全文获取类型
收费全文 | 288篇 |
免费 | 16篇 |
国内免费 | 4篇 |
专业分类
化学 | 176篇 |
晶体学 | 3篇 |
力学 | 12篇 |
数学 | 49篇 |
物理学 | 68篇 |
出版年
2023年 | 1篇 |
2022年 | 4篇 |
2021年 | 5篇 |
2020年 | 6篇 |
2019年 | 11篇 |
2018年 | 17篇 |
2017年 | 7篇 |
2016年 | 16篇 |
2015年 | 13篇 |
2014年 | 20篇 |
2013年 | 53篇 |
2012年 | 29篇 |
2011年 | 10篇 |
2010年 | 13篇 |
2009年 | 12篇 |
2008年 | 10篇 |
2007年 | 18篇 |
2006年 | 16篇 |
2005年 | 13篇 |
2004年 | 3篇 |
2003年 | 5篇 |
2002年 | 5篇 |
2001年 | 1篇 |
2000年 | 2篇 |
1998年 | 1篇 |
1997年 | 5篇 |
1988年 | 2篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1977年 | 3篇 |
1973年 | 1篇 |
1969年 | 1篇 |
1968年 | 2篇 |
1967年 | 1篇 |
排序方式: 共有308条查询结果,搜索用时 15 毫秒
1.
2.
A good photocatalyst with high efficiency can be synthesized easily using eco-friendly materials and processes. Our synthesized samples exhibit all of the aforementioned features. In this work, manganese co-doped ZnO at different weight percentages (3, 6, 9, and 15 wt.%) with and without 1.5 wt.% aluminum was synthesized by hydrothermal method, and their photocatalytic activity in aqueous solutions of methyl orange (MO) was investigated under visible light. The structural and optical properties of the samples were characterized using X-ray powder diffraction, Fourier-transform infrared spectroscopy, scanning electron microscopy, energy-dispersive X-ray analysis, and diffuse reflectance spectroscopy. In this work, Mn2+ ions in the 9%Mn/ZnO sample and Mn2+, Al3+ ions in the (9%Mn, 1.5%Al)/ZnO sample calcined at 800 °C were replaced instead with some Zn2+ ions in hexagonal wurtzite structures of ZnO. These structures were found next to each other in the form of a hexagonal shape that created 3D-hexagonal-like ZnO nanostructures. Finally, nanoparticles (NPs) and nano hexagonal-like ZnO nanostructures were, respectively, dispersed on the surface of 3D-hexagonal-like structure of 9%Mn/ZnO and (9%Mn, 1.5%Al)/ZnO. Diffuse reflectance spectroscopy analysis showed that the (9%Mn, 1.5%Al)/ZnO sample had more light absorption than 9%Mn/ZnO. However, contrary to our expectations, the 9%Mn/ZnO sample had better decolorization efficiency (94%) after 60 min under visible light, which could be attributed to a significant increase in the level of recombination by the aluminum ions. 相似文献
3.
Saba Hemmati Mohammad Yousefi Mirmehdi Hashemi Salehi Mahdis Amiri Malak Hekmati 《应用有机金属化学》2020,34(8):e5653
This paper develops a green method for in situ decorated of palladium nanoparticles over Fe3O4 nanoparticles, by utilizing Strawberry fruit extract and ultrasound irradiations, with no use of any toxic reducing agent. The structure's characterization is represented via diverse analytical methods such as FT-IR, FE-SEM, TEM, WDX, ICP, EDS and XXPS. Catalytic efficiency of magnetic Fe3O4@Strawberry/Pd nanocatalyst is investigated in production of different biphenyls with good turnover frequencies (TOF) and turnover numbers (TON) through Suzuki coupling reactions. Furthermore, the catalyst could be recovered and reused 7 runs without considerable palladium leaching or alteration in its performance. 相似文献
4.
Rezvan Salehi 《Numerical Algorithms》2017,74(4):1145-1168
In this paper, a meshless collocation method is considered to solve the multi-term time fractional diffusion-wave equation in two dimensions. The moving least squares reproducing kernel particle approximation is employed to construct the shape functions for spatial approximation. Also, the Caputo’s time fractional derivatives are approximated by a scheme of order O(τ 3?α ), 1< α < 2. Stability and convergence of the proposed scheme are discussed. Some numerical examples are given to confirm the efficiency and reliability of the proposed method. 相似文献
5.
N. Mahdavi-Amiri F. Salehi Sadaghiani 《4OR: A Quarterly Journal of Operations Research》2017,15(3):303-326
Recently, Luc defined a dual program for a multiple objective linear program. The dual problem is also a multiple objective linear problem and the weak duality and strong duality theorems for these primal and dual problems have been established. Here, we use these results to prove some relationships between multiple objective linear primal and dual problems. We extend the available results on single objective linear primal and dual problems to multiple objective linear primal and dual problems. Complementary slackness conditions for efficient solutions, and conditions for the existence of weakly efficient solution sets and existence of strictly primal and dual feasible points are established. We show that primal-dual (weakly) efficient solutions satisfying strictly complementary conditions exist. Furthermore, we consider Isermann’s and Kolumban’s dual problems and establish conditions for the existence of strictly primal and dual feasible points. We show the existence of primal-dual feasible points satisfying strictly complementary conditions for Isermann’s dual problem. Also, we give an alternative proof to establish necessary conditions for weakly efficient solutions of multiple objective programs, assuming the Kuhn–Tucker (KT) constraint qualification. We also provide a new condition to ensure the KT constraint qualification. 相似文献
6.
Journal of Solid State Electrochemistry - Due to the spread of wireless devices, the need to improve batteries is felt more than ever. Orthorhombic vanadium pentoxide is one of the cathodes that... 相似文献
7.
8.
Peyman Salehi Mohammad Mehdi Khodaei Amin Rostami 《Phosphorus, sulfur, and silicon and the related elements》2013,188(11):2235-2243
Alanine/chlorochromic acid/silica gel is a new and selective reagent for the efficient oxidation of sulfides, thiols, oximes, and alcohols. Oxidation of sulfides is solvent dependent. In chloroform at room temperature sulfoxides are formed as the major products, while in carbon tetrachloride or under solvent-free conditions solfones are produced in good-to-excellent yields. 相似文献
9.
10.
Ce(IV) as ceric ammonium nitrate can effectively catalyze ring opening of epoxides with halides under very mild conditions and easy procedure to give the corresponding β-chloro-and β-bromohydrins in excellent yields. The reactions occur with both substituted and unsubstituted quaternary ammonium halides and with high regio- and stereoselectivity. The reaction of optically active styrene oxide with chloride ion was found to be highly stereospecific and afforded the corresponding β-halohydrin in 96% ee. 相似文献