全文获取类型
收费全文 | 167篇 |
免费 | 2篇 |
国内免费 | 3篇 |
专业分类
化学 | 94篇 |
晶体学 | 3篇 |
力学 | 8篇 |
数学 | 43篇 |
物理学 | 24篇 |
出版年
2023年 | 2篇 |
2022年 | 5篇 |
2021年 | 4篇 |
2020年 | 6篇 |
2019年 | 12篇 |
2018年 | 7篇 |
2017年 | 4篇 |
2016年 | 5篇 |
2015年 | 1篇 |
2014年 | 5篇 |
2013年 | 10篇 |
2012年 | 12篇 |
2011年 | 16篇 |
2010年 | 6篇 |
2009年 | 6篇 |
2008年 | 7篇 |
2007年 | 8篇 |
2006年 | 8篇 |
2005年 | 6篇 |
2004年 | 4篇 |
2003年 | 10篇 |
2002年 | 6篇 |
2001年 | 4篇 |
2000年 | 2篇 |
1999年 | 1篇 |
1998年 | 4篇 |
1997年 | 2篇 |
1996年 | 2篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
排序方式: 共有172条查询结果,搜索用时 15 毫秒
41.
Chrostowska A Matrane A Maki D Khayar S Ushiki H Graciaa A Belachemi L Guillemin JC 《Chemphyschem》2012,13(1):226-236
Simple unsaturated and cyclopropylic isocyanides are synthesized by an efficient and simple approach. These compounds with gradually increasing distance between the unsaturated moiety and the isonitrile group are studied by UV photoelectron spectroscopy and quantum chemical calculations, and also compared to the corresponding nitriles. The first photoelectron band of the unsaturated compounds is linked to removal of an electron from the HOMO, which corresponds to CC multiple-bond ionization in antibonding interaction with the π-isocyanide bond (in the same plane) for conjugated systems, or in antibonding interaction with the pseudo-π-CH(2) group for isolated systems. For the 1-ethenyl derivatives, both cyano and isocyano groups act as a π-electron acceptor from the vinyl group, but the isocyano π system is much more strongly destabilized (ionization energies (IEs) shift to smaller values) by vinyl (3.12 eV) than the cyano π system is (2.70 eV). In comparison with the 1-ethynyl derivatives, a less pronounced destabilization (2.69 eV) of π(NC) by the ethynyl system (1.86 eV for π(CN)), and nearly the same order of magnitude of the energetic gap between the total antibonding (π(CC)-π(NC)) and the total bonding (π(CC)+π(NC)) IEs for ethenyl and ethynyl compounds are noted. The huge values of these last-named data for H(2)C=CH-NC (3.85 eV) and for HC≡C-NC (4.04 eV) reflect the strong interaction between the unsaturated carbon-carbon moiety and the isocyanide group, and thus more efficient conjugation than for the corresponding nitriles. 相似文献
42.
Kissi Benaissa Parron Vera Miguel Angel Rubio Cintas Maria Dlolores Dubujet Philippe Khamlichi Abdellatif Bezzazi Mohammed El Bakkali Larbi 《Applied Mathematical Modelling》2012
CFD simulation with enhanced modeling of turbulence and near-wall treatment is used to model water–clay mixtures flowing through a cylindrical pipe domain. Effects on the wall-shear stress resulting from varying water clay content and applied hydraulic gradient are analyzed. Various parametric studies were performed and had shown that the two-dimensional modelling introduced in the present study does not yield a uniform wall-shear stress along the pipe wall and that clay concentration affects significantly the wall-shear stress value. This is in contrast with the common hypothesis used in one-dimensional modeling approaches where this stress is assumed constant and which gives rise to uniform erosion along the pipe wall. The obtained results had enabled predicting more realistically erosion amount and had allowed for understanding the irregular eroded hole wall shape as observed experimentally after performing the standard hole erosion test. 相似文献
43.
Elaissi A Rouis Z Mabrouk S Salah KB Aouni M Khouja ML Farhat F Chemli R Harzallah-Skhiri F 《Molecules (Basel, Switzerland)》2012,17(3):3044-3057
The essential oils of fifteen Eucalyptus species harvested from the Jbel Abderrahman and Korbous arboreta (North East Tunisia) were screened for their antibacterial activities by the agar disc diffusion method. Eighteen major components as identified by GC/FID and GC/MS were selected for a study of the chemical and biological activity variability. The main one was 1,8-cineole, followed by spathulenol, trans-pinocarveol, α-pinene, p-cymene, globulol, cryptone, β-phellandrene, viridiflorol, borneol, limonene and isospathulenol. The chemical principal component analysis identified five species groups and subgroups, where each group constituted a chemotype, however that of the values of zone diameter of the inhibition (zdi) identified six groups of Eucalyptus oils, characterized by their antibacterial inhibition ability. The strongest activity was shown by E. platypus oil against Enterococcus faecalis and by E. lamannii oil against Staphylococcus aureus, Pseudomonas aeruginosa and Escherichia coli. A correlation between the levels of some major components and the antibacterial activities was observed. 相似文献
44.
Continuation of the phytochemical analysis of Erica cinerea fresh aerial parts resulted in the isolation of two new compounds with a very close chromatographic behavior. On the basis of spectroscopic evidence (UV, MS and NMR), the structures were established as (−)-(3S,6E)-1,9-bis(p-hydroxyphenyl)-3-hydroxynon-6-en-5-one 3-O-β-d-glucoside named 6,7-anhydroericaone 3-O-β-d-glucoside and (−)-(3S)-1,9-bis(p-hydroxyphenyl)-3-hydroxynonan-5,6-dione 3-O-β-d-glucoside named α-ericadione 3-O-β-d-glucoside. Unanticipated by its α-alkadione type structure —a very unusual feature in the plant kingdom— the latter metabolite was found as a mixture of the minor s-cis and the major s-trans conformers. Moreover, the GC-MS analysis of the aglycone moieties of such glucosides, pointed out the permanent absence of the molecular ion and the constant hydroxybenzylium base peak, as well as the conversion of the α-dione into the major α-keto-enol tautomer. 相似文献
45.
Mustapha Aitali Larbi El Firdoussi Abdellah Karim Alejandro F. Barrero Miguel Quirs 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(9):1088-1089
The title compound, [(S)‐2‐(anilinomethyl)pyrrolidine‐N,N′]‐chloro(η6‐para‐cymene)ruthenium(II) chloride, [RuCl‐(C10H14)(C11H16N2)]Cl, has been synthesized by the reaction of [RuCl2(p‐cymene)]2 (p‐cymene is para‐isopropyltoluene) with (S)‐2‐(anilinomethyl)pyrrolidine in triethylamine/2‐propanol. The Ru atom is in a pseudo‐tetrahedral environment coordinated by a chloride ligand, the aromatic hydrocarbon is linked in a η6 manner and the amine is linked via its two N atoms. The chloride anion is involved in hydrogen bonding with the diamine moieties through N—H?Cl interactions, with N?Cl distances of 3.273 (4) and 3.352 (4) Å. 相似文献
46.
Mouhammad El Hassan Laurent Keirsbulck Larbi Labraga 《Flow, Turbulence and Combustion》2009,82(3):359-374
The flow over a deep cavity at low subsonic velocity is considered in the present paper. The cavity length-to-depth aspect
ratio is L/H = 0.2. Single hot-wire measurements characterized the incident turbulent boundary layer and show the influence of the cavity
on the streamwise statistic components just downstream from the cavity. The streamwise mean and fluctuating velocity profiles
are affected by the cavity. PIV measurements reveal the presence for ejection-like events responsible of local perturbations
of the skewness and the flatness coefficients. Time-resolved PIV technic is also used to characterize phase properties of
shear layer oscillating cycle. It is shown that for deep cavity with first Rossiter mode, only one vortical structure is formed
at the cavity leading edge. Then, it grows while convecting downstream along the shear layer. A well-defined ejection process
begins after the vortex impact near the cavity downstream corner. A cylinder device placed spanwisely near the cavity leading
edge eliminates the resonance and highly modifies the behavior of the shear layer flow. In fact, the shear layer could be
divided into upper and lower parts with different structure aspects. 相似文献
47.
Bachir Douara Yannick J. Esvan Elisabeth Pereira Francis Giraud Yulia L. Volodina Dmitry N. Kaluzhny Alexander A. Shtil Fabrice Anizon Pascale Moreau 《Tetrahedron》2018,74(8):892-901
Pyrazole analogs of the staurosporine aglycon K252c were recently described as potent inhibitors of the three Pim protein kinase isoforms. To evaluate the impact of the introduction of a sugar moiety on the biological activities of this heterocyclic scaffold, four new glucosylated pyrazole analogs of K252c were synthesized. Their biological evaluation demonstrated that most active compounds 11 and 19 substituted by a β-d-glucosyl moiety at N12 or N13 positions exhibited antiproliferative activities toward HCT116 cells. 相似文献
48.
Lotfi Rghioui Lahcen El Ammari Larbi Benarafa Jean Pierre Wignacourt 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(7):i90-i91
The crystal structure of dipotassium caesium ytterbium bis(phosphate) is built up from regular independent PO4 tetrahedra and YbO6 octahedra sharing corners and arranged in layers. The structure is, in many respects, similar to that of glaserite. 相似文献
49.
Douaa Bekkai Yassine Oulad El Majdoub Hamid Bekkai Francesco Cacciola Natalizia Miceli Maria Fernanda Taviano Emilia Cav Tomader Errabii Roberto Lagan Vinci Luigi Mondello Mohammed LBachir El Kbiach 《Molecules (Basel, Switzerland)》2022,27(13)
This study aimed to investigate the phenolic profile and selected biological activities of the leaf and aerial extracts of three Ericaceae species, namely Erica multiflora, Erica scoparia, and Calluna vulgaris, collected from three different places in the north of Morocco. The phenolic composition of all extracts was determined by LC coupled with photodiode array and mass spectrometry detection. Among the investigated extracts, that of E. scoparia aerial parts was the richest one, with a total amount of polyphenols of 9528.93 mg/kg. Up to 59 phenolic compounds were detected: 52 were positively identified and 49 quantified—11 in C. vulgaris, 14 in E. multiflora, and 24 in E. scoparia. In terms of chemical classes, nine were phenolic acids and 43 were flavonoids, and among them, the majority belonged to the class of flavonols. The antioxidant activity of all extracts was investigated by three different in vitro methods, namely DPPH, reducing power, and Fe2+ chelating assays; E. scoparia aerial part extract was the most active, with an IC50 of 0.142 ± 0.014 mg/mL (DPPH test) and 1.898 ± 0.056 ASE/mL (reducing power assay). Further, all extracts were non-toxic against Artemia salina, thus indicating their potential safety. The findings attained in this work for such Moroccan Ericaceae species, never investigated so far, bring novelty to the field and show them to be valuable sources of phenolic compounds with interesting primary antioxidant properties. 相似文献
50.
DFT calculations with full geometry optimization using BP86-D and OPBE functionals have been performed on series of [(BDI)M(NH)]2(Bz) and [(BDI)M(NH)]2(Tol) (M = Ti, V, Nb, Cr, Mn, Fe, Co, and Ni; BDI = β-diketiminate; NH = imido group; Bz = benzene; and Tol = toluene) of various spin states (singlet S = 0, triplet S = 1, quintet S = 2, and singlet S = 0 of broken symmetry method). Depending on the metal nature and its electron count and the spin state, the six-membered ring in [(BDI)M(NH)]2(Bz) and [(BDI)M(NH)]2(Tol) adopts various hapticities that involve full or partial coordination, giving rise to a flat or a distorted ring, respectively. The NH2? imido group is linear or bent with respect to its sp or sp2 hybridization acting as a six- or a four-electron donor, respectively. The (BDI)? anion is a bidentate ligand as a six-electron donor. The optimized geometries do not show direct metal-metal bonding and correspond to long separations. The optimized structures for Nb metal are comparable to the available experimental ones. The Ziegler-Rauk energy decomposition analysis scheme was employed to characterize the geometry distortion, the steric interaction (electrostatic and Pauli), and the orbital interaction terms in the total bonding energy. The results showed that the interaction terms in all the studied complexes are governed by one third covalent and two thirds ionic characters, which are in agreement with the ΔEelstat (electrostatic) and ΔEorb (orbital) contributions, respectively, into the total attractive interaction (ΔEelstat + ΔEorb). 相似文献