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   185篇
  免费   13篇
  国内免费   2篇
电工技术   5篇
化学工业   53篇
金属工艺   5篇
机械仪表   6篇
建筑科学   19篇
能源动力   18篇
轻工业   4篇
水利工程   6篇
石油天然气   1篇
无线电   10篇
一般工业技术   31篇
冶金工业   13篇
原子能技术   1篇
自动化技术   28篇
  2023年   3篇
  2022年   8篇
  2021年   13篇
  2020年   9篇
  2019年   8篇
  2018年   21篇
  2017年   16篇
  2016年   7篇
  2015年   15篇
  2014年   7篇
  2013年   22篇
  2012年   12篇
  2011年   11篇
  2010年   4篇
  2009年   11篇
  2008年   5篇
  2007年   4篇
  2004年   1篇
  2003年   1篇
  2002年   1篇
  2001年   1篇
  1999年   1篇
  1998年   4篇
  1994年   3篇
  1991年   1篇
  1990年   2篇
  1985年   2篇
  1978年   1篇
  1977年   1篇
  1976年   1篇
  1975年   1篇
  1970年   2篇
  1969年   1篇
排序方式: 共有200条查询结果,搜索用时 78 毫秒
101.
Oxidative stress and inflammation play major roles in the pathogenesis of coronary heart disease including myocardial infarction (MI). The pathological progression following MI is very complex and involves a number of cell populations including cells localized within the heart, as well as cells recruited from the circulation and other tissues that participate in inflammatory and reparative processes. These cells, with their secretory factors, have pleiotropic effects that depend on the stage of inflammation and regeneration. Excessive inflammation leads to enlargement of the infarction site, pathological remodeling and eventually, heart dysfunction. Stem cell therapy represents a unique and innovative approach to ameliorate oxidative stress and inflammation caused by ischemic heart disease. Consequently, it is crucial to understand the crosstalk between stem cells and other cells involved in post-MI cardiac tissue repair, especially immune cells, in order to harness the beneficial effects of the immune response following MI and further improve stem cell-mediated cardiac regeneration. This paper reviews the recent findings on the role of antioxidation and immunomodulation in postnatal multipotent stem cell-mediated cardiac repair following ischemic heart disease, particularly acute MI and focuses specifically on mesenchymal, muscle and blood-vessel-derived stem cells due to their antioxidant and immunomodulatory properties.  相似文献   
102.
103.
Optimal crop water allocation has become more challenging in drier areas of the world (short of rainfall) due to increased water scarcity and more frequent droughts. alternative cropping patterns, reallocation of water resources and modification of irrigation are some of the strategies used to address droughts . A new optimization model is used in this study to find the optimal cropping patterns during droughts, while benefiting from deficit irrigation to decrease the total allocated water. Moreover, the proposed model is subjected to a proportional cutback constraint to meet optimized proportional water allocation under limited water condition. As a real case study, two related districts, namely Neku-abad and Abshar located in Zayandeh-rud River basin are considered. Zayandeh-rud river basin is located in the central part of Iran. For better illustration of model outputs, the proposed model was checked using various irrigation efficiency values (60–100 % in 10 % interval), water reduction ratios (0.0–0.4) and cutback parameters (λ a ?=?0.3,?λ n ?=?0.7, λ a ?=?0.51,?λ n ?=?0.49 and λ a ?=?λ n ?=?0.5). The results showed that the values of λ a ?=?0.51,?λ n ?=?0.49 presents the maximum proportionality in terms of water reduction among all the allocation units or users. Although different values of cutback parameters (e.g.: λ a ?=?0.3,?λ n ?=?0.7) maximize net benefits, they are not considered as proportionate decisions in the considered study area.  相似文献   
104.
Stach  Sebastian  Ţălu  Ştefan  Dallaev  Rashid  Arman  Ali  Sobola  Dinara  Salerno  Marco 《SILICON》2020,12(11):2563-2570
Silicon - The morphological stability of silicon single crystal wafers was investigated, after performing cleaning surface treatments based on moderate temperature annealing and plasma sputtering....  相似文献   
105.
By the inevitable scaling down of the feature size of the MOS transistors which are deeper in nanoranges, the CMOS technology has encountered many critical challenges and problems such as very high leakage currents, reduced gate control, high power density, increased circuit noise sensitivity and very high lithography costs. Quantum-dot cellular automata (QCA) owing to its high device density, extremely low power consumption and very high switching speed could be a feasible competitive alternative. In this paper, a novel 5-input majority gate, an important fundamental building block in QCA circuits, is designed in a symmetric form. In addition to the majority gate, a SR latch, a SR gate and an efficient one bit QCA full adder are implemented employing the new 5-input majority gate. In order to verify the functionality of the proposed designs, QCADesigner tool is used. The results demonstrate that the proposed SR latch and full adder perform equally well or in many cases better than previous circuits.  相似文献   
106.
Economizer use in data centers is an energy efficiency strategy that could significantly limit electricity demand in this rapidly growing economic sector. Widespread economizer implementation, however, has been hindered by potential reliability concerns associated with exposing information technology equipment to particulate matter of outdoor origin. This study explores the feasibility of using economizers in data centers to save energy while controlling particle concentrations with high-quality air filtration. Physical and chemical properties of indoor and outdoor particles were analyzed at an operating northern California data center equipped with an economizer under varying levels of air filtration efficiency. Results show that when improved filtration is used in combination with an economizer, the indoor/outdoor concentration ratios for most measured particle types were similar to levels when using conventional filtration without economizers. An energy analysis of the data center reveals that, even during the summer months, chiller savings from economizer use greatly outweigh any increase in fan power associated with improved filtration. These findings indicate that economizer use combined with improved filtration could reduce data center energy demand while providing a level of protection from particles of outdoor origin similar to that observed with conventional design.  相似文献   
107.
A silane‐containing diamine, bis(p‐aminophenoxy) diphenylsilane (BADPS), was prepared by the condensation of p‐aminophenol with dichlorodiphenyl silane in the presence of triethylamine. Then, BADPS was condensed with 4,4‐azobis(4‐cyanopentanoyl chloride) to prepare macroazoinitiators containing silane units (Si–MAIs). A series of poly(methyl methacrylate) gels containing silane were derived by the solution free‐radical crosslinking copolymerization of methyl methacrylate and ethylene glycol dimethacrylate monomers initiated by these macroazoinitiators at a total monomer concentration of 6 mol/L and 80°C. Si–MAIs were characterized with 1H‐NMR and 13C‐NMR spectroscopy, and the structural characteristics of the gels were also examined. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010  相似文献   
108.
An effort to analyze the viscoelasticity effects on transverse transport of neutral solutes between two miscible streams in an electrokinetic T‐sensor is presented. The analysis is based on an approximate analytical solution for the depthwise averaged concentration, assuming a channel of large width to depth ratio for which a one‐dimensional profile is sufficient for describing the velocity field. We show that the solution derived is surprisingly accurate even for very small channel aspect ratios and the maximum error reduces to only about 1% when the aspect ratio is 5. The developed model reveals that the mixing length for a viscoelastic fluid may be by far larger than that for a Newtonian fluid. Moreover, the Taylor dispersion coefficient for electroosmotic flow of viscoelastic fluids, which its determination is a main part of the analysis, is found to be an increasing function of both the elasticity level and the EDL thickness. © 2015 American Institute of Chemical Engineers AIChE J, 61: 4533–4541, 2015  相似文献   
109.
A highly efficient stereoselective method for the synthesis of functionalized spirooxindole derivatives with four contiguous stereogenic centers, including two adjacent quaternary stereogenic centers, was realized through an organocatalytic tandem Michael–Michael reaction. By employing a quinidine‐derived thiourea organocatalyst, the reaction between (E)‐2‐cyano‐2‐(2‐oxo‐1‐tritylindolin‐3‐ylidene)acetates and (E)‐1‐alkyl‐6‐nitro‐hex‐2‐en‐1‐ones yields the desired spirooxindole products in good yields (up to 90%) and with excellent stereoselectivities (up to 95:5 dr and 98% ee).

  相似文献   

110.
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