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   693篇
  免费   31篇
电工技术   2篇
综合类   1篇
化学工业   155篇
金属工艺   46篇
机械仪表   52篇
建筑科学   9篇
能源动力   20篇
轻工业   56篇
水利工程   4篇
石油天然气   1篇
无线电   76篇
一般工业技术   135篇
冶金工业   85篇
原子能技术   8篇
自动化技术   74篇
  2023年   3篇
  2022年   11篇
  2021年   17篇
  2020年   13篇
  2019年   22篇
  2018年   19篇
  2017年   21篇
  2016年   18篇
  2015年   23篇
  2014年   28篇
  2013年   54篇
  2012年   64篇
  2011年   58篇
  2010年   34篇
  2009年   30篇
  2008年   37篇
  2007年   31篇
  2006年   19篇
  2005年   26篇
  2004年   16篇
  2003年   25篇
  2002年   13篇
  2001年   15篇
  2000年   9篇
  1999年   12篇
  1998年   40篇
  1997年   23篇
  1996年   10篇
  1995年   6篇
  1994年   5篇
  1993年   4篇
  1992年   6篇
  1990年   1篇
  1989年   1篇
  1987年   1篇
  1985年   1篇
  1983年   2篇
  1982年   1篇
  1976年   2篇
  1975年   1篇
  1971年   1篇
  1969年   1篇
排序方式: 共有724条查询结果,搜索用时 15 毫秒
61.
62.
Arteriovenous malformation (AVM) is characterized by high-flow blood vessels connecting arteries and veins without capillaries. This disease shows increased angiogenesis and a pathophysiological hypoxic environment in proximal tissues. Here, we analyzed the effects of hypoxia on angiogenesis in the endothelial cells (ECs) of AVM and normal tissues. ECs from human normal and AVM tissues were evaluated using immunocytochemistry with CD31. In vitro tube formation under hypoxia was tested in both ECs using Matrigel. The relative expression of angiogenesis-related genes was measured using real-time PCR. Under normoxia, CD31 was significantly higher in AVM ECs (79.23 ± 0.65%) than in normal ECs (74.15 ± 0.70%). Similar results were observed under hypoxia in AVM ECs (63.85 ± 1.84%) and normal ECs (60.52 ± 0.51%). In the tube formation test under normoxic and hypoxic conditions, the junction count and total vessel length were significantly greater in AVM ECs than normal ECs. Under both normoxia and hypoxia, the angiogenesis-related gene FSTL1 showed a significantly higher expression in AVM ECs than in normal ECs. Under hypoxia, CSPG4 expression was significantly lower in AVM ECs than in normal ECs. Accordingly, the angiogenic effect was increased in AVM ECs compared with that in normal ECs. These results provide a basic knowledge for an AVM treatment strategy.  相似文献   
63.
A composite of poly(N‐vinylcarbazole) (PVK) containing gold nanoparticles (GNPs) was synthesized via simple solid‐state in situ bulk polymerization of N‐vinylcarbazole in the presence of GNPs at a high temperature. Both PVK and PVK–GNP composites were characterized by Fourier transform infrared (FTIR) and UV–vis spectroscopy. The surface morphology of the composites was studied by scanning electron microscopy (SEM), energy‐dispersive X‐ray spectroscopy, and transmission electron microscopy (TEM). Thermal stability was identified via thermogravimetric analysis. The composites were fabricated into films using the Langmuir–Schaefer process. The enhancement in the characteristics of room temperature I–V, pressure–area isotherms, and photoelectrochemical behaviors was observed in the composite films. Results suggest that a charge transfer process occurs across the hybrid at the interface of the PVK–GNP composites. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers  相似文献   
64.
The aim of this study was to identify of antimicrobial substances from Korean Lettuce (Youngia sonchifolia M.). Water and ethanol extracts of Youngia sonchifolia M. exhibited antimicrobial activities against the microorganisms tested. Ethanol extract showed strong antimicrobial activities against most Gram positive and Gram negative microorganisms, whereas no lactic acid bacteria and yeasts were not affected. The antimicrobial compound G-6 was isolated from the ethyl acetate fraction obtained by silica gel column chromatography and HPLC and was confirmed as stable against heat treatment. Molecular weight of G-6 was calculated as 154 kDa based on information in the MS spectrum. G-6 was identified as 2-nonynoic acid (C9H14O2) by UV, LC-EI/MS, and LC-CI/MS. In support of this, the chromatogram of G-6 was consistent with that of the 2-nonynoic acid standard. Antimicrobial activity of 2-nonynoic acid was identified in all samples, with a significant difference based on concentratio.  相似文献   
65.
66.
67.
When considering joint toxic apical effects at higher levels of biological organization, such as the growth of populations, the so-called pharmacological mode of action that relies on toxicological mechanistic effects on molecular target sites may not be relevant. Such effects on population growth rate will depend on the extent to which juvenile and adult survival rates and production rates (juvenile developmental rates and reproduction) are affected by toxic exposure and also by the sensitivity of population growth rates to life-history changes. In such cases, the ecotoxicological mode of action, defined as the crucial life-history trait processes and/or xenobiotic-life-history trait interactions underlying a toxicological effect on population growth rate, should be considered. Life-table response experiments with the crustacean Ceriodaphnia dubia exposed to single and ternary mixtures of nine compounds were conducted to test the hypothesis that joint effects on population growth rates could be predicted from the mixture constituent ecotoxicological mode of action. Joint effects of mixtures containing pharmacologically dissimilar compounds (cadmium, λ-cyhalothrin, and chlorpyrifos) that differentially affected life-history traits contributing to population growth rates were accurately predicted by the independent-action concept. Conversely, the concentration-addition concept accurately predicted joint effects of two different mixtures: one containing pharmacologically similar acting pyrethroids that also affected similarly life-history traits, the other one that included pharmacologically dissimilar compounds (3,4-dichloroaniline, sodium bromide, and fenoxycarb) acting mainly on reproduction rates. These results indicate that when assessing combined effects on population growth rate responses, selection of mixture toxicity conceptual models based on the ecotoxicological mode of action of mixture constituents provided more accurate predictions than those based on the pharmacological mode of action.  相似文献   
68.
Y.H. Huh  H.L. Beus   《Pattern recognition》1982,15(6):445-453
The Korean alphabet is a set of phonetic symbols which are combined to form characters, somewhat in the Chinese style. The phonetic quality of the symbols naturally limits the combinations that are useful, and character formation constraints further limit these combinations. Advantage of this is made in an on-line computer recognition system. Korean characters are entered by means of a graphic tablet, using the standard stroke sequences taught in schools. Recognition is perfect for carefully drawn characters and nearly so for characters written at an unhurried rate, provided the system is tuned to the writer's style.  相似文献   
69.
用作汽车轮胎增强材料的钢丝帘线是由盘条拉成细丝捻制而成。为满足轮胎的刚度需求,人们开发了不同类型的钢丝帘线。钢丝帘线的结构稳定性是其质量评估的重要因素之一。一般在钢丝帘线捻制工序后评估钢丝帘线的平直性和残余扭转。校直辊是利用周期弯曲变形来改善钢丝帘线的平直性和残余应力的一种装置。校直辊装置的工艺设计大多数情况下是基于工程师经验的反复试验,需要大量的时间和成本。因此需要一个有效工具来节省校直辊工艺设计的时间和成本。有限元分析模拟方法是校直辊工艺设计的一种有效选择。本工作提出通过有限元分析校直辊工艺数值模拟单层钢丝帘线质量的评估方法,以3×0.30单层钢丝帘线作为试验样品。简易模拟方法如  相似文献   
70.
Box-Behnken designs were used to optimize a process for sesame oil extraction by screw-pressing at low temperature (50 °C). Experimental designs included seed moisture content (SMC), pressing speed (PS), and restriction die (RD) as the main processing parameters. Extractions at pilot plant scale showed a peak in oil recovery (OR, 71.1 ± 2.80%) at 12.3% SMC, 4 mm RD, and 20 rpm PS. Theoretical models were scanned against experimental data in order to scale up the proposed oil extraction process to industrial scale. A fitted model for OR showed a maximum predicted value similar to the highest experimental value (74.4 ± 1.23%) under the following conditions: 8.03% SMC, 10 mm RD, and 20 rpm PS. Chemical quality parameters of oils obtained at both pilot and industrial scales were in the ranges stated in Codex (FAO/WHO) standards for non-refined sesame oil.  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