全文获取类型
收费全文 | 3811篇 |
免费 | 48篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 38篇 |
综合类 | 1篇 |
化学工业 | 384篇 |
金属工艺 | 94篇 |
机械仪表 | 66篇 |
建筑科学 | 88篇 |
矿业工程 | 7篇 |
能源动力 | 49篇 |
轻工业 | 230篇 |
水利工程 | 24篇 |
石油天然气 | 7篇 |
无线电 | 394篇 |
一般工业技术 | 331篇 |
冶金工业 | 1865篇 |
原子能技术 | 24篇 |
自动化技术 | 258篇 |
出版年
2021年 | 23篇 |
2020年 | 14篇 |
2019年 | 20篇 |
2018年 | 21篇 |
2017年 | 33篇 |
2016年 | 32篇 |
2015年 | 25篇 |
2014年 | 41篇 |
2013年 | 120篇 |
2012年 | 61篇 |
2011年 | 82篇 |
2010年 | 77篇 |
2009年 | 83篇 |
2008年 | 87篇 |
2007年 | 84篇 |
2006年 | 87篇 |
2005年 | 82篇 |
2004年 | 58篇 |
2003年 | 72篇 |
2002年 | 57篇 |
2001年 | 65篇 |
2000年 | 45篇 |
1999年 | 93篇 |
1998年 | 522篇 |
1997年 | 328篇 |
1996年 | 223篇 |
1995年 | 128篇 |
1994年 | 149篇 |
1993年 | 119篇 |
1992年 | 65篇 |
1991年 | 65篇 |
1990年 | 51篇 |
1989年 | 53篇 |
1988年 | 47篇 |
1987年 | 42篇 |
1986年 | 47篇 |
1985年 | 47篇 |
1984年 | 34篇 |
1983年 | 43篇 |
1982年 | 38篇 |
1981年 | 33篇 |
1980年 | 44篇 |
1979年 | 25篇 |
1978年 | 20篇 |
1977年 | 75篇 |
1976年 | 101篇 |
1974年 | 15篇 |
1972年 | 23篇 |
1971年 | 18篇 |
1970年 | 20篇 |
排序方式: 共有3860条查询结果,搜索用时 125 毫秒
41.
42.
Nickel molybdate catalysts used in several different upgrading reactions of coal-derived materials from low-rank Australian coals have been regenerated and their activity assessed using a number of physical and chemical techniques. Regeneration of spent coked catalysts for 20 hours in air at 450°C was sufficient to restore chemical hydrogenation activity to catalyst used for pre-asphaltene, asphaltene and oil upgrading, provided poisoning of the catalyst surface by other impurities, principally chlorine-containing molecules, had not occurred. 相似文献
43.
EA Jackson 《Canadian Metallurgical Quarterly》1991,44(8):4839-4853
44.
BE Gilbert C Knight FG Alvarez C Waldrep JR Rodarte V Knight WL Eschenbacher 《Canadian Metallurgical Quarterly》1997,156(6):1789-1793
Cyclosporine A (CsA) in liposomes of dilauroylphosphatidylcholine (DLPC), containing 118 micrograms of CsA/L of aerosol with a particle size of 1.6 to 1.7 micron diameter, was inhaled by 10 nonsmoking, normal volunteers each for 45 min. Aerosol was administered through an Aerotech II nebulizer (CIS-US, Inc., Bedford, MA) mouthpiece. Eight of the 10 volunteers had tracheal irritation and intermittent coughing following exposure. FEV1 and FVC values were mildly reduced, but returned to normal in 1 h. Blood chemical and hematologic values were unchanged at any time point after as opposed to before inhalation. Nine of the 10 volunteers later inhaled DLPC only, administered through the nebulizer mouthpiece. There was no change in FEV1 or FVC values, and there was no coughing or tracheal irritation. Subsequently, five of the volunteers who had previously had respiratory reactions inhaled CsA-DLPC liposome aerosol for 45-min, but through a mouth-only face mask. There was no tracheal irritation, coughing, or changes in spirometric measures. Blood concentrations of CsA at 15 min after the 45-min inhalation with a face mask averaged 83 +/- 42 ng/ml (mean +/- SD). At 24 h after treatment, CsA was undetectable in blood of the initial 10 volunteers. These studies indicate that CsA-DLPC liposome aerosol can be safely explored as a treatment for patients with moderately severe asthma. 相似文献
45.
46.
Jackson T.J. Engman E.T. Le Vine D. Schmugge T.J. Lang R. Wood E. Teng W. 《Geoscience and Remote Sensing, IEEE Transactions on》1994,32(1):201-206
MACHYDR0'90 was an experiment conducted in Pennsylvania in 1990 to study the synergistic use of remote sensors in multitemporal hydrologic studies. As part of this mission the pushbroom microwave radiometer was flown and used to produce brightness temperature maps. Verification studies and vegetation algorithms for mixed land cover areas are described 相似文献
47.
R Avner BE Reubinoff A Simon BS Zentner A Friedmann S Mitrani-Rosenbaum N Laufer 《Canadian Metallurgical Quarterly》1996,2(1):60-62
Intracranial osteolipomas are rare lesions which occur in the region of the tuber cinereum. All cases reported to date have been incidental autopsy findings. We describe a patient who presented with a variety of neurological symptoms and had a typical osteolipoma surgically removed. 相似文献
48.
Langston W.L. Williams J.T. Jackson D.R. Mesa F. 《Microwave Theory and Techniques》2003,51(12):2366-2377
By using a specific normalization, it is shown that the TM/sub 0/ radiation field from a leaky mode that is excited by a source on any printed-circuit structure can be represented in a unified manner. The general properties of the normalized leaky-mode radiation field are examined in detail for a variety of phase and attenuation constants, as well as distances from the source, and for different types of source excitations. The normalized leaky-mode radiation field is compared to similarly normalized geometrical-optics and far-field radiation expressions to provide further insight into the nature of the radiation fields in the near- and far-field regions. The results provide a general view of leaky-mode radiation properties independent of the type of planar transmission line or background structure. 相似文献
49.
Fuel cell-based automobiles have gained attention in the last few years due to growing public concern about urban air pollution
and consequent environmental problems. From an analysis of the power and energy requirements of a modern car, it is estimated
that a base sustainable power ofca. 50 kW supplemented with short bursts up to 80 kW will suffice in most driving requirements. The energy demand depends greatly
on driving characteristics but under normal usage is expected to be 200 Wh/km. The advantages and disadvantages of candidate
fuel-cell systems and various fuels are considered together with the issue of whether the fuel should be converted directly
in the fuel cell or should be reformed to hydrogen onboard the vehicle. For fuel cell vehicles to compete successfully with
conventional internal-combustion engine vehicles, it appears that direct conversion fuel cells using probably hydrogen, but
possibly methanol, are the only realistic contenders for road transportation applications. Among the available fuel cell technologies,
polymer-electrolyte fuel cells directly fueled with hydrogen appear to be the best option for powering fuel cell vehicles
as there is every prospect that these will exceed the performance of the internal-combustion engine vehicles but for their
first cost. A target cost of $ 50/kW would be mandatory to make polymer-electrolyte fuel cells competitive with the internal
combustion engines and can only be achieved with design changes that would substantially reduce the quantity of materials
used. At present, prominent car manufacturers are deploying important research and development efforts to develop fuel cell
vehicles and are projecting to start production by 2005. 相似文献
50.
B Cockeram A G Jackson R E Omlor R Srinivasan I Weiss 《Microscopy research and technique》1992,22(3):298-300
Ductile phase toughened composites contain phases with significantly different physical properties. Consequently, these phases thin at different rates depending on the sample preparation procedure. A new TEM foil preparation method for the ductile phase toughened Nb-10 a/o Si material has been developed. The method involves chemical thinning in a 70% nitric acid/30% hydrofluoric acid solution followed by electropolishing in a 12.5% sulfuric acid/87.5% methanol electrolyte at -40 degrees C. This procedure for making TEM foils results in large thin areas with the minimum of artifacts. Mechanical grinding of a sample followed by either ion milling, dimpling, or electropolishing produced foils with large electron transparent areas, but with uncharacteristic features of the original Nb-10 a/o Si alloy microstructure. These artifacts were identified as dislocations, surface mottling, and antiphase domains. 相似文献