quantities of Sn(ii) and Sn(iv). The nature of the substitutional defects was studied by X-ray diffraction, 133Cs and 119Sn solid state NMR, X-ray photoelectron spectroscopy and density functional theory calculations. The resulting mixed-valence compounds show intense visible and near infrared absorption due to intervalence charge transfer, as well as electronic transitions to and from localised Sn-based states within the band gap. Sn(ii) and Sn(iv) defects preferentially occupy neighbouring B-cation sites, forming a double-substitution complex. Unusually for a Sn(ii) compound, the material shows minimal changes in optical and structural properties after 12 months storage in air. Our calculations suggest the stabilisation of Sn(ii) within the double substitution complex contributes to this unusual stability. These results expand upon research on inorganic mixed-valent halides to a new, layered structure, and offer insights into the tuning, doping mechanisms, and structure–property relationships of lead-free vacancy-ordered perovskite structures.Mixed valence Sn doping of Cs3Bi2Br9 leads to broad visible light absorption. 相似文献
992.
993.
Semi‐interpenetrating polymer network (semi‐IPN) coatings were prepared by using castor oil‐based polyurethane (PU) and nitrocellulose (NC) with various viscosity‐average molecular weights (Mη) from 6 × 104 to 42 × 104, and coated on a regenerated cellulose (RC) film to obtain water‐resistant film. The PU/NC coatings and coated films, which were cured at 80°C for 5 min and 2 min, respectively, were investigated by infrared (IR) and ultraviolet (UV) spectroscopy, X‐ray diffraction, swelling test, strength test, dynamic mechanical thermal analysis (DMTA), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). The results show that the crosslink densities of the PU/NC semi‐IPNs were smaller than that of pure PU, and decreased with the decrease of Mη of nitrocellulose (NC Mη), indicating NC molecules cohered intimately with PU, and hindered the PU network formation. The physical and mechanical properties of the films coated with PU/NC coatings were significantly improved. With the increase of NC Mη, the strength and thermal stability of the coated films increased, but the pliability, water resistivity, and optical transmission decreased slowly. The PU/NC coating with low NC Mη more readily penetrated into the RC film, and reacted with cellulose, resulting in a strong interfacial bonding and dense surface caused by intimate blend of PU/NC in the coated films. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1623–1631, 1999 相似文献
994.
The aggregation of pachyman, β-(1 → 3)-D -glucan (Mw = 1.68 × 105) from the Poria cocos mycelia, was investigated using static and dynamic laser light scattering (LLS) in dimethyl sulfoxide (DMSO) containing about 15% water, which leads to large aggregates. Both the time dependence of hydrodynamic radius and the angle dependence of the scattering intensity were used to calculate the fractal dimension (df) of the aggregates. The aggregation rate and average size of aggregates increase dramatically with increasing the polymer concentration from 1.7 × 10−4 g/mL to 8.6 × 10−4 g/mL, and with the decrease of the solvent quality, that is, water content from 13 to 15%. In the cases, the fractal dimensions change from 1.94 to 2.43 and from 1.92 to 2.54, respectively, suggesting that transforms of aggregation processes: a slow process called reaction-limited cluster aggregation (RLCA) to a fast process called diffusion-limited cluster aggregation (DLCA) in different polymer concentrations and water content. The fractal dimensions above 2 of the fast aggregation is larger than the 1.75 predicted for the ideal DLCA model, suggesting that the aggregation involves a restructuring process through the interchain hydrogen bonding interaction. There are no aggregates of pachyman in DMSO without water, but aggregates formed in the DMSO containing 15% water at 25°C as a compact structure. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 3201–3207, 1999 相似文献
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996.
Lina Hemmingsson 《Numerical Linear Algebra with Applications》1996,3(1):21-44
Preconditioners to nonsymmetric, nondiagonally dominant systems of equations are constructed and examined numerically. The preconditioners are based on a Toeplitz approach with a certain symmetry that we define. The inversion of the preconditioners is defined through a Fast Modified Sine Transform. As a model problem we study the systems of equations arising from a implicit time-discretization with a large time-step of a scalar hyperbolic PDE. 相似文献
997.
ABSTRACT This study investigated the effects of coupled thermo-hydro- mechanical dynamics on an isotropic, uniform, fully saturated, and poroelastic half-space subgrade whose surface is subjected to either mechanical force or thermal load. In this paper, our formulation is deduced in the context of two theories of generalized thermoelasticity: the Lord-Shulman theory and the Green-Lindsay theory. We then deduce the general relationships among non-dimensional vertical displacement, excess pore water pressure, vertical stress, and temperature distribution using Normal Mode Analysis (NMA) and depict them graphically. NMA is a method using weighted residuals to derive analytical solutions and can thus solve partial differential equations more quickly compared to other methods. This study continues our work of applying NMA to derive theoretical results in the multi-field coupling of soil. Following the analysis, the theoretical results are illustrated with a numerical example and a Maple program is developed. Furthermore, the differences between the coupled thermo-hydro-mechanical dynamic model (THMD) and the thermo-elastic dynamic model (TED) are presented. This proposed derivation method can be widely applied in the geotechnical engineering field, especially with regard to the mechanical and thermal behaviors of commercial buildings, high-speed railways, and highway energy foundations. 相似文献
998.
999.
本工作采用一种改进的一膜两室渗透计和简便动态渗透压法测定了一系列聚合物的数均分子量,该法操作方便、快速、可靠,测定分子量相对误差在±5%以内。 相似文献
1000.
Lina T. Al Kury Aya Abdoh Kamel Ikbariah Bassem Sadek Mohamed Mahgoub 《Molecules (Basel, Switzerland)》2022,27(1)
Diabetes mellitus (DM) is a chronic metabolic condition characterized by persistent hyperglycemia due to insufficient insulin levels or insulin resistance. Despite the availability of several oral and injectable hypoglycemic agents, their use is associated with a wide range of side effects. Monoterpenes are compounds extracted from different plants including herbs, vegetables, and fruits and they contribute to their aroma and flavor. Based on their chemical structure, monoterpenes are classified into acyclic, monocyclic, and bicyclic monoterpenes. They have been found to exhibit numerous biological and medicinal effects such as antipruritic, antioxidant, anti-inflammatory, and analgesic activities. Therefore, monoterpenes emerged as promising molecules that can be used therapeutically to treat a vast range of diseases. Additionally, monoterpenes were found to modulate enzymes and proteins that contribute to insulin resistance and other pathological events caused by DM. In this review, we highlight the different mechanisms by which monoterpenes can be used in the pharmacological intervention of DM via the alteration of certain enzymes, proteins, and pathways involved in the pathophysiology of DM. Based on the fact that monoterpenes have multiple mechanisms of action on different targets in in vitro and in vivo studies, they can be considered as lead compounds for developing effective hypoglycemic agents. Incorporating these compounds in clinical trials is needed to investigate their actions in diabetic patients in order to confirm their ability in controlling hyperglycemia. 相似文献