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Navarrete Emilio Rojas Víctor Romero Mario Román J. Cáceres G. Henríquez Rodrigo Grez Paula Schrebler Ricardo Herrera Francisco Muñoz Eduardo C. 《Journal of Solid State Electrochemistry》2021,25(1):133-140
Journal of Solid State Electrochemistry - Cadmium telluride quantum dots (CdTe-QDs) can be deposited from colloidal solutions on glassy carbon (GC) electrodes potentiostatically. The immobilization... 相似文献
354.
Rubén Lázaro Pablo Barrio Claudia Finamore Raquel Román Santos Fustero 《Structural chemistry》2017,28(2):445-452
The presence of a halogen atom in the proximity of a homoallylic amine, obtained by asymmetric addition of allylzinc bromide to the corresponding tert-butyl sulfinimine, makes them versatile building blocks suitable to participate in several palladium-catalyzed processes, such as the intramolecular Heck reaction or the Sonogashira cross-coupling. The thus obtained ortho-alkynyl derivatives display two unsaturated functional groups which may be further modified by means of the intramolecular Pauson–Khand reaction or the ring-closing enyne metathesis. In this way, a variety of benzo-fused amines can be obtained in 2–3 steps from readily available starting materials. 相似文献
355.
Sean T. Hunt Tarit Nimmanwudipong Prof. Yuriy Román‐Leshkov 《Angewandte Chemie (International ed. in English)》2014,53(20):5131-5136
Transition‐metal carbides (TMCs) exhibit catalytic activities similar to platinum group metals (PGMs), yet TMCs are orders of magnitude more abundant and less expensive. However, current TMC synthesis methods lead to sintering, support degradation, and surface impurity deposition, ultimately precluding their wide‐scale use as catalysts. A method is presented for the production of metal‐terminated TMC nanoparticles in the 1–4 nm range with tunable size, composition, and crystal phase. Carbon‐supported tungsten carbide (WC) and molybdenum tungsten carbide (MoxW1?xC) nanoparticles are highly active and stable electrocatalysts. Specifically, activities and capacitances about 100‐fold higher than commercial WC and within an order of magnitude of platinum‐based catalysts are achieved for the hydrogen evolution and methanol electrooxidation reactions. This method opens an attractive avenue to replace PGMs in high energy density applications such as fuel cells and electrolyzers. 相似文献
356.
Péter Szabó Barnabás Kállai-Szabó Nikolett Kállai-Szabó István Sebe Romána Zelkó 《Cellulose (London, England)》2014,21(6):4419-4427
Water-soluble, nonionic cellulose-based fibers were prepared from aqueous hydroxypropyl cellulose gels of 5–13-μm diameter by using a high-speed rotary spinning technique. A combination of texture analysis and viscosity measurement was applied to determine the optimum concentration of hydroxypropyl cellulose gels for fiber formation. The examined concentration range of hydroxypropyl cellulose gels was 38–52 % w/w. The textural properties including the adhesiveness of gels of different concentrations were determined based on the load-distance and load-time curves, while the obtained fiber formation was visually observed with an optical microscope. The texture analysis method enabled the determination of the optimum gel concentration from the point of fiber formation. An unequivocal correlation was determined between the adhesiveness of gels and their fiber-forming ability. The adhesiveness has a local minimum where the productivity of the fiber formation process and the micromorphology of the emitted fibers are optimal. Statistical analysis of the distribution of fiber diameters confirmed that in case of the optimum concentration, the distribution approaches normality. Mechanical properties of the prepared fibers were also evaluated using texture analysis, which indicated that the fibers made of gels of the suggested optimum concentration had the most desirable elastic behavior. An optimum concentration range of hydroxypropyl cellulose exists that enables fiber formation with the required characteristics from the point of further pharmaceutical formulation processing. 相似文献
357.
Acid–Base Pairs in Lewis Acidic Zeolites Promote Direct Aldol Reactions by Soft Enolization
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Jennifer D. Lewis Dr. Stijn Van de Vyver Prof. Yuriy Román‐Leshkov 《Angewandte Chemie (International ed. in English)》2015,54(34):9835-9838
Hf‐, Sn‐, and Zr‐Beta zeolites catalyze the cross‐aldol condensation of aromatic aldehydes with acetone under mild reaction conditions with near quantitative yields. NMR studies with isotopically labeled molecules confirm that acid‐base pairs in the Si‐O‐M framework ensemble promote soft enolization through α‐proton abstraction. The Lewis acidic zeolites maintain activity in the presence of water and, unlike traditional base catalysts, in acidic solutions. 相似文献
358.
Benjamín Alonso Miguel Miranda Francisco Silva Vladimir Pervak Jens Rauschenberger Julio San Román Íñigo J. Sola Helder Crespo 《Applied physics. B, Lasers and optics》2013,112(1):105-114
We have post-compressed 25 fs (Fourier limit) amplified pulses in an argon-filled hollow-core fiber. The output pulses were compressed using a pair of wedges and chirped mirrors down to 4.5 fs (Fourier limit of 4.1 fs), which corresponds to less than two optical cycles. We then performed the characterization of the pulses by combining the d-scan and the STARFISH techniques. The temporal (and spectral) measurement of the pulses is done with d-scan, which is used as the reference to extend the characterization to the spatiotemporal (and spatiospectral) amplitude and phase of the pulses by means of STARFISH. The post-compressed pulses at the output of the hollow-fiber had an energy of 150 μJ. The analysis of the pulses revealed larger spectral broadening and blue-shift, and shorter duration at the center of the beam. For the first time, we demonstrate the complete characterization of intense ultra-broadband pulses in the sub-two-cycle regime, which provides an improved insight into the properties (space–time and space–frequency) of the pulses and is highly relevant for their applications. 相似文献
359.
Juan Pablo Fuentes-Martínez Isaim Toledo-Martínez Perla Román-Bravo Patricia García y García Carolina Godoy-Alcántar Marcela López-Cardoso Hugo Morales-Rojas 《Polyhedron》2009,28(18):3953-3966
One dinuclear chlorodiphenyltin (IV) dithiocarbamate complex (1) and four mononuclear complexes of general formula Ph2Sn(S2CNR)Cl (2, 3, 5, and 6) have been synthesized and characterized both in solid-state and solution. X-ray structures for complexes 1, 3 and 6 demonstrated a five-coordination geometry around of tin atoms, in which dithiocarbamate ligand chelates asymmetrically the metal center. As shown by 119Sn NMR spectroscopy, five-coordination geometry observed in the solid-state remains in solution. The stability of these chlorodiphenyltin(IV) dithiocarbamate complexes in the presence of biologically relevant anions such as acetate, dicarboxylates of general formula ?OOC-(CH2)n-COO? (n = 2–8), dihydrogenphosphate, hydrogensulfate, and halides has been examined in acetonitrile solutions. For all of these organotin(IV) complexes the displacement of the coordinated ligands (i.e., chloride and dithiocarbamate) from the organotin(IV) moiety occurred in the presence of monoanions like acetate, dihydrogenphosphate, hydrogensulfate and fluoride. A stepwise mechanism for ligand exchange is proposed based on UV–Vis, 1H, 13C and 119Sn spectroscopic data, as well as mass spectrometry. From UV–Vis titration experiments it was found that dicarboxylates with small spacers like malonate and succinate, acted differently in the exchange of the dithiocarbamate group in comparison to other monoanionic O donor ligands or dicarboxylates with longer chains, perhaps by following an intramolecular displacement of the coordinated ligand.The lability of these organotin(IV) dithiocarbamate compounds in solution hampers their use as stably host for anions, however, by taking advantage of the intrinsic chromogenic properties of free dithiocarbamate anions, or by attaching dithiocarbamate groups to well-known fluorescent moieties such as antracene, these complexes can sense the presence of O-donor anions at very low concentrations by displacement of the metal-coordinated dithiocarbamate. 相似文献
360.
Christopher Altman Jaroslaw Pykacz Romàn R. Zapatrin 《International Journal of Theoretical Physics》2004,43(10):2029-2040
We introduce superposition-based quantum networks composed of (i) the classical perceptron model of multilayered, feedforward neural networks and (ii) the algebraic model of evolving reticular quantum structures as described in quantum gravity. The main feature of this model is moving from particular neural topologies to a quantum metastructure which embodies many differing topological patterns. Using quantum parallelism, training is possible on superpositions of different network topologies. As a result, not only classical transition functions, but also topology becomes a subject of training. The main feature of our model is that particular neural networks, with different topologies, are quantum states. We consider high-dimensional dissipative quantum structures as candidates for implementation of the model. 相似文献