全文获取类型
收费全文 | 166篇 |
免费 | 7篇 |
专业分类
化学 | 122篇 |
晶体学 | 1篇 |
力学 | 2篇 |
数学 | 14篇 |
物理学 | 34篇 |
出版年
2023年 | 4篇 |
2022年 | 4篇 |
2021年 | 3篇 |
2020年 | 8篇 |
2019年 | 4篇 |
2018年 | 7篇 |
2017年 | 6篇 |
2016年 | 6篇 |
2015年 | 1篇 |
2014年 | 4篇 |
2013年 | 13篇 |
2012年 | 17篇 |
2011年 | 13篇 |
2010年 | 8篇 |
2009年 | 7篇 |
2008年 | 15篇 |
2007年 | 8篇 |
2006年 | 10篇 |
2005年 | 9篇 |
2004年 | 4篇 |
2002年 | 2篇 |
1999年 | 1篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1994年 | 1篇 |
1992年 | 1篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 2篇 |
1973年 | 1篇 |
1971年 | 1篇 |
1970年 | 1篇 |
1967年 | 1篇 |
1966年 | 1篇 |
排序方式: 共有173条查询结果,搜索用时 156 毫秒
131.
Epitaxially grown self-assembled InAs quantum dots (QDs) have found applications in optoelectronics. Efforts are being made
to obtain efficient quantum-dot lasers operating at longer telecommunication wavelengths, specifically 1.3 μm and 1.55 μm.
This requires narrow emission linewidth from the quantum dots at these wavelengths. In InAs/GaAs single layer quantum dot
(SQD) structure, higher InAs monolayer coverage for the QDs gives rise to larger dots emitting at longer wavelengths but results
in inhomogeneous dot-size distribution. The bilayer quantum dot (BQD) can be used as an alternative to SQDs, which can emit
at longer wavelengths (1.229 μm at 8 K) with significantly narrow linewidth (∼16.7 meV). Here, we compare the properties of
single layer and bilayer quantum dots grown with higher InAs monolayer coverage. In the BQD structure, only the top QD layer
is covered with increased (3.2 ML) InAs monolayer coverage. The emission line width of our BQD sample is found to be insensitive
towards post growth treatments. 相似文献
132.
In this paper, we present a new approach to obtain large size dots in an MBE grown InAs/GaAs multilayer quantum dot system. This is achieved by adding an InAlGaAs quaternary capping layer in addition to a high growth temperature (590°C) GaAs capping layer with the view to tune the emission wavelength of these QDs towards the 1.3 μm/0.95 eV region important for communication devices. Strain driven migration of In atoms from InAlGaAs alloy to the InAs QDs effectively increases the size of QDs. Microscopic investigations were carried out to study the dot size and morphology in the different layers of the grown samples. Methods to reduce structural defects like threading dislocations in multilayer quantum dot samples are also studied. 相似文献
133.
N. Halder R. Rashmi S. Chakrabarti C. R. Stanley Miriam Herrera Nigel D. Browning 《Applied Physics A: Materials Science & Processing》2009,95(3):713-720
We investigate the effect of in situ annealing during growth pause on the morphological and optical properties of self-assembled InAs/GaAs quantum dots (QDs).
The islands were grown at different growth rates and having different monolayer coverage. The results were explained on the
basis of atomic force microscopy (AFM) and photo-luminescence (PL) measurements. The studies show the occurrence of ripening-like
phenomenon, observed in strained semiconductor system. Agglomeration of the self-assembled QDs takes place during dot pause
leading to an equilibrium size distribution. The PL properties of the QDs are affected by the Indium desorption from the surface
of the QDs during dot pause annealing at high growth temperature (520°C) subsiding the effect of the narrowing of the dot
size distribution with growth pause. The samples having high monolayer coverage (3.4 ML) and grown at a slower growth rate
(0.032 ML s−1) manifested two different QD families. Among the islands the smaller are coherent defect-free in nature, whereas the larger
dots are plastically relaxed and hence optically inactive. Indium desorption from the island surface during the in situ annealing and inhomogeneous morphology as the dots agglomerate during the growth pause, also affects the PL emission from
these dot assemblies. 相似文献
134.
Heinz-Richard Halder 《Journal of Geometry》1974,5(2):147-157
In this paper we get necessary conditions for the existence of (k,n)-arcs K with the following property: Each point of K is incident with exactly m lines intersecting K in exactly m points. We prove that the set of tangent lines of such arcs forms an arc of the same type in the dual plane. Moreover we determine an upper bound for k for the existence of m-regular (k,n)-arcs. 相似文献
135.
S. Halder P. Gerber T. Schneller R. Waser 《Applied Physics A: Materials Science & Processing》2005,81(1):11-13
The electromechanical properties of thin films of barium titanate zirconate were studied with the help of a double-beam interferometer. Thin films of barium titanate zirconate (Ba(Ti1-xZrx)O3) of various compositions (x=0, 0.03, 0.05, 0.07, 0.1, 0.2, 0.3 and 0.4) were deposited by chemical solution deposition on Pt/TiO2/SiO2/Si substrates. The thin films show a strain of around 0.05 (at 200 kV/cm) for the unsubstituted BaTiO3 thin films. For higher Zr substitutions up to 5% the strain increases slightly and subsequently falls to 0.01 at 200 kV/cm for even higher Zr content. The d33 values were found to vary between 30 pm/V and 10 pm/V for 0x0.4. PACS 77.65.-j; 77.55.+f; 77.84.Dy 相似文献
136.
137.
Ultrastable Imine‐Based Covalent Organic Frameworks for Sulfuric Acid Recovery: An Effect of Interlayer Hydrogen Bonding
下载免费PDF全文
![点击此处可从《Angewandte Chemie (International ed. in English)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Arjun Halder Suvendu Karak Dr. Matthew Addicoat Saibal Bera Dr. Amit Chakraborty Shebeeb H. Kunjattu Dr. Pradip Pachfule Prof. Dr. Thomas Heine Prof. Dr. Rahul Banerjee 《Angewandte Chemie (International ed. in English)》2018,57(20):5797-5802
A rapid and scalable synthesis of six new imine‐linked highly porous and crystalline COFs is presented that feature exceptionally high chemical stability in harsh environments including conc. H2SO4 (18 m ), conc. HCl (12 m ), and NaOH (9 m ). This is because of the presence of strong interlayer C?H???N hydrogen bonding among the individual layers, which provides significant steric hindrance and a hydrophobic environment around the imine (?C=N?) bonds, thus preventing their hydrolysis in such an abrasive environment. These COFs were further converted into porous, crystalline, self‐standing, and crack‐free COF membranes (COFMs) with extremely high chemical stability for their potential applications for sulfuric acid recovery. The as‐synthesized COFMs exhibit unprecedented permeance for acetonitrile (280 Lm?2 h?1 bar?1) and acetone (260 Lm?2 h?1 bar?1). 相似文献
138.
A simple route for the synthesis of δ-amino-β-keto esters and δ-amino-β-diketones is reported. This involves regioselective addition of 1,3-dianions derived from ethyl acetoacetate and acetyl acetone to N-sulfonyl aldimines. The δ-amino-β-keto ester derivatives were further converted into the corresponding N-sulfonyl piperidines and N-sulfonyl azetidines. 相似文献
139.
Reaction of salicyldehyde thosemicarbazone (H2L1), 2-hydroxyacetophenone thiosemicarbazone (H2L2) and 2-hydroxynapthaldehyde thiosemicarbazone (H2L3) (general abbreviation H2L, where H2 stands for the two dissociable protons, one phenolic proton and one hydrazinic proton) with K2[PtCl4] afforded a family of polymeric complexes of type [{Pt(L)}n]. Reaction of the polymeric species with two monodentate ligands (D), viz. triphenylphosphine (PPh3) and 4-picoline (pic), yielded complexes of the type [Pt(L)(D)]. These mixed-ligand complexes were also obtained from the reaction of the thiosemicarbazones with [Pt(PPh3)2Cl2] and [Pt(pic)2Cl2]. The crystal structure of [Pt(PPh3)(L2)] has been determined. The thiosemicarbazone ligands are coordinated, via dissociation of the two protons, as dianionic tridentate O,N,S-donors. The [Pt(L)(D)] complexes show characteristic 1H NMR spectra and intense absorptions in the visible and ultraviolet region. They also fluoresce in the visible region at ambient temperature. 相似文献
140.