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131.
Computational aeroacoustic (CAA) simulation requires accurate schemes to capture the dynamics of acoustic fluctuations, which are weak compared with aerodynamic ones. In this paper, two kinds of schemes are studied and compared: the classical approach based on high order schemes for Navier–Stokes-like equations and the lattice Boltzmann method. The reference macroscopic equations are the 3D isothermal and compressible Navier–Stokes equations. A Von Neumann analysis of these linearized equations is carried out to obtain exact plane wave solutions. Three physical modes are recovered and the corresponding theoretical dispersion relations are obtained. Then the same analysis is made on the space and time discretization of the Navier–Stokes equations with the classical high order schemes to quantify the influence of both space and time discretization on the exact solutions. Different orders of discretization are considered, with and without a uniform mean flow. Three different lattice Boltzmann models are then presented and studied with the Von Neumann analysis. The theoretical dispersion relations of these models are obtained and the error terms of the model are identified and studied. It is shown that the dispersion error in the lattice Boltzmann models is only due to the space and time discretization and that the continuous discrete velocity Boltzmann equation yield the same exact dispersion as the Navier–Stokes equations. Finally, dispersion and dissipation errors of the different kind of schemes are quantitatively compared. It is found that the lattice Boltzmann method is less dissipative than high order schemes and less dispersive than a second order scheme in space with a 3-step Runge–Kutta scheme in time. The number of floating point operations at a given error level associated with these two kinds of schemes are then compared. 相似文献
132.
133.
Benoît Lessard Milan Marić 《Journal of polymer science. Part A, Polymer chemistry》2009,47(10):2574-2588
Methyl methacrylate/styrene (MMA/S), ethyl methacrylate/styrene (EMA/S) and butyl methacrylate/styrene (BMA/S) feeds (>90 mol % methacrylate) were copolymerized in 50 wt % p‐xylene at 90 °C with 10 mol % of additional SG1‐free nitroxide mediator relative to unimolecular initiator (BlocBuilder®) to yield methacrylate rich copolymers with polydispersities w/ n = 1.23–1.46. kpK values (kp = propagation rate constant, K = equilibrium constant) for MMA/S copolymerizations were comparable with previous literature, whereas EMA/S and BMA/S copolymerizations were characterized by slightly higher kpK's. Chain extensions with styrene at 110 °C initiated by the methacrylate‐rich macroinitiators (number average molecular weight n = 12.9–33.5 kg mol?1) resulted in slightly broader molecular weight distributions with w/ n = 1.24–1.86 and were often bimodal. Chain extensions with glycidyl methacrylate/styrene/methacrylate (GMA/S/XMA where XMA = MMA, EMA or BMA) mixtures at 90 °C using the same macroinitiators resulted frequently in bimodal molecular weight distributions with many inactive macroinitiators and higher w/ n = 2.01–2.48. P(XMA/S) macroinitiators ( n = 4.9–8.9 kg mol?1), polymerized to low conversion and purified to remove “dead” chains, initiated chain extensions with GMA/MMA/S and GMA/EMA/S giving products with w/ n ~ 1.5 and much fewer unreacted macroinitiators (<5%), whereas the GMA/BMA/S chain extension was characterized by slightly more unreacted macroinitiators (~20%). © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2574–2588, 2009 相似文献
134.
Haruhiko Fuwa Prof. Dr. Asami Saito Shinya Naito Keiichi Konoki Prof. Dr. Mari Yotsu‐Yamashita Prof. Dr. Makoto Sasaki Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(46):12807-12818
The stereocontrolled total synthesis of the originally proposed ( 1 ) and correct ( 2 ) structures of (+)‐neopeltolide, a novel marine macrolide natural product with highly potent antiproliferative activity against several cancer cell lines as well as potent antifungal activity, has been achieved by exploiting a newly developed Suzuki–Miyaura coupling/ring‐closing metathesis strategy. Alkylborate 44 , which was generated in situ from iodide 34 , was coupled with enol phosphate 8 by a Suzuki–Miyaura coupling. Ring‐closing metathesis of the derived diene 45 followed by stereoselective hydrogenation afforded tetrahydropyran 47 as a single stereoisomer in high overall yield from 34 . Our convergent strategy enabled us to construct the 14‐membered macrolactone core structure of 2 in a rapid and efficient manner. Total synthesis and biological evaluation of synthetic intermediates and designed synthetic analogues, performed to establish the structure–activity relationships of 2 , led to the discovery of a structurally simple yet potent cytotoxic analogue, 9‐demethylneopeltolide ( 54 ). 相似文献
135.
Nanoparticles were prepared by utilizing the thermosensitive aggregation of alpha-elastin and gamma ray crosslinking. Three different heating process, “Slow heating”, “Fast heating”, and “Heat shock”, were applied for the aggregation of the alpha-elastin and examined to yield nanoparticles by gamma rays crosslinking. As a result, only “Slow heating” process yielded nanoparticles with diameters of about ca. 300 nm above cloud point (CP) and about ca. 100 nm below CP, and a narrow size distribution above 1.0 mg/ml concentration (exclude 1.0 mg/ml). 相似文献
136.
Ai Jia Yang Xiao Jianying Hu Mari Asami Shoichi Kunikane 《Journal of chromatography. A》2009,1216(22):4655-4662
A sensitive method was developed for the trace determination of six tetracyclines and ten of their degradation products in influent, effluent, and river waters using liquid chromatography–electrospray tandem mass spectrometry detection, combined with Oasis hydrophilic–lipophilic balance (HLB) cartridge extraction and Oasis mixed-mode strong anion exchange (MAX) cartridge cleanup. Tetracyclines and their products were separated by liquid chromatography in 9.5 min, and the instrument detection limits were generally between 0.03 and 0.1 μg/L except for minocycline (0.5 μg/L). The chromatograms were improved through the MAX cleanup and no apparent matrix effect was found. The recoveries of all the target compounds except for 4-epianhydrochlortetracycline and anhydrochlortetracycline (34–52%) were 75–120% for influent, 61–103% for effluent, and 64–113% for river waters. The method detection limits (MDLs) of the analytes varied in the range of 0.8–17.5 ng/L in all studied matrices. The method was applied for the determination of tetracyclines and their products in a sewage treatment plant (STP) and surface waters in Beijing, China. Oxytetracycline (3.8–72.5 ng/L), tetracycline (1.9–16.5 ng/L), and five products including 4-epitetracycline, 4-epioxytetracycline, isochlortetracycline, anhydrotetracycline, and 4-epianhydrochlortetracycline (5.7–25.3 ng/L) were detected in wastewater, while only oxytetracycline and tetracycline (2.2 and 2.1 ng/L) were detected in surface water samples. 相似文献
137.
Stenger Fernanda Cristina Cechinel-Filho Valdir Meyre-Silva Christiane Bresolin Tania Mari Belle Rodrigues Clvis Antonio 《Chromatographia》2009,69(2):183-187
Chitosan was modified with lauroyl chloride to prepare a solid support for the application of matrix solid-phase dispersion (MSPD) for the extraction of flavonoids from the medicinal plant Aleurites moluccana. The laurylchitosan prepared by the homogenous and heterogeneous method, was characterized using analytical methods such as potentiometric titration and infrared spectroscopy. The hydrophobic properties were studied by naphthalene incorporation. The MSPD performance was evaluated by extraction of swertisin and 2″-O-rhamnosylswertisin from the leaves of A. moluccana. 相似文献
138.
Ken Hosoya Tomoko Mori Mari Sakamoto Takuya Kubo Kunimitsu Kaya 《Chromatographia》2009,70(5-6):699-704
We report the chromatographic properties of a new type of epoxy polymer-based monolithic capillary column, the Tetrad-C column. The column was prepared by a completely new method—reaction of a tetra-functional epoxy monomer, 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane (trade name Tetrad-C), with a diamine, 4-[(4-aminocyclohexyl)methyl)cyclohexane (BACM). This polymer monolith has no aromatic functional groups reducing chromatographic performance. The columns were carefully observed by scanning electron microscopy and evaluated chromatographically by use of a μ-HPLC system. It was found that morphological control of the epoxy polymer-based monolith was possible simply by changing the polymerization conditions, i.e., the polymerization temperature and/or the relative amounts of porogenic solvent and BACM. Another advantage was that volumetric shrinkage of the tetra-functional epoxy-based monolith during the polymerization reaction was much less than for the tri-functional epoxy-based monolithic (TEPIC) column reported in our previous paper. A Tetrad-C column 200 mm long afforded up to 10,000 plates for alkylbenzenes in reversed-phase-mode. This column can also work in HILIC mode, although the hydrophobicity of the column was greater than that of the TEPIC column. Heat treatment (160 °C for 2 h; to eliminate residual, unreacted, functional groups) had a negligible effect on column performance, indicating the columns were thermally stable. 相似文献
139.
Most of the studies devoted to elastography are focused on the estimation of the axial component of the strain. However when subjected to any load, whatever the direction, soft biological media deform in the three spatial dimensions. The aim of our work is to build a three dimensional strain mapping from data acquired with a 3D clinical sectorial probe. The estimation of radial strain is based on the estimation of local scaling factors. A method of cross-correlation of interpolated signals between adjacent radiofrequency lines was used to estimate the angular displacement and strain. For the sectorial strain estimation, the same displacement estimation technique has been implemented. The method has been tested on experimental data acquired on calibrated phantoms and compared to simulation. 相似文献
140.
Fabien Alibart Stéphane Pleutin Olivier Bichler Christian Gamrat Teresa Serrano‐Gotarredona Bernabe Linares‐Barranco Dominique Vuillaume 《Advanced functional materials》2012,22(3):609-616
A large effort is devoted to the research of new computing paradigms associated with innovative nanotechnologies that should complement and/or propose alternative solutions to the classical Von Neumann/CMOS (complementary metal oxide semiconductor) association. Among various propositions, spiking neural network (SNN) seems a valid candidate. i) In terms of functions, SNN using relative spike timing for information coding are deemed to be the most effective at taking inspiration from the brain to allow fast and efficient processing of information for complex tasks in recognition or classification. ii) In terms of technology, SNN may be able to benefit the most from nanodevices because SNN architectures are intrinsically tolerant to defective devices and performance variability. Here, spike‐timing‐dependent plasticity (STDP), a basic and primordial learning function in the brain, is demonstrated with a new class of synapstor (synapse‐transistor), called nanoparticle organic memory field‐effect transistor (NOMFET). This learning function is obtained with a simple hybrid material made of the self‐assembly of gold nanoparticles and organic semiconductor thin films. Beyond mimicking biological synapses, it is also demonstrated how the shape of the applied spikes can tailor the STDP learning function. Moreover, the experiments and modeling show that this synapstor is a memristive device. Finally, these synapstors are successfully coupled with a CMOS platform emulating the pre‐ and postsynaptic neurons, and a behavioral macromodel is developed on usual device simulator. 相似文献