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Scanning electron microscope (SEM) tribometric data on polycrystalline silicon (poly-Si) vs. poly-Si, Si(100) vs. Si(100)
and Si(111) vs. Si(111) interfaces, obtained in
Torr and in 0.2 Torr partial pressure of hydrogen gas (
) from room temperature to 850°C, were performed under standard and much slower thermal ramping rates. The friction data were analyzed per the methodology
described in part I of this paper series. The results indicate a highly beneficial friction- and wear-reducing regime within
a relatively narrow thermal region. This desirable region coincides with some chemisorption of excited species of molecular
hydrogen just before the mass thermal desorption of surface hydrides. These data represent the tribochemical equivalent of
a method routinely used in electronics, whereby deep electron traps (dangling Si bonds) are passivated by baking in molecular
hydrogen. The
also exerts a moderating influence on the size of the friction noise at all test temperatures. However, the general level
of friction beyond the beneficial thermal region is high. In parallel, the general wear rate of Si representative of the entire
range of standard thermal ramping in both atmospheric environments is in the extremely high 10-12m3/(N m) range. Operating strictly in the beneficial, low-friction thermal regime resulted in a several orders-of-magnitude
reduction in the wear rate over those measured under standard thermal ramping conditions. Although the results confirm previous
findings that Si is not a good material of construction for miniaturized moving mechanical assemblies (e.g., microbearings
and gears), there seems to be some limited possibility of gas-phase lubrication of Si micromechanisms with rarefied hydrogen
at surface temperatures between 100 and 300°C.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
24.
Quoc Ahn Tran Bastien Chevalier Miguel Angel Benz-Navarrete Pierre Breul Roland Gourvès 《Soils and Foundations》2019,59(6):2348-2355
This paper presents a calculation method for obtaining the continuous variation in stress between the tip and the soil during dynamic penetration tests, particularly in the case of using the Panda 3® penetration testing device. The originality of the method is that the tip stress can be computed continuously throughout the driving process. For each impact of the hammer on the penetrometer, data are recorded by sensors located at the top of the apparatus. Then, the stress at the tip and the displacement of the apparatus are calculated with a method based on the propagation of waves in the device. A three-dimensional numerical model of the penetration test, based on the Panda 3® specifications and using the discrete element method (DEM), is proposed in this paper. The purpose of the simulations is to validate the calculation method by comparing the curves of the tip stress versus the penetration distance obtained in two different ways, the first being the distance directly observed at the tip and the second being the distance calculated from the data recorded at the top of the penetrometer, as with the experimental device. The entire apparatus is represented, including the hammer, the rod, and the tip, and is driven into the model soil. The calculation method is applied, and the results are compared to the actual response of the soil to the driving of the penetrometer directly at the tip, which can be obtained with the numerical model. The responses are found to be very similar, confirming the theoretical framework and its underlying assumptions. This method is applied to dynamic penetration tests and provides the opportunity to obtain mechanical parameters other than the tip resistance from the tests. 相似文献
25.
For liquid ethylene gas (LEG) vessels, developing high‐efficient re‐liquefaction plant to handle the continuously yielded boil‐off gas (BOG) could significantly improve its energy efficiency. In this study, an ejector enhanced re‐liquefaction process (EERP) for LEG vessels is proposed to improve the performance of the conventional re‐liquefaction process (CRP) with a cascaded two‐stage compression refrigeration cycle. In Aspen HYSYS, an ejector model was developed to analyse the performance of the proposed cycle system. The effects of the evaporating pressure of upper cycle pR0 ' and the intermediate pressures of upper and bottom cycles (pR3 and pE3) on the performances of both the CRP and EERP were studied. The results show that better performances can be reached with lower pR0 ' for the CRP and EERP. In order to achieve the best performances, the optimal pR3 and pE3 are, respectively, lifted to 510 kPa and 630 kPa by the EERP. When the proposed cycle system with the EERP is employed to re‐liquefy 3000 kg/h of ethylene BOG, its coefficient of performance (COP) and exergy efficiency can be improved by 2.95–5.31% and 2.70–4.86% over that of the cycle system with the CRP. Correspondingly, the EERP could reduce the total power consumption of 15.7–27.9 kW compared to the CRP. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
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Lisbet Harboe 《Architectural Design》2015,85(2):82-87
Founded by Andreas Grøntvedt Gjertsen and Yashar Hanstad, TYIN tegnestue Architects grew out of an initiative to provide sleeping accommodation for an orphanage in Thailand when the principals were only third-year architecture students. Norwegian architect Lisbet Harboe explains how the student-architects built up a practice while in schools by refocusing their studies and those of their peers on learning through their own experiences of construction. 相似文献
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《Journal of the European Ceramic Society》2022,42(1):154-161
A series of high-k Ba4Nd28/3Ti18-yGa4y/3O54 (0≤y≤2, BNTG) ceramics with temperature stable and ultra-low dielectric loss were synthesized via the conventional solid-state reaction. The main phase of all BNTG ceramics demonstrated an orthorhombic tungsten-bronze structure, but the impurity phase (gallium-rich phase) was found in BNTG (y = 2) ceramic. Partial substitution of Ga3+ for Ti4+ in B-site was a valid method to improve the temperature stability and dielectric loss of BNTG ceramics. The variation of εr values of BNTG ceramics was dominated by the ionic polarizability. The ultra-low dielectric loss (ultra-high Q × f values) was associated with grain size, suppression of Ti3+ and impurity phase. The decrease of TCF values was highly dependent on the tilting of Ti-O octahedra and impurity phase. Finally, outstanding combination dielectric characteristics were achieved for BNTG microwave ceramics at y = 1.5 (εr = 72.8, Q × f = 14,600 GHz, TCF=+4.1 ppm/°C) and at y = 2 (εr = 70.3, Q × f = 15,500 GHz, TCF=+3.9 ppm/°C). 相似文献
30.
文章对可再生吸收剂的脱硫技术及其原理进行了比较全面的阐述,并且摘要介绍了各个工艺技术的优缺点。对于需要选择不同工艺路线的决策者,可以提供参考。 相似文献