全文获取类型
收费全文 | 217篇 |
免费 | 4篇 |
国内免费 | 4篇 |
专业分类
化学 | 136篇 |
晶体学 | 2篇 |
力学 | 16篇 |
数学 | 39篇 |
物理学 | 32篇 |
出版年
2022年 | 8篇 |
2021年 | 12篇 |
2020年 | 2篇 |
2019年 | 12篇 |
2018年 | 13篇 |
2017年 | 7篇 |
2016年 | 8篇 |
2015年 | 11篇 |
2014年 | 12篇 |
2013年 | 18篇 |
2012年 | 15篇 |
2011年 | 12篇 |
2010年 | 19篇 |
2009年 | 15篇 |
2008年 | 12篇 |
2007年 | 17篇 |
2006年 | 12篇 |
2005年 | 6篇 |
2004年 | 3篇 |
2003年 | 3篇 |
2002年 | 3篇 |
2000年 | 1篇 |
1997年 | 1篇 |
1996年 | 3篇 |
排序方式: 共有225条查询结果,搜索用时 390 毫秒
101.
Mark A. Beard Oana R. Ghita James McCabe Kenneth E. Evans 《Journal of Raman spectroscopy : JRS》2010,41(10):1283-1288
The dehydration kinetics of theophylline monohydrate is a two‐stage process. The first stage involves loosening of the crystal water followed by a second stage in which the water evaporates from the sample. During differential scanning calorimetry (DSC) measurements, the kinetics of the two stages can be dramatically altered because of the sample environment and DSC pan type. In‐depth understanding of how the sample environment alters the dehydration process and the kinetics involved requires more than DSC experiments alone. This paper describes the use of a novel, simultaneous thermal and spectral technique to monitor the dehydration kinetics of theophylline monohydrate. The analysis of the results obtained on the combined DSC‐near‐infrared and DSC‐Raman equipment clearly detects the two stages of the dehydration process and the polymorphic structural changes that take place. The combined technique provides a powerful method to monitor the dehydration of hydrous systems. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
102.
103.
V. Golovanov M. Viitala T. Kortelainen O. Cramariuc T.T. Rantala 《Surface science》2010,604(19-20):1784-1790
Siloxane is a favorable candidate as an anchor group that can be used to bind organic molecules to SnO2 surfaces, with a wide range of practical applications. Therefore, adsorption geometries and energies of siloxane coupler on the SnO2 (110) surface have been investigated in this study using quantum-chemical periodic density functional theory (DFT) calculations. We present a comparative study of different siloxane adsorption arrangements on pristine and fluorine doped SnO2 surface. According to the calculations, the surface doping with fluorine leads to stabilization of the siloxane network at the stannic oxide surface. The trend is analyzed in terms of additional charge provided by F impurities to the chemisorbed oxygen atoms thus increasing the ionicity of their bonding. Implications of the current findings for the design of organic-metal oxide interface with better thermo-stability and improved electronic properties are discussed. 相似文献
104.
Oana Mocioalca 《Journal of Functional Analysis》2005,222(2):385-434
We extend the Skorohod integral, allowing integration with respect to Gaussian processes that can be more irregular than any fractional Brownian motion. This is done by restricting the class of test random variables used to define Skorohod integrability. A detailed analysis of the size of this class is given; it is proved to be non-empty even for Gaussian processes which are not continuous on any closed interval. Despite the extreme irregularity of these stochastic integrators, the Skorohod integral is shown to be uniquely defined, and to be useful: an Ito formula is established; it is employed to derive a Tanaka formula for a corresponding local time; linear additive and multiplicative stochastic differential equations are solved; an analysis of existence for the stochastic heat equation is given. 相似文献
105.
Oana Ursache Constantin Gaina Viorica Gaina Nita Tudorachi Alexandra Bargan Cristian-Dragos Varganici Dan Rosu 《Journal of Thermal Analysis and Calorimetry》2014,118(3):1471-1481
Thermoreversible networks obtained by the Diels–Alder cycloaddition reaction of poly(vinyl furfural) with urethane bismaleimides containing polyether chain were synthesized. The formation of the networks was confirmed by attenuated total reflectance in conjunction with Fourier transform infrared spectroscopy (ATR–FTIR). The materials thermal properties were investigated using differential scanning calorimetry (DSC) and a coupling of dynamic thermogravimetry with Fourier transform infrared spectroscopy and mass spectrometry (TG–FTIR–MS) for pyrolysis behaviour under nitrogen atmosphere. A thermal decomposition mechanism of the networks and poly(vinyl furfural) was discussed via evolved gas analysis. The thermoreversibility of the networks was demonstrated by the presence of the endothermic peak characteristic to the retrodienic process on the DSC heating curves and also the appearance of the exothermic peak, due to the dienic process, on the DSC cooling curve. The dynamic contact angle and free surface energy values of the networks were determined. Measures of the heterogeneity and roughness of the surfaces suggested that the surfaces of the networks’ films are more homogenous than the initial poly(vinyl furfural) surface. Dynamic water vapour sorption studies were conducted. 相似文献
106.
New polyesters were prepared from several aromatic phosphonic dichlorides and a diolic monomer bearing a cyclic bulky group containing phosphorus. From kinetic investigation, the rates of polycondensation in melt were calculated and compared with those of the reaction between aromatic diols and phosphonic dichloride. Polyesters were analytically, spectral and thermally characterized and effect of structure on optical properties was investigated. 相似文献
107.
We define and study a class of summable processes, called additive summable processes, that is larger than the class used
by Dinculeanu and Brooks [D-B].
We relax the definition of a summable processesX:Ω×ℝ+→E⊂L(F, G) by asking for the associated measureI
X to have just an additive extension to the predictableσ-algebra ℘, such that each of the measures (I
X)
z
, forz∈(L
G
p
)*, beingσ-additive, rather than having aσ-additive extension. We define a stochastic integral with respect to such a process and we prove several properties of the
integral. After that we show that this class of summable processes contains all processesX:Ω×ℝ+→E⊂L(F, G) with integrable semivariation ifc
0 ∋G. 相似文献
108.
109.
110.
Spectral-Luminescent Properties and Molecular Orbital Treatment of Some Mono- and Difluoroquinolones
Polishchuk AV Karaseva ET Emelina TB Cramariuc O Karasev VE 《Journal of fluorescence》2011,21(3):1293-1300
Electronic absorption and luminescent spectra of nonfluorinated nalidixic (nlqH) and pipemidic acid (pifqH), monofluoroquinolones
– norfloxacin (nfqH) and pefloxacin (pfqH) as well as of their difluorinated analogs 1-ethyl-6,8-difluoro-1,4-dihydro-7-(1-(4-methylpiperazinyl)
– 4-oxo-3-quinolinecarboxylic (mdfqH) acid and 1-ethyl-6,8-difluoro-1,4-dihydro-7-(1-piperazinyl) – 4-oxo-3-quinolinecarboxylic
acid (dfqH) - were investigated. Quantum yields, lifetimes of excited states and rate constants of radiative and nonradiative
transitions of the compounds were measured. The Mulliken charges of atoms from these compounds were calculated by quantum-chemical
complex GAMESS. Differences in the electronic structures of these compounds and their spectral-luminescent characteristics
were compared with the data of the phototoxicity degree of fluoroquinolones. Analysis of the Mulliken charges of the difluoroquinolones
points to the changes of the redistribution of the electron density along π-conjugated system, and on the oxygen atoms of
the carbonyl and carboxyl groups. The analysis of the molecular orbitals involved in the electronic transitions of the compounds
revealed that both defluorination and piperazine photolysis are photodecomposition mechanisms which may take place in the
excited states of these compounds. The relationship between the location order of the π-π* excited levels of the FQs and the
degree of their phototoxicity has been determined 相似文献