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941.
A numerical simulation of the two-temperature model has been performed for Au, Ag, Cu and Al. Based on findings in the numerical simulation, an analytical model for the ablation rates in the high fluence regime is proposed. Furthermore, it is shown that a temperature-dependent electron-lattice coupling must be introduced to have qualitative agreement with the logarithmic growth in the low fluence regime. For aluminum, experimental ablation rates with varying fluence is presented and compared with the numerical simulation. 相似文献
942.
Joachim Thrane Sebastian Kuld Niels D. Nielsen Anker D. Jensen Jens Sehested Jakob M. Christensen 《Angewandte Chemie (International ed. in English)》2020,59(41):18189-18193
Catalytic methanol synthesis is one of the major processes in the chemical industry and may grow in importance, as methanol produced from CO2 and sustainably derived H2 are envisioned to play an important role as energy carriers in a future low‐CO2‐emission society. However, despite the widespread use, the reaction mechanism and the nature of the active sites are not fully understood. Here we report that methanol synthesis at commercially applied conditions using the industrial Cu/ZnO/Al2O3 catalyst is dominated by a methanol‐assisted autocatalytic reaction mechanism. We propose that the presence of methanol enables the hydrogenation of surface formate via methyl formate. Autocatalytic acceleration of the reaction is also observed for Cu supported on SiO2 although with low absolute activity, but not for Cu/Al2O3 catalysts. The results illustrate an important example of autocatalysis in heterogeneous catalysis and pave the way for further understanding, improvements, and process optimization of industrial methanol synthesis. 相似文献
943.
Fuxiang Ji Johan Klarbring Dr. Feng Wang Dr. Weihua Ning Dr. Linqin Wang Dr. Chunyang Yin Dr. José Silvestre Mendoza Figueroa Dr. Christian Kolle Christensen Dr. Martin Etter Prof. Thomas Ederth Prof. Licheng Sun Prof. Sergei I. Simak Prof. Igor A. Abrikosov Prof. Feng Gao 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(35):15303-15306
Environmentally friendly halide double perovskites with improved stability are regarded as a promising alternative to lead halide perovskites. The benchmark double perovskite, Cs2AgBiBr6, shows attractive optical and electronic features, making it promising for high-efficiency optoelectronic devices. However, the large band gap limits its further applications, especially for photovoltaics. Herein, we develop a novel crystal-engineering strategy to significantly decrease the band gap by approximately 0.26 eV, reaching the smallest reported band gap of 1.72 eV for Cs2AgBiBr6 under ambient conditions. The band-gap narrowing is confirmed by both absorption and photoluminescence measurements. Our first-principles calculations indicate that enhanced Ag–Bi disorder has a large impact on the band structure and decreases the band gap, providing a possible explanation of the observed band-gap narrowing effect. This work provides new insights for achieving lead-free double perovskites with suitable band gaps for optoelectronic applications. 相似文献
944.
Ole Christensen Hong Oh Kim Rae Young Kim 《Journal of Fourier Analysis and Applications》2011,17(4):640-655
The R-dual sequences of a frame {f
i
}
i∈I
, introduced by Casazza, Kutyniok and Lammers in (J. Fourier Anal. Appl. 10(4):383–408, 2004), provide a powerful tool in the analysis of duality relations in general frame theory. In this paper we derive conditions
for a sequence {ω
j
}
j∈I
to be an R-dual of a given frame {f
i
}
i∈I
. In particular we show that the R-duals {ω
j
}
j∈I
can be characterized in terms of frame properties of an associated sequence {n
i
}
i∈I
. We also derive the duality results obtained for tight Gabor frames in (Casazza et al. in J. Fourier Anal. Appl. 10(4):383–408,
2004) as a special case of a general statement for R-duals of frames in Hilbert spaces. Finally we consider a relaxation of the
R-dual setup of independent interest. Several examples illustrate the results. 相似文献
945.
Renato G. Freitas Ernesto C. Pereira Paul A. Christensen 《Electrochemistry communications》2011,13(10):1147-1150
In this work, Ptpc/Ir/Pt metallic multilayer nanostructured electrodes were prepared. The composition and number of the constituent metal layers were varied and the number of Ir and Pt layers studied were: 1.5:1.5, 1.5:10, 10:1.5, 10:10 and 250:250 Ir and Pt monolayers. The ethanol electrooxidation reaction and its products was studied using electrochemical in situ FTIR technique and could be observed as a selective cleavage of the ethanol CC bond in acidic electrolyte. Neither acetaldehyde nor acetic acid IR band could be observed for ethanol electrooxidation at 1.5 V vs. RHE over Ptpc/Ir250/Pt250 metallic multilayer electrodes. Also, the enhancement on CO2 production over this electrode was more than six times the amount observed using the Ptpc electrodes. Thus, the complete CC cleavage bond in ethanol molecule was observed, leading only CO2 as reaction product. 相似文献
946.
Christensen PA Hamnett A Linares-Moya D 《Physical chemistry chemical physics : PCCP》2011,13(12):5206-5214
This paper reviews work carried out over a number of years to try to elucidate the mechanism of oxygen reduction and methanol oxidation in alkaline solution. We have sought to achieve this by combining electrochemical, spectroscopic and solid-state chemical approaches, bringing together as wide a variety of techniques as possible both to shed light on the mechanisms and to point the way to more effective and efficient fuel cells. This work has become considerably more topical in recent years with the development of anion-exchange electrolyte membranes that can operate in alkaline environments, an important advance since it permits both the use of non-noble-metal catalysts and organic fuels at the anode, the latter precluded in aqueous alkaline electrolyte due to precipitation of inorganic carbonates at the electrode surface. 相似文献
947.
Christian Riber Ilia Rodushkin Henrik Spliid Thomas H. Christensen 《International journal of environmental analytical chemistry》2013,93(5):321-335
Chemical characterization of solid waste is a demanding task due to the heterogeneity of the waste. This article describes how 45 material fractions hand-sorted from Danish household waste were subsampled and prepared for chemical analysis of 61 substances. All material fractions were subject to repeated particle-size reduction, mixing, and mass reduction until a sufficiently small but representative sample was obtained for digestion prior to chemical analysis. The waste-fraction samples were digested according to their properties for maximum recognition of all the studied substances. By combining four subsampling methods and five digestion methods, paying attention to the heterogeneity and the material characteristics of the waste fractions, it was possible to determine 61 substances with low detection limits, reasonable variance, and high accuracy. For most of the substances of environmental concern, the waste-sample concentrations were above the detection limit (e.g. Cd?>?0.001?mg?kg?1, Cr?>?0.01?mg?kg?1, Hg?>?0.002?mg?kg?1, Pb?>?0.005?mg?kg?1). The variance was in the range of 5–100%, depending on material fraction and substance as documented by repeated sampling of two highly different material fractions (‘Vegetable food’ and ‘Shoes, leather, etc.’). Statistical analysis showed for the ‘Vegetable food’ that the variance could not be attributed to a single step in the procedure, whereas in the case of ‘Shoes, leather, etc.’, the first coarse shredding was the main source of variance (20–85% of the overall variation). Only by increasing the sample size significantly can this variance be reduced. The accuracy and short-term reproducibility of the chemical characterization were good, as determined by the analysis of several relevant certified reference materials. Typically, six to eight different certified reference materials representing a range of concentrations levels and matrix characteristics were included. Based on the documentation provided, the methods introduced were considered satisfactory for characterization of the chemical composition of waste-material fractions. 相似文献
948.
Hasan JA Japal KM Christensen ER Samalot-Freire LC 《Journal of AOAC International》2011,94(1):259-272
Clostridium difficile is a strict anaerobic spore-forming bacterium, and an increasingly common nosocomial pathogen. The U.S. Environmental Protection Agency (EPA) is responsible for the registration of disinfectants, including products designed to treat environmental surfaces contaminated with spores of C. difficile. Product efficacy data are required for registration; however, there is a lack of methodology for generating high-quality spore suspensions for evaluating product performance. As such, a study was carried out to select a suitable C. difficile strain and to develop a stand-alone method to prepare a spore suspension that meets specific criteria necessary for quantitative testing of disinfectants. The criteria are: (1) a spore titer of > 8 log10/mL, (2) > or = 90% spores to vegetative cells, and (3) resistance of spores (determined by viability) to 2.5 M hydrochloric acid (HCl). Several strains of C. difficile (toxigenic and nontoxigenic) were grown on various media (solid and liquid) for varying lengths of time to determine the best combination of incubation conditions and media to optimize spore production and quality. Once the spore production procedure was optimized, a toxigenic strain of C. difficile [American Type Culture Collection (ATCC) 43598] was selected for use in trials to verify repeatability from one production run to the next. The spore suspension was initiated by spreading vegetative cells of C. difficile (ATCC 43598) on CDC anaerobic 5% sheep blood agar plates and incubating for 7-10 days at 36 +/- 1 degrees C under anaerobic conditions. Spores were harvested when > or = 90% of the cells converted to spores as determined by observation using phase-contrast microscopy. The spores were washed three times with saline-Tween-80, resuspended in cold deionized water, heated to 70 degrees C for 10 min, evaluated microscopically for quality, and enumerated on cycloserine-cefoxitin-fructose agar containing horse blood and taurocholate. The spore suspension was used to inoculate brushed stainless steel carriers (1 cm in diameter) with and without a soil load in accordance with the Standard Quantitative Carrier Disk Test Method (ASTM E-2197-02) to determine carrier load. Once it was determined that > 6 log10 spores/carrier could be recovered, spores were evaluated for resistance to HCI. The sporulation method presented in this report is simple and repeatable and results in spore suspension of high titer (> 8 log10/mL) and quality (> or = 90% spores to vegetative cells) that met acid resistance criteria (spores were resistant to 2.5 M HCI for 10 min). In addition, recovery from brushed stainless steel carriers with and without soil load was > 6 log10 spores/carrier. A 6 log10 performance standard was set forth in the EPA's interim guidance for generating data to support a label claim for effectiveness against C. difficile spores on hard, nonporous surfaces. This precollaborative investigation successfully demonstrated the use of a methodology for in vitro production of C. difficile spores (ATCC 43598) necessary for conducting efficacy tests. A proposal will be submitted to the AOAC INTERNATIONAL Methods Committee on Antimicrobial Efficacy Testing for a collaborative study; see Appendix. 相似文献
949.
Neil Christensen Priscila de Aquino Celine Degrande Claude Duhr Benjamin Fuks Michel Herquet Fabio Maltoni Steffen Schumann 《The European Physical Journal C - Particles and Fields》2011,71(2):1541
We describe a framework to develop, implement and validate any perturbative Lagrangian-based particle physics model for further
theoretical, phenomenological and experimental studies. The starting point is FeynRules, a Mathematica package that allows to generate Feynman rules for any Lagrangian and then, through dedicated interfaces, automatically pass
the corresponding relevant information to any supported Monte Carlo event generator. We prove the power, robustness and flexibility
of this approach by presenting a few examples of new physics models (the Hidden Abelian Higgs Model, the general Two-Higgs-Doublet
Model, the most general Minimal Supersymmetric Standard Model, the Minimal Higgsless Model, Universal and Large Extra Dimensions,
and QCD-inspired effective Lagrangians) and their implementation/validation in FeynArts/FormCalc, CalcHep, MadGraph/MadEvent, and Sherpa. 相似文献