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71.
Ultrafast two-dimensional (2D) infrared vibrational echo experiments and theory are used to examine chemical exchange between solute-solvent complexes and the free solute for the solute phenol and three solvent complex partners, p-xylene, benzene, and bromobenzene, in mixed solvents of the partner and CCl4. The experiments measure the time evolution of the 2D spectra of the hydroxyl (OD) stretching mode of the phenol. The time-dependent 2D spectra are analyzed using time-dependent diagrammatic perturbation theory with a model that includes the chemical exchange (formation and dissociation of the complexes), spectral diffusion of both the complex and the free phenol, orientational relaxation of the complexes and free phenol, and the vibrational lifetimes. The detailed calculations are able to reproduce the experimental results and demonstrate that a method employed previously that used a kinetic model for the volumes of the peaks is adequate to extract the exchange kinetics. The current analysis also yields the spectral diffusion (time evolution of the dynamic line widths) and shows that the spectral diffusion is significantly different for phenol complexes and free phenol. 相似文献
72.
Hwang S Chi YS Lee BS Lee SG Choi IS Kwak J 《Chemical communications (Cambridge, England)》2006,(2):183-185
Asymmetric electrostatic interactions dependent on pH between the redox molecules and the terminal group on the top of the self-assembled monolayer (SAM) afford control of the electron transfer property of the SAM having the imidazole terminal group. 相似文献
73.
V. Singh S. Watanabe T. K. Gundu Rao J. F. D. Chubaci I. Ledoux-Rak H.-Y. Kwak 《Applied physics. B, Lasers and optics》2010,98(1):165-172
Er and Yb co-doped ZnAl2O4 phosphors were prepared by solution combustion synthesis and the identification of Er and Yb were done by energy-dispersive
X-ray analysis (EDX) studies. A luminescence at 1.5 μm, due to the 4I13/2 →4I15/2 transition, has been studied in the NIR region in Er and Yb co-doped ZnAl2O4 phosphors upon 980 nm CW pumping. Er-doped ZnAl2O4 exhibits two thermally stimulated luminescence (TSL) peaks around 174°C and 483°C, while Yb co-doped ZnAl2O4 exhibits TSL peaks around 170°C and 423°C. Electron spin resonance (ESR) studies were carried out to identify defect centres
responsible for TSL peaks observed in the phosphors. Room temperature ESR spectrum appears to be a superposition of two distinct
centres. These centres are assigned to an O− ion and F+ centre. O− ion appears to correlate with the 174°C TSL peak and F+ centre appears to relate with the high temperature TSL peak at 483°C in ZnAl2O4:Er phosphor. 相似文献
74.
We studied self-propagated combustion synthesis of transition-metal-doped tetragonal ZrO2 (t-ZrO2) with first principles-based one-dimensional diffusion reaction model. The optimal reaction condition for the combustion process was investigated by calculating energetic stability and surface reactivity of oxygen vacancy defects on (101) surface termination of t-ZrO2 using first-principles density functional methods. In the first-principles model, the surface was doped with 14 different metal impurities in the 4th and 5th row of the periodic table to examine the role of transition-metal doping on the combustion process. Results indicate that there are clear trends in the defect stability and reactivity depending upon the type of metal impurity and their relative location with respect to the oxygen vacancy. Surface density of states and charge density information also show that there is a trade-off between the vacancy stability and chemical activity of the surface defect states. Based on the thermodynamic information obtained from first principles, we analyze the combustion process of a Zr metal particle by using a one-dimensional diffusion-reaction model. The competition between the vacancy-assisted chemisorption and the vacancy diffusion results in an optimal point for rate of combustion reaction with respect to the vacancy stability. From this, we suggest a plausible screening strategy for metal-doping which can be applied at different temperatures and pressures, as well as with different particle sizes. Our analysis indicates that first-principles calculation provides key information that can be subsequently used for an optimization of the reaction rate for a self-sustained combustion process. An explicit inclusion of rates of defect and ionic transport will be introduced into our model in future work. 相似文献
75.
The kinetics of biomimetic mineralization at a fatty acid monolayer interface have been measured in situ by synchrotron x-ray reflectivity. The formation of biologically relevant amorphous calcium carbonate films is affected by soluble macromolecules, supersaturation rate of change, and Mg cations. We find that these solution conditions influence mineral film formation in a complementary fashion. Poly(sodium acrylate) extends the lifetime of metastable amorphous calcium carbonate, solution saturation controls the mineral film growth rate, and Mg cations create a longer induction time. This is the first quantification of potentially competitive biomineralization mechanisms that addresses nucleation and growth of the amorphous mineral phases, which are important in biomineralization. 相似文献
76.
We analyze an immersed interface finite element method based on linear polynomials on noninterface triangular elements and
piecewise linear polynomials on interface triangular elements. The flux jump condition is weakly enforced on the smooth interface.
Optimal error estimates are derived in the broken H
1-norm and L
2-norm. 相似文献
77.
Jong Ho Kim Byoung Kyu Kwak Chee Burm Shin Won Jin Jeon Hyeon-Soo Park Kyunghee Choi Jongheop Yi 《Applied Mathematical Modelling》2010
A spatial distribution multimedia fate model is proposed for the rigorous simulation of the environmental multimedia fate of hazardous chemicals emitted from a variety of sources. To solve the relevant equation, we introduce an explicit finite difference method applied to uniform grids. We assessed the numerical properties of the model, including stability and accuracy. A new dimensionless number (multimedia transport number) is proposed for determining the numerical stability of the unsteady-state method. The model was verified by comparison with analytical solutions for the transport of non-conservative substances in two-phase open-channel flow. The spatial resolution of the spatial distribution model was tested via a comparison with a general multimedia fate model in a practical application related to toluene emissions in Seoul, South Korea. 相似文献
78.
Gan Z Kwak HT Bird M Cross T Gor'kov P Brey W Shetty K 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2008,191(1):135-140
Resistive and resistive-superconducting hybrid magnets can generate dc magnetic fields much higher than conventional superconducting NMR magnets but the field spatial homogeneity and temporal stability are usually not sufficient for high-resolution NMR experiments. Hardware and technique development addressing these issues are presented for high-resolution NMR at magnetic fields up to 40T. Passive ferromagnetic shimming and magic-angle spinning are used effectively to reduce the broadening from inhomogeneous magnetic field. A phase correction technique based on simultaneous heteronuclear detection is developed to compensate magnetic field fluctuations to achieve high spectral resolution. 相似文献
79.
Sanghan Lee Wooyoung Jin Su Hwan Kim Se Hun Joo Gyutae Nam Pilgun Oh Young‐Ki Kim Sang Kyu Kwak Jaephil Cho 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(31):10588-10595
Oxygen vacancies (OV) are native defects in transition metal (TM) oxides and their presence has a critical effect on the physicochemical properties of the oxide. Metal oxides are commonly used in lithium‐ion battery (LIB) cathodes and there is still a lack of understanding of the role of OVs in LIB research field. Here, we report on the behavior of OVs in a single‐crystal LIB cathode during the non‐equilibrium states of charge and discharge. We found that microcrack evolution in a single crystal occurs due to OV condensation in specific crystallographic orientations generated by the continuous migration of OVs and TM ions. Moreover, understanding the effects of the presence and diffusion of OVs in metal oxides enables the elucidation of most of the conventional mechanisms of capacity fading in LIBs and provides new insights for new electrochemical applications. 相似文献
80.
Jin Ho Kwak 《Discrete Mathematics》2008,308(11):2156-2166
In this paper, we classify the reflexible regular orientable embeddings and the self-Petrie dual regular orientable embeddings of complete bipartite graphs. The classification shows that for any natural number n, say (p1,p2,…,pk are distinct odd primes and ai>0 for each i?1), there are t distinct reflexible regular embeddings of the complete bipartite graph Kn,n up to isomorphism, where t=1 if a=0, t=2k if a=1, t=2k+1 if a=2, and t=3·2k+1 if a?3. And, there are s distinct self-Petrie dual regular embeddings of Kn,n up to isomorphism, where s=1 if a=0, s=2k if a=1, s=2k+1 if a=2, and s=2k+2 if a?3. 相似文献