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71.
Meyers C Maes BU Loones KT Bal G Lemière GL Dommisse RA 《The Journal of organic chemistry》2004,69(18):6010-6017
Evidence for an interphase deprotonation of Pd(II)-amine complexes with weak carbonate base has been gained for the first time. When a rate-limiting deprotonation step is involved in the catalytic cycle, controlling the structure (shape and size of the particles) and/or molar excess of the carbonate base used can significantly increase the reaction rate of Buchwald-Hartwig aminations. By taking such a "base effect" into account a general protocol for the intermolecular amination of aryl iodides with all types of amines has been developed based on a standard Pd-BINAP catalyst, using cesium carbonate as the base. 相似文献
72.
Loones KT Maes BU Dommisse RA Lemière GL 《Chemical communications (Cambridge, England)》2004,(21):2466-2467
A new strategy for the synthesis of the title compounds via a regio- and chemoselective one-pot inter- and intramolecular Buchwald-Hartwig amination of 2-chloro-3-iodopyridine with aminoazines and -diazines is reported. 相似文献
73.
A detailed study on N,N-dimethylanilino donor-substituted cyanoethynylethenes shows that there is no correlation between the effectiveness of the donor-acceptor conjugation pathway and the lowest-energy transition in the UV/Vis absorption spectrum. 相似文献
74.
75.
Nikolaos V. Tzouras Ekaterina A. Martynova Xinyuan Ma Dr. Thomas Scattolin Dr. Benjamin Hupp Hendrik Busen Marina Saab Ziyun Zhang Dr. Laura Falivene Gianmarco Pisanò Prof. Dr. Kristof Van Hecke Prof. Dr. Luigi Cavallo Prof. Dr. Catherine S. J. Cazin Prof. Dr. Andreas Steffen Prof. Dr. Steven P. Nolan 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(46):11904-11911
The development of novel and operationally simple synthetic routes to carbene-metal-amido (CMA) complexes of copper, silver and gold relevant for photonic applications are reported. A mild base and sustainable solvents allow all reactions to be conducted in air and at room temperature, leading to high yields of the targeted compounds even on multigram scales. The effect of various mild bases on the N−H metallation was studied in silico and experimentally, while a mechanochemical, solvent-free synthetic approach was also developed. Our photophysical studies on [M(NHC)(Cbz)] (Cbz=carbazolyl) indicate that the occurrence of fluorescent or phosphorescent states is determined primarily by the metal, providing control over the excited state properties. Consequently, we demonstrate the potential of the new CMAs beyond luminescence applications by employing a selected CMA as a photocatalyst. The exemplified synthetic ease is expected to accelerate the applications of CMAs in photocatalysis and materials chemistry. 相似文献
76.
Dr. Himanshu Sekhar Jena Chidharth Krishnaraj Dr. Johannes Schmidt Dr. Karen Leus Prof. Dr. Kristof Van Hecke Prof. Dr. Pascal Van Der Voort 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(7):1548-1557
Covalent triazine frameworks (CTFs) have provided a unique platform in functional material design for a wide range of applications. This work reports a series of new CTFs with two new heteroaromatic building blocks (pyrazole and isoxazole groups) through a building-block transformation approach aiming for carbon capture and storage (CCS) and metal-free catalysis. The CTFs were synthesized from their respective building blocks [(4,4′-(1H-pyrazole-3,5-diyl)dibenzonitrile (pyz) and 4,4′-(isoxazole-3,5-diyl)dibenzonitrile (isox))] under ionothermal conditions using ZnCl2. Both of the building blocks were designed by an organic transformation of an acetylacetone containing dinitrile linker to pyrazole and isoxazole groups, respectively. Due to this organic transformation, (i) linker aromatization, (ii) higher surface areas and nitrogen contents, (iii) higher aromaticity, and (iv) higher surface basicity was achieved. Due to these enhanced properties, CTFs were explored for CO2 uptake and metal-free heterogeneous catalysis. Among all, the isox-CTF, synthesized at 400 °C, showed the highest CO2 uptake (4.92 mmol g−1 at 273 K and 2.98 mmol g−1 at 298 K at 1 bar). Remarkably, these CTFs showed excellent metal-free catalytic activity for the aerobic oxidation of benzylamine at mild reaction conditions. On studying the properties of the CTFs, it was observed that organic transformations and ligand aromatization of the materials are crucial factor to tune the important parameters that influence the CO2 uptake and the catalytic activity. Overall, this work highlights the substantial effect of designing new CTF materials by building-block organic transformations resulting in better properties for CCS applications and heterogeneous catalysis. 相似文献
77.
A macroscopic framework to model heat transfer in materials and composites, subjected to physical degradation, is proposed.
The framework employs the partition of unity concept and captures the change from conduction-dominated transfer in the initial
continuum state to convection and radiation-dominated transfer in the damaged state. The underlying model can be directly
linked to a mechanical cohesive zone model, governing the initiation and subsequent growth and coalescence of micro-cracks.
The methodology proved to be applicable for quasi-static, periodic, and transient problems. 相似文献
78.
79.
Ruiz-Cabello J Vuister GW Moonen CT van Gelderen P Cohen JS van Zijl PC 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2011,(2):446-466
A detailed theoretical and experimental treatment is given for gradient-enhanced heteronuclear correlation spectroscopy. Both multiple-quantum and single-quantum sequences are described. In addition to a comparison with conventional experiments using phase cycling, the effects of different gradient combinations are examined with respect to artifacts occurring in the heteronuclear dimension. The influence of gradient performance and diffusion on sensitivity is discussed. Approaches to attain phase-sensitive spectra are also analyzed. 相似文献
80.
Paredis K Ono LK Behafarid F Zhang Z Yang JC Frenkel AI Cuenya BR 《Journal of the American Chemical Society》2011,133(34):13455-13464
An in-depth understanding of the fundamental structure of catalysts during operation is indispensable for tailoring future efficient and selective catalysts. We report the evolution of the structure and oxidation state of ZrO(2)-supported Pd nanocatalysts (~5 nm) during the in situ reduction of NO with H(2) using X-ray absorption fine-structure spectroscopy and X-ray photoelectron spectroscopy. Prior to the onset of the reaction (≤120 °C), a NO-induced redispersion of our initial metallic Pd nanoparticles over the ZrO(2) support was observed, and Pd(δ+) species were detected. This process parallels the high production of N(2)O observed at the onset of the reaction (>120 °C), while at higher temperatures (≥150 °C) the selectivity shifts mainly toward N(2) (~80%). Concomitant with the onset of N(2) production, the Pd atoms aggregate again into large (6.5 nm) metallic Pd nanoparticles, which were found to constitute the active phase for the H(2)-reduction of NO. Throughout the entire reaction cycle, the formation and stabilization of PdO(x) was not detected. Our results highlight the importance of in situ reactivity studies to unravel the microscopic processes governing catalytic reactivity. 相似文献