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   8191篇
  免费   91篇
  国内免费   8篇
电工技术   37篇
综合类   1篇
化学工业   620篇
金属工艺   125篇
机械仪表   100篇
建筑科学   118篇
矿业工程   6篇
能源动力   72篇
轻工业   285篇
水利工程   19篇
石油天然气   8篇
无线电   539篇
一般工业技术   700篇
冶金工业   5312篇
原子能技术   33篇
自动化技术   315篇
  2021年   33篇
  2019年   25篇
  2018年   38篇
  2017年   28篇
  2016年   37篇
  2015年   30篇
  2014年   52篇
  2013年   149篇
  2012年   90篇
  2011年   98篇
  2010年   100篇
  2009年   117篇
  2008年   121篇
  2007年   115篇
  2006年   102篇
  2005年   101篇
  2004年   87篇
  2003年   111篇
  2002年   75篇
  2001年   91篇
  2000年   114篇
  1999年   230篇
  1998年   1559篇
  1997年   987篇
  1996年   612篇
  1995年   387篇
  1994年   306篇
  1993年   354篇
  1992年   86篇
  1991年   99篇
  1990年   133篇
  1989年   122篇
  1988年   118篇
  1987年   105篇
  1986年   87篇
  1985年   103篇
  1984年   68篇
  1983年   65篇
  1982年   63篇
  1981年   90篇
  1980年   85篇
  1979年   42篇
  1978年   30篇
  1977年   185篇
  1976年   313篇
  1975年   41篇
  1974年   37篇
  1973年   46篇
  1972年   23篇
  1970年   24篇
排序方式: 共有8290条查询结果,搜索用时 15 毫秒
51.
As an alternative to surgical splenectomy, partial splenic embolization was performed in seven children for hypersplenism manifested by splenomegaly, thrombocytopenia, leukopenia, and erythrocyte hemolysis. Within a few days, platelet and leukocyte counts rose significantly in all patients and were maintained in six of seven patients during a follow-up period of 9 to 69 months. Spleen size and abdominal distention also decreased significantly in all children. There were no infectious complications.  相似文献   
52.
This article is the second of two papers that review the field of spatially sensitive social scientific research into the links between social status and transport disadvantage. The first paper undertook a comprehensive review of the social scientific and transport planning literature to mark the level of development in the field and identify conceptual and methodological issues and constraints in this field of inquiry. The present article supports the advancement of socially and geographically sensitive transport research by opportunities for the development of more sophisticated spatial analytical methodologies. The approach we present is able to account for factors not previously addressed in either social or transport planning research, in particular the temporal dimensions of transport service accessibility. The article articulates the methodology through an empirical case study of socio-spatial transport disadvantage within the Gold Coast City. The article demonstrates that there are important theoretical and practical lessons to be gained for researchers and policy makers in addressing the social dimensions of transport and infrastructure provision. Further, the article argues that an attentiveness to new ways of combining and representing social and transport data-sets can promote policy relevant empirical social inquiry. The article also contributes in a productive way to the empirical knowledge of Australia's sixth-largest metropolitan area, which is often overlooked by urban scholars.  相似文献   
53.
α,β‐Unsaturated nitriles have been synthesized by Knoevenagel condensation of a carbonylic compound with malononitrile, assisted by sonochemical irradiation. Two alkaline‐promoted clays (Li+‐ and Cs+‐exchanged saponites) have been employed as catalysts. The influence of the carbonylic compound (benzaldehyde or cyclohexanone) and the use of a solvent on the catalytic activity have been studied. Remarkable increase in the conversion values has been found when the reaction is activated by ultrasound, as compared with the thermal activation. In this green, solvent‐free procedure, α,β‐unsaturated nitriles have been produced in very high yields (97%) when the Cs+‐saponite is used as catalyst. Copyright © 2004 Society of Chemical Industry  相似文献   
54.
Enhanced Image Detection on an ARM based Embedded System   总被引:2,自引:0,他引:2  
This paper presents a new technique for thedetection of Integrated Circuits within images of Printed Circuit Boards autonomouslyand without the need to be assisted by CAD data. The technique is a key partof a suite of algorithms targeted for an embedded System On Chip architecturebased on the ARM7 platform for real time detection of PCB images for diagnosticpurposes. The technique has a significant reduction in complexity when comparedto conventional approaches such as the Hough Transform. The reduction in complexitymakes the approach ideal for an embedded vision application suchas the one described in this paper. This paper presents the technique, thetarget embedded architecture and results showing the reduction in complexitywhen compared to a Hough Transform.  相似文献   
55.
56.
57.
The growth in beer of 15 brewery strains of Lactobacillus was detected using the automatic conductance measuring technique afforded by the Malthus 8 Growth Analyser. 0·15% ammonium chloride was added to the beer as an electrolyte and sodium acetate was used to raise the pH from ca 4·0 to 4·2 or above. No measurable responses were obtained using unmodified beer. The value of the method for development in routine brewery microbiological control is briefly discussed.  相似文献   
58.
59.
In this letter, we conduct analysis on the optimum design for RF-to-optical up-converter in coherent optical OFDM systems using an optical I/Q modulator. We first derive closed-form expressions for the nonlinearity in the optical I/Q modulator, represented by two-tone intermodulation products as a function of the bias point and modulation index. Additionally, we perform a numerical simulation to identify Q-penalty and the excess modulation insertion loss under various transmitter conditions. We find that in contrast to the direct-detected system, the optimal modulator bias point for the coherent system is pi, where the Q-penalty and excess loss are minimized  相似文献   
60.
Polarization-insensitivity is achieved in a reflective spatial light modulator by laying a quarter-wave plate (QWP) at the incident wavelength directly over the mirror pixels of a silicon backplane, and forming a nematic Freedrickcz cell over the QWP to modulate the reflected phase. To achieve the highest drive voltage from the available silicon process, a switched voltage common front electrode design is described, with variable amplitude square wave drive to the pixels to maintain constant root-mean-square drive and minimize phase fluctuations during the dc balance refresh cycle. The silicon has been fabricated and liquid-crystal-on-silicon cells both with and without the QWP assembled; applications include optically transparent switches for optical networks, beam steering for add-drop multiplexers for wavelength-division-multiplexing telecommunications, television multicast, and holographic projection.  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