全文获取类型
收费全文 | 259篇 |
免费 | 6篇 |
专业分类
化学 | 137篇 |
晶体学 | 5篇 |
力学 | 34篇 |
数学 | 41篇 |
物理学 | 48篇 |
出版年
2023年 | 1篇 |
2022年 | 7篇 |
2021年 | 10篇 |
2020年 | 10篇 |
2019年 | 10篇 |
2018年 | 14篇 |
2017年 | 12篇 |
2016年 | 17篇 |
2015年 | 6篇 |
2014年 | 15篇 |
2013年 | 30篇 |
2012年 | 27篇 |
2011年 | 19篇 |
2010年 | 11篇 |
2009年 | 16篇 |
2008年 | 8篇 |
2007年 | 10篇 |
2006年 | 8篇 |
2005年 | 9篇 |
2004年 | 2篇 |
2003年 | 7篇 |
2002年 | 1篇 |
2001年 | 2篇 |
2000年 | 3篇 |
1997年 | 1篇 |
1994年 | 1篇 |
1993年 | 2篇 |
1989年 | 2篇 |
1986年 | 1篇 |
1984年 | 1篇 |
1981年 | 2篇 |
排序方式: 共有265条查询结果,搜索用时 218 毫秒
211.
Local universal relations are relations between stress and kinematic variables which hold for all materials of a particular class irrespective of specific material parameters. A method is developed for obtaining local universal relations for most first gradient materials. The currently known local universal relations for isotropic elastic materials have been extended to all isotropic first gradient materials under constant step deformation histories and have also been extended to all isotropic first gradient materials undergoing arbitrary time dependent triaxial extensions along fixed material directions. It has been shown that universal relations exist for some anisotropic materials. A set of pseudo-universal relations has been obtained for anisotropic elastic materials which can be used to decouple the material functions. These pseudo-universal relations contain some, but not all, material functions. A global universal relation has been developed for the extension and torsion of an isotropic cylindrical shaft which holds for all incompressible first gradient materials. 相似文献
212.
In this paper, we study the unsteady flow of a generalized second grade fluid. Specifically, we solve numerically the linear momentum equations for the flow of this viscoelastic shear-thinning (shear-thickening) fluid surrounding a solid cylindrical rod that is suddenly set into longitudinal and torsional motion. The equations are made dimensionless. The results are presented for the shear stresses at the wall, related to the drag force; these are physical quantities of interest, especially in oil-drilling applications. 相似文献
213.
Jaime Retuert Alicia Nuez Francisco Martínez Mehrdad Yazdani-Pedram 《Macromolecular rapid communications》1997,18(2):163-167
This work reports the synthesis of a novel polymeric organic-inorganic hybrid. The inorganic component is a silica network obtained by controlled hydrolysis of tetraethyl orthosilicate via sol-gel process and the organic counterpart is partially deacetylated chitin (CHI). The resulting polymer hybrids were homogeneous transparent film forming glassy materials being compatible through a wide composition range. Simultaneous thermal analysis of a CHI/silica 1:1 mixture confirms the intermolecular complex formation between organic and inorganic polymers. 相似文献
214.
Yan Cao Afrasyab Khan Hanzaleh Balakheyli Andrew Ng Kay Lup Mohammad Ramezani Taghartapeh Hassan Mirzaei Seyed Reza Khandoozi Alireza Soltani Mehrdad Aghaei Fatemeh Heidari Shaheen M. Sarkar Ahmad B. Albadarin 《Arabian Journal of Chemistry》2021,14(7):103200
The adsorption of penicillamine (PCA) on pure B12N12 and B12CaN12 nanocages in aqueous and chloroform solvents has been evaluated using density functional theory (DFT) calculations. The interaction of PCA on B12N12 nanocages is chemisorption through its four nucleophilic sites: amine, carbonyl, hydroxyl and thiol. The most stable adsorption configuration was achieved when zwitterionic PCA adsorbs via its carbonyl group in water with value of ?1.723 eV, in contrast, when neutral PCA adsorbs via its amine group in chloroform with value of ?1.68 eV. Intercalated calcium ion within B12N12 nanocage (B12CaN12) was shown to attract PCA onto nanocage surface, resulting in higher solubility and adsorption energy after their complexation in water and chloroform. The adsorption of multiple PCA molecules from their amine and carbonyl groups on pure and B12CaN12 nanocages were also evaluated where two and three molecules can be chemisorbed on boron atoms of the nanocage surfaces with the adsorption energy per PCA reduces slightly with the increasing the amount of drugs due to the curvature effects. Molecular docking study indicates that PCA from its NH2 group on B12CaN12 nanocage has the best binding affinity and inhibition potential of tumor necrosis factor-alpha (TNF-α) and Interleukin-1 (IL-1) receptors as compared with the other adsorption systems. Molecular docking and ADMET analysis displayed that the chosen compounds pass Lipinski Rule and have appropriate pharmacokinetic features suitable as models for developing anti-inflammatory agents. 相似文献
215.
In this study, density functional theory (DFT) molecular modeling studies were performed to explore mechanisms underlying the interactions of cocatalysts in Ziegler–Natta olefin polymerization using a range of commercially available cocatalysts, namely, trimethylaluminum (in monomeric and dimeric form, Al2Me6), dimethylaluminum chloride (in monomeric and dimeric form, Al2Me4Cl2), and triisobutylaluminum. In this regard, after exploring structural and electronic features of cocatalysts, by steric maps and conceptual DFT, their interaction with possible impurities in hydrocarbon solvents and monomer feeds such as NH3, CH3OH, H2O, H2S, CO2, and O2 was considered. Then, activation of Ti species, adsorbed on the (110) and (104) surfaces, with the assistance of cocatalysts was studied as well. In this aspect, two possible reactions were investigated: (i) formation of first vacancy on Ti center and (ii) formation of first Ti–C bond by transalkylation reaction with cocatalysts. Finally, the effect of cocatalysts on the stereospecificity of Ti center adsorbed on the (110) surface was also taken into account by DFT calculations. 相似文献
216.
ABSTRACTPrecipitate hardening is a key strengthening mechanism in metallic alloys. Classical models for precipitate hardening are based on the average behaviour of an ensemble of precipitates, and fail to capture the complexity of dislocation-precipitate interactions that have recently been observed at individual precipitates in simulations and in-situ electron microscopy. In order to achieve tailored mechanical properties, detailed deformation mechanisms at specific precipitates that account for precipitate size, crystallography, and defect structure must be understood, but has been challenging to achieve experimentally. Here, in-situ scanning electron microscope mechanical testing is used to obtain the compressive stress–strain behaviour at an individual, incoherent Au precipitate within a Cu nanocube, and determine the influence of precipitate and cube size on yield strength and strain hardening. TEM imaging and strain mapping of the initial structure shows misfit dislocations at the Au precipitate, threading dislocations that traverse the Cu shell, and localised and anisotropic strain near the precipitate and threading dislocation. These nanocubes have yield strengths of 800–1000?MPa and strain hardening rate of 1–4?GPa. Yield strength is found to depend on the distance from the precipitate interface to the cube edge, while strain hardening depends on both cube size and precipitate size. An analytical model is developed to quantify the contribution of Orowan looping, Orowan stress, back stress and image stress to plasticity at the Au precipitate. Orowan stress is found to be the largest contributor, followed by back stress and image stress. 相似文献
217.
Ashkan Khoshyan Mehrdad Pourtahmasb Fahimeh Feizpour Maasoumeh Jafarpour Abdolreza Rezaeifard 《应用有机金属化学》2019,33(2)
A novel heterogeneous one‐pot protocol is developed for tandem aerobic synthesis of benzimidazoles through dehydrogenative coupling of primary benzylic alcohols and aromatic diamines co‐catalysed by Keplerate‐type {Mo72V30} polyoxometalate and N‐hydroxyphthalimide (NHPI). The catalytic system also works well for the synthesis of benzimidazoles using benzaldehydes, as commonly used starting materials, in the absence of NHPI. The high activity of the solid nanocluster provides standard conditions avoiding current limitations of oxidation methods including high catalyst loadings. The spectral results and leaching experiments revealed that the nanocapsule preserved its structural integrity after being reused in consecutive runs. 相似文献
218.
Amir M. Niroumand Walter Mérida Michael Eikerling Mehrdad Saif 《Electrochemistry communications》2010,12(1):122-124
In this work, pressure-induced voltage oscillations are explored as a novel diagnostic tool for PEFC cathodes. In this method, a small signal oscillation is imposed on the cathode outlet pressure. As a response to this pressure perturbation, the fuel cell voltage exhibits oscillations with the same frequency. The amplitude ratio and phase difference between the voltage and pressure oscillations embody diagnostic information about the operating conditions and processes in the PEFC cathode. 相似文献
219.
Djavanshir Djozan Mehrdad Mahkam Bahram Ebrahimi 《Journal of chromatography. A》2009,1216(12):2211-2219
A monolithic ametryn molecular-imprinted polymer based on a simple polymerization method was fabricated for use as new solid-phase microextraction (SPME) fiber, which can be coupled with GC and GC/MS for selective extraction and analysis of triazine herbicides. Methacrylic acid (MAA), ethylene glycol dimethacrylate (EDMA) and ametryn bear role of functional monomer, cross-linker and template, respectively. In the optimized conditions the fabricated fiber showed better molecular recognition abilities for methylthiotriazine herbicides than chloro-triazine herbicides. By use of bi-Langmuir isotherm model the evaluated equilibrium constants for ametryn were 0.01 and 890.69 μM−1, and the numbers of binding sites were 129.98 and 5.82 nmol g−1, respectively. The high extraction efficiency was obtained for ametryn, prometryn, terbutryn, atrazine, simazine, propazine, and cyanazine, yielding the detection limits of 14, 28, 45, 56, 85, 95 and 74 ng mL−1, respectively by GC with flame ionization detection. The reliability of the prepared fiber for extraction of ametryn and other analogues in real samples has been investigated and proved by using spiked samples such as tap water, rice, maize, and onion. 相似文献
220.