全文获取类型
收费全文 | 151篇 |
免费 | 6篇 |
国内免费 | 1篇 |
专业分类
化学 | 122篇 |
晶体学 | 1篇 |
数学 | 18篇 |
物理学 | 17篇 |
出版年
2023年 | 1篇 |
2022年 | 1篇 |
2021年 | 2篇 |
2020年 | 6篇 |
2019年 | 5篇 |
2018年 | 3篇 |
2017年 | 3篇 |
2016年 | 5篇 |
2015年 | 2篇 |
2014年 | 8篇 |
2013年 | 7篇 |
2012年 | 8篇 |
2011年 | 12篇 |
2010年 | 7篇 |
2009年 | 3篇 |
2008年 | 13篇 |
2007年 | 7篇 |
2006年 | 8篇 |
2005年 | 19篇 |
2004年 | 4篇 |
2003年 | 4篇 |
2002年 | 2篇 |
2001年 | 3篇 |
2000年 | 1篇 |
1999年 | 1篇 |
1997年 | 2篇 |
1995年 | 1篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1984年 | 1篇 |
1982年 | 1篇 |
1978年 | 2篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1974年 | 1篇 |
1971年 | 1篇 |
1968年 | 1篇 |
1941年 | 1篇 |
1934年 | 2篇 |
1930年 | 2篇 |
排序方式: 共有158条查询结果,搜索用时 15 毫秒
41.
Pászti Z Hakkel O Keszthelyi T Berkó A Balázs N Bakó I Guczi L 《Langmuir : the ACS journal of surfaces and colloids》2010,26(21):16312-16324
Gold based model systems exhibiting the structural versatility of nanoparticle ensembles and being accessible for surface spectroscopic investigations are expected to provide new information about the adsorption of carbon monoxide, a key process influencing the CO oxidation activity of this noble metal in nanoparticulate form. Accordingly, in the present work the interaction of CO is studied with an ion bombardment modified Au(111) surface by means of a combination of photoelectron spectroscopy (XPS and UPS), sum frequency generation vibrational spectroscopy (SFG), and scanning tunneling microscopy (STM). While no adsorption was found on intact Au(111), data collected on the ion bombarded surface at cryogenic temperatures indicated the presence of stable CO adsorbates below 190 K. A quantitative evaluation of the C 1s XPS spectra and the surface morphology explored by STM revealed that the step edge sites created by ion bombardment are responsible for CO adsorption. The identification of the CO binding sites was confirmed by density functional theory (DFT) calculations. Annealing experiments up to room temperature showed that at temperatures above 190 K unstable adsorbates are formed on the surface under dynamic exposure conditions that disappeared immediately when gaseous CO was removed from the system. Spectroscopic data as well as STM records revealed that prolonged CO exposure at higher pressures of up to 1 mbar around room temperature facilitates massive atomic movements on the roughened surface, leading to its strong reordering toward the structure of the intact Au(111) surface, accompanied by the loss of the CO binding capacity. 相似文献
42.
Orsolya Jójárt-Laczkovich Piroska Szabó-Révész 《Journal of Thermal Analysis and Calorimetry》2010,102(1):243-247
Amorphization is nowadays a method that is frequently applied in the pharmaceutical industry. The primary aim of this study
is to achieve the amorphization of clopidogrel hydrogen sulphate as an active pharmaceutical ingredient (API) with various
solvents and to choose the most suitable one. A secondary aim was to determine the glass-transition temperature (T
g) of this API and to classify it as a good or poor glass former. To investigate the amorphous form, differential scanning
calorimetry, X-ray powder diffraction, and FT-IR analysis were applied. The melting point (T
m) was 177.4 °C (450.6 K), and T
g was determined to be 88.9 °C (362.1 K). The quotient T
g/T
m was 0.80, and this API was therefore classified as a good glass former. 相似文献
43.
Yoshihara T Druzhinin SI Demeter A Kocher N Stalke D Zachariasse KA 《The journal of physical chemistry. A》2005,109(8):1497-1509
For the electron acceptor/donor molecule N-phenylpyrrole (PP), the fast intramolecular charge transfer (ICT) reaction accompanied by dual fluorescence from a locally excited (LE) and an ICT state is investigated in alkyl cyanide solvents as a function of temperature. After a comparison of the X-ray crystal structure of PP with calculations from the literature, absorption and fluorescence spectra of PP in a series of solvents over a wide polarity range are discussed. ICT with PP strongly depends on solvent polarity and starts to appear in solvents more polar than diethyl ether. From an analysis of the ICT/LE fluorescence quantum yield ratio Phi'(ICT)/Phi(LE), approximate data for the change in enthalpy -DeltaH of the ICT reaction of PP are obtained, ranging from 9 kJ/mol in acetonitrile (MeCN) to 4 kJ/mol in n-butyl cyanide (BuCN). From ICT and LE fluorescence decays of PP measured as a function of temperature, the forward (Ea = 9 kJ/mol in ethyl cyanide (EtCN) and 6 kJ/mol in MeCN) and backward (Ed = 16 kJ/mol in EtCN and MeCN) ICT reaction barriers are determined. From these data, -Delta H (7 kJ/mol (EtCN); 10 kJ/mol (MeCN)) is calculated, in good agreement with the results coming from Phi'(ICT)/Phi(LE). The data for Ea show that the forward ICT barrier becomes smaller with increasing solvent polarity, whereas the absence of change for Ed comes from the compensating increase of -DeltaH. Both observations are indicative of a late transition state for the LE --> ICT reaction. For PP in EtCN and MeCN, the ICT radiative rate constant k'(f)(ICT) increases with temperature. This is caused by the ICT low transition dipole moment and hence does not contain information on the molecular structure (twisted or planar) of the ICT state. The fast ICT observed with PP supports our previous conclusion, based on a comparison of PP with its planarized derivative fluorazene, that the pyrrole and phenyl moieties in the ICT state of PP are coplanar and possess substantial electronic coupling. 相似文献
44.
Abstract— The effect of inactivation of water-splitting enzyme on the thermoluminescence of isolated chloroplasts was investigated. The inhibitory treatments used included Tris-washing, alkaline pH in the presence of the uncoupler gramicidin, incubation with a high concentration of magnesium ions and different chaotropic agents. It was found that inhibition of oxygen evolution resulted in the disappearance of the main thermoluminescence band at +20°C. The A band which appears at — 10°C and has been related to the S4 state of the water-splitting enzyme (Inoue, 1981) was not considerably affected by the inhibition of oxygen evolution. The results presented here indicate that the participation of the S4 state of water-splitting enzyme in the generation of the A band should be reinvestigated. 相似文献
45.
Demeter Krupka 《International Journal of Theoretical Physics》1978,17(5):359-368
The second-order generally invariant Lagrangians for the metric fields are studied within the framework of the Ehresmann theory of jets. Such a Lagrangian is a function on an appropriate fiber bundle whose structure group is the groupL
n
3 of invertible 3-jets with source and target at the origin 0 of the real,n-dimensional Euclidean spaceR
n, and whose type fiber is the manifold Tn
2(Rn* R
n*) of 2-jets with source at 0 R
n and target in the symmetric tensor productR
n*
Rn*. Explicit formulas for the action ofL
n
3 onT
n
2(Rn* R
n*) are considered, and a complete system of differential identities for the generally invariant Lagrangians is obtained. 相似文献
46.
47.
Demeter Krupka Olga Krupková Geoff Prince 《Differential Geometry and its Applications》2007,25(5):518-542
In this paper, vector fields which are symmetries of the contact ideal are studied. It is shown that contact symmetries of the Helmholtz form transform a dynamical form to a dynamical form which is variational (i.e. comes as the Euler-Lagrange form from a Lagrangian). The case of dynamical forms representing first-order classes in the variational sequence is analysed in detail, which means, by the variational sequence theory, that systems of ordinary differential equations of order ?3 are concerned. 相似文献
48.
László K Czakkel O Josepovits K Rochas C Geissler E 《Langmuir : the ACS journal of surfaces and colloids》2005,21(18):8443-8451
Small-angle X-ray scattering (SAXS) measurements using contrast variation are reported for activated carbons prepared from poly(ethyleneterephthalate). The carbon surfaces are functionalized to different degrees by cold and hot nitric acid treatment. The latter treatment reduces the surface area by 75%, but the pore size distribution in the micropore range is hardly affected. Seven liquids, n-hexane, i-octane, i-propanol, cyclohexane, toluene, alpha-pinene, and nitrobenzene, in addition to water vapor, were used as contrast modifiers. Although the values of the specific surface area S(X) deduced from these measurements are relatively insensitive to the solvent, the detailed SAXS spectra reveal interactions occurring on different spatial scales that depend on the surface chemistry of the carbon and on the physicochemical properties of the solvent. In the most heavily oxidized sample, the amphiphilic molecule i-propanol stabilizes the surface structure, whereas nonpolar molecules make the rough surface smoother. In the untreated and the lightly functionalized carbons, water vapor at 50% relative humidity condenses only partially in the micropores at room temperature, whereas in the heavily treated sample condensation in the micropores is practically complete. 相似文献
49.
L. Keszthelyi I. Demeter Z. Sz kefalvi-Nagy L. Varga Z. Z mori 《Nuclear Physics A》1968,120(3):540-544
The g-factor of the 320 keV first excited state of 51V measured by Coulomb excitation in Fe-V alloy was found to be g = 1.54±0.13. 相似文献
50.