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21.
A method for the determination of molecular oxygen in a great variety of liquid and gaseous samples has been developed. The method seems adaptable for control analysis by reason of its sensitivity, rapidity and ease of operation. It gives accurate determinations in the presence of many chemical substances which interfere with other methods. It is based on the variation in corrosion potential of the aluminium electrode, caused by oxygen, and exemplifies use of the corrosion phenomenon in analytical chemistry. 相似文献
22.
Domenica Borra Tommaso Lorenzi 《Zeitschrift für Angewandte Mathematik und Physik (ZAMP)》2013,64(3):419-437
This paper presents a hybrid model for opinion formation in a large group of agents exposed to the persuasive action of a small number of strong opinion leaders. The model is defined by coupling a finite difference equation for the dynamics of leaders opinion with a continuous integro-differential equation for the dynamics of the others. Such a definition stems from the idea that the leaders are few and tend to retain original opinions, so that their dynamics occur on a longer time scale with respect to the one of the other agents. A general well-posedness result is established for the initial value problem linked to the model. The asymptotic behavior in time of the related solution is characterized for some general parameter settings, which mimic distinct social scenarios, where different emerging behaviors can be observed. Analytical results are illustrated and extended through numerical simulations. 相似文献
23.
Different carbonaceous materials, such as single‐walled carbon nanotubes (SWCNTs) and glassy carbon submitted to an electrochemical activation at +1.80 V (vs. SCE) for 900 s, have been used with the aim of comparing their performances in the development of enzyme electrodes. Commercial SWCNTs have been pretreated with 2.2 M HNO3 for 20 h prior to use. The utility of activated GC as promising material for amperometric oxidase‐based biosensors has been confirmed. With glucose oxidase (GOx) as a model enzyme, glucose was efficiently detected up to 1 mM without the use of a mediator. Both electrodes operated in stirred solutions of 0.1 M phosphate buffer (pH 5.5), containing dissolved oxygen, at a potential of ?0.40 V vs. SCE. Although the performances of the two carbonaceous materials were comparable, the biosensors based on activated GC were characterized by a practically unchanged response 40 days after the fabrication, a better signal to noise ratio, and a little worse sensitivity. In addition, the preparation procedure of such biosensors was more simple, rapid and reproducible. 相似文献
24.
25.
Giuseppe Schirripa Spagnolo Giorgio Guattari Carmine Sapia Dario Ambrosini Domenica Paoletti Giorgio Accardo 《Optics and Lasers in Engineering》2000,33(2):141
In the present work, we propose a simple optical method to perform profilometry on works of art. The method is based on the projection of a Ronchi grating onto the surface to be analyzed. When viewed at an angle different from the projection angle, the grid pattern appears deformed by the surface shape. This pattern is digitized, by a high-resolution CCD camera, and then processed using a Fourier transform analysis. The technique is free from the errors caused by higher harmonic components of the grating pattern. Furthermore, the method relies on very simple equipment and it is therefore suitable for in situ measurements. Theoretical details and examples of the technique in operation are given. 相似文献
26.
The orthorhombic crystal structure of [Co2(CO)6(μ‐CO)(μ‐C4O2H2)] ( 1 ) was determined at 150 K (Fig. 1). Two C−H⋅⋅⋅O bonds connect the molecules, forming waving ribbons along the b axis. The experimental electron density, determined with the aspherical‐atom formalism, was analyzed with the topological theory of molecular structure. The presence of the Co−Co bond critical point indicates for the first time the existence of a metal−metal bond in a system with bridged ligands. The bond critical properties of the intramolecular bonds and of the intermolecular interactions show features similar to those found in [Mn2(CO)10], confirming our previously established bonding classification for organometallic and coordination compounds. 相似文献
27.
The motion tracking enhancement technique (MTE) is a recently introduced method to improve the accuracy of tomographic PIV
measurements at seeding density higher than currently practiced. The working principle is based on the fact that the particle
field and its projections are correlated between the two exposures. Therefore, information from subsequent exposures can be
shared within the tomographic reconstruction process of a single object, which largely reduces the energy lost into ghost particles. The study follows a previous work based on synthetic particle images, showing that the MTE technique has an effect similar
to that of increasing the number of cameras. In the present analysis, MTE is applied to Tomographic PIV data from two time-resolved
experiments on turbulent shear flows: a round jet at Re = 5,000 (f
acq = 1,000 Hz) and a turbulent boundary layer at the trailing edge of an airfoil (Re
c = 370,000) measured at 12,000 Hz. The application of MTE is extended to the case of more than two recordings. The performance
is assessed comparing the results from a lowered number of cameras with respect to the full tomographic imaging system. The
analysis of the jet flow agrees with the findings of numerical simulations provided the results are scaled taking into account the concept of MTE efficiency based on the volume fraction where ghost-pairs (Elsinga et al. 2010a) are produced. When a large fraction of fluid has uniform motion (stagnant fluid surrounding the jet), only a moderate reduction
in ghost intensity is expected by MTE. Nevertheless, a visible recovery of reconstruction quality is observed for the 3-cameras system when
MTE is applied making use of 3 recordings. In the turbulent boundary layer, the objective is set to increase the seeding density
beyond current practice, and the experiments are performed at approximately 200,000 particles/megapixel. The measurement robustness
is monitored with the signal-to-noise ratio S/N for the cross-correlation analysis. An estimate of the precision error is
obtained for the turbulent boundary layer case following the peak height of the spatio-temporal cross-correlation function
(frozen-turbulence). The MTE approach appears to be essential for the increase in robustness and measurement precision at such seeding density. 相似文献
28.
The flow field at the tip region of a scaled DHC Beaver aircraft propeller, running at transonic speed, has been investigated
by means of a multi-plane stereoscopic particle image velocimetry setup. Velocity fields, phase-locked with the blade rotational
motion, are acquired across several planes perpendicular to the blade axis and merged to form a 3D measurement volume. Transonic
conditions have been reached at the tip region, with a revolution frequency of 19,800 rpm and a relative free-stream Mach
number of 0.73 at the tip. The pressure field and the surface pressure distribution are inferred from the 3D velocity data
through integration of the momentum Navier-Stokes equation in differential form, allowing for the simultaneous flow visualization
and the aerodynamic loads computation, with respect to a reference frame moving with the blade. The momentum and pressure
data are further integrated by means of a contour-approach to yield the aerodynamic sectional force components as well as
the blade torsional moment. A steady Reynolds averaged Navier-Stokes numerical simulation of the entire propeller model has
been used for comparison to the measurement data. 相似文献
29.
30.
The disagreement between free surface scalar experiments and the two-dimensional (2D) transport equation is discussed. An effective diffusivity coefficient, \(\kappa _{{\rm eff}}\) , is introduced and defined as the quotient between variance decay and mean gradient square. In all the experiments performed, \(\kappa _{{\rm eff}}\) is significantly larger than the scalar diffusivity, \(\kappa \) . Three mechanisms are identified as responsible for the differences between the quasi two-dimensional (Q2D) experiments and the 2D behaviour of a diffusive scalar. These are the vertical velocity gradients, the free surface divergence and the gravity currents induced by the scalar. These mechanisms, which affect the diffusive term in the 2D transport equation for large Péclet number ( \(Pe\gg 1\) ), are evaluated for steady and time-dependant laminar flows driven by electromagnetic body forces. 相似文献