全文获取类型
收费全文 | 88篇 |
免费 | 1篇 |
国内免费 | 2篇 |
专业分类
化学 | 53篇 |
晶体学 | 2篇 |
力学 | 2篇 |
数学 | 12篇 |
物理学 | 22篇 |
出版年
2022年 | 2篇 |
2021年 | 2篇 |
2020年 | 1篇 |
2019年 | 1篇 |
2018年 | 4篇 |
2017年 | 2篇 |
2016年 | 8篇 |
2015年 | 2篇 |
2014年 | 5篇 |
2013年 | 5篇 |
2012年 | 6篇 |
2011年 | 6篇 |
2010年 | 3篇 |
2009年 | 2篇 |
2008年 | 5篇 |
2007年 | 4篇 |
2006年 | 4篇 |
2005年 | 4篇 |
2004年 | 5篇 |
2003年 | 1篇 |
2002年 | 4篇 |
1999年 | 1篇 |
1998年 | 1篇 |
1997年 | 1篇 |
1995年 | 2篇 |
1994年 | 1篇 |
1991年 | 4篇 |
1989年 | 1篇 |
1984年 | 2篇 |
1972年 | 1篇 |
1965年 | 1篇 |
排序方式: 共有91条查询结果,搜索用时 15 毫秒
81.
Quantification of actinides in the complex environmental, biological, process and waste streams samples requires multiple steps like selective preconcentration and matrix elimination, solid source preparations generally by evaporation or electrodeposition, and finally alpha spectrometry. To minimize the sample manipulation steps, a membrane based isotope dilution alpha spectrometry method was developed for the determination of plutonium concentrations in the complex aqueous solutions. The advantages of this method are that it is Pu(IV) selective at 3 M HNO3, high preconcentration factor can be achieved, and obviates the need of solid source preparation. For this, a thin phosphate-sulfate bifunctional polymer layer was anchored on the surface of microporous poly(ethersulfone) membrane by UV induced surface grafting. The thickness of the bifunctional layer on one surface of the poly(ethersulfone) membrane was optimized. The thickness, physical and chemical structures of the bifunctional layer were studied by secondary ionization mass spectrometry (SIMS), scanning electron microscopy (SEM) and SEM-EDS (energy-dispersive spectroscopy). The optimized membrane was used for preconcentration of Pu(IV) from aqueous solutions having 3-4 M HNO3, followed by direct quantification of the preconcentrated Pu(IV) by isotope dilution alpha spectrometry using 238Pu spike. The chemical recovery efficiency of Pu(IV) was found to be 86 ± 3% below Pu(IV) loading capacity (1.08 μg in 2 × 1 cm2) of the membrane sample. The experiments with single representative actinides indicated that Am(III) did not sorb to significant extent (7%) but U(VI) sorbed with 78 ± 3% efficiency from the solutions having 3 M HNO3 concentration. However, Pu(IV) chemical recovery in the membrane remained unaffected from the solution containing 1:1000 wt. proportion of Pu(IV) to U(VI). Pu concentrations in the (U, Pu)C samples and in the irradiated fuel dissolver solutions were determined. The results thus obtained were found to be in good agreement with those obtained by conventional alpha spectrometry, biamperometry and thermal ionization mass spectrometry. 相似文献
82.
Energy calibration of superheated droplet detector is discussed in terms of the effective recoil nucleus threshold energy and the reduced superheat. This provides a universal energy calibration curve valid for different liquids used in this type of detector. Two widely used liquids, R114 and C4F10, one for neutron detection and the other for weakly interacting massive particles (WIMPs) dark matter search experiment, have been compared. Liquid having recoil nuclei with larger values of linear energy transfer (LET) provides better neutron-γ discrimination. Gamma (γ) response of C4F10 has also been studied and the results are discussed. Behaviour of nucleation parameter with the effective recoil nucleus threshold energy and the reduced superheat have been explored. 相似文献
83.
In this paper, we have developed a physics-based model for surface potential, channel potential, electric field and drain current for AlGaN/GaN high electron mobility transistor with high-K gate dielectric using two-dimensional Poisson equation under full depletion approximation with the inclusion of effect of polarization charges. The accuracy of the model has been verified and is found to be in good agreement with the simulated results. 相似文献
84.
The N4O3 coordinating heptadentate ligand afforded binuclear complex [Cu 2(H 2L)(mu-OH)](ClO4)2 (1) and [Cu2(L)(H2O)2]PF6 (2). In complex 1, two copper ions are held together by mu-phenoxo and mu-hydroxo bridges, whereas in complex 2, the copper centers are connected only by a mu-phenoxo bridge. In 1, both the Cu(II) centers have square pyramidal geometry (tau=0.01-0.205), whereas in the case of 2, one Cu(II) center has square pyramidal (tau=0.2517) and other one has square based pyramidal distorted trigonal bipyramidal (tau=0.54) geometry. Complexes 1 and 2 show an strong intramolecular and very weak antiferromagnetic interaction, respectively. Density-functional theory calculations were performed to establish the magneto structural correlation between the two paramagnetic copper(II) centers. Both of the complexes display a couple of one-electron reductive responses near -0.80 and -1.10 V. The complexes show significant catalytic activity at pH 8.5 on the oxidation of 3,5-di- tert-butylcatechol (3,5-DTBC) to 3,5-di- tert-butylquinone (3,5-DTBQ), and the activity measured in terms of kcat=29-37 h(-1). 相似文献
85.
Sudip Baguli Sumana Mondal Chhotan Mandal Santu Goswami Debabrata Mukherjee 《化学:亚洲杂志》2022,17(1):e202100962
The electron-rich cyclopentadienyl and the analogous indenyl and fluorenyl ligands (collectively denoted here as Cp’) have been impactful in stabilizing electron-deficient metal centers including the highly electropositive alkaline earths. Being in the s-block, the group 2 metals follow a major periodic variation in their atomic and ionic properties which is reflected in those Cp’ compounds. This article presents an overview of this class of compounds for all the five metals from beryllium to barium (radium is excluded for its radioactivity), highlighting their systematic variation. 相似文献
86.
López GE Colón-Díaz I Cruz A Ghosh S Nicholls SB Viswanathan U Hardy JA Auerbach SM 《The journal of physical chemistry. A》2012,116(4):1283-1288
We report gas-phase electronic structure calculations on helical peptides that act as scaffolds for imidazole-based hydrogen-bonding networks (proton wires). We have modeled various 21-residue polyalanine peptides substituted at regular intervals with histidines (imidazole-bearing amino acids), using a hybrid approach with a semiempirical method (AM1) for peptide scaffolds and density functional theory (B3LYP) for proton wires. We have computed energy landscapes including barriers for Grotthuss-shuttling-type proton motions though wires supported on 3(10)-, α- and π-helical structures, showing the 3(10)- and α-helices to be attractive targets in terms of high proton affinities, low Grotthuss shuttling barriers, and high stabilities. Moreover, bias forces provided by the helical dipole moments were found to promote unidirectional proton translocation. 相似文献
87.
Amitava Dutta Mahammad Ali Sumana Gangopadhyay Pradyot Banerjee 《Journal of Chemical Sciences》1994,106(4):881-886
The electron transfer reactions of Mo(CN)8
4, W(CN)8
4− and Fe(CN)6
4− with the manganese (III) complex oftrans-cyclohexane-1,2-diamine-N,N,N′,N′-tetraacetic acid have been studied by stopped-flow spectrophotometry in the pH range 2.0–6.5.
Analysis of kinetic data conforms to an outer-sphere process in each case. The validity of Marcus’ crossreaction relation
to these reactions is fairly satisfactory. 相似文献
88.
Abstract— Results concerning absorption-emission spectra and fluorescence quantum yields at 77 and 298K. triplet absorption spectra, and quantum yields of intersystem crossing and photoisomerization at 298 K, are presented for 11- cis β-apo-14'-carotenal (C22 -Ald), the immediate higher homologue of 11- cis retinal. The absorption spectra are characterized by two band-systems with maxima at 390–400 and 270–280 nm, respectively. Upon cooling from 298 to 77 K, the intensities of these two band-systems undergo changes in opposite directions indicating 12-s- cis: 12- s-trans conformational changes. No intermediate band-system analogous to the one located at 270–310 nm in cis retinals is observed for 11- cis C22 -Ald. In nonpolar hydrocarbon solvents (e. g. cyclohexane) at room temperature, quantum yields of fluorescence (0.01), intersystem crossing (0.6) and photoisomerization (0.4) are all quite pronounced. The photophysical and photochemical properties of 11- cis C22 -Ald are discussed in the light of similarities and dissimilarities with those of all- trans C22 -Ald and 11- cis retinal under comparable conditions. 相似文献
89.
Abstract— The spectra of absorption, fluorescence and excitation of monolayers and thin films containing chlorophyll a together with a carotenoid (cis-β-carotene, trans-β-carotene, fucoxanthin, or zeaxanthin), were measured at — 196°C. The concentration ratios used, (Chl)/(Car), were 6:1, 4:1, 3:1, 2:1, 1:1 and 1:3, and the area densities, 3·70, 2·55, 1·76, 0·71, 0·37 and 0·17 nm2/pigment molecule. In dilute monolayers, (3·70 nm2/molecule), with a constant concentration ratio (Chl)/(Car) = 3:1, evidence of three β-carotene forms, with absorption bands at 460, 500 and 520 nm (C460, C500 and C520), and of a chlorophyll a form with an absorption band at 669–672 (Chl669–672) was found. On increasing the density to 0·2–0·3 nm2/molecule, a conversion of C460 and C520 into C500, was observed, and several more additional (probably more strongly aggregated) chlorophyll a forms appeared, with absorption bands at 672–733 nm. With excess carotene [(Chi)/(Car) = 1:3] the forms C460, C500, C520 and Chl669–672 were present even in the most dense films (0·2–0·3 nm2/molecule). The same was found with other carotenoids: if one of the pigments was in excess, aggregated forms of the other tended to disappear. In the transfer of energy from carotenoids to chlorophyll a, C500 was found to be the main donor. In layers with a concentration ratio (Chl)/(Car) = 3:1, the efficiency of transfer was less than 10 per cent at the lowest density used (3·70 nm2/molecule); it increased to 50 per cent, as the density was increased to 0·20 nm2/molecule. When the relative concentration of the carotenoid was increased to (Chl)/(Car) = 1:1, the efficiency of energy transfer dropped to 25 per cent even at 0·20 nm2/molecule. It seems that the efficiency of energy transfer between carotene molecules (prior to its transfer to chlorophyll a) is low, and effective transfer occurs only between β-carotene and immediately adjacent chlorophyll a molecules. 相似文献
90.
In this study the electron transfer theory for the high frequency intramolecular mode and low frequency medium mode has been rederived using different methods. For a single-mode case when the reactant surface is not in a thermal equilibrium but in a thermocoherent state the authors have derived the rate and discussed about the quantum features of the rate. In the limit of very low and very high temperatures the expressions are derived analytically and compared with the case of thermal distribution. Secondly, a Franck-Condon factor for a multimode displaced, distorted, and Duschinsky rotated adiabatic potential surfaces has been derived to obtain the rate. Lastly, a systematic investigation is made to show the temperature dependence on the rate due to displacement, distortion, and Duschinsky rotation of the harmonic potential energy surfaces of the reactant and product manifold. 相似文献