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排序方式: 共有250条查询结果,搜索用时 15 毫秒
201.
Gerardo Caballero Mariana Gallo JavierM. Montserrat AdolfoM. Iribarren 《Helvetica chimica acta》2002,85(5):1284-1294
We describe the stereoselective synthesis of (2′S)‐2′‐deoxy‐2′‐C‐methyladenosine ( 12 ) and (2′S)‐2′‐deoxy‐2′‐C‐methylinosine ( 14 ) as well as their corresponding cyanoethyl phosphoramidites 16 and 19 from 6‐O‐(2,6‐dichlorophenyl)inosine as starting material. The methyl group at the 2′‐position was introduced via a Wittig reaction (→ 3 , Scheme 1) followed by a stereoselective oxidation with OsO4 (→ 4 , Scheme 2). The primary‐alcohol moiety of 4 was tosylated (→ 5 ) and regioselectively reduced with NaBH4 (→ 6 ). Subsequent reduction of the 2′‐alcohol moiety with Bu3SnH yielded stereoselectively the corresponding (2′S)‐2′‐deoxy‐2′‐C‐methylnucleoside (→ 8a ). 相似文献
202.
Maricruz Rangel-Galvn María Eugenia Castro Jose Manuel Perez-Aguilar Norma A. Caballero Alejandro Rangel-Huerta Francisco J. Melendez 《Molecules (Basel, Switzerland)》2022,27(2)
The cannabinoid receptors (CB1/CB2) and the T-type calcium channels are involved in disorders associated with both physiological pain and depressive behaviors. Valuable pharmacological species carbazole derivatives such as the NMP-4, NMP-7, and NMP-181 (Neuro Molecular Production) regulate both biological entities. In this work, DFT calculations were performed to characterize theoretically their structural and chemical reactivity properties using the BP86/cc-pVTZ level of theory. The molecular orbital contributions and the chemical reactivity analysis reveal that a major participation of the carbazole group is in the donor-acceptor interactions of the NMP compounds. The DFT analysis on the NMP compounds provides insights into the relevant functional groups involved during the ligand-receptor interactions. Molecular docking analysis is used to reveal possible sites of interaction of the NMP compounds with the Cav3.2 calcium channel. The interaction energy values and reported experimental evidence indicate that the site denominated as “Pore-blocking”, which is formed mainly by hydrophobic residues and the T586 residue, is a probable binding site for the NMP compounds. 相似文献
203.
José Bonilla-Cruz Laura Caballero Martha Albores-Velasco Enrique Saldívar-Guerra Judith Percino Víctor Chapela 《Macromolecular Symposia》2007,248(1):132-140
Recently we reported an experimental and theoretical (simulation) investigation on the mechanism of the induction period and the initial polymerization stages in the nitroxide mediated autopolymerization of styrene. In this paper we extend some of the results presented there and perform preliminary induction period experiments for the study of the mechanism and kinetics of the spontaneous copolymerization of styrene (S) and maleic anhydride (MA) in the presence of TEMPO and 4-OH-TEMPO. With even small amounts of MA (2% wt) the induction period is dramatically reduced by a factor of about 20 in comparison with the nitroxide-mediated styrene autopolymerization at 120 °C. Our results suggest that the initiation mechanism involves a first step of reaction between S and MA. We speculate that this reaction is a Diels-Alder cycloaddition followed by hydrogen abstraction through a monomer or TEMPO assisted homolysis to form a radical pair (monomer case) or a single radical (TEMPO case), which either initiates polymerization or is trapped by TEMPO depending on the conditions. Hall and Padias have studied similar electron donor-acceptor co-monomer pairs and favor the formation of a tetramethylene diradical as the initiating species for spontaneous copolymerization. In any case, the rate-limiting step would be the initial reaction of S and MA. These induction experiments allow us to obtain an initial estimate of the order of magnitude for the kinetic constant of the rate-limiting step, as 10−6 Lmol−1s−1. 相似文献
204.
V. M. Jiménez A. Caballero A. Fernández J. C. Sánchez-López A. R. González-Elipe J. F. Trigo J. M. Sanz 《Surface and interface analysis : SIA》1997,25(9):707-714
Calibration of the probing depth by x-ray absorption spectroscopy (XAS) in oxide materials is intended by measurement of the total electron yield (TEY) of electrons ejected by absorption of the radiation. Measurements have been carried out for three series of electrolytic metal oxide overlayers with different thickness. The experiments have been conducted at the Ti K, Ta LIII and Zr K edges. Analysis of the XAS spectra is carried out by factor analysis and conventional Fourier transformation and fitting analysis. The data showed that the information depth by XAS follows the order ZrO2>TiO2>Ta2O5 at the Ti K, Ta LIII and Zr K edges. As an alternative, the absorption spectra of the same samples were measured in the conversion electron yield (CEY) mode: i.e. by measuring the current of He+ ions produced by the ejected electrons in an atmosphere of He in contact with the sample. Here, the information depth is slightly different from that obtained by TEY. © 1997 by John Wiley & Sons, Ltd. 相似文献
205.
Lidia González Dr. Fabiola Zapata Dr. Antonio Caballero Prof. Pedro Molina Prof. Carmen Ramírez de Arellano Prof. Ibon Alkorta Prof. José Elguero 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(22):7533-7544
Several bis‐triazolium‐based receptors have been synthesized and their anion‐recognition capabilities have been studied. The central chiral 1,1′‐bi‐2‐naphthol (BINOL) core features either two aryl or ferrocenyl end‐capped side arms with central halogen‐ or hydrogen‐bonding triazolium receptors. NMR spectroscopic data indicate the simultaneous occurrence of several charge‐assisted aliphatic and heteroaromatic C?H noncovalent interactions and combinations of C?H hydrogen and halogen bonding. The receptors are able to selectively interact with HP2O73?, H2PO4?, and SO42? anions, and the value of the association constant follows the sequence: HP2O73?>SO42?>H2PO4?. The ferrocenyl end‐capped 72+?2 BF4 ? receptor allows recognition and differentiation of H2PO4? and HP2O73? anions by using different channels: H2PO4? is selectively detected through absorption and emission methods and HP2O73? by using electrochemical techniques. Significant structural results are the observation of an anion???anion interaction in the solid state (2:2 complex, 62+? [ H2P2O7 ] 2? ), and a short C?I???O contact is observed in the structure of the complex [ 8 2+][SO4]0.5[BF4]. 相似文献
206.
207.
Judith Caballero‐Jimnez Yasmi Reyes Ortega Sylvain Berns Roberto Escudero 《Acta Crystallographica. Section C, Structural Chemistry》2014,70(8):754-757
The title complex, catena‐poly[di‐μ3‐acetato‐κ6O:O:O′‐tetra‐μ2‐acetato‐κ4O:O;κ4O:O′‐diaquabis(pyridine‐κN)trimanganese(II)], [Mn3(CH3COO)6(C6H5N)2(H2O)2]n, is a true one‐dimensional coordination polymer, in which the MnII centres form a zigzag chain along [010]. The asymmetric unit contains two metal centres, one of which (Mn1) lies on an inversion centre, while the other (Mn2) is placed close to an inversion centre on a general position. Since all the acetates behave as bridging ligands, although with different μ2‐ and μ3‐coordination modes, a one‐dimensional polymeric structure is formed, based on trinuclear repeat units (Mn1...Mn2...Mn2′), in which the Mn2 and Mn2′ sites are related by an inversion centre. Within this monomeric block, the metal–metal separations are Mn1...Mn2 = 3.36180 (18) Å and Mn2...Mn2′ = 4.4804 (3) Å. Cation Mn1, located on an inversion centre, displays an [MnO6] coordination sphere, while Mn2, on a general position, has a slightly stronger [MnO5N] ligand field, as the sixth coordination site is occupied by a pyridine molecule. Both centres approximate an octahedral ligand field. The chains are parallel in the crystal structure and interact via hydrogen bonds involving coordinated water molecules. However, the shortest metal–metal separation between two chains [5.3752 (3) Å] is large compared with the intrachain interactions. These structural features are compatible with a single‐chain magnet behaviour, as confirmed by preliminary magnetic studies. 相似文献
208.
Z.J. Jiao Z.G. Lu J.R. Liu P.J. Poole P.J. Barrios D. Poitras G. Pakulski J. Caballero X.P. Zhang 《Optics Communications》2012,285(21-22):4372-4375
Linewidth enhancement factor (LEF) of InAs/InP quantum dot (QD) multi-wavelength lasers (MWLs) emitting around 1.5 μm is investigated both above and below the threshold. Above the threshold, LEFs at three different wavelengths around the gain peak of 1.53 μm by the injection locking technique are obtained to be 1.63, 1.37 and 1.59. Then by Hakki–Paoli method LEF is found to decrease with increased current and shows a value of less than 1 below the threshold. These small LEF values have clearly indicated that our developed InAs/InP QDs are perfect and promising gain materials for QD MWLs, QD mode-locked lasers (QD MLLs) and QD distributed-feedback (QD DFB) lasers around 1.5 μm. 相似文献
209.
Rojas Víctor Cáceres Gustavo López Silvana Henríquez Rodrigo Grez Paula Schrebler Ricardo Navarrete Emilio Herrera Francisco Caballero Álvaro Gómez-Cámer Juan Luis Aristizábal Juliet Muñoz Eduardo 《Journal of Solid State Electrochemistry》2023,27(4):865-872
Journal of Solid State Electrochemistry - In this work, the performance of copper (II) hexacyanoferrate(III) (CuHCF) as a cathode material for sodium-ion batteries was studied. The compound was... 相似文献
210.
Àlex Díaz-Jiménez Roger Monreal-Corona Dr. Albert Poater Dr. María Álvarez Elena Borrego Prof. Dr. Pedro J. Pérez Dr. Ana Caballero Prof. Dr. Anna Roglans Dr. Anna Pla-Quintana 《Angewandte Chemie (International ed. in English)》2023,62(5):e202215163
The trapping of the elusive vinylogous position of a vinyl carbene with an aliphatic C(sp3)−H bond has been achieved for the first time during a silver-catalyzed carbene/alkyne metathesis (CAM) process. A Tpx-containing silver complex first promotes the generation of a donor-acceptor silver carbene which triggers CAM, generating a subsequent donor-donor vinyl silver carbene species, which then undergoes a selective vinylogous C(sp3)−H bond insertion, leading to the synthesis of a new family of benzoazepines. Density functional theory (DFT) calculations unveil the reaction mechanism, which allows proposing that the C−H bond insertion reaction takes place in a stepwise manner, with the hydrogen shift being the rate determining step. 相似文献