全文获取类型
收费全文 | 196篇 |
免费 | 1篇 |
专业分类
化学 | 128篇 |
晶体学 | 3篇 |
力学 | 3篇 |
数学 | 12篇 |
物理学 | 51篇 |
出版年
2023年 | 1篇 |
2022年 | 3篇 |
2021年 | 5篇 |
2020年 | 4篇 |
2019年 | 2篇 |
2018年 | 2篇 |
2017年 | 1篇 |
2016年 | 3篇 |
2015年 | 2篇 |
2014年 | 9篇 |
2013年 | 18篇 |
2012年 | 13篇 |
2011年 | 33篇 |
2010年 | 6篇 |
2009年 | 5篇 |
2008年 | 5篇 |
2007年 | 13篇 |
2006年 | 15篇 |
2005年 | 6篇 |
2004年 | 5篇 |
2003年 | 1篇 |
2002年 | 8篇 |
2001年 | 2篇 |
2000年 | 4篇 |
1997年 | 3篇 |
1996年 | 2篇 |
1995年 | 3篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1992年 | 1篇 |
1991年 | 2篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1987年 | 2篇 |
1986年 | 4篇 |
1984年 | 1篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 1篇 |
排序方式: 共有197条查询结果,搜索用时 250 毫秒
181.
Melquizedeque B. Alves Vianney O. Santos jr. Valerio C. D. Soares Paulo A. Z. Suarez Joel C. Rubim 《Journal of Raman spectroscopy : JRS》2008,39(10):1388-1395
Anionic species formed in mixtures of 1‐n‐butyl‐3‐methylimidazolium chloride (BMICl) with different amounts of niobium pentachloride (NbCl5) or zinc dichloride (ZnCl2) were investigated by Raman spectroscopy. In the BMICl and NbCl5 ionic mixtures the presence of the anion NbCl6− was detected for all compositions (molar fraction, X) and a mixture of this anion and the neutral Nb2Cl10 in acid ones. Two different anions were observed for basic mixtures of BMICl and ZnCl2: ZnCl42−(0 < X < 0.35) and Zn2Cl62−(X > 0.3), whereas for acidic ones three species were detected: Zn2Cl62−(X < 0.7), Zn3Cl82−(X > 0.7) and Zn4Cl102−(X > 0.7). It has also been observed that in both cases, the formation of larger anions causes a shift of the C H stretching modes to higher wavenumbers as the result of a decrease in the hydrogen bond between Cl and the hydrogens from the cation. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
182.
Reliable diffusion coefficients, D, for the diffusion of perchlorate anions into polypyrrole films during polymeric oxidation were obtained from chronoamperometric results. Two different models were used to calculate D: the Cottrell equation and the electrochemically stimulated conformational relaxation (ESCR) model. As expected, the initial Cottrell hypothesis was far from swelling/shrinking polymeric electrodes and the obtained D range was from 10(-10) to 10(-6) cm(2) s(-1). The ESCR model, based on the internal diffusion that takes place from regions where the steady state of oxidation has already been reached to regions where the oxidation is only just beginning, provided values of D ranging from 0.4 x 10(-9) to 2.2 x 10(-9) cm(2) s(-1), which is close to the values expected for a gel. When a constant amplitude is kept for the potential step, D increases with increasing initial anodic potentials, i.e., from increasingly swollen films. When it is stepped to the same oxidation potential, D decreases when starting from more cathodic potentials, i.e., from a more compact structure. These changes in D can be attributed to (i) swelling processes during oxidation, giving a gel-like structure; (ii) compacting processes at increasing cathodic potentials; (iii) the increasing thickness of the film during oxidation; and (iv) a decrease in film viscosity during the swelling process. 相似文献
183.
Nanoscale energy deposition by X-ray absorbing nanostructures 总被引:1,自引:0,他引:1
Carter JD Cheng NN Qu Y Suarez GD Guo T 《The journal of physical chemistry. B》2007,111(40):11622-11625
Here we wish to demonstrate a unique property of nanomaterials: energy deposition with nanometer precision from low-energy electrons released from these nanostructures interacting with hard X-ray radiation in aqueous solution. Three effects combine to cause this phenomenon: (1) localized absorption of X-rays by nanostructures, (2) effective release of low-energy electrons from small nanostructures, and (3) efficient deposition of energy in water in the form of radicals and electrons. This combination creates localized X-ray absorption and localized energy deposition of nanometer precision. We confirmed the theoretically predicted nanoscale energy deposition distribution by measuring hydroxyl radical-induced DNA strand breaks, and observed enhanced damage to a 5600-bp DNA molecule from approximately 10 chemically conjugated small gold nanoparticles under X-ray radiation. These results provide a general guidance to applications of this new concept in many fields including radiation chemistry, radiology, radiation oncology, biochemistry, biology, and nanotechnology. 相似文献
184.
Lyaskovskyy V Suarez AI Lu H Jiang H Zhang XP de Bruin B 《Journal of the American Chemical Society》2011,133(31):12264-12273
The mechanism of cobalt(II) porphyrin-catalyzed benzylic C-H bond amination of ethylbenzene, toluene, and 1,2,3,4-tetrahydronaphthalene (tetralin) using a series of different organic azides [N(3)C(O)OMe, N(3)SO(2)Ph, N(3)C(O)Ph, and N(3)P(O)(OMe)(2)] as nitrene sources was studied by means of density functional theory (DFT) calculations and electron paramagnetic resonance (EPR) spectroscopy. The DFT computational study revealed a stepwise radical process involving coordination of the azide to the metal center followed by elimination of dinitrogen to produce unusual "nitrene radical" intermediates (por)Co(III)-N(?)Y (4) [Y = -C(O)OMe, -SO(2)Ph, -C(O)Ph, -P(O)(OMe)(2)]. Formation of these nitrene radical ligand complexes is exothermic, predicting that the nitrene radical ligand complexes should be detectable species in the absence of other reacting substrates. In good agreement with the DFT calculations, isotropic solution EPR signals with g values characteristic of ligand-based radicals were detected experimentally from (por)Co complexes in the presence of excess organic azide in benzene. They are best described as nitrene radical anion ligand complexes (por)Co(III)-N(?)Y, which have their unpaired spin density located almost entirely on the nitrogen atom of the nitrene moiety. These key cobalt(III)-nitrene radical intermediates readily abstract a hydrogen atom from a benzylic position of the organic substrate to form the intermediate species 5, which are close-contact pairs of the thus-formed organic radicals R'(?) and the cobalt(III)-amido complexes (por)Co(III)-NHY ({R'(?)···(por)Co(III)-NHY}). These close-contact pairs readily collapse in a virtually barrierless fashion (via transition state TS3) to produce the cobalt(II)-amine complexes (por)Co(II)-NHYR', which dissociate to afford the desired amine products NHYR' (6) with regeneration of the (por)Co catalyst. Alternatively, the close-contact pairs {R'(?)···(por)Co(III)-NHY} 5 may undergo β-hydrogen-atom abstraction from the benzylic radical R'(?) by (por)Co(III)-NHY (via TS4) to form the corresponding olefin and (por)Co(III)-NH(2)Y, which dissociates to give Y-NH(2). This process for the formation of olefin and Y-NH(2) byproducts is also essentially barrierless and should compete with the collapse of 5 via TS3 to form the desired amine product. Alternative processes leading to the formation of side products and the influence of different porphyrin ligands with varying electronic properties on the catalytic activity of the cobalt(II) complexes have also been investigated. 相似文献
185.
Rodríguez H Martin O Suarez M Martín N Albericio F 《Molecules (Basel, Switzerland)》2011,16(11):9620-9635
Here we describe the efficient synthesis of alkyl 4-arylsubstituted-6-chloro-5-formyl-2-methyl-1,4-dihydropyridine-3-carboxylates and 4-arylsubstituted-4,7-dihydro-furo[3,4-b]pyridine-2,5(1H,3H)-diones via microwave-accelerated reaction of alkyl 4-arylsubstituted-2-methyl-6-oxo-1,4,5,6-tetrahydro-3-pyridinecarboxylates with the appropriate reagents. This eco-friendly approach to these valuable dihydropyridine derivatives does not involve the harsh or highly contaminating conditions common in classical heating and offers a reduction or even elimination of solvent use and recovery, simplification of the work-up procedures, facility of scale up, and low energy consumption, in addition to moderate to higher yields. 相似文献
186.
Khachatryan V Sirunyan AM Tumasyan A Adam W Bergauer T Dragicevic M Erö J Fabjan C Friedl M Frühwirth R Ghete VM Hammer J Hänsel S Hartl C Hoch M Hörmann N Hrubec J Jeitler M Kasieczka G Kiesenhofer W Krammer M Liko D Mikulec I Pernicka M Rohringer H Schöfbeck R Strauss J Taurok A Teischinger F Wagner P Waltenberger W Walzel G Widl E Wulz CE Mossolov V Shumeiko N Suarez Gonzalez J Benucci L Cerny K De Wolf EA Janssen X Maes T Mucibello L Ochesanu S Roland B Rougny R Selvaggi M Van Haevermaet H 《Physical review letters》2011,106(20):201804
Dijet angular distributions are measured over a wide range of dijet invariant masses in pp collisions at √s = 7 TeV, at the CERN LHC. The event sample, recorded with the CMS detector, corresponds to an integrated luminosity of 36 pb?1. The data are found to be in good agreement with the predictions of perturbative QCD, and yield no evidence of quark compositeness. With a modified frequentist approach, a lower limit on the contact interaction scale for left-handed quarks of Λ? = 5.6 TeV (Λ? = 6.7 TeV) for destructive (constructive) interference is obtained at the 95% confidence level. 相似文献
187.
Chatrchyan S Khachatryan V Sirunyan AM Tumasyan A Adam W Bergauer T Dragicevic M Erö J Fabjan C Friedl M Frühwirth R Ghete VM Hammer J Hänsel S Hoch M Hörmann N Hrubec J Jeitler M Kiesenhofer W Krammer M Liko D Mikulec I Pernicka M Rahbaran B Rohringer H Schöfbeck R Strauss J Taurok A Teischinger F Wagner P Waltenberger W Walzel G Widl E Wulz CE Mossolov V Shumeiko N Suarez Gonzalez J Bansal S Benucci L De Wolf EA Janssen X Maes J Maes T Mucibello L Ochesanu S Roland B Rougny R Selvaggi M 《Physical review letters》2011,107(5):052302
A comparison of the relative yields of Υ resonances in the μ(+)μ(-) decay channel in Pb-Pb and pp collisions at a center-of-mass energy per nucleon pair of 2.76 TeV is performed with data collected with the CMS detector at the LHC. Using muons of transverse momentum above 4 GeV/c and pseudorapidity below 2.4, the double ratio of the Υ(2S) and Υ(3S) excited states to the Υ(1S) ground state in Pb-Pb and pp collisions, [Υ(2S+3S)/Υ(1S)](Pb-Pb)/[Υ(2S+3S)/Υ(1S)](pp), is found to be 0.31(-0.15)(+0.19)(stat)±0.03(syst). The probability to obtain the measured value, or lower, if the true double ratio is unity, is calculated to be less than 1%. 相似文献
188.
Babul Chandra Nath Sebastin Suarez Fabio Doctorovich Tapashi G. Roy Ricardo Baggio 《Acta Crystallographica. Section C, Structural Chemistry》2013,69(7):689-695
Two copper complex solvatomorphs, namely (3,10‐C‐meso‐3,5,7,7,10,12,14,14‐octamethyl‐1,4,8,11‐tetraazacyclotetradecane)bis(perchlorato‐κO)copper(II) 1.2‐hydrate, [Cu(ClO4)2(C18H40N4)]·1.2H2O, (I), and (3,10‐C‐meso‐3,5,7,7,10,12,14,14‐octamethyl‐1,4,8,11‐tetraazacyclotetradecane)bis(perchlorato‐κO)copper(II), [Cu(ClO4)2(C18H40N4)], (II), are described and compared with each other and with a third, already reported, anhydrous diastereomer, denoted (III). Both compounds present very similar centrosymmetic coordination environments, with the CuII cation lying on an inversion centre in a distorted 4+2 octahedral environment, defined by the macrocyclic N4 group in the equatorial sites and two perchlorate groups in trans‐axial positions [one of the perchlorate ligands in (I) is partially disordered]. The most significant difference in molecular shape is seen in the orientation of the perchlorate anions, and the influence of this on the intramolecular hydrogen bonding is discussed. The (partially) hydrated state of (I) favours the formation of chains along [011], while the anhydrous character of (II) and (III) promotes loosely bound structures with low packing indices. 相似文献
189.
Sabina Yasmin Sebastin Suarez Fabio Doctorovich Tapashi G. Roy Ricardo Baggio 《Acta Crystallographica. Section C, Structural Chemistry》2013,69(8):862-867
The three transition‐metal complexes, (meso‐5,7,7,12,14,14‐hexamethyl‐1,4,8,11‐tetraazacyclotetradecane‐κ4N)bis(perchlorato‐κO)copper(II), [Cu(ClO4)2(C18H40N4)], (I), (meso‐5,7,7,12,14,14‐hexamethyl‐1,4,8,11‐tetraazacyclotetradecane‐κ4N)bis(nitrato‐κO)zinc(II), [Zn(NO3)2(C18H40N4)], (II), and aquachlorido(meso‐5,7,7,12,14,14‐hexamethyl‐1,4,8,11‐tetraazacyclotetradecane‐κ4N)copper(II) chloride, [CuCl(C18H40N4)(H2O)]Cl, (III), are described. The molecules display a very similarly distorted 4+2 octahedral environment for the cation [located at an inversion centre in (I) and (II)], defined by the macrocycle N4 group in the equatorial sites and two further ligands in trans‐axial positions [two O–ClO3 ligands in (I), two O–NO2 ligands in (II) and one chloride and one aqua ligand in (III)]. The most significant difference in molecular shape resides in these axial ligands, the effect of which on the intra‐ and intermolecular hydrogen bonding is discussed. In the case of (I), all strong hydrogen‐bond donors are saturated in intramolecular interactions, while weak intermolecular C—H...O contacts result in a three‐dimensional network. In (II) and (III), instead, there are N—H and O—H donors left over for intermolecular interactions, giving rise to the formation of strongly linked but weakly interacting chains. 相似文献
190.
Cristian Paz Robles Darío Mercado Sebastin Suarez Ricardo Baggio 《Acta Crystallographica. Section C, Structural Chemistry》2014,70(12):1112-1115
A cocrystal, C15H22O3·C15H22O3, (I), obtained from Drimys winteri, is composed of two isomeric drimane sesquiterpene lactones, namely valdiviolide, (Ia), and 11‐epivaldiviolide, (Ib), neither of which has been reported in the crystal form. Both diastereoisomers present three chiral centres at sites 5, 10 and 11, with an SSR sequence in (Ia) and an SSS sequence in (Ib). O—H...O hydrogen bonds bind molecules into chains running along [20] and the chains are in turn linked by π–π stacking interactions to define planar weakly interacting arrays parallel to (001). 相似文献