全文获取类型
收费全文 | 891篇 |
免费 | 30篇 |
国内免费 | 6篇 |
专业分类
化学 | 565篇 |
晶体学 | 14篇 |
力学 | 28篇 |
数学 | 75篇 |
物理学 | 245篇 |
出版年
2023年 | 4篇 |
2022年 | 20篇 |
2021年 | 16篇 |
2020年 | 20篇 |
2019年 | 31篇 |
2018年 | 34篇 |
2017年 | 31篇 |
2016年 | 28篇 |
2015年 | 28篇 |
2014年 | 54篇 |
2013年 | 77篇 |
2012年 | 43篇 |
2011年 | 70篇 |
2010年 | 37篇 |
2009年 | 43篇 |
2008年 | 49篇 |
2007年 | 35篇 |
2006年 | 32篇 |
2005年 | 26篇 |
2004年 | 29篇 |
2003年 | 18篇 |
2002年 | 14篇 |
2001年 | 8篇 |
2000年 | 3篇 |
1999年 | 7篇 |
1998年 | 11篇 |
1997年 | 3篇 |
1996年 | 12篇 |
1995年 | 9篇 |
1994年 | 16篇 |
1993年 | 9篇 |
1992年 | 14篇 |
1991年 | 9篇 |
1990年 | 10篇 |
1989年 | 11篇 |
1988年 | 3篇 |
1987年 | 4篇 |
1986年 | 6篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1983年 | 6篇 |
1982年 | 5篇 |
1981年 | 5篇 |
1980年 | 5篇 |
1978年 | 2篇 |
1977年 | 5篇 |
1976年 | 3篇 |
1975年 | 4篇 |
1973年 | 3篇 |
1972年 | 2篇 |
排序方式: 共有927条查询结果,搜索用时 15 毫秒
921.
Ganesh V Pal SK Kumar S Lakshminarayanan V 《Journal of colloid and interface science》2006,296(1):195-203
Self-assembled monolayers (SAMs) of liquid crystalline thiol-terminated alkoxycyanobiphenyl molecules with different alkyl chain lengths on Au surface have been studied for the first time using electrochemical techniques such as cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The barrier property of the SAM-modified surfaces was evaluated using two different redox probes, namely potassium ferro/ferri cyanide and hexaammineruthenium(III) chloride. It was found that for short-length alkyl chain thiol (C5) the electron transfer reaction of hexaammineruthenium(III) chloride takes place through tunneling mechanism. In contrast, redox reaction of potassium ferro/ferri cyanide is almost completely blocked by the SAM-modified Au surface. From the impedance data, a surface coverage value of >99.9% was calculated for all the thiol molecules. 相似文献
922.
[structures: see text] A serious drawback of peptide nucleic acids (PNAs) from an application perspective that has not been adequately dealt with is nondiscrimination of identical DNA and RNA sequences. An analysis of the available X-ray and NMR solution structures of PNA complexes with DNA and RNA suggested that it might be possible to rationally impart DNA/RNA duplex binding selectivity by tuning the dihedral angle beta of the flexible ethylenediamine part of the PNA backbone (II) via suitable chemical modifications. Cyclohexanyl PNAs (chPNAs) with beta approximately = 65 degrees were designed on the basis of this rationale. The chPNAs introduced remarkable differences in duplex stabilities among their DNA and RNA complexes, with melting temperatures (deltaTm(RNA-DNA) = +16-50 degrees C) depending on the number of modifications and the stereochemistry. This is a highly significant, exceptional binding selectivity of a mix sequence of PNA to RNA over the same DNA sequence as that seen to date. In contrast, cyclopentanyl PNAs (cpPNAs) with beta approximately = 25 degrees hybridize to DNA/RNA strongly without discrimination because of the ring puckering of the cyclopentane ring. The high affinity of chPNAs to bind to RNA without losing base specificity will have immediate implications in designing improved PNAs for therapeutic and diagnostic applications. 相似文献
923.
B. Bialecki M. Ganesh K. Mustapha 《Numerical Methods for Partial Differential Equations》2006,22(5):1052-1069
We propose and analyze a Crank–Nicolson quadrature Petrov–Galerkin (CNQPG) ‐spline method for solving semi‐linear second‐order hyperbolic initial‐boundary value problems. We prove second‐order convergence in time and optimal order H2 norm convergence in space for the CNQPG scheme that requires only linear algebraic solvers. We demonstrate numerically optimal order Hk, k = 0,1,2, norm convergence of the scheme for some test problems with smooth and nonsmooth nonlinearities. © 2006 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2006 相似文献
924.
Synthesis of optically pure 2,3,4-trisubstituted tetrahydrofurans is described employing a two-step Michael-Evans aldol cyclization strategy. The approach is successfully applied for the total synthesis of furano lignan natural product (+)-magnolone. 相似文献
925.
V. K. Ganesh S. Banumathi D. Velmurugan K. Ravikumar 《Crystal Research and Technology》1999,34(7):929-934
The crystal structure of the title compound was determined from X-ray diffraction data using direct methods. The crystals are tetragonal, a = b = 17.618 (1) A, c = 10.121(2) A, Z = 8, V = 3141.5(7) A3, space group P4(2)/n. The structure was refined by full-matrix least-squares to a final R value of 0.052. The central dihydropyridine ring is nearly planar while the outer two rings adopt half chair conformation. 相似文献
926.
Gunjan Chauhan Suvarcha Chauhan Surbhi Soni Anand Kumar Devendra Singh Negi Indra Bahadur 《中国化学会会志》2023,70(4):879-893
CoS@MorphcdtH NPs and CoS@4-MPipzcdtH NPs were synthesized by precipitation method involving three mechanisms: inclusion, occlusion, and adsorption. The synthesized NPs were characterized with the help of UV-Vis spectroscopy, FESEM-EDAX, powder x-ray diffraction, TEM, ESIMS, TG/DSC analysis. The morphology of the CoS@MorphcdtH NPs and CoS@4-MPipzcdtH NPs were hexagonal and rectangular, and the particles were in the range 7–12 nm. UV–visible spectral measurements showed surface plasmon resonance at 320 nm–340 nm with band gap of 3.65 eV–3.86 eV. The catalytically active CoSNPs called were investigated for the reduction of 4-nitrophenol (4-NP) via hydrogenation using sodium borohydride (NaBH4) as a reducing agent. Both the CoS NPs successfully reduced 4-NP to 4- aminophenol (4-AP) in a short time, catalytic performances are almost unchanged for the first five cycles. Herein, we report the preparation and characterizations of efficient active CoS NPs consisting carbodithioic acid framework as a support/capping material, along with catalytic property. 相似文献
927.
R. Sathyalakshmi V. Kannan R. Bairava Ganesh P. Ramasamy 《Crystal Research and Technology》2007,42(1):78-83
L(+)Glutamic acid hydrochloride [HOOC (CH2)2CH(NH2) COOH·HCl], a monoamino dicarboxylic acid salt of L‐Glutamic acid was synthesized and the synthesis was confirmed by FTIR analysis. Solubility of the material in water was determined. Pure and Thiourea doped L‐Glutamic acid hydrochloride crystals were grown by low temperature solution growth using solvent evaporation technique. XRD, UV‐Vis‐NIR analyses were carried out for both pure and thiourea doped crystals. The crystals were qualitatively analyzed by EDAX analysis and the presence of thiourea was confirmed. The cell parameters of L‐Glutamic acid hydrochloride have been determined as a = 5.151 Å, b = 11.79 Å, c = 13.35 Å by X‐ray diffraction analysis and it crystallizes in orthorhombic space group P212121. UV‐Vis‐NIR spectra analysis showed good optical transmission in the entire visible region for both pure and doped crystals. Micro hardness of both pure and doped crystals has been determined using Vickers micro hardness tester. The SHG efficiencies of both pure and doped crystals were determined using Kurtz powder test and pure L‐Glutamic acid hydrochloride crystal was found to possess better efficiency than thiourea doped L‐Glutamic acid hydrochloride crystals. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献