全文获取类型
收费全文 | 5896篇 |
免费 | 117篇 |
国内免费 | 6篇 |
专业分类
电工技术 | 59篇 |
综合类 | 1篇 |
化学工业 | 1040篇 |
金属工艺 | 110篇 |
机械仪表 | 95篇 |
建筑科学 | 230篇 |
矿业工程 | 24篇 |
能源动力 | 123篇 |
轻工业 | 496篇 |
水利工程 | 35篇 |
石油天然气 | 19篇 |
无线电 | 407篇 |
一般工业技术 | 853篇 |
冶金工业 | 1705篇 |
原子能技术 | 63篇 |
自动化技术 | 759篇 |
出版年
2021年 | 55篇 |
2020年 | 38篇 |
2019年 | 42篇 |
2018年 | 42篇 |
2017年 | 47篇 |
2016年 | 66篇 |
2015年 | 57篇 |
2014年 | 91篇 |
2013年 | 300篇 |
2012年 | 166篇 |
2011年 | 198篇 |
2010年 | 178篇 |
2009年 | 213篇 |
2008年 | 249篇 |
2007年 | 244篇 |
2006年 | 234篇 |
2005年 | 177篇 |
2004年 | 163篇 |
2003年 | 146篇 |
2002年 | 159篇 |
2001年 | 123篇 |
2000年 | 131篇 |
1999年 | 119篇 |
1998年 | 194篇 |
1997年 | 171篇 |
1996年 | 151篇 |
1995年 | 122篇 |
1994年 | 115篇 |
1993年 | 117篇 |
1992年 | 112篇 |
1991年 | 54篇 |
1990年 | 95篇 |
1989年 | 79篇 |
1988年 | 81篇 |
1987年 | 94篇 |
1986年 | 87篇 |
1985年 | 115篇 |
1984年 | 110篇 |
1983年 | 104篇 |
1982年 | 100篇 |
1981年 | 90篇 |
1980年 | 61篇 |
1979年 | 80篇 |
1978年 | 79篇 |
1977年 | 82篇 |
1976年 | 96篇 |
1975年 | 72篇 |
1974年 | 52篇 |
1973年 | 43篇 |
1972年 | 41篇 |
排序方式: 共有6019条查询结果,搜索用时 406 毫秒
11.
Y.M. Wong W.P. Kang J.L. Davidson J.H. Huang D.V. Kerns 《Diamond and Related Materials》2008,17(4-5):552-555
A novel integrated vacuum field emission (VFE) differential amplifier (diff-amp) utilizing carbon nanotube (CNT) emitters has been developed. A dual-mask microfabrication process was employed to achieve a VFE diff-amp by integrating identical CNT VFE transistors with built-in split gates and integrated anodes. The identical pair of triode amplifiers was well-matched in their device characteristics. The measured ac small-signal characteristics of the diff-amp showed a common-mode-rejection ratio (CMRR) of ~ 320 (~ 50 dB). The proposed analytical model of the CMRR was verified to be in good agreement with the experimental data. The successful implementation of the CNT diff-amp demonstrates a new way to achieve temperature and radiation tolerant VFE integrated microelectronics. 相似文献
12.
Studies of elemental distributions within discrete coal macerals: Use of secondary ion mass spectrometry and X-ray photoelectron spectroscopy 总被引:3,自引:0,他引:3
N.Stewart Mclntyre Ronald R. Martin William J. Chauvin C.Gordon Winder James R. Brown J.Anthony MacPhee 《Fuel》1985,64(12):1705-1712
Secondary ion mass spectrometry has been used to measure qualitatively the distributions of many trace and minor elements within some well-characterized coal macerals: vitrinite, fusinite and exinite. Complementary information was obtained by using X-ray photoelectron spectroscopy. Within the vitrinite specimens studied, a widely-dispersed largely inorganic aluminosilicate phase was identified, which contained a number of other trace elements. By contrast, within the organic-rich phase of this macerai, titanium was detected in a very even distribution; this suggests that some titanium may be bonded in an organic complex. The fusinite was shown to contain elevated concentrations of calcium, magnesium and fluorine, dispersed over a large portion of the maceral. The high fluorine content could be identified as an organo-fluoro compound using XPS. Exinite was found to contain lower concentrations of most elements, compared to other macerals. The organic composition of this maceral was significantly different from that of surrounding macerals; this could be seen from the enhanced emission of the C2H2-secondary ion and images of this ion thus clearly outlined the position of such macerals. 相似文献
13.
The presence of long chain acyl:CoA synthetases in mammalian microsomes and mitochondria has been established previously by
Aas (Biochim. Biophys. Acta 231, 32–47 [1971]). The presence of a plasma membrane-associated enzyme was investigated in rat hepatocyte plasma membranes,
where an enzyme exhibiting high activity and with a preferred substrate of 18-carbon chain length was discovered. The results
are consistent with the presence of a single enzyme. The effect of the degree of unsaturation of the fatty acid substrates
was not as pronounced as that arising from the length of the carbon chain. The pattern of substrate preference of the enzyme
was ω3 polyenoic fatty acids >ω6 polyenoic acids >ω9 monoenoic acids > saturated acids. This may relate to the similar substrate
preference pattern exhibited by the fatty acyl desaturase enzymes. The role played by long chain acyl:CoA synthetase in hepatocyte
metabolism is uncertain, but it may relate to the incorporation of polyenoic fatty acids from the circulation into cell membranes
and the trapping of other fatty acids within the cell for further metabolism. 相似文献
14.
Ronald R. Delyser Sheila S. Thompson Jerry Edelstein Corinne Lengsfeld Albert J. Rosa Paul J. Rullkoetter Robert Whitman Margaret Whitt 《工程教育杂志》2003,92(3):269-273
A team of faculty members at the University of Denver changed the learning environment in key courses in the Department of Engineering from predominately teacher centered to student centered. Through this funded project new grading methods were implemented, classrooms were renovated and wired with studio layouts to facilitate learning, the Engineering Circuits Laboratory was rewired and instrumented for automated data acquisition and reporting, and two new pedagogical approaches were developed. At the onset of the project, six goals were established related to student learning. The introduction of industry standard hardware and software provided students with unprecedented hands‐on experience and project related activities stimulated faculty innovations in other current and future courses. Assessment results indicate that the new grading system improved the clarity of expectations for students before assignments were given resulting in increased reported motivation for learning in many courses. Even though course GPAs did not always reflect higher achievement on graded work, faculty members firmly believe that deeper understanding was achieved because more complex material was assimilated. 相似文献
15.
Multiobjective evaluation of advanced manufacturing system technology investments with risk 总被引:2,自引:0,他引:2
Advanced manufacturing system technologies are difficult to evaluate using ordinary financial measures owing to the presence of risk and significant intangible factors. In this paper a methodology is proposed that quantifies financial, strategic, and tactical attributes of each alternative. Attribute values are denned for each period of project life. Both project life and attributes are treated as random variables. Attributes are discounted to the current time and the multiple objectives are combined by composite programming. The distribution of the combined objective is estimated. The procedure is demonstrated on an actual case study. 相似文献
16.
Kang W.P. Wisitsora-at A. Davidson J.L. Kerns D.V. 《Electron Device Letters, IEEE》1998,19(10):379-381
A boron-doped diamond field emitter diode with ultralow turn-on voltage and high emission current is reported. The diamond field emitter diode structure with a built-in cap was fabricated using molds and electrostatic bonding techniques. The emission current versus anode voltage of the capped diamond emitter diode with boron doping, sp2 content, and vacuum thermal electric (VTE) treatment shows a very low turn-on voltage of 2 V. A high emission current of 1 μA at an anode voltage of less than 10 V can be obtained from a single diamond tip. The turn-on voltage is significantly lower than comparable silicon field emitters 相似文献
17.
Amines such as dopamine, norepinephrine and epinephrine were analysed in the brain regions of O.mossambicus exposed to quinalphos, phenthoate and their combination for 96 hr. The three types of treatments significantly (P < 0.05) altered the amines level at various intervals in the brain regions. 相似文献
18.
19.
Expression of a human homeobox-containing gene is regulated by 1,25(OH)2D3 in bone cells 总被引:1,自引:0,他引:1
JE Hodgkinson CL Davidson J Beresford PT Sharpe 《Canadian Metallurgical Quarterly》1993,1174(1):11-16
The seasonal variation in the nutrient composition of Enhydra fluctuans and Marsilea quadrifolia, two edible semi-aquatic plants, was studied in order to promote their consumption as green leafy vegetables. Both plants had a high crude protein content throughout all harvesting seasons. Enhydra fluctuans had a low ash content and was a good source of beta-carotene (3.7 to 4.2 mg/100 g on a fresh weight basis). Marsilea quadrifolia exhibited wide fluctuations between seasons and was not very promising in nutrient composition when compared to other commonly used green leafy vegetables. 相似文献
20.
This article discusses the phenomenon of youth violence from a psychology of gender perspective. Although other factors are discussed--including gun availability, violence-related media influence, family and caretaker factors, and effects of teasing and bullying--the intention is to highlight new thinking on the potential relationship between boys' traditional masculine socialization experiences and violence. In this new perspective, traditional masculine socialization estranges and isolates many boys from their genuine inner lives and vital connections to others, which is theorized to heighten their risk of engaging in acts of violence. The authors identify school and community programs that may be helpful in counteracting damaging socialization experiences and supporting boys' healthier emotional and psychological development. Finally, the article discusses approaches that psychologists and other mental health professionals can use to help address this vital issue. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献