全文获取类型
收费全文 | 228篇 |
免费 | 17篇 |
国内免费 | 3篇 |
专业分类
化学 | 126篇 |
力学 | 8篇 |
数学 | 67篇 |
物理学 | 47篇 |
出版年
2023年 | 1篇 |
2022年 | 2篇 |
2021年 | 8篇 |
2020年 | 12篇 |
2019年 | 16篇 |
2018年 | 15篇 |
2017年 | 14篇 |
2016年 | 12篇 |
2015年 | 12篇 |
2014年 | 13篇 |
2013年 | 29篇 |
2012年 | 22篇 |
2011年 | 19篇 |
2010年 | 10篇 |
2009年 | 6篇 |
2008年 | 21篇 |
2007年 | 10篇 |
2006年 | 10篇 |
2005年 | 4篇 |
2004年 | 2篇 |
2003年 | 6篇 |
2000年 | 1篇 |
1995年 | 1篇 |
1983年 | 1篇 |
1976年 | 1篇 |
排序方式: 共有248条查询结果,搜索用时 31 毫秒
31.
The biosensor was constructed for determination of glucose by using glucose oxidase enzyme immobilized on poly(thiophene-3-boronic acid) (PTBA). Boronic acid functionalized polythiophene layer was obtained by electrochemical polymerization of Thiophene (Th) and thiophene-3-boronic acid (TBA) with different monomer rations. The reconstitution of the apo-glucose oxidase (apo-GOx) on a complexed flavin adenine dinucleotide (FAD) linked to polythiophene boronic acid (PTBA) monolayer yields an electrically contacted enzyme monolayer. The GOx-reconstituted enzyme electrode exhibited excellent electrocatalytic activities toward the reduction and oxidation of hydrogen peroxide as well. The PTBA/FAD/GOx biosensor shows an excellent performance for glucose at +0.4 V with a high sensitivity (2.14 μA/mM) and lower response time (~5 s) in a wide concentration range of 0.5–18 mM (correlation coefficient of 0.9952). Furthermore, the effects of applied potential, pH, temperature, electroactive interference, stability and reusability of the biosensors were discussed. 相似文献
32.
H.T. Eyyubolu Y. Baykal E. Sermutlu Y. Cai 《Applied physics. B, Lasers and optics》2008,92(2):229-235
For a weak turbulence propagation environment, the scintillation index of the lowest order Bessel–Gaussian beams is formulated.
Its triple and single integral versions are presented. Numerical evaluations show that at large source sizes and large width
parameters, when compared at the same source size, Bessel–Gaussian beams tend to exhibit lower scintillations than the Gaussian
beam scintillations. This advantage is lost however for excessively large width parameters and beyond certain propagation
lengths. Large width parameters also cause rises and falls in the scintillation index of off-axis positions toward the edges
of the received beam. Comparisons against the fundamental Gaussian beam are made on equal source size and equal power basis.
PACS 42.25.Dd; 42.25.Bs; 42.68.Bz; 42.68.-w 相似文献
33.
Journal of Thermal Analysis and Calorimetry - In this study, the characteristics of mixed convection heat transfer of nanofluids in circular microchannels with 500 μm diameter were... 相似文献
34.
M. Sc. Emre Babaoglu Prof. Dr. Gerhard Hilt 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(41):8879-8884
An electrochemical iodine-mediated transformation of enamino-esters for the synthesis of 2H-azirine-2-carboxylates is presented. In addition, a thermic conversion of azirines to 4-carboxy-oxazoles in quantitative yield without purification was described. Both classes 2H-azirines-2-carboxylates and the 4-carboxy-oxazoles are substructures in natural products and therefore are of considerable interest for synthetic and pharmaceutical chemists. The optimization was not performed in a conventional manner with a one-factor-at-a-time process but with a Design of Experiments (DoE) approach. Beside a broad substrate scope the reaction was also employed to a robustness screen, a sensitivity assessment, and complemented with mechanistic considerations from cyclic voltammetry experiments. 相似文献
35.
We propose a sequential learning policy for ranking and selection problems, where we use a non-parametric procedure for estimating the value of a policy. Our estimation approach aggregates over a set of kernel functions in order to achieve a more consistent estimator. Each element in the kernel estimation set uses a different bandwidth to achieve better aggregation. The final estimate uses a weighting scheme with the inverse mean square errors of the kernel estimators as weights. This weighting scheme is shown to be optimal under independent kernel estimators. For choosing the measurement, we employ the knowledge gradient policy that relies on predictive distributions to calculate the optimal sampling point. Our method allows a setting where the beliefs are expected to be correlated but the correlation structure is unknown beforehand. Moreover, the proposed policy is shown to be asymptotically optimal. 相似文献
36.
37.
An efficient one-pot synthetic methodology has been developed for the benzylic amination reactions of methyl-substituted azine N-oxides that operate under mild conditions. The reaction was found to tolerate quinoline and isoquinoline N-oxides with electron donating and withdrawing substituents as the electrophilic reaction partners as well as a broad range of nucleophilic primary, secondary and aromatic amines, affording the benzylic amination products in up to 82% yield. 相似文献
38.
Simultaneous Identification of Spectral Properties and Sizes of Multiple Particles in Solution with Subnanometer Resolution 下载免费PDF全文
Assist. Prof. Engin Karabudak Dr. Emre Brookes Dr. Vladimir Lesnyak Prof. Dr. Nikolai Gaponik Prof. Dr. Alexander Eychmüller Johannes Walter Dr. Doris Segets Prof. Wolfgang Peukert Dr. Wendel Wohlleben Assoc. Prof. Borries Demeler Prof. Dr. Helmut Cölfen 《Angewandte Chemie (International ed. in English)》2016,55(39):11770-11774
We report an unsurpassed solution characterization technique based on analytical ultracentrifugation, which demonstrates exceptional potential for resolving particle sizes in solution with sub‐nm resolution. We achieve this improvement in resolution by simultaneously measuring UV/Vis spectra while hydrodynamically separating individual components in the mixture. By equipping an analytical ultracentrifuge with a novel multi‐wavelength detector, we are adding a new spectral discovery dimension to traditional hydrodynamic characterization, and amplify the information obtained by orders of magnitude. We demonstrate the power of this technique by characterizing unpurified CdTe nanoparticle samples, avoiding tedious and often impossible purification and fractionation of nanoparticles into apparently monodisperse fractions. With this approach, we have for the first time identified the pure spectral properties and band‐gap positions of discrete species present in the CdTe mixture. 相似文献
39.
Increased consumption of fossil fuels in industrial production has led to a significant elevation in the emission of greenhouse gases and to global warming. The most effective international action against global warming is the Kyoto Protocol, which aims to reduce carbon emissions to desired levels in a certain time span. Carbon trading is one of the mechanisms used to achieve the desired reductions. One of the most important implications of carbon trading for industrial systems is the risk of uncertainty about the prices of carbon allowance permits traded in the carbon markets. In this paper, we consider stochastic and time series modeling of carbon market prices and provide estimates of the model parameters involved, based on the European Union emissions trading scheme carbon allowances data obtained for 2008–2012 period. In particular, we consider fractional Brownian motion and autoregressive moving average–generalized autoregressive conditional heteroskedastic modeling of the European Union emissions trading scheme data and provide comparisons with benchmark models. Our analysis reveals evidence for structural changes in the underlying models in the span of the years 2008–2012. Data‐driven methods for identifying possible change‐points in the underlying models are employed, and a detailed analysis is provided. Our analysis indicated change‐points in the European Union Allowance (EUA) prices in the first half of 2009 and in the second half of 2011, whereas in the Certified Emissions Reduction (CER) prices three change‐points have appeared, in the first half of 2009, the middle of 2011, and in the second half of 2012. These change‐points seem to parallel the global economic indicators as well. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
40.
Bayram?KilicEmail author Sunay?Turkdogan Aykut?Astam Sümeyra?Seniha?Baran Mansur?Asgin Emre?Gur Yusuf?Kocak 《Journal of nanoparticle research》2018,20(1):11
Developing efficient and cost-effective photoanode plays a vital role determining the photocurrent and photovoltage in dye-sensitized solar cells (DSSCs). Here, we demonstrate DSSCs that achieve relatively high power conversion efficiencies (PCEs) by using one-dimensional (1D) zinc oxide (ZnO) nanowires and copper (II) oxide (CuO) nanorods hybrid nanostructures. CuO nanorod-based thin films were prepared by hydrothermal method and used as a blocking layer on top of the ZnO nanowires’ layer. The use of 1D ZnO nanowire/CuO nanorod hybrid nanostructures led to an exceptionally high photovoltaic performance of DSSCs with a remarkably high open-circuit voltage (0.764 V), short current density (14.76 mA/cm2 under AM1.5G conditions), and relatively high solar to power conversion efficiency (6.18%) . The enhancement of the solar to power conversion efficiency can be explained in terms of the lag effect of the interfacial recombination dynamics of CuO nanorod-blocking layer on ZnO nanowires. This work shows more economically feasible method to bring down the cost of the nano-hybrid cells and promises for the growth of other important materials to further enhance the solar to power conversion efficiency. 相似文献