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   23494篇
  免费   2930篇
  国内免费   1044篇
电工技术   273篇
技术理论   2篇
综合类   1115篇
化学工业   6801篇
金属工艺   1420篇
机械仪表   760篇
建筑科学   1446篇
矿业工程   496篇
能源动力   1634篇
轻工业   2013篇
水利工程   216篇
石油天然气   1346篇
武器工业   327篇
无线电   3391篇
一般工业技术   4987篇
冶金工业   577篇
原子能技术   164篇
自动化技术   500篇
  2024年   87篇
  2023年   766篇
  2022年   645篇
  2021年   996篇
  2020年   1049篇
  2019年   984篇
  2018年   841篇
  2017年   953篇
  2016年   915篇
  2015年   923篇
  2014年   1525篇
  2013年   1536篇
  2012年   1572篇
  2011年   1762篇
  2010年   1248篇
  2009年   1365篇
  2008年   1168篇
  2007年   1383篇
  2006年   1297篇
  2005年   1089篇
  2004年   882篇
  2003年   840篇
  2002年   585篇
  2001年   542篇
  2000年   481篇
  1999年   378篇
  1998年   285篇
  1997年   248篇
  1996年   233篇
  1995年   184篇
  1994年   160篇
  1993年   116篇
  1992年   86篇
  1991年   72篇
  1990年   42篇
  1989年   41篇
  1988年   21篇
  1987年   26篇
  1986年   18篇
  1985年   33篇
  1984年   15篇
  1983年   16篇
  1982年   14篇
  1981年   5篇
  1980年   7篇
  1979年   4篇
  1975年   2篇
  1974年   2篇
  1964年   2篇
  1951年   13篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
塔里木油田水碳酸盐平衡系数与有机酸的意义   总被引:3,自引:2,他引:1  
李伟  刘宝珺  闵磊 《石油学报》2003,24(5):32-35
根据统计学规律,对塔里木盆地油田水进行了研究,阐明了该盆地油田水的碳酸盐平衡系数(简称为RC)与有机酸的基本特征。从油田水的无机组分与有机组分的统计分析中发现了油田水的碳酸盐平衡系数与有机酸存在明显的负相关性,进一步论证了碳酸盐平衡系数和有机酸与油气聚集及油气性质的关系。碳酸盐平衡系数越低及低碳有机酸的含量越高,它们与油藏,尤其是与 轻质油或气藏的关系越密切。从两者的关系中初步了解到有机酸的溶蚀作用对油气藏中储层次生孔隙的形成应有较重要的影响。  相似文献   
52.
卟啉类光电功能材料的研究进展   总被引:6,自引:0,他引:6  
卟啉及其衍生物是一类具有优良的光电性能的有机半导体材料.引起人们广泛的关注。本文对卟啉类光电材料在模拟生物光合作用中心的光致电荷转移和能量转移,有机太阳能电池.分子光电器件。有机电致发光和光存储等领域的研究进展做一简要介绍。  相似文献   
53.
In this paper, we review some of the advantages and disadvantages of nickel silicide as a material for the electrical contacts to the source, drain and gate of current and future CMOS devices. We first present some of the limitations imposed on the current cobalt silicide process because of the constant scaling, of the introduction of new substrate geometries (i.e. thin silicon on insulator) and of the modifications to the substrate material (i.e. SiGe). We then discuss the advantages of NiSi and for each of the CoSi2 limitations, we point out why Ni is believed to be superior from the point of view of material properties, miscibility of phases and formation mechanisms. Discussion follows on the expected limitations of NiSi and some of the possible solutions to palliate these limitations.  相似文献   
54.
Effect of stoichiometry on microstructures, electrochemical properties and PCT characteristics of the alloys MI(Ni0.71Co0.15-Al0.06Mn0.08)x (MI=Lanthanum-rich Michmetal, x=4.6~5.2) have been investigated. The lattice constants a, c, and cellvolumes of non-stoichiometric alloys are bigger than those of the stoichiometric alloy. With the increasing stoichiometry x,the value of a decreases, and the value of c and cell volume increases except for those of the stoichiometric alloy; the plateaupressure of PCT curve, discharge capacity and cycling stability all increase. The alloy with x=5.2 shows the highest dischargecapacity and the best cycling stability among the studied alloys.  相似文献   
55.
Grapevine powdery mildew ( Erysiphe necator) affects grape yield and fruit quality worldwide. Managers of conventional vineyards rely mainly on synthetic fungicides and sulfur to control powdery mildew, while in organic vineyards sulfur is the main control agent, often in rotation with canola-based oils, bicarbonates and biological control agents. The efficacy of those materials has not been evaluated critically under field conditions in Australia. Accordingly, a range of materials showing most promise in previous greenhouse trials (Crisp et al. 2006 Australian Journal of Grape and Wine Research 12 , pp. 192–202) were assessed via field trials in commercial vineyards. Applications of either milk or whey (alone, or mixed with a canola oil-based product), as well as applications of potassium bicarbonate (commercial formulation), all reduced the severity of powdery mildew compared with untreated vines. Eight applications of a 1:10 dilution of milk, 45 g/L whey powder or programs comprising rotations of potassium bicarbonate plus oil and whey, applied at 10–14 day intervals, reduced the severity of powdery mildew to levels not significantly different from that on vines sprayed with sulfur (wettable powder, 3–6 g/L). However, the relative control of powdery mildew by the test materials in field trials was dependent on the susceptibility of the grapevine cultivar and the extent of spray coverage achieved. In vineyards where highly susceptible cultivars were planted, and spray coverage was compromised, the resultant control of powdery mildew was reduced; and sometimes to commercially unacceptable levels.  相似文献   
56.
57.
58.
不同表面预处理对有机电致发光显示器性能的影响   总被引:1,自引:1,他引:0  
从生产角度研究了基板表面的预处理工艺对OLED性能的影响,分别用UVOzone、氧Plasma以及两者相结合的方式对基板进行表面处理,并按照生产工艺制作器件,从接触角、方阻以及光电特性等测试结果对各种表面处理的样品进行比较。结果表明以上处理都改善了器件性能,不同程度提高了器件的清洁度、亮度和发光效率,其中UVOzone和氧Plasma结合的方式处理效果最为显著,器件在10V时亮度达到79920cd/m2,比其他两种处理方式亮度提高约25%。  相似文献   
59.
Organic solar cells are a promising route towards large‐area and low‐price photovoltaic systems. The devices are composed of at least two layers: the hole‐transport layer and the electron‐transport layer. The light absorption can occur in one or both layers. At the interface of the layers the excitons are separated into charge carriers, and every layer deals with one type of carrier. Higher efficiencies of the separation process can be obtained by using a mixed layer containing both materials to obtain a very high interface area. Although the structure of the mixed layers used plays a crucial role for the device performance, until now the morphologies have not been elucidated. In order to correlate physical and optical findings with structure and morphology for the materials in question, electron microscopy experiments were performed on the single components as well as on the layer systems. The conventional electron microscope is a poor phase microscope. As consequence, weak‐phase objects like organic molecules have to be stained or imaged under strong defocus to produce an observable contrast. Artifacts caused by chemical staining and the appearance of Fresnel diffraction using the defocus technique represent the main problems of conventional microscopy. These artifacts can be avoided using electron holography. Holograms of ultrathin sections of thin layers composed of organic dye molecules were recorded. Subsequently, the phase images were reconstructed. In this manner, we succeeded in obtaining high‐contrast electron micrographs without applying staining or defocus. In addition, holograms of crystalline C60 and zinc phthalocyanine were successfully recorded. Holography has been shown to be a useful tool to image beam‐sensitive and weak‐phase objects without artifacts.  相似文献   
60.
A new ordered structure of the C60 derivative PCBM ([6‐6]‐phenyl C61‐butyric acid methyl ester) is obtained in thin films based on the blend PCBM:regioregular P3HT (poly(3‐hexylthiophene)). Rapid formation of needlelike crystalline PCBM structures of a few micrometers up to 100 μm in size is demonstrated by submitting the blended thin films to an appropriate thermal treatment. These structures can grow out to a 2D network of PCBM needles and, in specific cases, to spectacular PCBM fans. Key parameters to tune the dimensions and spatial distribution of the PCBM needles are blend ratio and annealing conditions. The as‐obtained blended films and crystals are probed using atomic force microscopy, transmission electron microscopy, selected area electron diffraction, optical microscopy, and confocal fluorescence microscopy. Based on the analytical results, the growth mechanism of the PCBM structures within the film is described in terms of diffusion of PCBM towards the PCBM crystals, leaving highly crystalline P3HT behind in the surrounding matrix.  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