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   13989篇
  免费   353篇
  国内免费   54篇
电工技术   212篇
综合类   12篇
化学工业   3105篇
金属工艺   251篇
机械仪表   303篇
建筑科学   647篇
矿业工程   98篇
能源动力   385篇
轻工业   975篇
水利工程   130篇
石油天然气   164篇
武器工业   1篇
无线电   855篇
一般工业技术   2069篇
冶金工业   3315篇
原子能技术   158篇
自动化技术   1716篇
  2022年   127篇
  2021年   170篇
  2020年   148篇
  2019年   161篇
  2018年   184篇
  2017年   186篇
  2016年   211篇
  2015年   172篇
  2014年   238篇
  2013年   833篇
  2012年   469篇
  2011年   645篇
  2010年   416篇
  2009年   455篇
  2008年   585篇
  2007年   558篇
  2006年   545篇
  2005年   458篇
  2004年   366篇
  2003年   371篇
  2002年   384篇
  2001年   245篇
  2000年   237篇
  1999年   252篇
  1998年   217篇
  1997年   236篇
  1996年   238篇
  1995年   243篇
  1994年   245篇
  1993年   294篇
  1992年   248篇
  1991年   186篇
  1990年   210篇
  1989年   217篇
  1988年   169篇
  1987年   215篇
  1986年   206篇
  1985年   250篇
  1984年   223篇
  1983年   203篇
  1982年   182篇
  1981年   192篇
  1980年   163篇
  1979年   183篇
  1978年   182篇
  1977年   137篇
  1976年   142篇
  1975年   172篇
  1974年   134篇
  1973年   133篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
Objective: We ask whether subjective socioeconomic status (SES) predicts who develops a common cold when exposed to a cold virus. Design: 193 healthy men and women ages 21-55 years were assessed for subjective (perceived rank) and objective SES, cognitive, affective and social dispositions, and health practices. Subsequently, they were exposed by nasal drops to a rhinovirus or influenza virus and monitored in quarantine for objective signs of illness and self-reported symptoms. Main Outcome Measures: Infection, signs and symptoms of the common cold, and clinical illness (infection and significant objective signs of illness). Results: Increased subjective SES was associated with decreased risk for developing a cold for both viruses. This association was independent of objective SES and of cognitive, affective and social disposition that might provide alternative spurious (third factor) explanations for the association. Poorer sleep among those with lesser subjective SES may partly mediate the association between subjective SES and colds. Conclusions: Increased Subjective SES is associated with less susceptibility to upper respiratory infection, and this association is independent of objective SES, suggesting the importance of perceived relative rank to health. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
992.
In a fluidized catalyst bed, the reactant gas transfers from the bubble phase to the emulsion phase and reactions proceed in the emulsion phase. The catalyst particles around the bubbles should contact the gases containing a high concentration of the reactants. Therefore, the effect of the catalysts around the bubbles is very important for estimating the conversion and selectivity in the reactor. In order to study the role of these catalysts, the hydrogenation of carbon dioxide was carried out in a fluidized catalyst bed. Based on the results, the amount of the catalyst that was effective for the reaction was calculated. In addition, the shape of the bubbles ascending in the fluidized catalyst bed was observed using a fast X-ray computer tomography (CT) scanner. The structure of the bubbles in the fluidized catalyst bed was very complicated and the surface area of the bubbles was much greater than the obtained when assuming spherical shaped bubble. By assuming that effective catalysts existed around the bubbles, the thickness of catalyst layer was obtained. Finally, the 3-dimensional images of the catalyst layers around the bubbles were reconstructed.  相似文献   
993.
This special issue highlights ongoing research to address some of the challenges in the design of large ICs with dimensions well below 100 nm. The Gigascale Systems Research Center is organized around four themes and a design driver, and each is represented in this issue. There is also an exciting interview with Intel chair Craig Barrett. Accompanying the theme articles are three sidebars written by industry leaders (Richard Oehler of AMD, Ajith Amerasekera of Texas Instruments, and Leon Stok of IBM) on the challenges they see on the horizon, the paths being taken to address these challenges, and the role university programs can play. In addition, a Perspectives article by John Zolper discusses the value of this collaborative program to US national interests, including national security. Finally, there is a Last Byte column by the FCRP executive director Betsy Weitzman.  相似文献   
994.
The thermodynamic and electrical effects of residual carbon in glass–barium titanate composites were investigated. Thermodynamic arguments are made suggesting that new phases form through carbothermal reactions between carbon and titanate-based dielectrics. Experimentally, it was shown that the reduced dielectric separated by insulating glass in the grain boundaries gave rise to a dielectric relaxation at room temperature consistent with the Maxwell–Wagner model. The conductivity of the dielectric was calculated based on the relaxation frequencies, allowing an estimate of the local oxygen activity due to the presence of carbon. This activity was consistent with the equilibrium oxygen activity for carbon oxidation at the processing temperature, and eight orders of magnitude different from the oxygen activity in the furnace atmosphere.  相似文献   
995.
Incremental advances in semiconductor device testing have improved device quality and reliability. New test methods applied to dies at the wafer level are now significantly improving the reliability of devices sold to the increasing bare-die market and reducing burn-in requirements for packaged devices.  相似文献   
996.
997.
998.
Athabasca bitumen was characterized by dividing it into sixteen pseudo components. Using mean boiling point, molecular weight and specific gravity data, the critical properties of the pseudo components were estimated from available correlations. Two approaches for the prediction of bitumen surface tension were investigated. It was found that the surface tensions predicted by the principle of corresponding states and the Rice-Teja correlations were in general agreement with the published experimental data. In addition, these models successfully predicted the effect of temperature on surface tension at temperatures greater than about 60°C.  相似文献   
999.
1000.
Magnetic resonance images of the brain were obtained from 2 gorillas (Gorilla gorilla gorilla), 4 orangutans (Pongo pygmaeus), 14 chimpanzees (Pan troglodytes), and 4 bonobos (Pan paniscus), The region on the motor cortex of humans identified as responsible for motor skill of the hand (the "knob") was identified in this sample on consecutive 1-mm axial scans. The shape of the knob area was traced on each scan from both hemispheres, and the area from all scans was summed to calculate the knob volume. The width of the knob was also measured and correlated highly with knob volume. A significant population-level leftward asymmetry in the volume and width of the knob was revealed (p?  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