全文获取类型
收费全文 | 3047篇 |
免费 | 113篇 |
国内免费 | 23篇 |
专业分类
电工技术 | 66篇 |
综合类 | 2篇 |
化学工业 | 659篇 |
金属工艺 | 104篇 |
机械仪表 | 80篇 |
建筑科学 | 43篇 |
矿业工程 | 4篇 |
能源动力 | 115篇 |
轻工业 | 145篇 |
水利工程 | 26篇 |
石油天然气 | 30篇 |
无线电 | 317篇 |
一般工业技术 | 669篇 |
冶金工业 | 498篇 |
原子能技术 | 38篇 |
自动化技术 | 387篇 |
出版年
2024年 | 10篇 |
2023年 | 44篇 |
2022年 | 63篇 |
2021年 | 89篇 |
2020年 | 102篇 |
2019年 | 73篇 |
2018年 | 88篇 |
2017年 | 105篇 |
2016年 | 96篇 |
2015年 | 71篇 |
2014年 | 104篇 |
2013年 | 242篇 |
2012年 | 109篇 |
2011年 | 158篇 |
2010年 | 134篇 |
2009年 | 127篇 |
2008年 | 134篇 |
2007年 | 130篇 |
2006年 | 99篇 |
2005年 | 69篇 |
2004年 | 65篇 |
2003年 | 56篇 |
2002年 | 58篇 |
2001年 | 44篇 |
2000年 | 48篇 |
1999年 | 44篇 |
1998年 | 110篇 |
1997年 | 83篇 |
1996年 | 54篇 |
1995年 | 60篇 |
1994年 | 68篇 |
1993年 | 30篇 |
1992年 | 27篇 |
1991年 | 26篇 |
1990年 | 32篇 |
1989年 | 23篇 |
1988年 | 28篇 |
1987年 | 20篇 |
1986年 | 22篇 |
1985年 | 27篇 |
1984年 | 19篇 |
1983年 | 18篇 |
1982年 | 14篇 |
1981年 | 12篇 |
1980年 | 17篇 |
1979年 | 15篇 |
1978年 | 15篇 |
1977年 | 18篇 |
1976年 | 29篇 |
1975年 | 13篇 |
排序方式: 共有3183条查询结果,搜索用时 15 毫秒
11.
Removal of gaseous and vapor constituents of environmental tobacco smoke (ETS) by activated carbons in a packed bed arrangement was studied under dynamic conditions and was compared with that by silica gel and molecular sieve 13X. ETS is a mixture of sidestream smoke and exhaled mainstream smoke, and it consists of various organic and inorganic compounds, trace heavy metals, and particulate matters. Due to the complex nature of ETS-air mixture, its removal from indoors is a challenging task. For experimentation in a laboratory, the ETS was produced from a specially designed smoking apparatus that simulated the puffng of a cigarette by a person. Air containing ETS was passed through a bed containing about 25 grams of activated carbon at room temperature. The flow rate of air-ETS mixture through the bed was 4000 cm3/min. The relative humidity of the air was 50% and contained about 35 to 40 ppm of hydrocarbons as measured as methane-equivalent. The number of particles in the inlet air stream were in the range of 30,000 to 35,000 particles/cm3. About 60% of hydrocarbons present in ETS were removed at these operating conditions for a period of about 70 hours. Based on 15 adsorption and regeneration cycles, it was noted that the carbon bed did not loose its capacity for ETS significantly as indicated by the BET surface area and water adsorption data. At the beginning of an adsorption cycle, the carbon bed captured a significant number of particles. However, the bed rapidly lost its particle capture effciency as the experiment progressed. The number of particles in the outlet air stream was found to be the same as that of the inlet stream within five minutes. 相似文献
12.
Rachinger's method of separating 1 and 2 doublets in X-ray emission spectra is applied for the first time to separate the superimposed doublets due to spin-orbit coupling. This method has been applied to separate closely lying doublets such as (Ag 4p3/2and Ag 4p1/2, (Ni 3p3/2and Ni 3p1/2) and (Cu 3p3/2and Cu 3p1/2). The intensities ratios of the separated peaks are measured and compared with the ratios obtained from a first-order calculation. An excellent agreement between the measured and calculated ratios are obtained. Residual background intensities compared with the estimated values are found to agree within certain uncertainties. 相似文献
13.
A series of experiments were carried out on three commercial steels to explore the possibility for characterizing tempered martensite embrittlement (TME) by Rockwell, macro-, and micro-Vickers hardness tests. The results indicate distinct hardness peaks in two steels and an inflection in the other around the TME temperature. A new analytical approach for examining the slope of hardness-tempering temperature plots appears to reveal the TME phenomenon more sensitively. Dilatometric examinations substantiate that the temperature of hardness peak/inflection occurs beyond the second stage of tempering. 相似文献
14.
The concept of control signals is fundamental to digital design. It evokes the notion of one or more signals that influence computation on other signals in a system, and regulate the behavior of the system. A formal definition of control signals is presented. It is argued that knowledge of the control signals in a complex design such as a microprocessor or a computer is crucial to the comprehension and specification of the design and that knowledge of the control signals of a design leads to a more efficient hardware implementation. The identification of control signals in two microprocessors are presented as examples 相似文献
15.
Rates of coke formation during steam pyrolysis of naphtha have been investigated in a jet-stirred reactor both for sodium silicate coated and uncoated Inconel 600 surfaces in the temperature range of 1078–1108 K. Coke formation rates were significantly reduced on sodium silicate coated plates due to the passivation of the metal surface. However, the coking rates gradually increased with successive decokings of the coated surface. 相似文献
16.
The superplastic properties of a rapidly solidified, high strength P/M Al alloy and the same alloy reinforced with SiC particulates
(SiC
p
) have been studied. To prepare superplastic test materials, a matrix alloy powder of composition 7.2Zn-2.4Mg-2Cu-0.2Zr-0.12Cr-0.2Co
(Kaiser PM-64) and the powder mixed with 10 to 20 vol pct SiC
p
(~5 μm diameter) were thermomechanically processed to very fine equiaxed grain structures of ~6 μm and ~8 μm, respectively.
Superplasticity in these materials was evaluated by characterizing (1) high temperature stability, (2) dynamic grain growth,
(3) strain rate sensitivity, (4) flow stress behavior, (5) cavitation and cavitation control, and (6) total superplastic strain.
It was observed that the PM-64 alloy could achieve a total elongation of over 800 pct, while the SiCp reinforced alloy could attain an elongation greater than 500 pct before failure. Also, it was shown that with the use of
hydrostatic pressure during superplastic flow, cavitation could be controlled. Observations were made of the effect SiC
p
reinforcement particles had on the superplastic flow stress behavior. Interpretations are proposed to explain the role of
particulates during superplastic straining. 相似文献
17.
18.
DJ Benos BH Hahn JK Bubien SK Ghosh NA Mashburn MA Chaikin GM Shaw EN Benveniste 《Canadian Metallurgical Quarterly》1994,91(2):494-498
Infection by human immunodeficiency virus type 1 (HIV-1) is often complicated by a variety of neurological abnormalities. The most common clinical syndrome, termed acquired immunodeficiency syndrome (AIDS) dementia complex, presents as a subcortical dementia with cognitive, motor, and behavioral disturbances and is unique to HIV-1 infection. The pathogenesis of this syndrome is poorly understood but is believed to involve interactions among virally infected macrophages/microglia, astrocytes, and neurons. In this study, we show that exposure of primary rat and human astrocytes to heat-activated HIV-1 virions, or to eukaryotically expressed HIV-1 and HIV-2 envelope glycoproteins (gp120) stimulates amiloride-sensitive Na+/H+ antiport, potassium conductance, and glutamate efflux. These effects are blocked specifically by amiloride, an inhibitor of Na+/H+ antiport and by the selective removal of gp120 with immobilized monoclonal antibody. As a result of modulation of astrocytic function by gp120, the ensuing neuronal depolarization and glutamate exposure could activate both voltage-gated and N-methyl-D-aspartate-regulated Ca2+ channels, leading to increases in intraneuronal Ca2+ and neuronal death. These findings implicate the astrocyte directly in the pathogenesis of AIDS dementia complex. 相似文献
19.
H. S. Tripathi B. Mukherjee S. K. Das A. Ghosh G. Banerjee 《Bulletin of Materials Science》2003,26(2):217-220
Mullite was developed by reaction sintering of sillimanite beach sand and calcined alumina. Two varieties of sillimanite beach
sand viz. S and Z having different compositions were selected. Synthesis and properties of mullite were very much dependent
on the sillimanite beach sand composition. Presence of higher amount of impurities in the Z-variety of sillimanite sand favours
the densification by liquid phase formation. Presence of zircon in Z-variety increases the hardness and fracture toughness.
Alumina addition improves the mechanical/thermomechanical properties of the samples. Mullite retains the usual orthorhombic
habit of sillimanite. Rounded to sub rounded zirconia dispersed within the mullite matrix of the sample ZA is noticed. 相似文献
20.
Dhyanjyoti Deka Deepu S. Joseph Somnath Ghosh Michael J. Mills 《Metallurgical and Materials Transactions A》2006,37(5):1371-1388
This paper develops an experimentally validated computational model based on crystal plasticity for the analysis of two-phase
α/β Ti-6242 polycrystalline alloys. A rate-dependent elastic-crystal plasticity model is incorporated in this model to accommodate
anisotropy in material behavior and tension-compression asymmetry inherent to this alloy. A combination of microtesting, orientation
imaging microscopy, computational simulations, and minimization process, involving genetic algorithms, is implemented in this
study for careful characterization and calibration of the material parameters. Size effects are considered in this analysis
through a simple scaling process. A homogenized equivalent model of the primary α with transformed β colonies is developed
for incorporation in the Ti-6242 FE model. The polycrystalline Ti-6242 computational model incorporates accurate phase volume
fractions, as well as statistically equivalent orientation distributions to those observed in the orientation imaging microscopy
scans. The effects of orientation, misorientations, and microtexture distributions are investigated through simulations by
this computational model. The model is used to simulate constant strain rate and creep tests in compression and tension, and
the results are compared with experiments. The effects of microstructure and creep-induced load-shedding on the localization
of microstructural stresses and strains are studied for potential crack initiation criteria. 相似文献