首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   1366篇
  免费   21篇
  国内免费   1篇
电工技术   14篇
综合类   4篇
化学工业   301篇
金属工艺   15篇
机械仪表   35篇
建筑科学   33篇
矿业工程   10篇
能源动力   37篇
轻工业   101篇
水利工程   15篇
石油天然气   6篇
无线电   86篇
一般工业技术   197篇
冶金工业   363篇
原子能技术   16篇
自动化技术   155篇
  2022年   9篇
  2021年   7篇
  2018年   15篇
  2017年   15篇
  2016年   6篇
  2015年   16篇
  2014年   22篇
  2013年   55篇
  2012年   37篇
  2011年   51篇
  2010年   40篇
  2009年   46篇
  2008年   51篇
  2007年   46篇
  2006年   44篇
  2005年   37篇
  2004年   32篇
  2003年   30篇
  2002年   40篇
  2001年   32篇
  2000年   21篇
  1999年   27篇
  1998年   62篇
  1997年   45篇
  1996年   43篇
  1995年   28篇
  1994年   30篇
  1993年   31篇
  1992年   24篇
  1991年   21篇
  1990年   34篇
  1989年   34篇
  1988年   35篇
  1987年   21篇
  1986年   20篇
  1985年   24篇
  1984年   20篇
  1983年   16篇
  1982年   22篇
  1981年   25篇
  1980年   15篇
  1979年   11篇
  1978年   18篇
  1977年   14篇
  1976年   22篇
  1975年   13篇
  1974年   13篇
  1973年   16篇
  1972年   7篇
  1971年   8篇
排序方式: 共有1388条查询结果,搜索用时 31 毫秒
31.
32.
33.
This paper discusses the adoption of a pluralist theoretical framework – one that is also multiparadigmatic – for conducting and publishing information system (IS) research. The discussion is illustrated by a single case study involving the Australian cotton industry. The theoretical framework is informed by three sociological theories, each with its particular paradigmatic assumptions: structuration theory as a meta‐theory, and diffusion of innovations and gender relations as lower‐level theories from notionally opposing paradigms. Theoretical pluralism helped to produce rich findings, illuminating both the social nature of women farmers' roles, the materiality of the cotton farming context, the characteristics of the decision support systems in use and the recursive way in which human agency and institutional pressures shape each other. Because users of so‐called divergent paradigms often face criticism based on the incommensurability issue, one of the main contributions of this paper is to discuss the value of a pluralist and multiparadigmatic theoretical framework in dealing with complex IS social phenomena.  相似文献   
34.
Data have been presented which indicate a positive relationship between thetrans-isomer content of a hydrogenated oil and the congeal point, Wiley melting-point, and solids index. It has also been shown that cottonseed oil and soybean oil undergo substantially the same type of reaction under identical hydrogenating conditions. This conclusion is based on the relationship oftrans-isomer formation to total reduction in unsaturation up to the point that equilibrium is reached and saturation of thetrans-isomers occurs. This equilibrium was noted at between 60–70 iodine value. The relationship oftrans-isomer formation to the total reduction in double bonds can be expressed as the hydrogenation index. This is a reliable indication of the type of reaction taking place up to the point where appreciable hydrogenation of thetrans-isomers occur.  相似文献   
35.
36.
In the modeling of physical systems, such as chemical reactions, nonlinear models in a set of unknown parameters are commonly developed. Using the method of least squares for model fitting the efficiency of the process is measured by the large sample variance of the parameter estimates. Designs which yield desirable properties in the linear case, such as factorial and central composite designs, are often utilized in the nonlinear model setting. In this paper a method for transforming these standard designs, yielding more efficient estimators, in the nonlinear model case is proposed. The procedure is demonstrated on a typical kinetic reaction model.  相似文献   
37.
38.
The antioxidant vitamin E, -tocopherol, was tested as a candidate elicitor of alterable antiherbivory in soybean plants against cabbage looper larvae. Although a nonspecific antioxidant, vitamin E proved elicitory to the involved sulfhydryl-dependent receptor-energy transducer protein in soybean plasma membrane. Effects of -tocopherol were dependent on dosage, time, and space in the plant. The observed elicited effects were all decreases in herbivory. The best negative phytochemical correlate of looper feeding was the percentage of increased total HPLC peak area of extractables from elicited as compared to nonelicited leaves. Some specific compounds, e.g., glyceollins, were quantitatively major components of the total profile of secondary metabolites.  相似文献   
39.
"Alumina" Surface Modification of Silicon Nitride for Colloidal Processing   总被引:11,自引:0,他引:11  
Two different methods are used to coat silicon nitride particles with an alumina precursor to make Si3N4 behave like Al2O3 in aqueous slurries. The first method involves the precipitation of an aluminum hydroxycarbonate from dissolved Al(NO3)3 during the decomposition of urea. In the second method, dry silicon nitride powder is reacted with aluminum tri- sec -butoxide in hexane at room temperature. Both methods produce a coated powder in which the electrophoretic and rheological properties of aqueous slurries mimic those of alumina. When salt is added to slurries consisting of coated Si3N4 powder, all rheological evidence suggests the presence of a short-range repulsive potential that produces a weakly attractive particle network similar to that previously reported for Al2O3 powder. Although electrophoretic and rheological data showed that the coated powder behaved like Al2O3, consolidation data indicated that slurries of coated powder with added salt did not pack to high density. In addition, these bodies were not plastic as found for bodies consolidated from dispersed and salt-added Al2O3 slurries.  相似文献   
40.
Commercial silicon nitride powder with A12O3 and Y2O3 additives was hot-pressed to complete density. The resulting microstructure contained elongated grains with no trace of remaining α-Si3N4. The aspect ratio of the elongated grains increased with increasing soak time at a fixed hot-pressing temperature. X-ray diffraction analysis showed that the crystalline phase in the hot-pressed samples was β-sialon (Si6−zAlzOzN8−z) with z values that increased with soak time. The fracture strength and fracture toughness of the samples increased as the aspect ratio of the grains increased. The Vickers hardness decreased slightly as the soak time was increased, which was attributed to a grain size effect. Wear tests of silicon nitride against silicon nitride were conducted on a reciprocating pin-on-disk apparatus with paraffin oil as a lubricant. Correlation studies of wear with microstructure and mechanical properties were performed. The wear rate increased rapidly with increasing soak time in spite of the increased strength and toughness. This was attributed to increased third-body wear caused by pullout of pieces from the wear surface. The pullout mechanism was not conclusively identified. However, TEM examination showed clear evidence of dislocation motion under the wear scar. Grain boundary microstresses caused by the anisotropic thermal expansion and elastic properties of the elongated grains may have contributed to the observed pullout.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号