全文获取类型
收费全文 | 318篇 |
免费 | 6篇 |
国内免费 | 2篇 |
专业分类
化学 | 178篇 |
力学 | 32篇 |
数学 | 42篇 |
物理学 | 74篇 |
出版年
2023年 | 1篇 |
2021年 | 3篇 |
2019年 | 2篇 |
2018年 | 4篇 |
2017年 | 2篇 |
2016年 | 7篇 |
2015年 | 2篇 |
2014年 | 5篇 |
2013年 | 12篇 |
2012年 | 11篇 |
2011年 | 21篇 |
2010年 | 21篇 |
2009年 | 28篇 |
2008年 | 25篇 |
2007年 | 19篇 |
2006年 | 18篇 |
2005年 | 10篇 |
2004年 | 7篇 |
2003年 | 7篇 |
2002年 | 12篇 |
2001年 | 3篇 |
2000年 | 5篇 |
1999年 | 8篇 |
1998年 | 12篇 |
1997年 | 10篇 |
1996年 | 11篇 |
1995年 | 2篇 |
1994年 | 5篇 |
1993年 | 10篇 |
1992年 | 12篇 |
1991年 | 6篇 |
1990年 | 4篇 |
1989年 | 3篇 |
1988年 | 4篇 |
1987年 | 1篇 |
1986年 | 3篇 |
1982年 | 2篇 |
1980年 | 4篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1968年 | 1篇 |
排序方式: 共有326条查询结果,搜索用时 437 毫秒
21.
The direct reaction of iron pentacarbonyl with diethylamidocyclohexadiene gave three isomeric tricarbonyliron complexes, 1, 2 and 3. Only 1 isomerized to give 2 under acidic conditions, whereas 3 remained unchanged. The chemical properties of the tricarbonyl(amidocyclohexadiene)iron complexes differed from those of the tricarbonyl(carboxycyclohexadiene)iron complexes. Complex 3 which underwent no hydride abstraction with triphenylmethyl hexafluorophosphate, has an exo stereochemistry. 相似文献
22.
Synthesis and properties of novel poly(amide-imide)s containing pendent diphenylamino groups 总被引:1,自引:0,他引:1
A new dicarboxylic acid, 2,4-bis(N-trimellitoyl)triphenylamine, bearing two preformed imide rings was synthesized from the condensation of 2,4-diaminotriphenylamine and trimellitic anhydride at 1:2 molar ratio. A series of poly(amide-imide)s (PAIs) with inherent viscosities of 0.38-0.66 dl/g were prepared by triphenyl phosphite-activated polycondensation from the diimide-dicarboxylic acid with various aromatic diamines. All the resulting PAIs were readily soluble in a variety of organic solvents and formed strong and tough films via solution casting. These PAIs have useful levels of thermal stability associated with moderately high glass-transition temperatures (259-314 °C) and 10% weight loss temperatures in excess of 530 °C in nitrogen or in air. 相似文献
23.
24.
The purpose of this paper is to construct two superimposed optimization methods for solving the mixed equilibrium problem and variational inclusion. We show that the proposed superimposed methods converge strongly to a solution of some optimization problem. Note that our methods do not involve any projection. 相似文献
25.
Aerobic oxidation of a series of 2,3-dihydro-1H-perimidines to the corresponding 4- and 6-perimidinones via visible light photoredox catalysis using Ru(bpy)32+ as a catalyst was reported. The scope and limitation of this oxidation were investigated and a possible photochemical mechanism was proposed. 相似文献
26.
T S Wu M S Kao P L Wu F W Lin L S Shi M J Liou C Y Li 《Chemical & pharmaceutical bulletin》1999,47(3):375-382
Thirty-two new bakkenolides, bakkenolides-Db (1)--Dh(7), -Fa(8), -Fb(9), -I(10)--M(14), -Na(15), -Nb(16), -O(17)--T(22), -Ua (23), -Ub(24), -V(25)--X(27), -Ya(28), -Yb(29), -Za(30), -Zb(31) and -III(32), from the roots of Petasites formosanus together with thirty known compounds were isolated. The structures were characterized by spectral analysis. The locations, C-1 and/or C-9 of bakkenolide skeleton, of the substituents, such as acetoxy, isobutyroyloxy and isovaleroyloxy groups, can be determined by the chemical shifts of their signals and the H-1 and/H-9 in the 1H-NMR spectra. The cytotoxicity was also discussed. 相似文献
27.
An extension of the Osher upwind scheme to non-equilibrium reacting flows is presented, Owing to the presence of source terms, the Riemann problem is no longer self-similar and therefore its approximate solution becomes tedious. With simplicity in mind, a linearized approach which avoids an iterative solution is used to define the intermediate states and sonic points. The source terms are treated explicitly. Numerical computations are presented to demonstrate the feasibility, efficiency and accuracy of the proposed method. The test problems include a ZND (Zeldovich-Neumann-Doring) detonation problem for which spurious numerical solutions which propagate at mesh speed have been observed on coarse grids. With the present method, a change of limiter causes the solution to change from the physically correct CJ detonation solution to the spurious weak detonation solution. 相似文献
28.
29.
Y.-K. Kuo J.-R. Chen M.-L. Chen B.-T. Liou 《Applied physics. B, Lasers and optics》2007,86(4):623-631
The physical and optical properties of compressively strained InGaAsP/InGaP quantum wells for 850-nm vertical-cavity surface-emitting
lasers are numerically studied. The simulation results show that the maximum optical gain, transparency carrier densities,
transparency radiative current densities, and differential gain of InGaAsP quantum wells can be efficiently improved by employing
a compressive strain of approximately 1.24% in the InGaAsP quantum wells. The simulation results suggest that the 850-nm InGaAsP/InGaP
vertical-cavity surface-emitting lasers have the best laser performance when the number of quantum wells is one, which is
mainly attributed to the non-uniform hole distribution in multiple quantum wells due to high valence band offset.
PACS 42.55.Px; 78.20.-e; 78.20.Bh; 78.30.Fs 相似文献
30.
Guey‐Sheng Liou Po‐Han Lin Hung‐Ju Yen Yang‐Yen Yu Wen‐Chang Chen 《Journal of polymer science. Part A, Polymer chemistry》2010,48(6):1433-1440
In this study, a novel synthetic route was developed to prepare polyimide–nanocrystalline–titania hybrid optical films with a relatively high titania content (up to 50 wt %) and thickness (20–30 μm) from soluble polyimides containing hydroxyl groups. Two series of newly soluble polyimides were synthesized from the hydroxy‐substituted diamines with various commercial tetracarboxylic dianhydrides. The hydroxyl groups on the backbone of the polyimides could provide the organic–inorganic bonding and resulted in homogeneous hybrid solutions by controlling the mole ratio of titanium butoxide/hydroxyl group. AFM, SEM, TEM, and XRD results indicated the formation of well‐dispersed nanocrystalline‐titania. The flexible hybrid films could be successfully obtained and revealed relatively good surface planarity, thermal dimensional stability, tunable refractive index, and high optical transparency. A three‐layer antireflection coating based on the hybrid films was prepared and showed a reflectance of less than 0.5% in the visible range indicated its potential optical applications. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1433–1440, 2010 相似文献