全文获取类型
收费全文 | 280篇 |
免费 | 4篇 |
专业分类
化学 | 192篇 |
晶体学 | 7篇 |
力学 | 12篇 |
数学 | 24篇 |
物理学 | 49篇 |
出版年
2022年 | 6篇 |
2021年 | 6篇 |
2020年 | 2篇 |
2019年 | 3篇 |
2018年 | 7篇 |
2017年 | 4篇 |
2016年 | 5篇 |
2015年 | 6篇 |
2014年 | 4篇 |
2013年 | 20篇 |
2012年 | 14篇 |
2011年 | 26篇 |
2010年 | 10篇 |
2009年 | 9篇 |
2008年 | 14篇 |
2007年 | 21篇 |
2006年 | 14篇 |
2005年 | 6篇 |
2004年 | 6篇 |
2003年 | 3篇 |
2002年 | 5篇 |
2001年 | 3篇 |
1999年 | 2篇 |
1998年 | 7篇 |
1997年 | 4篇 |
1996年 | 3篇 |
1994年 | 4篇 |
1993年 | 3篇 |
1992年 | 2篇 |
1991年 | 2篇 |
1989年 | 5篇 |
1988年 | 2篇 |
1987年 | 3篇 |
1985年 | 2篇 |
1984年 | 5篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1978年 | 6篇 |
1977年 | 5篇 |
1976年 | 3篇 |
1975年 | 7篇 |
1974年 | 3篇 |
1973年 | 2篇 |
1972年 | 1篇 |
1965年 | 1篇 |
1963年 | 1篇 |
1960年 | 1篇 |
排序方式: 共有284条查询结果,搜索用时 15 毫秒
121.
Structural,optical, electrical and luminescence properties of electron beam evaporated CdSe:In films
M. G. Syed Ahamed Basheer K. S. Rajni V. S. Vidhya V. Swaminathan A. Thayumanavan K. R. Murali M. Jayachandran 《Crystal Research and Technology》2011,46(3):261-266
CdSe:In films were prepared by electron beam evaporation technique using CdSe and In2Se3 (purity ∼99.9%) pellets. The crystal structure of the films with and without Indium, measured by X‐ray diffraction (XRD), showed a typical wurtzite structure, higher Indium doping shifts the peak angle to higher side along with the broadening of the peaks. X‐ray photoelectron spectroscopy (XPS) studies indicated binding energies corresponding to 54 eV (Se3d5/2), 444 eV (In 3d5/2), 411 eV (Cd 3d3/2), (Cd 3d5/2). Atomic force microscope (AFM) studies indicated a uniform surface.The grain size decreases with increase of In doping. A decrease in the band gap was observed with increase of dopant concentration. Resistivity of the films is in the range of 10‐3 Ωcm. Carrier density was in the range of 1021 cm‐3 for the films. The photolumineasenec spectra (PL) spectra indicated three peaks. The peak intensity decreases as the Indium concentration increases. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
122.
In this work, using subordination results for the Cesáro sum of certain analytic functions, a concept called Cesáro stable is given and two conjectures in this direction are also proposed. Using an extension of Vietoris’ theorem on positivity of cosine sums, some results on positivity of cosine and sine sums are obtained. These results are useful in discussing some particular cases of the proposed conjectures. 相似文献
123.
124.
Fang J Guo Y Lu G Raston CL Iyer KS 《Dalton transactions (Cambridge, England : 2003)》2011,40(13):3122-3124
Doped lanthanum phosphate nanocrystals are a class of fluorescent material of enormous interest, presenting an unusual dichotomy on the nanoscale. The quantum yields of these crystals drops significantly in the nanoscale when compared with the corresponding bulk yields. Herein we show that the suppression of their thermodynamically favored 1-D growth in the nanoscale results in an increase in the quantum yield. This is possible by inducing heterogeneous nucleation of the crystals on the surface of single walled carbon nanotubes. 相似文献
125.
Fluorimetric titrations of 4-hydroxydiphenyl ether and its anion give stretched sigmoid curves with two inflection points. This reveals that the rates of excited state proton exchange are comparable to the rates of deactivation of the conjugate pair. These curves are analyzed using the lifetimes of the species. The excited state equilibrium constants determined from rate constants and by other methods are compared. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 861–867, 1997 相似文献
126.
127.
Residual structures in denatured proteins have acquired importance in recent years owing to their role as protein-folding
initiation sites. Locating these structures in proteins has proved quite formidable, requiring techniques like NMR. Here in
this report, we take advantage of the ubiquitous presence of tryptophan residues in residual structures to hunt for their
presence using steady-state fluorescence spectroscopy. The surface accessibility and rotational dynamics of tryptophan in
putative residual structures among ten different proteins, namely glucagon, melittin, subtilisin carlsberg, myelin basic protein,
ribonuclease T1, human serum albumin, barstar mutant, bovine serum albumin, lysozyme and Trp-Met-Asp-Phe-NH2 peptide, was studied using steady state fluorescence quenching and anisotropy, respectively. Five proteins, namely ribonuclease
T1, bovine serum albumin, melittin, barstar and hen egg white lysozyme appear likely to possess tryptophan(s) in hydrophobic
clusters based on their reduced bimolecular quenching rates and higher steady-state anisotropy in proportion to their chain
length. We also show that the fluorescence emission maximum of tryptophan is insensitive to the presence of residual structures. 相似文献
128.
Dr. Jaume Garcia‐Amorós Subramani Swaminathan Prof. Salvatore Sortino Prof. Françisco M. Raymo 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(33):10276-10284
The covalent attachment of a carbazole fluorophore to an oxazine photochrome permits the reversible activation of fluorescence under optical control. Ultraviolet irradiation with a pulsed laser opens the oxazine ring to shift bathochromically the absorption of the carbazole component. Concomitant visible illumination excites selectively the carbazole fluorophore of the photochemical product to produce fluorescence. The photogenerated and fluorescent species reverts spontaneously on a submicrosecond timescale to the initial nonemissive state of the carbazole–oxazine dyad. The photochemical and photophysical properties engineered into this particular molecular switch allow the convenient monitoring of plasmonic effects on photochemical reactions with fluorescence measurements. In close proximity to silver nanoparticles, visible illumination with a continuous‐wave laser also results in fluorescence activation. The metallic nanostructures enable the two‐photon excitation of the oxazine component to induce the photochromic transformation and then facilitate the one‐photon excitation of the photochemical product to generate fluorescence. Thus, these operating principles offer the opportunity to avoid altogether the need of pulsed ultraviolet irradiation to trigger the photochromic transformation and, instead, allow fluorescence activation with a single visible source operating at low illumination power. 相似文献
129.
Muttaiya Sundaralingam Richard G. Brennan Panchanadam Swaminathan Tuli P. Haromy William B. Drendel James N. Bemiller 《Journal of carbohydrate chemistry》2013,32(1):85-103
Abstract The title compounds 1 and 2 (both C15O15NH21) crystallized in the monoclinic space group P21 (Z = 2) with a=8.864(1), b=8.346(1), c =13.569(1)Å, β =114.12(1), V=918.1(2)A3, D(calc) = 1.358 g/cc for compound 1, and a=15–045(1), b=8.106(1), c=7.491(1)Å, β =97.23(1)°, V=906.4(3)Å3 D(calc)= 1.375 g/cc, for compound 2. The structures were solved by direct methods and refined by the full-matrix least squares technique to R indices of 0.010 and 0.046, respectively. Both compounds are in the α ? D configuration and adopt the unusual 2C5, (1C4) chair conformation with the carbamoyl groups on the anomeric carbon atoms equatorially oriented. In this conformation the orientations of the substituents are 2e, 3a, 4a, 5a and 6a in 1 and 2e, 3a, 4a, 5e and 6a in 2 which leads to unfavorable 1,3-diaxial interactions. The “reverse anomeric effect” which induces the 2c5 chair conformation in these compounds, may have its origin in the unfavorable steric interactions found in the 5c2 (4C1) conformation where the carbamoyl group is axially oriented. Furthermore, the 2C5 conformation is stabilized by the N-H … O intramolecular hydrogen bond between the carbamoyl nitrogen atom and the pyranosyl ring oxygen atom. Semi-empirical energy calculations reveal that the rotational freedom of the carbamoyl group is greater for the equatorial orientation (2C5) than for the axial orientation (5C2). 相似文献
130.
Dendritic chelating agents. 1. Cu(II) binding to ethylene diamine core poly(amidoamine) dendrimers in aqueous solutions 总被引:2,自引:0,他引:2
Diallo MS Christie S Swaminathan P Balogh L Shi X Um W Papelis C Goddard WA Johnson JH 《Langmuir : the ACS journal of surfaces and colloids》2004,20(7):2640-2651
This paper describes an investigation of the uptake of Cu(II) by poly(amidoamine) (PAMAM) dendrimers with an ethylenediamine (EDA) core in aqueous solutions. We use bench scale measurements of proton and metal ion binding to assess the effects of (i) metal ion-dendrimer loading, (ii) dendrimer generation/terminal group chemistry, and (iii) solution pH on the extent of binding of Cu(II) in aqueous solutions of EDA core PAMAM dendrimers with primary amine, succinamic acid, glycidol, and acetamide terminal groups. We employ extended X-ray absorption fine structure (EXAFS) spectroscopy to probe the structures of Cu(II) complexes with Gx-NH2 EDA core PAMAM dendrimers in aqueous solutions at pH 7.0. The overall results of the proton and metal ion binding measurements suggest that the uptake of Cu(II) by EDA core PAMAM dendrimers involves both the dendrimer tertiary amine and terminal groups. However, the extents of protonation of these groups control the ability of the dendrimers to bind Cu(II). Analysis of the EXAFS spectra suggests that Cu(II) forms octahedral complexes involving the tertiary amine groups of Gx-NH2 EDA core PAMAM dendrimers at pH 7.0. The central Cu(II) metal ion of each of these complexes appears to be coordinated to 2-4 dendrimer tertiary amine groups located in the equatorial plane and 2 axial water molecules. Finally, we combine the results of our experiments with literature data to formulate and evaluate a phenomenological model of Cu(II) uptake by Gx-NH2 PAMAM dendrimers in aqueous solutions. At low metal ion-dendrimer loadings, the model provides a good fit of the measured extent of binding of Cu(II) in aqueous solutions of G4-NH2 and G5-NH2 PAMAM dendrimers at pH 7.0. 相似文献