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   1625762篇
  免费   31704篇
  国内免费   9888篇
电工技术   38374篇
技术理论   10篇
综合类   10892篇
化学工业   284668篇
金属工艺   68170篇
机械仪表   47861篇
建筑科学   52571篇
矿业工程   13365篇
能源动力   52096篇
轻工业   124877篇
水利工程   16988篇
石油天然气   41241篇
武器工业   673篇
无线电   205018篇
一般工业技术   299212篇
冶金工业   196489篇
原子能技术   34900篇
自动化技术   179949篇
  2021年   18357篇
  2020年   14094篇
  2019年   16361篇
  2018年   19062篇
  2017年   18490篇
  2016年   23971篇
  2015年   20074篇
  2014年   31934篇
  2013年   91639篇
  2012年   41122篇
  2011年   55047篇
  2010年   47555篇
  2009年   55219篇
  2008年   50281篇
  2007年   47447篇
  2006年   48896篇
  2005年   43465篇
  2004年   44653篇
  2003年   44163篇
  2002年   42882篇
  2001年   39888篇
  2000年   38252篇
  1999年   38179篇
  1998年   56340篇
  1997年   46408篇
  1996年   40304篇
  1995年   33893篇
  1994年   31411篇
  1993年   31050篇
  1992年   27159篇
  1991年   24115篇
  1990年   24352篇
  1989年   23421篇
  1988年   21842篇
  1987年   20053篇
  1986年   19331篇
  1985年   22604篇
  1984年   22553篇
  1983年   20486篇
  1982年   19490篇
  1981年   19642篇
  1980年   18230篇
  1979年   18630篇
  1978年   17908篇
  1977年   18077篇
  1976年   19718篇
  1975年   16070篇
  1974年   15543篇
  1973年   15660篇
  1972年   13122篇
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
991.
Vaccination with peptides that induce a specific immune response is a potential prophylactic or therapeutic strategy against viral infections and tumors. Because of the extensive polymorphism of the HLA loci, synthetic peptide vaccines must consist of a cocktail of peptides that bind specifically to different HLA molecules. Such cocktails should be optimized for the target population as each population has its specific HLA gene frequencies. To achieve maximum population coverage with a minimum number of peptides, information is needed on the ranking of the most frequent HLA phenotypes. We introduce the minimal phenotype panel, which is the smallest combination of HLA antigens selected so that the proportion of individuals in a population that express at least one of the antigens in the panel exceeds a desired minimum value. We developed a method for assembling minimal phenotype panels based on known HLA class I gene frequencies. We give an example based on a set of 2446 well-defined HLA-typed, random, healthy, unrelated, Dutch Caucasoid individuals. In addition, we discuss the possibility of assembling minimal phenotype panels based on two-locus haplotypes, which enables the assembly of phenotype panels from the antigens of both loci.  相似文献   
992.
993.
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   
994.
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   
995.
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   
996.
997.
998.
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   
999.
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   
1000.
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   
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