全文获取类型
收费全文 | 228篇 |
免费 | 10篇 |
专业分类
化学 | 152篇 |
晶体学 | 1篇 |
力学 | 9篇 |
数学 | 17篇 |
物理学 | 59篇 |
出版年
2023年 | 5篇 |
2022年 | 7篇 |
2021年 | 6篇 |
2020年 | 7篇 |
2019年 | 9篇 |
2018年 | 7篇 |
2017年 | 16篇 |
2016年 | 10篇 |
2015年 | 10篇 |
2014年 | 14篇 |
2013年 | 29篇 |
2012年 | 21篇 |
2011年 | 10篇 |
2010年 | 16篇 |
2009年 | 8篇 |
2008年 | 11篇 |
2007年 | 8篇 |
2006年 | 9篇 |
2005年 | 4篇 |
2004年 | 3篇 |
2003年 | 5篇 |
2002年 | 6篇 |
2001年 | 1篇 |
1997年 | 1篇 |
1995年 | 1篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1992年 | 1篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1982年 | 1篇 |
排序方式: 共有238条查询结果,搜索用时 31 毫秒
31.
We have derived all the charged fluid spheres described by a space-time with its hypersurfaces t = const. as spheroids subject to a particular form of electric field intensity. Only one out of the four solutions so obtained is reducible to its uncharged counterpart in the absence of the charge. 相似文献
32.
Simple kinetic models which take account of the formation of islands of adsorbate on a catalyst surface are proposed, and are compared with an elementary step model for CO oxidation and oxidation of a CO-butene or CO-propylene mixture. The island models give fits to data from step change transient experiments which are comparable with the elementary step model, and give better fits to steady-state and continuously oscillating data (the latter with hydrocarbon present). Theoretical predictions of chaotic behaviour in CO oxidation can be obtained with the island models. Comparisons between island models suggest that islands of CO have the most significant effect on simulations at the experimental conditions. 相似文献
33.
The title compound, C26H24N2O6S, (I), crystallizes in the monoclinic space group, P21/c, with cell parameters a = 16.248(1), b = 7.927(1), c = 19.371(4) ?, β = 105.295(2)°, Z = 4. The central pyrimidine ring in the compound (I) is significantly puckered, assuming a screw-boat conformation. The C11–C16 benzene ring stands vertical while thiazole and
C18–C23 benzene rings are coplanar to the mean plane of pyrimidine ring having dihedral angles of 87.48(12), 3.63(11) and
0.94(12)°, respectively. In the absence of potential hydrogen bonding interaction, the crystal packing is influenced by intramolecular
C-H…S interaction and intermolecular C-H…π interactions. 相似文献
34.
35.
In this paper, we propose a credibilistic framework for portfolio selection problem using an expected value multiobjective model with fuzzy parameters. We consider short term return, long term return, risk and liquidity as key financial criteria. A solution procedure comprising fuzzy goal programming and fuzzy simulation based real-coded genetic algorithm is developed to solve the model. The proposed solution approach is considered advantageous particularly for the cases where the fuzzy parameters of the problem may assume any general functional form. An empirical study is included to illustrate the usefulness of the proposed model and solution approach in real-world applications of portfolio selection. 相似文献
36.
Nisha Kushwah Soumyaditya Mula Amey P. Wadawale Meenakshi Joshi Kedarnath Gotluru Mukesh Kumar Tapan K. Ghanty Sandip K. Nayak Vimal K. Jain 《Journal of heterocyclic chemistry》2019,56(9):2499-2507
Salicylaldimine Schiff bases represent an important class of hetero‐polydentate ligands capable of forming mononuclear, binuclear, and polynuclear complexes with transition and non‐transition metals. In this report, we developed an easy synthesis of BODIPY‐based salicylaldimine Schiff bases and synthesized five new derivatives. These were characterized by elemental analysis, infrared, UV‐Vis, nuclear magnetic resonance spectroscopy, and X‐ray crystallography. Finally, one of the Schiff bases was reacted with BF3·OEt2 to synthesize corresponding bis‐BF2 boron complex. The photophysical and electrochemical properties of the Schiff bases and the boron complex were evaluated and rationalized by theoretical calculations. The bis‐BF2 boron complex showed excited state charge redistribution, thus could be useful as sensitizers for designing new dye‐sensitized solar cells. 相似文献
37.
C. P. Kaushik Raj Luxmi Mukesh Kumar Dharmendra Singh Krishan Kumar Ashima Pahwa 《合成通讯》2019,49(1):118-128
A library of twenty five 1,2,3-triazoles bridged with amine-amide functionalities have been synthesized from reaction of N-substituted(prop-2-yn-1-yl)amines (2a–2e), 2-bromo-N-arylacetamides (4a–4e) and sodium azide through copper(I)-catalyzed alkyne-azide cycloaddition. The synthesized compounds were characterized by using FTIR, 1H NMR, 13C NMR, and HRMS techniques. The structures of synthesized 5a (CCDC 1569245) and 5h (CCDC 1569249) were also confirmed by X-ray crystallography. Antifungal evaluation of newly synthesized triazoles was carried out against – Candida albicans and Aspergillus niger. Biological screening of synthesized 1,2,3-triazoles revealed moderate to good antifungal activity against tested strains. 相似文献
38.
Mukesh Kumar Alaria A. K. Sinha A. Bera V. Srivastava 《International Journal of Infrared and Millimeter Waves》2008,29(12):1083-1090
The main objective of the paper is to make an efficient design of the input and output coaxial coupler for a helix TWTs. An
approach has been developed for the efficient design and analysis of the coaxial couplers in the practical situation. Normally
multi-section impedance transformer approach is used for any wide band coupler. For a space helix TWT, coupler should be wide
bandwidth and small size. In this case coupler is matched with helix slow wave structure and the standard 50-ohm connectors.
The simulated return loss (dB) profile for different type of couplers is obtained by using Ansoft HFSS, CST microwave studio
and compares those with experimental results. The tip loss design at sever ends for the input and the output section has been
also optimized. 相似文献
39.
Mukesh Agrawal Andrij Pich Nikolaos E. Zafeiropoulos Manfred Stamm 《Colloid and polymer science》2008,286(5):593-601
Submicron hollow spheres are an interesting class of materials that receive significant attention nowadays. Closed and mechanically
robust homogeneous hollow titania microspheres with as much shell thickness as 130 nm were fabricated by coating polystyrene
beads with titania nanoparticles using sol–gel chemistry and subsequently removing the core either via heating or a chemical
dissolution process. The thickness of the titania shell deposited on polystyrene core was finely tuned between 100 and 130 nm
by varying the concentration of titania precursor, i.e., Ti(OEt)4 salt from 0.5 to 2 mM during the coating process. The obtained hybrid core–shell particles and hollow microspheres were characterized
by scanning electron microscopy, transmission electron microscopy, infrared spectroscopy, X-ray diffraction, and thermo-gravimetric
analysis. The approach employed is well suited to the preparation of titania-coated polystyrene hybrid particles and hollow
titania spheres, which can find their applications as novel building blocks with unique optical properties for fabrication
of advanced materials, catalyst, and drug delivery system. 相似文献
40.
Mukesh Kumar Biyala Krishna Sharma Monika Swami Nighat Fahmi Ran Vir Singh 《Transition Metal Chemistry》2008,33(3):377-381
The monobasic bidentate Schiff base complexes of palladium(II) and platinum(II) derived from 1H-indol-2,3-dione thiosemicarbazone
(L1H) and 1H-indol-2,3-dione semicarbazone (L2H) have been characterized on the basis of elemental analysis, molecular weight determinations, i.r., 1H n.m.r. and u.v. spectral studies. Based on these studies a square planar environment around the metal atoms has been proposed.
Antimicrobial effects of both the ligands and their complexes on different species of pathogenic fungi and bacteria have been
recorded and these are found to possess significant fungicidal and bactericidal properties. 相似文献