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   816202篇
  免费   10101篇
  国内免费   1598篇
电工技术   15372篇
综合类   1035篇
化学工业   125476篇
金属工艺   33973篇
机械仪表   26603篇
建筑科学   19218篇
矿业工程   5185篇
能源动力   20568篇
轻工业   67311篇
水利工程   9228篇
石油天然气   17072篇
武器工业   43篇
无线电   90652篇
一般工业技术   164242篇
冶金工业   140858篇
原子能技术   18171篇
自动化技术   72894篇
  2021年   6880篇
  2019年   6618篇
  2018年   15380篇
  2017年   15553篇
  2016年   14420篇
  2015年   7916篇
  2014年   13039篇
  2013年   36047篇
  2012年   21656篇
  2011年   31653篇
  2010年   26030篇
  2009年   27913篇
  2008年   28695篇
  2007年   29600篇
  2006年   21846篇
  2005年   21672篇
  2004年   20275篇
  2003年   19705篇
  2002年   18530篇
  2001年   17942篇
  2000年   17274篇
  1999年   17292篇
  1998年   40522篇
  1997年   29349篇
  1996年   22936篇
  1995年   17650篇
  1994年   16049篇
  1993年   15691篇
  1992年   12122篇
  1991年   11604篇
  1990年   11498篇
  1989年   11235篇
  1988年   10841篇
  1987年   9571篇
  1986年   9469篇
  1985年   10889篇
  1984年   9841篇
  1983年   9353篇
  1982年   8434篇
  1981年   8686篇
  1980年   8187篇
  1979年   8270篇
  1978年   8042篇
  1977年   9066篇
  1976年   11504篇
  1975年   7165篇
  1974年   6846篇
  1973年   6988篇
  1972年   5928篇
  1971年   5470篇
排序方式: 共有10000条查询结果,搜索用时 140 毫秒
931.
932.
High division of the brachial artery was observed in two cadavers, during routine dissection of upper extremities. In the first case, the brachial artery of the right upper extremity was divided into its two terminal branches immediately after passing between the lateral and medial roots of the median nerve and just below the origin of the profunda brachii artery. The lateral branch was the radial artery, located in the space normally occupied by the brachial artery and the medial one was the ulnar artery. In the second case, the brachial artery was divided into its two terminal branches just below the origin of the profunda brachii artery. Accurate knowledge of the relationships and course of these major arterial conduits and particularly of their variational patterns, is of considerable practical importance in the conduct of reperative surgery in the arm, forearm and hand.  相似文献   
933.
934.
The thermal decomposition products of pyridinium sulfate differ from those of pyridinium sulfate supported on zirconia which in turn differs from that of pyridine adsorbed on a sulfated zirconia. Unsupported pyridinium sulfate decomposes to produce pyridine and sulfuric acid, and these subsequently react to produce oxides of carbon and sulfur. Zirconia that is sulfated and then exposed to pyridine does not release detectable amount of pyridine during heating in an inert gas; rather the pyridine undergoes oxidation reduction reactions simultaneously to release CO2 and sulfur compounds. Pyridinium sulfate supported on zirconia decomposes upon heating to release pyridine and sulfuric acid, which reacts with the zirconia. The desorption of pyridine in one case and only CO2/SOx in the other case suggests that sulfated zirconia does not contain Brønsted acidity that can form pyridinium sulfate.  相似文献   
935.
The potential of using artificially simulated neural networks as intelligent, adaptive process-monitoring devices is discussed. The investigation is considered as a method for automatic, intelligent exception reporting for quality control applications. The technique is also compared with the conventional statistical approaches of principal component analysis and Kohonen's feature map. The applications of the technique in aerospace and manufacturing environments are presented and a possible extension of the method to incorporate a diagnostic function is discussed.Seconded from Cheltenham and Gloucester College of Higher Education as a Royal Society/SERC Research Fellow at Smith's Industries Aerospace and Defence Systems, Bishop's Cleeve, Cheltenham, UK.  相似文献   
936.
The paper presents the findings of a survey that investigated the level of quality management practice within some 150 UK companies from a sample of 500. It provides a snapshot of practice at the time of the survey, and assesses the impact of government quality initiatives particularly, the TickIT scheme at that time. The survey methodology is described, together with the results and conclusions. The sample has been graded by size of company, which the authors consider to have a significant effect upon the adoption of quality practices. The survey highlights the need to encourage small companies to adopt quality practices and to assist them with the short-term costs incurred.  相似文献   
937.
A sensor for simultaneous electric and magnetic field measurement has been described by M. Kanda (see ibid., vol.EMC-26, no.3, p.102-10, 1984). It relies upon measuring the voltage across precisely matched loads at opposite sides of a loop antenna. A modification to the theory is presented to account for unmatched loading of the loop. Measured results of wave impedance over a 10-400-MHz range demonstrate the accuracy of the modified theory as well as highlighting a novel calibration technique  相似文献   
938.
The authors have fabricated 1.3-μm InAsP-InP separate-confinement-heterostructure (SCH) strained-layer double-quantum-well (SL-DQW) laser diodes (LDs) by metalorganic chemical vapor deposition (MOCVD). A low threshold current density of 410 A/cm 2 was obtained. The CW threshold current was as low as 1.8 mA at 20°C, and maximum CW operating temperature of 120°C was obtained. These characteristics are almost the same as those of well-designed GaInAsP-InP SL-QW LDs. Further improvement of the characteristics of InAsP-InP LDs is expected by optimizing the device structure  相似文献   
939.
This investigation focuses on the correlation between the crystallographic orientation of grains with respect to magnetic properties in Co-Cr films. Based on a distribution measured for the (0002) crystallographic pole densities, modified formulae describing the texture were used to calculate the coercivity Hc, the squareness ratio Rs (Mr⊥/TMs) and the anisotropy field Ha for Co-Cr films. In general, calculated values for the coercive force He agreed well with the measured values. The calculated Rs⊥. values were much larger than the measured ones, however, indicating that the influence of the demagnetizing field and the magnetostriction on the orientation of the magnetization cannot be neglected. On leave from Institute of Computing Technology, Academia Sinica, P.O.Box 2704-6, Beijing, P.R. China.  相似文献   
940.
Heat transfer of highly consistent shear-thinning fluids flowing in a horizontal cylindrical channel has been investigated numerically and experimentally when the outer channel wall is subjected to a constant convective heat exchange. The case considered being cooling, a possible ice deposit must be taken into account. The variation of the rheological properties with temperature must be considered as well.  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