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41.
The present work reports isothermal gas/solid equilibration kinetics for Nb-doped TiO(2) (0.65 atom %) at elevated temperatures (1073-1298 K) within narrow ranges of oxygen activity spanning between 10(-13) Pa and 75 kPa. The equilibration kinetics were monitored using electrical conductivity measurements. The kinetic data were used to determine the chemical diffusion coefficient (D(chem)). D(chem) as a function of p(O(2)) exhibits a complex dependence, which is considered in terms of defect disorder and the related concentrations of electronic charge carriers. The activation energy of D(chem) in the p(O(2)) range 10 Pa < p(O(2)) < 75 kPa varies in the range 88.0-98.2 kJ/mol. It is important to note that the chemical diffusion coefficient in strongly reduced conditions [p(O(2)) = 10(-9) Pa] exhibits a negative temperature dependence of D(chem) (-67.2 kJ/mol). This finding indicates that under these conditions transport in a chemical potential gradient is consistent with metallic charge transport. 相似文献
42.
The present work derived defect disorder diagram representing the effect of oxygen activity on the concentration of both ionic and electronic defects for undoped TiO2. This diagram was determined using the equilibrium constants derived in the present work, including (i) the intrinsic electronic equilibrium constant, (ii) the equilibrium constant for the formation of oxygen vacancies, and (iii) equilibrium constant for the formation of titanium vacancies. These equilibrium constants are consistent with three properties determined independently, including: electrical conductivity, thermoelectric power and change of mass determined by thermogravimetry. The derived defect disorder diagram may be used for tailoring semiconducting properties of TiO2 that are desired for specific applications through the selection of optimized processing conditions. 相似文献
43.
Z. Bak R. Jaroszewicz 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,64(2):231-235
A localized spin system of fractal symmetry with indirect exchange between them is considered. We define a specific class
of fractals as the “net fractals” which display multidimensional logarithmic periodicity. Basing on this property we model
the effective indirect exchange interaction by the conventional RKKY exchange with the logarithmic coordinates playing role
of the real space ones. Finally, we discuss the case of non-ideal “net fractals” in which fractional dynamics of the electrons
is expected. In this case we show that RKKY exchange integrals are given by the formulas derived under assumption that a system
has a fractional spectral dimension. 相似文献
44.
Quantitative determination of omega-6 and omega-3 polyunsaturated fatty acids in human plasma and urine with high accuracy and precision provides significant information to monitor the underlying etiology of several diseases. In this regard, liquid chromatography-mass spectrometry is a good choice owing to its great selectivity and sensitivity. Additionally, the hybrid quadrupole–time of flight–mass spectrometer systems provides easy identification of target compounds with superior mass measurements. In this study, an analytical method has been developed for simple, accurate and simultaneous determination of linoleic acid, arachidonic acid, docosahexaenoic acid and eicosapentaenoic acid in a short chromatographic analysis period. The developed method is suitable for the quantitative detection of these four compounds with detection limits ranging between 1.1–3.0 ng ml−1 and its applicability was assessed in human urine and plasma samples. As a result, acceptable accuracy (between 83 and 111%) and good precision (<6%) were obtained for target compounds using matrix matching calibration strategy. 相似文献
45.
Ádám Pálvölgyi Zsolt Rapi Olivér Ozohanics Gábor Tóth György Keglevich Péter Bakó 《Research on Chemical Intermediates》2018,44(3):1627-1645
Chiral monoaza-15-crown-5-type lariat ethers annelated to alkyl 4,6-O-benzylidene-α- and β-d-glucopyranosides have been synthesized. These macrocycles generated significant asymmetric induction as phase-transfer catalysts in a few two-phase reactions. The catalytic effect of the lariat ethers with methoxy, ethoxy, and i-propoxy substituents on C-1 of the sugar unit in both α and β positions was compared. In liquid–liquid two-phase reactions, the nature and position of the substituents did not have much effect. The α-anomers were somewhat more efficient in terms of enantioselectivity than the β forms. In asymmetric Darzens condensations, in the epoxidation of trans-chalcone, in the Michael addition of β-nitrostyrene and diethyl acetamidomalonate, and in the reaction of 2-benzylidene-1,3-indandione with diethyl bromomalonate, maximum enantioselectivities of 73, 94, 78, and 72%, respectively, were obtained in presence of glucopyranoside-based lariat ethers as catalysts. 相似文献
46.
Introducing Fe2+ into Nickel–Iron Layered Double Hydroxide: Local Structure Modulated Water Oxidation Activity 下载免费PDF全文
Zhao Cai Daojin Zhou Maoyu Wang Seong‐Min Bak Yueshen Wu Zishan Wu Yang Tian Xuya Xiong Dr. Yaping Li Dr. Wen Liu Prof. Samira Siahrostami Dr. Yun Kuang Prof. Xiao‐Qing Yang Dr. Haohong Duan Prof. Zhenxing Feng Prof. Hailiang Wang Prof. Xiaoming Sun 《Angewandte Chemie (International ed. in English)》2018,57(30):9392-9396
Exploring materials with regulated local structures and understanding how the atomic motifs govern the reactivity and durability of catalysts are a critical challenge for designing advanced catalysts. Herein we report the tuning of the local atomic structure of nickel–iron layered double hydroxides (NiFe‐LDHs) by partially substituting Ni2+ with Fe2+ to introduce Fe‐O‐Fe moieties. These Fe2+‐containing NiFe‐LDHs exhibit enhanced oxygen evolution reaction (OER) activity with an ultralow overpotential of 195 mV at the current density of 10 mA cm?2, which is among the best OER catalytic performance to date. In‐situ X‐ray absorption, Raman, and electrochemical analysis jointly reveal that the Fe‐O‐Fe motifs could stabilize high‐valent metal sites at low overpotentials, thereby enhancing the OER activity. These results reveal the importance of tuning the local atomic structure for designing high efficiency electrocatalysts. 相似文献
47.
Megyes T Bálint S Bakó I Grósz T Pálinkás G 《Journal of the American Chemical Society》2008,130(29):9206-9207
Wide-angle X-ray diffraction and molecular dynamics simulation has been used to perform complete structural characterization of nitromethane solution of a 16-membered gold(I) ring. The joint application of these two methods was an adequate tool to describe not only the structure of the complex but also the solvation properties of the complex in nitromethane and the effect of the solvation on the bulk structure. It has been found that a relatively diffuse slightly distorted solvation shell is formed around the complex, following the shape of the molecule. Nitromethane molecules in the solvation sphere are distributed randomly; no special orientation can be detected. The interaction energy of the complex with nitromethane molecules is attractive. In bulk, besides the antiparallel orientation of the nitromethane molecules, T-shape orientation and long-range order in antidipole orientation can also be detected. 相似文献
48.
Saiki A. Funakubo H. Mizutani N. Shinozaki K. Bak T. Nowotny J. Rekas M. Sorrel C. C. 《Journal of Thermal Analysis and Calorimetry》1999,57(3):875-881
The extent of the surface charge, that develops during oxidation of zirconia, is determined using work function measurements for both bulk specimen and thin films. The bulk specimen of yttria-doped zirconia (10 mol%) exhibits maxima of the surface electrical effect at 373 and 973 K (130 and 280 mV, respectively) that can be considered in terms of oxygen chemisorption and oxygen non-stoichiometry. Thin film of undoped zirconia exhibits a maximum at 473 K (260 eV). Addition of yttria (10 mol%) to the thin film results in a substantial reduction of the maximum, to about 140 eV, that is shifted up to 600 K.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献
49.
Zygmunt Bak 《Czechoslovak Journal of Physics》1999,49(11):1525-1529
Within an analytical approach we study the RKKY interaction mediated by the electron gas, which shows fractional spectral
dimensionality. We derive formula for the RKKY exchange integral in a system of nonintegral dimensionality. Also the modifications
of magnetic interaction and magnetic moments in metallic overlayers due to the surface/interface effects are considered.
Presented at the VIII-th Symposium on Surface Physics, Třešt’ Castle, Czech Republic, June 28 – July 2, 1999. 相似文献
50.
This paper overviews the present state of understanding on properties of the electrode material LiCoO2 as well as the impact of these properties on the electrode performance in lithium batteries. The properties that are important
for applications, such as structure, non-stoichiometry, defect chemistry and related electrical properties are considered. 相似文献