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991.
Luchowski R Sabnis S Szabelski M Sarkar P Raut S Gryczynski Z Borejdo J Bojarski P Gryczynski I 《Journal of luminescence》2010,130(12):2446-2451
Concentration is a key determining factor in the fluorescence properties of organic fluorophores. We studied self-quenching of disodium fluorescein (uranin) fluorescence in polyvinyl alcohol (PVA) thin films. The concentration dependent changes in brightness and anisotropy were followed by a lifetime decrease. We found that at a concentration of 0.54 M, the lifetime decreases to 7 ps. At a concentration of 0.18 M the lifetime was 10 ps with the relatively high quantum yield of 0.002. In these conditions the fluorescence intensity decay was homogeneous (well approximated by a single lifetime). We realized that such a sample was an ideal fluorescence lifetime standard for spectroscopy and microscopy, and therefore characterized instrument response functions for a time-domain technique. We show that self-quenched uranin enables measurements free of the color effect, making it a superior choice for a lifetime reference over scattered light. 相似文献
992.
Massiot D Hiet J Pellerin N Fayon F Deschamps M Steuernagel S Grandinetti PJ 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2006,181(2):310-315
We show that the two-dimensional one pulse (TOP) representation of magic-angle spinning nuclear magnetic resonance data of half-integer quadrupolar nuclei has significant advantages over the conventional one-dimensional spectrum. The TOP spectrum, which correlates NMR frequency to spinning sideband order, provides a rapid determination of the number of sites as well as the size of the their quadrupolar coupling. Additionally, synchronous acquisition spectra of the central and satellite transition resonances can be separated by different projections of the TOP spectrum, with higher resolution spectra often found in the satellite transitions projection. A previously perceived problem of centerband aliasing in TOP can be eliminated with an algorithm that uses larger subspectral widths and the sideband order dimension to distinguish centerbands from sidebands. 相似文献
993.
We present new, high resolution Hall effect and magnetoresistance measurements across the metamagnetic transition in the heavy fermion compound CeRu2Si2 . The results, and ambiguities in the interpretation of de Haas-van Alphen data, force us to rethink the notion that the transition is accompanied by an abrupt f-electron localization. Instead, we explain our data assuming a continuous evolution of the Fermi surface, which sees one of the spin-split sheets of the heaviest surface shrink to a point. 相似文献
994.
Mitia Duerinckx Julian Fischer 《Annales de l'Institut Henri Poincaré (C) Analyse Non Linéaire》2018,35(5):1267-1319
We establish the existence of a global solution for a new family of fluid-like equations, which are obtained in certain regimes in [24] as the mean-field evolution of the supercurrent density in a (2D section of a) type-II superconductor with pinning and with imposed electric current. We also consider general vortex-sheet initial data, and investigate the uniqueness and regularity properties of the solution. For some choice of parameters, the equation under investigation coincides with the so-called lake equation from 2D shallow water fluid dynamics, and our analysis then leads to a new existence result for rough initial data. 相似文献
995.
Julian Bello Maksudul Mowla Nicholas Troise Joanna Soyring Julia Borgesi Jiwook Shim 《Electrophoresis》2019,40(7):1082-1090
Solid‐state nanopore based biosensors are cost effective, high‐throughput engines for single molecule detection of biomolecules with the added benefit of size modification. Progress in the translation of the science into a viable diagnostic tool is impeded by inadequate sensitivity of data acquisition systems in detection of fast DNA translocations through the pore. To combat this, slowing the transport of DNA through the nanopore by use of various media or by altering experimental parameters is common. Applying a concentration gradient of KCl in the experimental ionic solution has been shown to effectively prolong dwell times as well as increase the capture rate of DNA by the nanopore. Our previous work has corroborated the ability of LiCl ionic solution to slow down the transport of dsDNA through the nanopore by up to 10‐fold through cation‐DNA interactions. However, this drastically reduced the event occurrence frequency, thus hindering the efficacy of this system as a reliable biosensor downstream. Here, we present the use of a concentration gradient of lithium chloride ionic solution to increase the event frequency of single molecule dsDNA translocation through a solid state nanopore. By using 0.5 M/3 M LiCl on the cis/trans chambers respectively, average dwell times experienced up to a 3‐fold increase when compared to experiments run in symmetric 1 M LiCl. Additionally, experiments using the 0.5 M/3 M displayed a greater than 10‐fold increase in event frequency, confirming the capture propensity of the asymmetric conditions. 相似文献
996.
We present theoretical calculations, based on a random phasor sum model, which show that the optical coherence tomography speckle contrast ratio is dependent on the local density of scattering particles in a sample, provided that the effective number of scatterers in the probed volume is less than about five. We confirm these theoretical predictions experimentally, using suspensions of microspheres in water. The observed contrast ratios vary in value from the Rayleigh limit of 0.52 to in excess of 2, suggesting that the contrast ratio could be useful in optical coherence tomography, particularly when imaging in ultrahigh-resolution regimes. 相似文献
997.
Philipp M. Holstein Julian J. Holstein Eduardo C. Escudero-Adán Olivier Baudoin Antonio M. Echavarren 《Tetrahedron: Asymmetry》2017,28(10):1321-1329
The present study investigates a synthetically simple ferrocene derivatization of natural products and active pharmaceutical ingredients. Seven new crystal structures are analyzed together with 16 structures of ferrocene derivatives reported previously. In all cases, the unambiguous determination of the absolute structure was established from anomalous dispersion using the methods of Flack and Parsons. A comparison with other derivatization approaches shows the advantage of the described ferrocene derivatization for establishing the absolute configuration of novel compounds. 相似文献
998.
Julian Szczesny James A. Birrell Felipe Conzuelo Wolfgang Lubitz Adrian Ruff Wolfgang Schuhmann 《Angewandte Chemie (International ed. in English)》2020,59(38):16506-16510
The incorporation of highly active but also highly sensitive catalysts (e.g. the [FeFe] hydrogenase from Desulfovibrio desulfuricans) in biofuel cells is still one of the major challenges in sustainable energy conversion. We report the fabrication of a dual‐gas diffusion electrode H2/O2 biofuel cell equipped with a [FeFe] hydrogenase/redox polymer‐based high‐current‐density H2‐oxidation bioanode. The bioanodes show benchmark current densities of around 14 mA cm?2 and the corresponding fuel cell tests exhibit a benchmark for a hydrogenase/redox polymer‐based biofuel cell with outstanding power densities of 5.4 mW cm?2 at 0.7 V cell voltage. Furthermore, the highly sensitive [FeFe] hydrogenase is protected against oxygen damage by the redox polymer and can function under 5 % O2. 相似文献
999.
Julian M. Rotter Roman Guntermann Michael Auth Andre Mhringer Andreas Sperlich Vladimir Dyakonov Dana D. Medina Thomas Bein 《Chemical science》2020,11(47):12843
Covalent organic frameworks (COFs) define a versatile structural paradigm combining attractive properties such as crystallinity, porosity, and chemical and structural modularity which are valuable for various applications. For the incorporation of COFs into optoelectronic devices, efficient charge carrier transport and intrinsic conductivity are often essential. Here, we report the synthesis of two imine-linked two-dimensional COFs, WTA and WBDT, featuring a redox-active Wurster-type motif based on the twisted tetragonal N,N,N′,N′-tetraphenyl-1,4-phenylenediamine node. By condensing this unit with either terephthalaldehyde (TA) or benzodithiophene dialdehyde (BDT), COFs featuring a dual-pore kagome-type structure were obtained as highly crystalline materials with large specific surface areas and mesoporosity. In addition, the experimentally determined high conduction band energies of both COFs render them suitable candidates for oxidative doping. The incorporation of a benzodithiophene linear building block into the COF allows for high intrinsic macroscopic conductivity. Both anisotropic and average isotropic electrical conductivities were determined with van der Pauw measurements using oriented films and pressed pellets, respectively. Furthermore, the impact of different dopants such as F4TCNQ, antimony pentachloride and iodine on the conductivities of the resulting doped COFs was studied. By using the strong organic acceptor F4TCNQ, a massive increase of the radical cation density (up to 0.5 radicals per unit cell) and long-term stable electrical conductivity as high as 3.67 S m−1 were achieved for the anisotropic transport in an oriented film, one of the highest for any doped COF to date. Interestingly, no significant differences between isotropic and anisotropic charge transport were found in films and pressed pellets. This work expands the list of possible building nodes for electrically conducting COFs from planar systems to twisted geometries. The achievement of high and stable electrical conductivity paves the way for possible applications of new COFs in organic (opto)electronics.Covalent organic frameworks define a versatile structural paradigm combining various attractive properties. The impact of different dopants on the conductivity of imine-linked 2D COFs featuring a redox-active Wurster-type motif was studied. 相似文献
1000.
Novel Organocatalytic Activation of Unmodified Morita–Baylis–Hillman Alcohols for the Synthesis of Bicyclic α‐Alkylidene‐Ketones 下载免费PDF全文
Dr. Julian Stiller Dorota Kowalczyk Dr. Hao Jiang Prof. Dr. Karl Anker Jørgensen Dr. Łukasz Albrecht 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(41):13108-13112
The organocatalytic activation of Morita–Baylis–Hillman alcohols via H‐bonding‐iminium‐ion formation is demonstrated for the first time. This activation strategy enables the Morita‐Baylis–Hillman alcohols to undergo a formal SN2′ reaction. In combination with the well‐established enamine reactivity, this creates a new reactivity pattern. The application of this new activation mode for the synthesis of bicyclic α‐alkylidene‐ketones is demonstrated. The developed reaction sequence proceeds efficiently affording nature‐inspired target products with four contiguous stereogenic centers in a highly stereoselective manner. 相似文献