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   2339篇
  免费   48篇
  国内免费   5篇
电工技术   103篇
综合类   3篇
化学工业   513篇
金属工艺   62篇
机械仪表   55篇
建筑科学   36篇
矿业工程   1篇
能源动力   100篇
轻工业   133篇
水利工程   10篇
石油天然气   1篇
无线电   243篇
一般工业技术   447篇
冶金工业   472篇
原子能技术   59篇
自动化技术   154篇
  2023年   9篇
  2022年   30篇
  2021年   42篇
  2020年   14篇
  2019年   21篇
  2018年   26篇
  2017年   22篇
  2016年   39篇
  2015年   36篇
  2014年   43篇
  2013年   106篇
  2012年   58篇
  2011年   110篇
  2010年   79篇
  2009年   103篇
  2008年   89篇
  2007年   95篇
  2006年   88篇
  2005年   74篇
  2004年   57篇
  2003年   61篇
  2002年   54篇
  2001年   53篇
  2000年   60篇
  1999年   59篇
  1998年   183篇
  1997年   113篇
  1996年   83篇
  1995年   53篇
  1994年   56篇
  1993年   50篇
  1992年   33篇
  1991年   31篇
  1990年   25篇
  1989年   37篇
  1988年   28篇
  1987年   20篇
  1986年   27篇
  1985年   30篇
  1984年   15篇
  1983年   15篇
  1982年   22篇
  1981年   17篇
  1980年   21篇
  1979年   12篇
  1978年   11篇
  1977年   10篇
  1976年   41篇
  1975年   9篇
  1973年   9篇
排序方式: 共有2392条查询结果,搜索用时 13 毫秒
1.
A tri-gate bulk MOSFET design utilizing a low-aspect-ratio channel is proposed to provide an evolutionary pathway for CMOS scaling to the end of the roadmap. 3-D device simulations indicate that this design offers the advantages of a multi-gate FET (reduced variability in performance and improved scalability) together with the advantages of a conventional planar MOSFET (low substrate cost and capability for dynamic threshold-voltage control).  相似文献   
2.
The length of potassium titanate fibers produced by several conventional methods averages 50 μm, with a maximum of 100 μm. Extremely long fibers (most >1000 μm long) were obtained by calcination in N2 gas flowing at 5.2×10-4 m/s.  相似文献   
3.
A new gram-positive, nonmotile coccus is described. Strains IFO 12422T (T = type strain) and IFO 15385 in the Institute for Fermentation, Osaka, culture collection, which were isolated from soil and water, respectively, have the following chemotaxonomic characteristics: menaquinone MK-9(H4); G + C content of DNA of 67 mol%; and LL-diaminopimelic acid, alanine, glycine, and glutamic acid in a molar ratio of ca. 1:2:1:1 (type A3 gamma). Mycolic acids are not present. The taxonomic characteristics of these organisms are different from those of previously described gram-positive, high-G + C-content cocci. The partial 16S rRNA sequence indicated that IFO 12422T represents a distinct line of descent among gram-positive bacteria with a high G + C content. The name Luteococcus japonicus gen. nov., sp. nov. is proposed. The type strain is strain IFO 12422.  相似文献   
4.
To help in clarifying the relationship between the time lag and attenuation of nitrogen (N) loads generated in agricultural catchments, long-term trends in activities that generate N loads and in environmental N loads were estimated in catchments in Japan and Korea dominated by non-point-source emissions. Our approach used statistical data and geographical information system software to analyze pollutant loads. The method was successful in both countries because of the availability of well-developed statistics, geographical information, and weather and water quality monitoring systems, and the accumulation of research data concerning the generation of N loads and the fate of N in soils. Comparison of environmental loads with the loads observed in river water at the outlet of each catchment revealed that: (1) the effect of changes in the environmental load in a catchment appeared almost immediately in the river water quality in Korea, but did not appear clearly even 10 years later in Japan; and (2) the strength of the attenuation appeared to be much lower in Korea than in Japan. These findings suggest that regional characteristics play important roles in the sensitivity of water quality to load-generating activities.  相似文献   
5.
The longitudinal electric field of single and double Gaussian laser beams are used to accelerate electrons. The longitudinal field of the single beam is concentrated on the axis and is favourable for acceleration. A set of two beams is considered. Beams run parallel, collinearly, overlap partially and have a phase difference iπ in between. As a result, the transverse components of fields cancel each other while the longitudinal components are double-fold. In both schemes, the electrons are accelerated in lengths of the Rayleigh range, which is common to the plasma-based accelerators.  相似文献   
6.
This paper deals with an advanced static Var compensator (ASVC) using quad-series voltage-source PAM inverters. The ASVC consists of four three-phase voltage-source inverters with a common dc capacitor and four three-phase transformers, each primary winding of which is connected in series with each other. Each inverter outputs a square-wave voltage, while the synthesized output voltage of the ASVC has a 24-step wave shape. This results not only in a great reduction of harmonic currents and dc voltage ripples but also in fewer switching and snubbing losses. In this paper, transient analysis is performed with the focus on the response of reactive power and the resonance between the dc capacitor and ac reactors. Experimental results obtained from a small-rated laboratory model of 10 kVA are also shown to verify analytical results based on the p-q transformation. The analytical results help in the design of system parameters such as the capacity of the dc capacitor and feedback gains.  相似文献   
7.
The effects of various cytokines on survival and differentiation of an astrocyte progenitor cell line (AP-16) were examined. Epidermal growth factor (EGF) deprivation caused death of AP-16 cells by apoptosis. Transforming growth factor-alpha (TGF-alpha) and basic fibroblast growth factor (bFGF) prevented the apoptosis occurring in the absence of EGF. Leukemia inhibitory factor (LIF) and ciliary neurotrophic factor (CNTF) induced glial fibrillary acidic protein (GFAP) and decreased A2B5 antigen in AP-16 cells, indicating that these cytokines induced AP-16 cells to differentiate into astrocytes.  相似文献   
8.
A simple, accurate and universal relationship between MOSFET drain current in saturation, effective channel length, and gate drive has been found. It can be explained by a simple analytical model, whose validity is supported by numerical simulation. The model shows that the length of a velocity saturated region is a crucial parameter for describing MOSFET performance, particularly for short channel devices. The shrinkage of the length deteriorates the merit of channel length scaling  相似文献   
9.
10.
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