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41.
In this paper the previously introduced wavefront analysis is extended to heterogeneous reaction systems, which consist of several reaction steps. It is shown how three mainly informations obtained at the wavefront, namely the damping of the wavefront, the time-gradients at the wavefront and the propagation velocity of the wavefront, can be used for kinetic investigations of a reaction step under consideration. 相似文献
42.
43.
Uwe Gbureck Jake E. Barralet Michael Hofmann Roger Thull 《Journal of the American Ceramic Society》2004,87(2):311-313
It was found that prolonged high-energy ball-milling of Hilgenstokite (tetracalcium phosphate, TTCP) resulted in a decrease in both particle and crystallite size, leading to a mechanical activation of the compound. This mechanically activated material demonstrated a high reactivity such that, in contrast to highly crystalline TTCP, a setting reaction with water to nanocrystalline hydroxyapatite (HA) and Ca(OH)2 could be achieved at 37°C. However, crystalline TTCP is practically unreactive at physiologic temperatures because of the formation of a thin HA layer on the particle surface preventing further reaction. 相似文献
44.
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46.
Gerhard Bayer Martin Hofmann Ludwig J. Gauckler 《Journal of the American Ceramic Society》1991,74(9):2205-2208
New oxide compounds with α-PbO2 structure have been synthesized by solid-state reactions. These are derived from ZrTiO4 and HfTiO4 by a different kind of ionic substitution. The thermal expansion behavior of these phases was investigated by means of a dilatometer and an X-ray heating diffractometer. These measurements revealed rather low expansion for some of the Zr(Me3+ /Me5+ )O4 , solid solutions. This behavior is attributed to their high expansion anisotropy, which leads to extended formation of microcracks. 相似文献
47.
Peter E. Neerincx Martin Hofmann Oleksandr Gorodetskyi Kirill Feldman Jan Vermant Han E. H. Meijer 《Polymer Engineering and Science》2021,61(4):1257-1269
Relatively recently, we advanced a route to create, in a controlled fashion, combined horizontal and vertical stratified structures by simple and energy-efficient processing operations employing static mixing elements. While in state-of-the-art static mixing the focus is on layer multiplication, here the aim is to create hierarchical fractal structures. Therefore, the main question addressed in this article is how structures, rather than layers, can be multiplied. The key aspect is the addition of layers on the sides or in the midplane of the flow during the process; every addition step increases the hierarchy by one level. This article derives the general formalism for forming fractal structures with controlled hierarchy, and we develop the language required to design and construct the dies. The main part of the article addresses this main topic and is based on the splitting serpentine static mixer geometry that can be easily made on the parting surfaces of a mold on both the micro- and the macroscale. The second part of the article addresses the strategy to minimize the number of mirroring steps, eventually avoiding mirroring completely, and is based on the rotation-free multiflux static mixer geometry. With the design language derived, complex hierarchical fractal structures can be generated simply by changing the number and sequence of operators within extrusion dies or molds, providing a one-step solution to produce material structures for potential use in diverse applications ranging from advanced mechanical systems to photovoltaic devices, where controlled assembly of dissimilar materials, and the realization of huge interfaces and genuine cocontinuity throughout the cross section, is critical. 相似文献
48.
This article describes the investigation of a new generation of vacuum plasma sprayed CoNiCrAlY coatings on NiCr20Ti in the
sprayed as well as the laser-treated condition. The aim of the study was the improvement of MCrAlY coating properties by modifying
the microstructure through laser remelting with 5-kW Co2: lasers. Parameter analysis and optimization was carried out for the vacuum plasma spraying process, as well as for the laser
remelting technique. The effect of the laser treatment on microstructure, quality of the coatings, and oxidation as well as
hot gas corrosion behavior are reported. 相似文献
49.
Surface resolidification experiments using a high power CO2-laser have been performed on an Al2O3ZrO2 containing 36.8 at.% ZrO2 eutectic alloy at beam velocities between 0.3 and 8 mm·s−1. The local growth rate has been measured by observation of the orientation of the microstructure using scanning electron microscopy. In the whole range of velocities, the structure is essentially a regular lamellar eutectic and the value of the growth productλ2V was found to be ≈ 9.6·10−17 m3·s−1. The measured eutectic spacings were compared with Jackson and Hunt model. Using thermophysical properties from the literature, the measured spacings were more than four times larger than the calculated ones. Assuming all parameters of the growth relationship except the diffusion coefficient to be of the right order of magnitude or to have a negligible influence, agreement is found when using a larger liquid diffusion coefficient,DL≈5·10−10m2·s−1. 相似文献
50.
The B-C-Ti system has been critically assessed and calculated in the temperature region of 1400 °C up to the melting range
employing the Thermocalc program system. The liquid phase is described using a substitutional model. The ternary solid solubility
of boron in titanium carbide has been taken into account by using a two-sublattice model (Ti)1(B,C,Va),. The calculated isotherms and isopleths are presented and compared with the experimental information. The B-C-Ti
reaction scheme is presented including the Ti3B4 phase. 相似文献