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991.
Graziano Baccolini Carla Boga Gabriele Micheletti 《Phosphorus, sulfur, and silicon and the related elements》2013,188(11):2303-2315
In this article, we present a study about the non-enzymatic hydrolysis of phosphoenolpyruvate (PEP) by following the reaction course through 31P NMR spectroscopy. We have demonstrated that PEP in water exists mainly as a very stable cyclic pentacoordinate phosphorus compound in equilibrium with other cyclic forms. This explains the PEP stability in water. In contrast, after addition of an alcohol to a PEP aqueous solution, other very unstable cyclic pentacoordinated intermediates are formed, which immediately collapse, giving a feasible phosphorylation of the alcohol. It is known that cyclic pentacoordinated phosphorus intermediates are favored over the corresponding acyclic intermediates by a factor of 106–108, and this preference, found also in this study, might be the “driver mechanism” able to overcome the clutter of abiotic chemistry, thus permitting formation of pre-RNA molecules probably with a “self-organized process.” 相似文献
992.
Gabriele?IngrossoEmail author Sebastiano?Calchi?Novati Francesco?De Paolis Philippe?Jetzer Achille?Nucita Alexander?Zakharov 《General Relativity and Gravitation》2011,43(4):1047-1060
Several exoplanets have been detected towards the Galactic bulge with the microlensing technique. We show that exoplanets in M31 may also be detected with the pixel-lensing method, if telescopes making high cadence observations of an ongoing microlensing event are used. Using a Monte Carlo approach we find that the mean mass for detectable planetary systems is about 2 M J. However, even small mass exoplanets (\({M_{\rm P} < 20 M_{\oplus}}\)) can cause significant deviations, which are observable with large telescopes. We reanalysed the POINT-AGAPE microlensing event PA-99-N2. First, we test the robustness of the binary lens conclusion for this light curve. Second, we show that for such long duration and bright microlensing events, the efficiency for finding planetary-like deviations is strongly enhanced with respect to that evaluated for all planetary detectable events. 相似文献
993.
994.
In this study, the concept of multifunctional alkaline pulping has been approved to produce high-purity and high-yield dissolving
pulps. The selective removal of hemicelluloses was achieved by either water autohydrolysis (PH) or alkaline extraction (E)
both applied as pre-treatments prior to cooking. Alternatively, hemicelluloses were isolated after oxygen delignification
in a process step denoted as cold caustic extraction (CCE). Eucalyptus globulus wood chips were used as the raw material for kraft and soda-AQ pulping. In all process modifications sulfur was successfully
replaced by anthraquinone. By these modifications purified dissolving pulps were subjected to TCF bleaching and comprehensive
viscose and lyocell application tests. All pulps met the specifications for dissolving pulps. Further more, CCE-pulps showed
a significantly higher yield after final bleaching. Morphological changes such as ultrastructure of the preserved outer cell
wall layers, specific surface area and lateral fibril aggregate dimension correlated with the reduced reactivity towards regular
viscose processing. The residual xylan after alkali purification depicted a lower content of functional groups and a higher
molecular weight and was obviously entrapped in the cellulose fibril aggregates which render the hemicelluloses more resistant
to steeping in the standard viscose process. Simultaneously, the supramolecular structure of the cellulose is partly converted
from cellulose I to cellulose II by the alkaline purification step which did not influence the pulps reactivity significantly. Nevertheless, these differences in pulp parameters did not affect the lyocell process due to the outstanding solubility of
the pulps in NMMO. Laboratory spinning revealed good fiber strength for both, regular viscose and lyocell fibers. The high
molecular weight xylan of the CCE-treated pulps even took part in fiber forming. 相似文献
995.
Zeynep Alp Alessandro Ciccola Ilaria Serafini Alessandro Nucara Paolo Postorino Alessandra Gentili Roberta Curini Gabriele Favero 《Molecules (Basel, Switzerland)》2022,27(20)
The aim of this research is to study and diagnose for the first time the Polaroid emulsion transfer in the contemporary artist Paolo Gioli’s artworks to provide preliminary knowledge about the materials of his artworks and the appropriate protocols which can be applied for future studies. The spectral analysis performed followed a multi-technical approach first on the mock-up samples created following Gioli’s technique and on one original artwork of Gioli, composed by: FORS (Fiber Optics Reflectance), Raman, and FTIR (Fourier-Transform InfraRed) spectroscopies. These techniques were chosen according to their completely non-invasiveness and no requirement for sample collection. The obtained spectra from FTIR were not sufficient to assign the dyes found in the transferred Polaroid emulsion. However, they provided significant information about the cellulose-based materials. The most diagnostic results were obtained from FORS for the determination of the dye developers present in the mock-up sample which was obtained from Polacolor Type 88 and from Paolo Gioli’s original artwork created with Polacolor type 89. 相似文献
996.
Gabriele Milani 《International Journal of Solids and Structures》2011,48(2):326-345
A homogenization model for periodic masonry structures reinforced with continuous FRP grids is presented. Starting from the observation that a continuous grid preserves the periodicity of the internal masonry layer, rigid-plastic homogenization is applied directly on a multi-layer heterogeneous representative element of volume (REV) constituted by bricks, finite thickness mortar joints and external FRP grids. In particular, reinforced masonry homogenized failure surfaces are obtained by means of a compatible identification procedure, where each brick is supposed interacting with its six neighbors by means of finite thickness mortar joints and the FRP grid is applied on the external surfaces of the REV. In the framework of the kinematic theorem of limit analysis, a simple constrained minimization problem is obtained on the unit cell, suitable to estimate – with a very limited computational effort – reinforced masonry homogenized failure surfaces.A FE strategy is adopted at a cell level, modeling joints and bricks with six-noded wedge shaped elements and the FRP grid through rigid infinitely resistant truss elements connected node by node with bricks and mortar. A possible jump of velocities is assumed at the interfaces between contiguous wedge and truss elements, where plastic dissipation occurs. For mortar and bricks interfaces, a frictional behavior with possible limited tensile and compressive strength is assumed, whereas for FRP bars some formulas available in the literature are adopted to reproduce the delamination of the truss from the support.Two meaningful structural examples are considered to show the capabilities of the procedure proposed, namely a reinforced masonry deep beam (0°/90° continuous reinforcement) and a masonry beam in simple flexion for which experimental data are available. Good agreement is found between present model and alternative numerical approaches. 相似文献
997.
998.
999.
Mariella Cecchi Mauro Marini Gabriele Villari 《NoDEA : Nonlinear Differential Equations and Applications》2009,6(2):173-190
((without abstract.)) 相似文献
1000.
Uri Admon David Donohue Helmut Aigner Gabriele Tamborini Olivier Bildstein Maria Betti 《Microscopy and microanalysis》2005,11(4):354-362
Physical, chemical, and isotopic analyses of individual radioactive and other particles in the micron-size range, key tools in environmental research and in nuclear forensics, require the ability to precisely relocate particles of interest (POIs) in the secondary ion mass spectrometer (SIMS) or in another instrument, after having been located, identified, and characterized in the scanning electron microscope (SEM). This article describes the implementation, testing, and evaluation of the triangulation POIs re-location method, based on microscopic reference marks imprinted on or attached to the sample holder, serving as an inherent coordinate system. In SEM-to-SEM and SEM-to-SIMS experiments re-location precision better than 10 microm and 20 microm, respectively, is readily attainable for instruments using standard specimen stages. The method is fast, easy to apply, and facilitates repeated analyses of individual particles in different instruments and laboratories. 相似文献