全文获取类型
收费全文 | 243篇 |
免费 | 6篇 |
专业分类
化学 | 180篇 |
晶体学 | 2篇 |
力学 | 4篇 |
数学 | 36篇 |
物理学 | 27篇 |
出版年
2023年 | 1篇 |
2022年 | 10篇 |
2021年 | 18篇 |
2020年 | 10篇 |
2019年 | 5篇 |
2018年 | 6篇 |
2017年 | 3篇 |
2016年 | 4篇 |
2015年 | 10篇 |
2014年 | 9篇 |
2013年 | 20篇 |
2012年 | 18篇 |
2011年 | 21篇 |
2010年 | 14篇 |
2009年 | 11篇 |
2008年 | 22篇 |
2007年 | 12篇 |
2006年 | 12篇 |
2005年 | 10篇 |
2004年 | 9篇 |
2003年 | 4篇 |
2002年 | 6篇 |
1999年 | 1篇 |
1998年 | 1篇 |
1997年 | 1篇 |
1995年 | 3篇 |
1994年 | 2篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1979年 | 1篇 |
排序方式: 共有249条查询结果,搜索用时 166 毫秒
121.
Cristian Vasile Grigoras Anca Giorgiana Grigoras 《Journal of Thermal Analysis and Calorimetry》2011,103(2):661-668
Standard and StepScan DSC studies have been performed on a series of statistical methacrylate copolymers with electron-donor
and electron-acceptor pendant groups that form intramolecular electron transfers. From standard DSC analysis we concluded
that glass transition temperature slowly increased with increasing electron-acceptor monomeric moiety ratio up to 0.5 in the
main chain. Using StepScan DSC method we calculated the size and volume of cooperative rearranging region as well mean temperature
fluctuation at glass transition temperature. It was estimated also the average number of monomer units in the cooperative
rearranging region. All parameters were calculated according to the method proposed by Donth based on Heat Capacity Spectroscopy.
The results show that the presence of intermonomeric electron transfers decreased the chain mobility, as well as the cooperativity
of relaxation processes of these structures in the glass transition range. This is reflected by minimal values of these parameters
around 0.4 ratio of copolymer composition. Such behavior is similar to that of crosslinked or confined systems (e.g., nanocomposites,
thin films) that have reduced chain mobility. 相似文献
122.
Anca Mihaela Mocanu Lucia Odochian N. Apostolescu C. Moldoveanu 《Journal of Thermal Analysis and Calorimetry》2011,103(1):283-291
The article is devoted to a comparative study on the thermal degradation of some new diazoaminoderivatives under both air
and nitrogen atmosphere by TG-FTIR analysis. The TG–DTG–DTA curves show the thermal degradation in air to present two temperature
domains: an endothermic one identical to the case of the degradation under nitrogen and an exothermic one which is not to
be found under nitrogen atmosphere. The identification of the gaseous species released by degradation in air within the endothermic
domain made evident the presence of the same components of the degradation in nitrogen atmosphere. In the exothermic domain
of the sample degradation in air, the CO2, H2O, SO2 species result by the burning of the molecular residues of the first domain. The obtained results afforded a degradation
mechanism to be advanced that coincide for the endothermic domain with that of degradation under nitrogen atmosphere. Due
to the importance of these compounds as possible reaction initiators and also as potentially bioactive substances (herbicides,
acaricides, fungicides), the study on their thermal degradation could give useful information on the environmental impact
of the degradation products resulting by the thermal processing of the plants which could possible retain these compounds,
when the initial degradation temperature is exceeded. 相似文献
123.
124.
Pop A Silvestru A Gimeno MC Laguna A Kulcsar M Arca M Lippolis V Pintus A 《Dalton transactions (Cambridge, England : 2003)》2011,40(46):12479-12490
Reactions between methyldiphenylphosphane selenide, SePPh(2)Me, and different group 11 metal starting materials {CuCl, [CuNO(3)(PPh(3))(2)], AgOTf, [AgOTf(PPh(3))] (OTf = OSO(2)CF(3)), [AuCl(tht)], [Au(C(6)F(5))(tht)] and [Au(C(6)F(5))(3)(tht)] (tht = tetrahydrothiophene)} were performed in order to obtain several new species with metal-selenium bonds. The new complexes [CuCl(SePPh(2)Me)] (1), [AgOTf(SePPh(2)Me)] (2), [AuCl(SePPh(2)Me)] (5), [Au(C(6)F(5))(SePPh(2)Me)] (6) and [Au(C(6)F(5))(3)(SePPh(2)Me)] (7) were isolated and structurally characterized in solution by multinuclear NMR spectroscopy ((1)H, (31)P, (77)Se and (19)F where appropriate). Solid products were isolated also from the reactions between SePPh(2)Me and [CuNO(3)(PPh(3))(2)] or [AgOTf(PPh(3))], respectively. NMR experiments, including low temperature (1)H and (31)P NMR, revealed for them a dynamic behaviour in solution, involving the transfer of selenium from PPh(2)Me to PPh(3). In case of the isolated silver(i) containing solid an equilibrium between, respectively, monomeric [AgOTf(PPh(3))(SePPh(2)Me)] (3) and [AgOTf(PPh(2)Me)(SePPh(3))] (4), and dimeric [Ag(PPh(3))(μ-SePPh(2)Me)](2)(OTf)(2) (3a) and [Ag(PPh(2)Me)(μ-SePPh(3))](2)(OTf)(2) (4a) species was observed in solution. In case of the isolated copper(i) containing solid the NMR studies brought no clear evidence for a similar behaviour, but it can not be excluded in a first stage of the reaction. However the transfer of selenium between the two triorganophosphanes takes place also in this case, but the NMR spectra suggest that the final reaction mixture contains the free triorganophospane selenides SePPh(2)Me and SePPh(3) as well as the complex species [CuNO(3)(PPh(3))(2)], [CuNO(3)(PPh(2)Me)(2)] and [CuNO(3)(PPh(3))(PPh(2)Me)] in equilibrium. Single-crystal X-ray diffraction studies revealed monomeric structures for the gold(I) 6 and gold(III) 7 complexes. In case of compound 6 weak aurophilic gold(I)···gold(I) contacts were also observed in the crystal. DFT calculations were performed in order to understand the solution behaviour of the silver(I) and copper(I) species containing both P(III) and P(V) ligands, to verify the stability of possible dimeric species and to account for the aurophilic interactions found for 6. In addition, the nature of the electronic transitions involved in the absorption/emission processes observed for 6 and 7 in the solid state were also investigated by means of TD-DFT calculations. 相似文献
125.
Anca Stănescu 《代数通讯》2013,41(5):1697-1726
We define crossed product categories and we show that they are equivalent with cleft comodule categories. We also prove that a comodule category is cleft if and only if it is Hopf–Galois and has a normal basis. As an application we show that the category of Hopf modules over a cleft linear category and the category of modules over the coinvariant subcategory are equivalent. 相似文献
126.
Anca Capatina 《Numerical Functional Analysis & Optimization》2013,34(7-8):817-828
We are interested in finding the coefficient of friction which leads us to a given displacement on the contact surface between an elastic solid body and a rigid foundation. The mathematical formulation of the problem is an optimal control problem governed by a quasivariational inequality. We obtain an approximative caracterization, by using two families of penalized and regularized problems, for a given optimal control. 相似文献
127.
Rideout MC Boldt JL Vahi-Ferguson G Salamon P Nefzi A Ostresh JM Giulianotti M Pinilla C Segall AM 《Molecular diversity》2011,15(4):989-1005
Holliday junctions (HJs) are critical intermediates in many recombination-dependent DNA repair pathways. Our lab has previously
identified several hexameric peptides that target HJ intermediates formed in DNA recombination reactions. One of the most
potent peptides, WRWYCR, is active as a homodimer and has shown bactericidal activity partly because of its ability to interfere
with DNA repair proteins that act upon HJs. To increase the possibility of developing a therapeutic targeting DNA repair,
we searched for small molecule inhibitors that were functional surrogates of the peptides. Initial screens of heterocyclic
small molecule libraries resulted in the identification of several N-methyl aminocyclic thiourea inhibitors. Like the peptides, these inhibitors trapped HJs formed during recombination reactions
in vitro, but were less potent than the peptides in biochemical assays and had little antibacterial activity. In this study,
we describe the screening of a second set of libraries containing somewhat larger and more symmetrical scaffolds in an effort
to mimic the symmetry of a WRWYCR homodimer and its target. From this screen, we identified several pyrrolidine bis-cyclic
guanidine inhibitors that also interfere with processing of HJs in vitro and are potent inhibitors of Gram-negative and especially
Gram-positive bacterial growth. These molecules are proof-of-principle of a class of compounds with novel activities, which
may in the future be developed into a new class of antibiotics that will expand the available choices for therapy against
drug-resistant bacteria. 相似文献
128.
George Denis Alexandru Popescu Cristian Scheau Ioana Anca Badarau Mihai-Daniel Dumitrache Ana Caruntu Andreea-Elena Scheau Daniel Octavian Costache Raluca Simona Costache Carolina Constantin Monica Neagu Constantin Caruntu 《Molecules (Basel, Switzerland)》2021,26(1)
Gastrointestinal (GI) cancers are a group of diseases with very high positions in the ranking of cancer incidence and mortality. While they show common features regarding the molecular mechanisms involved in cancer development, organ-specific pathophysiological processes may trigger distinct signaling pathways and intricate interactions with inflammatory cells from the tumoral milieu and mediators involved in tumorigenesis. The treatment of GI cancers is a topic of increasing interest due to the severity of these diseases, their impact on the patients’ survivability and quality of life, and the burden they set on the healthcare system. As the efficiency of existing drugs is hindered by chemoresistance and adverse reactions when administered in high doses, new therapies are sought, and emerging drugs, formulations, and substance synergies are the focus of a growing number of studies. A class of chemicals with great potential through anti-inflammatory, anti-oxidant, and anti-tumoral effects is phytochemicals, and capsaicin in particular is the subject of intensive research looking to validate its position in complementing cancer treatment. Our paper thoroughly reviews the available scientific evidence concerning the effects of capsaicin on major GI cancers and its interactions with the molecular pathways involved in the course of these diseases. 相似文献
129.
Andrei Rotaru Anca Moanţă Cătălin Constantinescu Marius Dumitru Horia Octavian Manolea Andreea Andrei Maria Dinescu 《Journal of Thermal Analysis and Calorimetry》2017,128(1):89-105
Azoic dyes are compounds of interest from the point of view of their potential applications, such as the use of liquid crystals in optoelectronic and organic electroluminescent devices, or may be employed as template matrices for producing high-aspect ratio inorganic nanomaterials. Herein, 4-[(4-chlorobenzyl)oxy]-3,4′-dichloroazobenzene azoic dye, known as CODA, is selected as a choice compound among such materials due to its liquid crystalline properties and may be further used as nanostructured material in various applications. Thermokinetic study of CODA azoic dye thermal decomposition in air flow atmosphere was performed by employing thermogravimetric data; the kinetic parameters of the two decomposition steps were obtained under non-isothermal linear regimes, by means of multi-heating rates methods. Differential and integral “model-free” kinetic methods like Friedmann, Kissinger–Akahira–Sunose and Ortega, the invariant kinetic parameters method and the Perez-Maqueda et al. criterion (by Coats–Redfern and differential equations) were used. The kinetic study reveals very different behaviour related to the two decomposition steps of CODA, with complex processes composed of more than one kinetic mechanism for each of those, as indicated also by the Gotor et al. master plot method. Modern devices incorporating such materials tend to use them as thin films due to their specific properties; the CODA thin films were deposited on silicon substrates by matrix-assisted pulsed laser evaporation technique, using a Nd:YAG laser working at the wavelength of 266 nm. The preservation of the CODA compound after the transfer on the substrates was confirmed by Fourier transform infrared spectroscopy, while the morphology and topography of the deposited materials and of the thin film surfaces were investigated by atomic force microscopy and optical microscopy. 相似文献
130.
Iuliana Sebarchievici Anca Lascu Gheorghe Fagadar-Cosma Anca Palade Ionela Fringu Mihaela Birdeanu Bogdan Taranu Eugenia Fagadar-Cosma 《Comptes Rendus Chimie》2018,21(3-4):327-338
The developments concerning new hybrids based on porphyrin derivatives and colloids destined for the detection of ascorbic acid (AA) in the relevant range for medical investigations are presented. Mn(III) tetratolylporphyrin chloride (MnTTPCl), spherical gold colloid (n-Au), and their hybrid (MnTTPCl/n-Au) were chosen to be comparatively investigated by ultraviolet–visible spectroscopy in the presence of AA. The hybrid material (MnTTPCl/n-Au) has the best capacity to detect concentrations of AA in the range of 2.6 × 10?6–4.38 × 10?5 M. Modified glassy carbon (GC) electrodes were obtained by thin film deposition of MnTTPCl, n-Au alone, and in successive mixed thin films, comparing their response during the electrochemical oxidation of AA. The electrocatalytic effect of the MnTTPCl on the AA oxidation is justified both by the increase in the peak current density and by the shift toward more negative potentials (0.024 V). The GC/MnTTPCl electrode has the best electrocatalytic effect for the AA oxidation and is promising for sensor applications. 相似文献