全文获取类型
收费全文 | 413篇 |
免费 | 9篇 |
专业分类
电工技术 | 14篇 |
综合类 | 1篇 |
化学工业 | 50篇 |
金属工艺 | 3篇 |
机械仪表 | 7篇 |
建筑科学 | 17篇 |
能源动力 | 3篇 |
轻工业 | 43篇 |
水利工程 | 2篇 |
石油天然气 | 3篇 |
无线电 | 70篇 |
一般工业技术 | 38篇 |
冶金工业 | 74篇 |
原子能技术 | 5篇 |
自动化技术 | 92篇 |
出版年
2021年 | 3篇 |
2020年 | 4篇 |
2019年 | 3篇 |
2018年 | 4篇 |
2016年 | 11篇 |
2015年 | 5篇 |
2014年 | 8篇 |
2013年 | 36篇 |
2012年 | 8篇 |
2011年 | 16篇 |
2010年 | 7篇 |
2009年 | 22篇 |
2008年 | 13篇 |
2007年 | 27篇 |
2006年 | 17篇 |
2005年 | 16篇 |
2004年 | 19篇 |
2003年 | 10篇 |
2002年 | 21篇 |
2001年 | 6篇 |
2000年 | 13篇 |
1999年 | 12篇 |
1998年 | 22篇 |
1997年 | 19篇 |
1996年 | 14篇 |
1995年 | 6篇 |
1994年 | 6篇 |
1993年 | 7篇 |
1992年 | 3篇 |
1991年 | 3篇 |
1990年 | 7篇 |
1989年 | 2篇 |
1988年 | 3篇 |
1986年 | 6篇 |
1985年 | 8篇 |
1984年 | 3篇 |
1983年 | 4篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1969年 | 2篇 |
1963年 | 1篇 |
1959年 | 1篇 |
排序方式: 共有422条查询结果,搜索用时 15 毫秒
341.
Dr. Cliff Stoll 《Computers & Security》1988,7(6)
For 10 months, we monitored a systematic attack on 450 computers attached to the Defense Data Network. By analyzing the success of these attacks, we can estimate the vulnerability of nodes on the Milnet and (by extrapolation) civilian computers. We analyzed a particular type of attack: an outsider who attempts to log in by guessing at commonly used account name/password combinations.An outsider can expect some degree of access into about 13% of Milnet computers. Access to a programming environment is possible in at least 4%, and system manager privileges can be obtained by strangers in 2% of the sampled sites. Since this is only one of several methods used to enter these systems, these estimates are lower limits; other methods of entry can permit access to still more systems. These weaknesses are due to poor administration of computers, as well as systems distributed by vendors with security features disabled. 相似文献
342.
Kevin LaMalva Luke Bisby John Gales Thomas Gernay Elie Hantouche Cliff Jones Ali Morovat Robert Solomon Jose Torero 《火与材料》2020,44(3):341-351
For furnace testing of fire-resistant floor and roof assemblies in the United States, the ASTM E 119 standard (and similarly the UL 263 standard) permits two classifications for boundary conditions: “restrained” and “unrestrained.” When incorporating tested assemblies into an actual structural system, the designer, oftentimes a fire protection or structural engineer, must judge whether a “restrained” or “unrestrained” classification is appropriate for the application. It is critical that this assumption be carefully considered and understood, as many qualified listings permit a lesser thickness of applied fire protection for steel structures (or less concrete cover for concrete structures) to achieve a certain fire resistance rating if a “restrained” classification is confirmed, as compared with an “unrestrained” classification. The emerging standardization of structural fire engineering practice in the United States will disrupt century-long norms in the manner to which structural behavior in fire is addressed. For instance, the current edition of the ASCE/SEI 7 standard will greatly impact how designers consider restraint. Accordingly, this paper serves as an exposé of the “restrained vs unrestrained” paradigm in terms of its paradoxical nature and its controversial impact on the industry. More importantly, potential solutions toward industry rectification are provided for the first time in a contemporary study of this paradigm. 相似文献
343.
Straat M. Kaden M. Gay M. Villmann T. Lampe A. Seiffert U. Biehl M. Melchert F. 《Neural computing & applications》2020,32(24):18085-18099
Neural Computing and Applications - In this contribution, we consider the classification of time series and similar functional data which can be represented in complex Fourier and wavelet... 相似文献
344.
J. Cliff Jones Markus Wahle James Bailey Tom Moorhouse Benjamin Snow Joe Sargent 《Journal of the Society for Information Display》2020,28(3):211-223
Liquid crystal lenses have promise in optical systems owing to their tunability combined with low electrical power, cost, and weight. A good example of such a system is switchable contact lenses for the correction of age‐related presbyopia. Sufficiently large phase modulation can be done using nematic liquid crystals in a meniscus lens configuration. However, the birefringent materials are inherently polarisation dependent, usually requiring orthogonal polarisations to be focussed separately. A novel method is presented for producing polarisation independent lenses based on reactive mesogens. Results are presented for a 2‐level and 3‐level diffractive Fresnel lenses, and the promise of the technique for use in refractive lenses such as contact lenses is discussed. 相似文献
345.
346.
347.
Background
Because a fundamental understanding of rate and accumulation principles is important for engineering students across all subdisciplines, a method is needed to assess their understanding of these principles.Purpose/Hypothesis
This article discusses the development of the Rate and Accumulation Concept Inventory (RACI) instrument and provides an analysis of its validity and reliability. The RACI is designed to test students’ (1) overall mastery of rate and accumulation concepts and (2) mastery of specific rate and accumulation concepts (e.g., mathematics, mass flow, and heat flow).Design/Methods
Exploratory findings of students’ conceptual understanding prompted the development of a preliminary RACI instrument. Two pilot studies were conducted, with adjustments made to the instrument between each. Data from the second pilot were used to assess evidence of validity and reliability through classical test theory, item response theory, and structural equation modeling.Results
Validity and reliability evidence indicates that the RACI can be used to measure students’ overall understanding of the concepts identified, though several items require revision or removal. Issues of potential construct underrepresentation were found in two of the conceptual categories.Conclusions
The evidence of reliability and validity indicates the appropriateness of the RACI for assessing engineering students’ overall understanding of rate and accumulation principles. Additional research is needed to further enhance the validity and reliability of the RACI as a diagnostic tool, particularly in measuring students’ understanding of rate and accumulation concepts in particular physical contexts. 相似文献348.
S.D.Deevi M.R.Hajaligol A.Cliff Lilly G.S.Fleischhauer Research Center Philip Morris USA Commerce Road Richmond VA U.S.A. 《中国有色金属学会会刊》1999,(Z1)
1 INTRODUCTIONAmongtheintermetallics,ironaluminidesbasedonFe3AlandFeAlareattractiveforhightemperatureapplicationsduetotheirexcellentoxidationandcorrosionresistancesinbothoxidizingandcorrosiveatmospheres[1].Inaddition,theyexhibitlowdensitiesandreason… 相似文献
349.
The devolatilisation behaviour of Yallourn brown coal was investigated under rapid heating conditions using two different flash pyrolysers: a fluid-bed reactor giving coal particle heating rates of 104 °Cs?1 with a gas residence time of about 0.5 s and a shock tube which generated heating rates of the order of 107 °Cs?1 and a 1 ms reaction time. Yields of products are reported covering pyrolysis temperatures in the range 400–2300 °C. Hydrocarbon gas yields reached maximum values which were remarkably similar for both reactors although occurring at different temperatures. Carbon oxide production was also similar for both reactors with CO yields reaching 30% wt/wt daf coal. These high yields of CO are very different from those reported for slow heating conditions. It appears that on flash heating, coal decomposition pathways change in a manner which increases CO yields at the expense of H20 and to a lesser extent C02, resulting in the volatilisation of additional carbon from the coal. 相似文献
350.
Eric N Kaufman Abhijeet P Borole Robert Shong Jerry L Sides Cliff Juengst 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1999,74(10):1000-1004
Biological removal of organic sulfur from petroleum feedstocks may offer an attractive alternative to conventional thermochemical treatment due to the mild operating conditions and greater reaction specificity afforded by the nature of biocatalysis. Previous investigations have either reported the desulfurization of model sulfur compounds in organic solvents or gross desulfurization of crude oil without data on which sulfur species were being removed. This study reports initial sulfur speciation data for thiophenic sulfur compounds present in crude oil which may be used as a guide both as to which species are treated by the biocatalyst investigated as well as to where biocatalyst development is needed to improve the extent of biological desulfurization when applied to whole crudes. Biodesulfurization of two different crude oils in the 22–31 ° API specific gravity range with total sulfur contents between 1 and 2% is demonstrated in 1‐dm3 batch stirred reactors using wild type Rhodococcus sp IGTS8. While analysis of the crudes before and after biodesulfurization did not reveal a decrease in total sulfur, GC–MS did reveal significant (43–99%) desulfurization of dibenzothiophenes (DBT) and substituted DBTs. Fractionation of the whole crude, followed by analysis using gas chromatography–sulfur chemiluminescence detection (GC–SCD) of the aromatic fraction of the Van Texas crude oil, demonstrated a reduction of sulfur in this fraction from 3.8% to 3.2%. This research indicates that IGTS8 may be capable of biodesulfurization of refined products such as gasoline and diesel whose predominant sulfur species are dibenzothiophenes. Further biocatalyst development would be needed for effective treatment of the spectrum of sulfur‐bearing compounds present in whole crudes. 相似文献