全文获取类型
收费全文 | 185篇 |
免费 | 8篇 |
国内免费 | 3篇 |
专业分类
化学 | 155篇 |
晶体学 | 1篇 |
力学 | 5篇 |
数学 | 10篇 |
物理学 | 25篇 |
出版年
2022年 | 3篇 |
2021年 | 13篇 |
2020年 | 1篇 |
2019年 | 3篇 |
2018年 | 1篇 |
2017年 | 4篇 |
2016年 | 4篇 |
2015年 | 4篇 |
2014年 | 8篇 |
2013年 | 19篇 |
2012年 | 11篇 |
2011年 | 7篇 |
2010年 | 5篇 |
2009年 | 7篇 |
2008年 | 10篇 |
2007年 | 10篇 |
2006年 | 9篇 |
2005年 | 11篇 |
2004年 | 17篇 |
2003年 | 14篇 |
2002年 | 9篇 |
2000年 | 5篇 |
1999年 | 8篇 |
1997年 | 4篇 |
1996年 | 3篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1982年 | 1篇 |
1977年 | 2篇 |
1972年 | 1篇 |
排序方式: 共有196条查询结果,搜索用时 15 毫秒
121.
Lucian-Cristian Pop Nadia Katir Annie Castel Luminita Silaghi-Dumitrescu Fabien Delpech Ioan Silaghi-Dumitrescu Heinz Gornitzka Desmond MacLeod-Carey Nathalie Saffon 《Journal of organometallic chemistry》2009,694(9-10):1562-1566
New phosphenium cations stabilized by bidentate monoanionic N-isopropyl-2-(isopropylamino)troponiminate or 2-(isopropylamino)troponate units have been synthesized. These complexes were characterized by 31P, 1H and 13C NMR spectroscopies, and the molecular structures were determined by X-ray crystallography. These data indicate the formation of N,N′- and N,O-chelate derivatives having three-coordinate phosphorous atoms included in planar heterobicycles. Moreover, computational studies support the presence of high delocalization of the positive charge into the π-conjugated carbon backbone and of the high-lying phosphorus lone-pair orbital. 相似文献
122.
The acidity of tert-butyl alcohol in near- and supercritical water: a polarizable continuum approach
We use a polarizable continuum approach to study the acidity of tert-butyl alcohol in water at ambient, near-critical, and supercritical conditions. In the most straightforward calculation, the bare ionic species (the tert-butoxy anion and the hydronium cation) are placed in cavities surrounded by a dielectric continuum, using a dielectric constant corresponding to the state point. A second method is first to solvate these ions with a small number of explicit water molecules and then surround this cluster with the dielectric. This is the cluster-continuum approach. We discuss the advantages and disadvantages of these two schemes and we also discuss various ways in which the second method can be implemented. No method showed quantitative agreement with all available experimental results but the first, straightforward method was the most successful in predicting the correct trends. From both a numerical and a theoretical point of view, we believe this is the method of choice. 相似文献
123.
Dr. Monique Chan‐Huot Prof. Stephen Wimperis Prof. Christel Gervais Prof. Geoffrey Bodenhausen Dr. Luminita Duma 《Chemphyschem》2015,16(1):204-215
Deuterium (2H) magic‐angle spinning (MAS) nuclear magnetic resonance is applied to monitor the dynamics of the exchanging labile deuterons of polycrystalline L ‐histidine hydrochloride monohydrate‐d7 and α‐oxalic acid dihydrate‐d6. Direct experimental evidence of fast dynamics is obtained from T1Z and T1Q measurements. Further motional information is extracted from two‐dimensional single‐quantum (SQ) and double‐quantum (DQ) MAS spectra. Differences between the SQ and DQ linewidths clearly indicate the presence of motions on intermediate timescales for the carboxylic moiety and the D2O in α‐oxalic acid dihydrate, and for the amine group and the D2O in L ‐histidine hydrochloride monohydrate. Comparison of the relaxation rate constants of Zeeman and quadrupolar order with the relaxation rate constants of the DQ coherences suggests the co‐existence of fast and slow motional processes. 相似文献
124.
O. Carp L. Patron E. Segal R. Barjega M. Brezeanu 《Journal of Thermal Analysis and Calorimetry》1999,56(2):513-518
Bd. Republicii, Nr. 13, sector 2, Bucharest The thermal behaviour of the polynuclear coordination compounds [Fe12?xSr(malic)19?1.5x]·18H2O and [Fe12?xSr(gluc)19?1.5x]·20H2O precursors of strontium hexaferrite was investigated, and a decomposition mechanism is proposed. A pure hexaferrite with a mean crystallite size value of about 250 Å was obtained after 5 h calcination at 800°C of the gluconic precursor (x=1.5). 相似文献
125.
Luminita Silaghi‐Dumitrescu Ion Silaghi‐Dumitrescu Ionel Haiduc Rubn‐Alfredo Toscano Vernica García‐Montalvo Raymundo Cea‐Olivares 《无机化学与普通化学杂志》1999,625(2):347-351
The distortion from the octahedral geometry is discussed for Indium(III) 1,1‐dithio complexes (dithiophosph(in)ates, dithiocarbamates, dithioarsinates) and isostructural chromium(III) compounds in relation with the bite of the ligands, the S…S repulsion within the four members rings and S…S interligand distances. The crystal and molecular structures of In(S2AsR2)3 (R = Me, Ph) have been determined by single crystal X‐ray diffraction. The dithioarsinate ligands are basically monomeric and isobidentate, with average values for arsenic‐sulphur bond distances of 2.135 Å for dimethyl and 2.137 Å for diphenyl complex. The average In–S distances are identical (2.634 Å) in both cases. 相似文献
126.
Stela Dragan Demetra Dragan Mariana Cristea Anton Airinei Luminita Ghimici 《Journal of polymer science. Part A, Polymer chemistry》1999,37(4):409-418
We report on the formation of the polycation/dye/polyanion (PC/D/PA) complexes by the interaction between nonstoichiometric polycation/dye (PC/D) complexes with polyanions. Polycations differed in their content of the (N,N‐dimethyl‐2‐hydroxypropylene ammonium chloride) units in the main chain. Poly(sodium acrylate) (NaPA), poly(sodium 2‐acrylamido‐2‐methylpropane sulfonate) (NaPAMPS) and poly(sodium styrenesulfonate) (NaPSS) were used as polyanions. Crystal Ponceau 6R (CP6R) and Ponceau 4R (P4R) with two or three sulfonic groups were used as anionic dyes. The interaction between nonstoichiometric PC/D complexes and polyanions was followed by UV‐VIS spectroscopy, viscometry, and conductometry measurements. Formation of PC/D/PA complexes takes place mainly by the electrostatic interaction between the polyanion and the free positive charges of the nonstoichiometric PC/D complex. The stoichiometry and the stability of the tricomponent complexes depended on the polycation structure, the structure and molecular weight of polyanion, the dye structure, and the P/D molar ratio. A high amount of the dye was excluded from the complex before the end point when a branched polycation was used. The higher the solubility of the dye the lower the stability of the PC/D/PA complexes. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 409–418, 1999 相似文献
127.
Luminita Ghimici Stela Dragan Florin Popescu 《Journal of Polymer Science.Polymer Physics》1997,35(16):2571-2581
The interaction of several mono-, di-, and trivalent anions with cationic polyelectrolytes having different contents in N,N-dimethyl-2-hydroxypropylen ammonium chloride units (polymer A) or tertiary amine N-atoms and PEG (polymer PEGA) in the main chain was studied by viscosimetric and conductometric measurements. Both methods have shown a stronger interaction for tri- and bi- than for univalent counterions. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 2571–2581, 1997 相似文献
128.
Luminita Capatina Edoardo Marco Napoli Giuseppe Ruberto Lucian Hritcu 《Molecules (Basel, Switzerland)》2021,26(23)
Origanum vulgare ssp. hirtum has been used as medicinal herbs promoting antioxidant, anti-inflammatory, antimicrobial, and neuroprotective activities. We investigated the protective effects and the mechanism of O. vulgare ssp. hirtum essential oil (OEO) on cognitive impairment and brain oxidative stress in a scopolamine (Sco)-induced zebrafish (Danio rerio) model of cognitive impairment. Our results show that exposure to Sco (100 µM) leads to anxiety, spatial memory, and response to novelty dysfunctions, whereas the administration of OEO (25, 150, and 300 µL/L, once daily for 13 days) reduced anxiety-like behavior and improved cognitive ability, which was confirmed by behavioral tests, such as the novel tank-diving test (NTT), Y-maze test, and novel object recognition test (NOR) in zebrafish. Additionally, Sco-induced brain oxidative stress and increasing of acetylcholinesterase (AChE) activity were attenuated by the administration of OEO. The gas chromatography–mass spectrometry (GC-MS) analyses were used to elucidate the OEO composition, comprising thymol (38.82%), p-cymene (20.28%), and γ-terpinene (19.58%) as the main identified components. These findings suggest the ability of OEO to revert the Sco-induced cognitive deficits by restoring the cholinergic system activity and brain antioxidant status. Thus, OEO could be used as perspective sources of bioactive compounds, displaying valuable biological activities, with potential pharmaceutical applications. 相似文献
129.
Luminita Muntean Ion Grosu Gerard Plé Sorin Mager Ioan Silaghi-Dumitrescu 《Monatshefte für Chemie / Chemical Monthly》2000,131(9):975-983
Summary. The synthesis and the stereochemistry of new spiro-1,3-perhydrooxazines are reported. The stereoisomerism of these compounds
is discussed considering the data of conformational analysis, the helical chirality of the spiro[5.5]undecane skeleton, and
the triligand virtual chiral center belonging to the 1,3-perhydrooxazine ring.
Received February 21, 2000. Accepted (revised) April 18, 2000 相似文献
130.
Luminita Muntean Ion Grosu Gerard Plé Sorin Mager Ioan Silaghi-Dumitrescu 《Monatshefte für Chemie / Chemical Monthly》2000,51(11):975-983
The synthesis and the stereochemistry of new spiro-1,3-perhydrooxazines are reported. The stereoisomerism of these compounds is discussed considering the data of conformational analysis, the helical chirality of the spiro[5.5]undecane skeleton, and the triligand virtual chiral center belonging to the 1,3-perhydrooxazine ring. 相似文献