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161.
Aqueous uranium(VI) hydrolysis species characterized by attenuated total reflection Fourier-transform infrared spectroscopy 总被引:1,自引:0,他引:1
The speciation of uranium(VI) in micromolar aqueous solutions at ambient atmosphere was studied by attenuated total reflection Fourier-transform infrared (ATR FT-IR) spectroscopy and by speciation modeling applying the updated NEA thermodynamic database. It can be shown that reliable infrared spectra of micromolar U(VI) solutions are obtained abolishing the restrictions of previous spectroscopic investigations to millimolar concentrations and, consequently, to the acidic pH range. A significant change of the U(VI) speciation can be derived from the spectral alterations of the absorption band representing the antisymmetric stretching mode (nu3) of the UO2(2+) ion observed upon lowering the U(VI) concentration from the milli- to the micromolar range at a constant pH 4 value. The acquisition of spectra of diluted U(VI) solutions allows the increase of the pH up to 8.5 without the risk of formation of colloidal or solid phases. The infrared spectra are compared to the results of the computed speciation patterns. Although a complete interpretation of the spectra can not be given at this state of knowledge, the spectral data strongly suggest the presence of monomeric U(VI) hydroxo species already showing up at a pH value > or = 2.5 and dominating the speciation at pH 3. This is in contradiction to the predicted speciation where the fully hydrated UO2(2+) is expected to represent the main species at pH values below 4. At ambient pH, a more complex speciation is suggested compared to the results of the computational modeling technique. The predicted dominance of the UO2(CO3)3(4-) complex at pH > or = 8 was not confirmed by the infrared data. However, the infrared spectra indicate the formation of hydroxo complexes obviously containing carbonate ligands. 相似文献
162.
Structural Design Principle of Small‐Molecule Organic Semiconductors for Metal‐Free,Visible‐Light‐Promoted Photocatalysis
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Lei Wang Wei Huang Run Li Dr. Dominik Gehrig Prof. Paul W. M. Blom Prof. Katharina Landfester Dr. Kai A. I. Zhang 《Angewandte Chemie (International ed. in English)》2016,55(33):9783-9787
Herein, we report on the structural design principle of small‐molecule organic semiconductors as metal‐free, pure organic and visible light‐active photocatalysts. Two series of electron‐donor and acceptor‐type organic semiconductor molecules were synthesized to meet crucial requirements, such as 1) absorption range in the visible region, 2) sufficient photoredox potential, and 3) long lifetime of photogenerated excitons. The photocatalytic activity was demonstrated in the intermolecular C?H functionalization of electron‐rich heteroaromates with malonate derivatives. A mechanistic study of the light‐induced electron transport between the organic photocatalyst, substrate, and the sacrificial agent are described. With their tunable absorption range and defined energy‐band structure, the small‐molecule organic semiconductors could offer a new class of metal‐free and visible light‐active photocatalysts for chemical reactions. 相似文献
163.
In this paper we consider a non-trivial link between Baskakov type operators and their genuine Durrmeyer type modification as well as the kth order Kantorovich variant. Recursion formulas for the moments and the images of monomials are proved in order to derive asymptotic expansions. Furthermore we investigate convexity properties of the linking operators and the limiting behavior for certain function spaces. 相似文献
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Markus Daub Guido Schneider Katharina Schratz 《Mathematical Methods in the Applied Sciences》2016,39(18):5371-5380
In a singular limit, the Klein–Gordon (KG) equation can be derived from the Klein–Gordon–Zakharov (KGZ) system. We point out that for the original system posed on a d‐dimensional torus, the solutions of the KG equation do not approximate the solutions of the KGZ system. The KG system has to be modified to make correct predictions about the dynamics of the KGZ system. We explain that this modification is not necessary for the approximation result for the whole space with d≥3. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
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Simone Dill Katharina Gibson Jochen Glaser Sonja Tragl H.‐Jürgen Meyer Prof. Dr. 《无机化学与普通化学杂志》2007,633(2):274-279
Synthesis and Structure of the Basic Alkaline Earth Nitrates Sr2(OH)3NO3 and Ba2(OH)3NO3 Sr2(OH)3NO3 and Ba2(OH)3NO3 were synthesized from mixtures of freshly prepared strontium or barium hydroxides and their corresponding nitrates in evacuated quartz glass ampoules at 420 °C and 360 °C, respectively. Single crystals of Sr2(OH)3NO3 were obtained in a solidified Sr(NO3)2 melt after subsequent heating and cooling cycles in air up to 600 °C. The crystal structure of the strontium compound was refined from single crystal and powder X‐ray data. Sr2(OH)3NO3 crystallizes hexagonally in the space group (No. 189) with Z = 1 and the lattice parameters a = 6.624(2) Å and c = 3.560(1) Å (single crystal data). The powder pattern of Ba2(OH)3NO3 was indexed isotypically to Sr2(OH)3NO3 with the lattice parameters a = 6.9260(1) Å and c = 3.8086(1) Å, and the crystal structure was refined from powder X‐ray data. Alkaline earth ions in the structures are surrounded trigonal‐prismatically by six hydroxide ions. These prisms are sharing their trigonal faces along [001] building up columns. These columns are connected in the ab‐plane by shared edges, and form hexagonal tunnels with the nitrate groups stacked inside. Infrared and thermoanalytical data of Sr2(OH)3NO3 are presented. 相似文献
170.
Osswald P Struckmeier U Kasper T Kohse-Höinghaus K Wang J Cool TA Hansen N Westmoreland PR 《The journal of physical chemistry. A》2007,111(19):4093-4101
The influences of fuel-specific destruction pathways on flame chemistry are determined for two isomeric ester fuels, methyl acetate, CH3(CO)OCH3, and ethyl formate, H(CO)OC2H5, used as model representatives for biodiesel compounds, and their potential for forming air pollutants is addressed. Measurements are presented of major and intermediate species mole fractions in premixed, laminar flat flames using molecular-beam sampling and isomer-selective VUV-photoionization mass spectrometry. The observed intermediate species concentrations depend crucially on decomposition of the different radicals formed initially from the fuels. The methyl acetate structure leads to preferential formation of formaldehyde, while the ethyl formate isomer favors the production of acetaldehyde. Ethyl formate also yields higher concentrations of the C2 species (C2H2 and C2H4) and C4 species (C4H2 and C4H4). Benzene concentrations, while larger for ethyl formate, are at least an order of magnitude smaller for both flames than seen for simple hydrocarbon fuels (ethylene, ethane, propene, and propane). 相似文献