全文获取类型
收费全文 | 2472篇 |
免费 | 97篇 |
国内免费 | 52篇 |
学科分类
工业技术 | 2621篇 |
出版年
2024年 | 18篇 |
2023年 | 44篇 |
2022年 | 38篇 |
2021年 | 46篇 |
2020年 | 73篇 |
2019年 | 67篇 |
2018年 | 66篇 |
2017年 | 61篇 |
2016年 | 59篇 |
2015年 | 81篇 |
2014年 | 113篇 |
2013年 | 164篇 |
2012年 | 126篇 |
2011年 | 179篇 |
2010年 | 111篇 |
2009年 | 119篇 |
2008年 | 110篇 |
2007年 | 119篇 |
2006年 | 107篇 |
2005年 | 93篇 |
2004年 | 98篇 |
2003年 | 89篇 |
2002年 | 85篇 |
2001年 | 82篇 |
2000年 | 57篇 |
1999年 | 72篇 |
1998年 | 76篇 |
1997年 | 46篇 |
1996年 | 35篇 |
1995年 | 24篇 |
1994年 | 10篇 |
1993年 | 20篇 |
1992年 | 14篇 |
1991年 | 5篇 |
1990年 | 20篇 |
1989年 | 6篇 |
1988年 | 6篇 |
1987年 | 11篇 |
1986年 | 4篇 |
1985年 | 13篇 |
1984年 | 20篇 |
1983年 | 17篇 |
1982年 | 16篇 |
1980年 | 1篇 |
排序方式: 共有2621条查询结果,搜索用时 15 毫秒
81.
《Advanced Powder Technology》2021,32(11):4167-4176
Hexagonal Boron nitride nanoplatelet (BNNP) with the combination of excellent mechanical properties, high-temperature thermal stability, and self-lubrication is a promising strengthening agent in plasma-sprayed composite coatings. However, it is a significant challenge to produce plasma sprayable feedstocks with homogeneously dispersed BNNPs owing to the intrinsic agglomeration of BNNPs. In this research, three powder preparation processes (electrostatic interaction, ball milling, and shear mixing) were employed to disperse BNNPs in Ni-Cr-Cr2O3 (NCCO) powders. The shear mixing process presents a competitive advantage in powder preparation, providing stable shear force and achieving exfoliated BNNPs homogeneous distribution in the composite powders. The spray drying technique was finally utilized to obtain spherical agglomerated BNNP-NCCO feedstocks with characteristics of relatively smooth surface and uniform size distribution. Hence, shear mixing and spray drying processes are expected to produce large-scale spherical composite powders with a homogeneous distribution of 2D layered nanomaterials for industrial application. 相似文献
82.
《Ceramics International》2021,47(23):33405-33412
In this study, SnO2@MnO2@graphite (SMG) anode material is prepared via a facile ball-milling approach combined with hydrothermal treatment. SnO2 and MnO2 nanoparticles are evenly dispersed on numerous sheet-like graphite. MnO2 can not only play a catalytic role for facilitating the conversion reaction of Sn/Li2O to SnO2, but also as a barrier to impede the coarsening of Sn in the composite. Meanwhile, graphite nanosheets could serve as an ideal volume expansion buffer and good electron conductor. Consequently, the SMG anode delivers superior reversible capacity of 1048.5 mAhg−1, ideal rate capability of 522.2 mAhg−1 at 5.0 A g-1 and stable long-life cyclic performance of 814.8 mAhg−1 at 1.0 A g-1 after 1000 cycles. This result indicates that the incorporation of MnO2, graphite nanosheet and SnO2 have a great potential in enhancing the performance of SnO2-based anode for battery applications. 相似文献
83.
The results of current investigation demonstrate that mechanochemical processing can be used to synthesize high purity Fe2B nanocrystals by selecting well-optimized milling conditions, reaction paths and proper starting materials. Microstructure, phase analyses, specific surface area, and magnetic properties of the synthesized nanocrystals were examined by using X-ray diffraction/spectroscopy, electron microscopy, nitrogen adsorption–desorption methods following Brunauer-Emmett-Teller equation and vibrating sample magnetometer techniques, respectively. Removal of MgO impurity phase by leaching the resulting powder in the acetic acid solution yielded single phase Fe2B nanocrystals with the crystallite size and specific surface area of 12.5 nm and 29 m2/g, respectively. Magnetization results clearly indicated the ferromagnetic behavior of Fe2B nanocrystals with saturation magnetization observed around 96.26 emu·g?1. Electron microscope images revealed coaxial/spherical powder shape and morphology of the single-phase Fe2B nanocrystals. 相似文献
84.
The fluid film pressure and temperature fields have been measured simultaneously under laboratory conditions at one land of a circumferential groove journal bearing (CGJB), together with friction torque and oil flow rate, during a time span from stand-still startup to the development of a thermally stabilized steady operating regime.A very fine measurement grid—that is, 216 pressure and 180 temperature points spread across the axial and circumferential directions—has been obtained by joining and synchronizing measurements from separate test runs while rigorously re-creating the test conditions.The study confirmed that the pressure field is established faster than the temperature field, that film rupture occurs both from cavitation nuclei downstream the minimum film thickness and through air ingestion from the environment. Furthermore, the high pressures in the convergent zone stabilize relatively quickly, whereas the low pressures in the divergent zone cavitated region require a longer time to stabilize. The cavitated region reverse flow appearance has been identified thermally through upstream-oriented isotherms. This study is the first to present the transient evolutions of pressure and temperature fields. 相似文献
85.
R.A. Varin L. Zbroniec M. Polanski Y. Filinchuk R. Černý 《International Journal of Hydrogen Energy》2012
Manganese borohydride (Mn(BH4)2) was successfully synthesized by a mechano-chemical activation synthesis (MCAS) from lithium borohydride (LiBH4) and manganese chloride (MnCl2) by applying high energy ball milling for 30 min. For the first time a wide range of molar ratios n = 1, 2, 3, 5, 9 and 23 in the (nLiBH4 + MnCl2) mixture was investigated. During ball milling for 30 min the mixtures release only a very small quantity of H2 that increases with the molar ratio n but does not exceed ∼0.2 wt.% for n = 23. However, longer milling duration leads to more H2 released. For the equimolar ratio n = 1 the principal phases synthesized are Li2MnCl4, an inverse cubic spinel phase, and the Mn(BH4)2 borohydride. For n = 2 a LiCl salt is formed which coexists with Mn(BH4)2. With the n increasing from 3 to 23 LiBH4 is not completely reacted and its increasing amount is retained in the microstructure coexisting with LiCl and Mn(BH4)2. Gas mass spectrometry during Temperature Programmed Desorption (TPD) up to 450 °C shows the release of hydrogen as a principal gas with a maximum intensity around 130–150 °C accompanied by a miniscule quantity of borane B2H6. The intensity of the B2H6 peak is 200–600 times smaller than the intensity of the corresponding H2 peak. In situ heating experiments using a continuous monitoring during heating show no evidence of melting of Mn(BH4)2 up to about 270–280 °C. At 100 °C under 1 bar H2 pressure the ball milled n = 2 and 3 mixtures are capable of desorbing quite rapidly ∼4 wt.% H2 which is a very large amount of H2 considering that the mixture also contains 2 mol of LiCl salt. The H2 quantities experimentally desorbed at 100 and 200 °C do not exceed the maximum theoretical quantities of H2 expected to be desorbed from Mn(BH4)2 for various molar ratios n. It clearly confirms that the contribution from B2H6 evolved is negligibly small (if any) when desorption occurs isothermally in the practical temperature range 100–200 °C. It is found that the ball milled mixture with the molar ratio n = 3 exhibits the highest rate constant k and the lowest apparent activation energy for dehydrogenation, EA ∼ 102 kJ/mol. Decreasing or increasing the molar ratio n below or above 3 increases the apparent activation energy. Ball milled mixtures with the molar ratio n = 2 and 3 discharge slowly H2 during storage at room temperature and 40 °C. The addition of 5 wt.% nano-Ni with a specific surface area of 60.5 m2/g substantially enhances the rate of discharge at 40 °C. 相似文献
86.
Five fully formulated wind turbine gear oils were characterised. The gear oils have 320 ISO VG grade and different formulations: ester, mineral, PAO, PAG and mineral+PAMA.A back-to-back FZG test machine, with re-circulating power, was used and a torque-cell was included on the test rig in order to measure the torque loss. Eight thermocouples were included to monitor the temperatures in different locations of the test rig.Tests at 1.13, 2.26 and 6.79 m/s were performed for different FZG load stages: K1, K5, K7 and K9. Both gearboxes were jet-lubricated with an oil flow of 3 l/min. The input flow temperature was kept almost constant (80 ±1 °C).Friction generated between the meshing teeth, shaft seals and rolling bearing losses was predicted. 相似文献
87.
Permeability and dynamic elastic moduli of controlled porosity ultra-precision aerostatic structures
Porous ceramic aerostatic bearings enable precise and smooth motion and improved stiffness compared with widely used orifice restrictor bearings. However, the processing techniques so far used are too complex or rely in lowering the sintering temperature to increase fluid flow. 相似文献
88.
Mieczyslaw Korzynski Tomasz Zarski Katarzyna Korzynska 《Journal of Materials Processing Technology》2011,211(12):1982-1988
The present work compares the states of the surface textures and the oscillatory fatigue strengths of specimens made of an AZ91 alloy after turning and dynamic bearing ball peening. It was found that the specimens ball peened at different time have similar surface geometric structure parameters but different strengthening intensity. It was shown that fatigue strength follows greater peening intensity and random and isotropic surface. It was also ascertained that improving (by peening) the condition of the surface layer means enhancing fatigue strength by 20–87% compared with turning. 相似文献
89.
90.
《Structure and Infrastructure Engineering》2013,9(12):1600-1615
Bearings are used to isolate bridge substructures from the lateral forces induced by creep, shrinkage and seismic displacements. They are set in one or two support lines parallel to the transverse axis of the pier cap and are typically anchored to the deck and to the pier cap. This detailing makes them susceptible to possible tensile loading. During an earthquake, the longitudinal displacements of the deck induce rotations to the pier caps about a transverse axis, which in turn cause tensile (uplift) and compressive displacements to the bearings. Tensile displacements of bearings, due to the pier rotations, have not been addressed before and questions about the severity of this uplift effect arise, because tensile loading of bearings is strongly related to elastomer cavitation and ruptures. An extended parametric study revealed that bearing uplift may occur in isolated bridges, while uplift effect is more critical for the bearings on shorter piers. Tensile displacements of bearings were found to be significantly increased when the isolators were eccentrically placed with respect to the axis of the pier and when flexible isolators were used for the isolation of the bridge. The results of this study cannot be generalised as bridge response is strongly case-dependent and the approach has limitations, which are related to the modelling approach and to the fact that emphasis was placed on the longitudinal response of bridges. 相似文献