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   1531281篇
  免费   26629篇
  国内免费   7008篇
电工技术   34650篇
综合类   6410篇
化学工业   274229篇
金属工艺   65002篇
机械仪表   43651篇
建筑科学   46697篇
矿业工程   11534篇
能源动力   50556篇
轻工业   113182篇
水利工程   15553篇
石油天然气   37887篇
武器工业   132篇
无线电   198120篇
一般工业技术   289807篇
冶金工业   171316篇
原子能技术   34235篇
自动化技术   171957篇
  2021年   15853篇
  2020年   12098篇
  2019年   14849篇
  2018年   17337篇
  2017年   16820篇
  2016年   22348篇
  2015年   17803篇
  2014年   29136篇
  2013年   88704篇
  2012年   36488篇
  2011年   49834篇
  2010年   43958篇
  2009年   52199篇
  2008年   46021篇
  2007年   43426篇
  2006年   45049篇
  2005年   40115篇
  2004年   42025篇
  2003年   41963篇
  2002年   40789篇
  2001年   37628篇
  2000年   35999篇
  1999年   35288篇
  1998年   48191篇
  1997年   40874篇
  1996年   36350篇
  1995年   31248篇
  1994年   29221篇
  1993年   29119篇
  1992年   26182篇
  1991年   23303篇
  1990年   23676篇
  1989年   22730篇
  1988年   21237篇
  1987年   19497篇
  1986年   18857篇
  1985年   22197篇
  1984年   22386篇
  1983年   20272篇
  1982年   19263篇
  1981年   19416篇
  1980年   17977篇
  1979年   18475篇
  1978年   17736篇
  1977年   17486篇
  1976年   18424篇
  1975年   15996篇
  1974年   15474篇
  1973年   15586篇
  1972年   12998篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
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   
952.
953.
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   
954.
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   
955.
956.
957.
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   
958.
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   
959.
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   
960.
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