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   1584857篇
  免费   25730篇
  国内免费   7061篇
电工技术   35485篇
综合类   6467篇
化学工业   277326篇
金属工艺   67049篇
机械仪表   47135篇
建筑科学   47771篇
矿业工程   11987篇
能源动力   50504篇
轻工业   120943篇
水利工程   16152篇
石油天然气   38618篇
武器工业   149篇
无线电   200651篇
一般工业技术   300595篇
冶金工业   187630篇
原子能技术   34765篇
自动化技术   174421篇
  2021年   15640篇
  2020年   11936篇
  2019年   14714篇
  2018年   19770篇
  2017年   19625篇
  2016年   23295篇
  2015年   17668篇
  2014年   28779篇
  2013年   88266篇
  2012年   38136篇
  2011年   53898篇
  2010年   46778篇
  2009年   54642篇
  2008年   49279篇
  2007年   47512篇
  2006年   46273篇
  2005年   42708篇
  2004年   43651篇
  2003年   43191篇
  2002年   41843篇
  2001年   38325篇
  2000年   36648篇
  1999年   35952篇
  1998年   51965篇
  1997年   43710篇
  1996年   38070篇
  1995年   32361篇
  1994年   30096篇
  1993年   29910篇
  1992年   26633篇
  1991年   23833篇
  1990年   24151篇
  1989年   23268篇
  1988年   21766篇
  1987年   20003篇
  1986年   19381篇
  1985年   22689篇
  1984年   22609篇
  1983年   20587篇
  1982年   19456篇
  1981年   19552篇
  1980年   18192篇
  1979年   18672篇
  1978年   17909篇
  1977年   18057篇
  1976年   19441篇
  1975年   16149篇
  1974年   15630篇
  1973年   15739篇
  1972年   13209篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
891.
本文概述了离子注入过程中污染产生的原因和防止污染的措施,特别强调了对微粒污染和金属污染的防护以满足ULSI加工对离子注入的要求。  相似文献   
892.
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   
893.
The paper covers a simple idea. If we sample an aperture, we can obtain valid patterns over a limited angular region about the normal to the aperture. The same expression can be used with near-field measurements. I reduced the expression to a nomograph. A nomograph allows one to rapidly test various choices. In the second half of the paper, I answer questions caused by the February column which discussed polarization (Milligan, IEEE Antennas. Propag. Mag., vol.38, no.1, p.56-8, 1996)  相似文献   
894.
The formation of mullite was investigated using microcomposite powders which consist of α-alumina cores and amorphous silica coatings. Differential thermal analysis and X-ray diffraction showed that the mullitization reaction was endothermic. In contrast, mullite forms exothermically in samples prepared by sol-gel processing. The results are shown to be consistent with available thermodynamic data for mullite formation from different alumina and silica phases.  相似文献   
895.
896.
897.
The objective of this study is to determine the economic and operational impact on energy cost of incorporating large photovoltaic (PV) and wind energy conversion systems (WECS) into the electric utility generation mix. In most cases, PV and WECS power outputs are subtracted from the utility load with the expectation that conventional generation would meet the residual load. This approach is valid for small penetration levels and/or for PV and WECS facilities connected near load centers, However, several constraints such as thermal generation characteristics, fuel supply and delivery, spinning reserve requirements, and hydro availability are not adequately represented in this process. To determine the optimal value of large-scale PV and WECS applications, a new methodology that would take into account the aforementioned constraints as well as a more global penetration is developed. Results indicate that while high hydro availability increases PV penetration levels, high ramping rates can also significantly increase penetration levels  相似文献   
898.
Roos  G. Hoefflinger  B. 《Electronics letters》1993,29(24):2103-2104
A process-inherent NAND2 device is presented for a three-dimensional CMOS integration with epitaxial lateral overgrowth and chemo-mechanical polishing. The required 'OR' function of the two PMOS transistors is achieved by one silicon volume, which is controlled by a back gate and a conventional front gate. Almost symmetrical characteristics are measured for the front and the back gates.<>  相似文献   
899.
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   
900.
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   
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