全文获取类型
收费全文 | 1494篇 |
免费 | 51篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 21篇 |
化学工业 | 356篇 |
金属工艺 | 37篇 |
机械仪表 | 43篇 |
建筑科学 | 26篇 |
能源动力 | 67篇 |
轻工业 | 102篇 |
水利工程 | 3篇 |
石油天然气 | 5篇 |
无线电 | 177篇 |
一般工业技术 | 304篇 |
冶金工业 | 167篇 |
原子能技术 | 20篇 |
自动化技术 | 218篇 |
出版年
2023年 | 13篇 |
2022年 | 46篇 |
2021年 | 44篇 |
2020年 | 45篇 |
2019年 | 29篇 |
2018年 | 67篇 |
2017年 | 51篇 |
2016年 | 54篇 |
2015年 | 36篇 |
2014年 | 57篇 |
2013年 | 126篇 |
2012年 | 61篇 |
2011年 | 61篇 |
2010年 | 54篇 |
2009年 | 85篇 |
2008年 | 43篇 |
2007年 | 51篇 |
2006年 | 49篇 |
2005年 | 34篇 |
2004年 | 30篇 |
2003年 | 28篇 |
2002年 | 22篇 |
2001年 | 12篇 |
2000年 | 26篇 |
1999年 | 21篇 |
1998年 | 50篇 |
1997年 | 25篇 |
1996年 | 37篇 |
1995年 | 19篇 |
1994年 | 20篇 |
1993年 | 24篇 |
1992年 | 19篇 |
1991年 | 11篇 |
1990年 | 11篇 |
1989年 | 12篇 |
1988年 | 11篇 |
1987年 | 9篇 |
1986年 | 8篇 |
1985年 | 15篇 |
1984年 | 14篇 |
1983年 | 13篇 |
1982年 | 10篇 |
1981年 | 8篇 |
1980年 | 16篇 |
1979年 | 14篇 |
1978年 | 12篇 |
1977年 | 9篇 |
1976年 | 10篇 |
1975年 | 7篇 |
1974年 | 5篇 |
排序方式: 共有1546条查询结果,搜索用时 0 毫秒
61.
Lyci George Vadym DrozdAndriy Durygin Jiuhua ChenSurendra K. Saxena 《International Journal of Hydrogen Energy》2009
Mg2FeH6 was synthesized by ball milling MgH2 and Fe (2:1 molar ratio) mixture for 72 h followed by heating at 400 °C under H2 pressure. The hydride formation, its structure and homogeneity were investigated by scanning electron microscopy, X-ray diffraction, transmission electron microscopy and Raman spectroscopy. High pressure in situ synchrotron X-ray diffraction and Vienna ab initio simulation were used to determine bulk modulus of the sample. The bulk modulus of Mg2FeH6 was found to be 75.4(4) GPa by optimized experiment and 76.3 GPa by theoretical simulation. From high temperature in situ X-ray diffraction study the volumetric thermal expansion coefficient of Mg2FeH6 was found to be αv = 5.85(3) × 10−5 + 7.47(7) × 10−8 (T − To)/°C. Decomposition of Mg2FeH6 was observed at 425 °C and the decomposition products were Mg, Fe and H2. 相似文献
62.
63.
64.
Use of the nanoindentation technique for studying microstructure/crack interactions in the fatigue of 4340 steel 总被引:2,自引:0,他引:2
Fan Yang Ashok Saxena Laura Riester 《Metallurgical and Materials Transactions A》1998,29(12):3029-3036
The objectives of this research are to study the influence of microstructure on the fatigue crack growth behavior in 4340
steel and to explore the application of the nanoindentation technique for determining the plastic deformation zone at a fatigue
crack tip. Two heat treatment conditions were chosen for the steel: annealed and quenched plus tempered. The annealed steel
consists of coarse pearlite and proeutectoid ferrite, while the quenched and tempered steel consists of fine tempered martensite.
Fatigue crack propagation tests were conducted on disklike compact (DCT) specimens. Subsequently, the nanoindentation technique
was applied to quantitatively determine the plastic deformation zone at fatigue crack tips. The plastic deformation zone size
determined by the nanoindentation test seems larger than the cyclic deformation zone calculated using the fracture mechanics
equation, which involves many assumptions. The fatigue crack growth test results show that the annealed steel has a higher
resistance to crack growth than the quenched and tempered steel. The fatigue crack in the annealed steel tends to grow along
pearlite domain boundaries, or the cementite/ferrite interfaces within a pearlite domain. In contrast, the fatigue crack in
the quenched and tempered steel tends to traverse the fine martensite laths. Consequently, the actual crack path in the annealed
steel is rougher than in the quenched and tempered steel and more secondary cracks are observed in the annealed steel. 相似文献
65.
66.
67.
The design details of a 0.254 m stainless steel cylindrical fluidized bed pilot plant facility, whose fabrication, installation and testing have been recently completed, are described. It primarily consists of a fluidized-bed reactor, fluidizing air-supply system, solids feeder, off-gas cleaning and exhaust system, and cooling water-supply system for heat-transfer tubes provided in the bed and in the freeboard sections. The plant is operated at ambient pressure in the temperature range 300–600 K, both in the batch and continuous modes for solids feed. Bed-pressure drop measurements as a function of fluidizing velocity for two different bed heights reveal that the quality of fluidization is good. Similar experiments have been conducted with the continuous solids feed. The heat-transfer coefficient between the bed and an immersed stainless steel U-tube is measured as a function of fluidizing air velocity at five different temperatures. The effects on bed-to-tube heat-transfer rate of solids feed rate, bed height, air-flow rate, and bed temperature are examined. All of these observed variations are interpreted in terms of the solids mixing and bubble mechanics in the bed. 相似文献
68.
A queueing model with finite buffer size, mixed input traffic (Poisson and burst Poisson arrivals), synchronous transmission and server interruptions through a Bernoulli sequence of independent random variables is studied. Using average burst length, traffic intensity and input traffic mixture ratio as parameters, the relationships among buffer size, overflow probability and expected message queueing delay are obtained. An integrated digital voice-data system with synchronous time division multiplexing (STDM) for a large number of voice sources and mixed arrival process for data messages is considered as an application for this model. The results of this study are portrayed on graphs and may be used as guidelines in buffer design problems in digital voice-data systems. The queueing model developed is quite general in a sense that it covers pure Poisson and burst Poisson arrival processes and the mixture of the two as well. 相似文献
69.
The thickness dependence of the dielectric constant of Er2O3 films was studied. It was found that for films less than 700 Å thick and greater than 1300 Å the dielectric constant ε shows the usual behaviour of increasing with increasing thickness and then assuming the limiting bulk value. However, for films of intermediate thicknesses (700–1300 Å) the dielectric constant first decreases, attains a minimum value and then increases to obtain the bulk value. It is suggested, based on electron microscope observations, that this curious thickness dependence of ε arises because of the transformations from (i) amorphous to crystalline and (ii) f.c.c. type to b.c.c. type crystalline phases in the films. 相似文献
70.
Rotating biological contactor is being widely used for wastewater treatment but there is an apparent lack of knowledge about the rate at which oxygen transfer occurs, in physical and biological system. In this study the transfer of oxygen from air to water by a rotating disc air-liquid contactor in physical system is investigated. The oxygen transfer model suggested by Kim and Molof, Water Sci. Technol. 14 (1982) 569, was modified and the developed model is termed as modified Kim and Molof model. The model was calibrated by using available data in literature and validated by experiments conducted in this study. The effect of significant physical parameters was integrated into a single term and is termed as volume renewal number. The modified Kim and Molof model was compared with the other available models. The coefficient of determination (R(2)) for the modified Kim and Molof model obtained is 0.95 which is much higher than in the other available models. Thereby the model is expected to estimate oxygen transfer more accurately. Further, a simplified linear model between K(L)a and the volume renewal number is proposed. Both modified Kim and Molof and linear model estimate the overall oxygen transfer coefficient (K(L)a) accurately. 相似文献