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   466687篇
  免费   8518篇
  国内免费   4022篇
电工技术   10065篇
技术理论   5篇
综合类   4130篇
化学工业   70716篇
金属工艺   19768篇
机械仪表   15076篇
建筑科学   13634篇
矿业工程   3304篇
能源动力   12018篇
轻工业   40593篇
水利工程   5335篇
石油天然气   10343篇
武器工业   446篇
无线电   54040篇
一般工业技术   87952篇
冶金工业   79865篇
原子能技术   11223篇
自动化技术   40714篇
  2022年   3248篇
  2021年   4947篇
  2020年   3677篇
  2019年   4132篇
  2018年   6486篇
  2017年   6707篇
  2016年   6901篇
  2015年   5538篇
  2014年   8719篇
  2013年   21186篇
  2012年   13764篇
  2011年   18171篇
  2010年   14583篇
  2009年   16452篇
  2008年   16691篇
  2007年   16449篇
  2006年   14350篇
  2005年   13201篇
  2004年   12391篇
  2003年   11504篇
  2002年   11188篇
  2001年   11071篇
  2000年   10472篇
  1999年   10886篇
  1998年   25231篇
  1997年   18065篇
  1996年   14017篇
  1995年   10792篇
  1994年   9291篇
  1993年   9210篇
  1992年   6742篇
  1991年   6454篇
  1990年   6185篇
  1989年   6190篇
  1988年   5829篇
  1987年   5191篇
  1986年   5163篇
  1985年   5763篇
  1984年   5300篇
  1983年   4916篇
  1982年   4583篇
  1981年   4690篇
  1980年   4581篇
  1979年   4361篇
  1978年   4350篇
  1977年   4903篇
  1976年   6437篇
  1975年   3717篇
  1974年   3670篇
  1973年   3748篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
This paper presents a new self-routing packet network called the plane interconnected parallel network (PIPN). In the proposed design, the traffic arriving at the network is shaped and routed through two banyan network based interconnected planes. The interconnections between the planes distribute the incoming load more homogeneously over the network. The throughput of the network under uniform and heterogeneous traffic requirements is studied analytically and by simulation. The results are compared with the results of the baseline network and another banyan network based parallel interconnection network. It is shown that, for the proposed design, a higher degree of heterogeneity results in better performance  相似文献   
42.
A comprehensive survey of photosensitivity in silica glasses and optical fiber is reviewed. Recent work on understanding the mechanisms contributing to germanium or aluminum doped fiber photosensitivity is discussed within the framework of photoelastic densification models  相似文献   
43.
A new lateral MOS-gated thyristor, called the Base-Current-Controlled Thyristor, is described. This device is designed so that most holes at the on-stage reach the P base through the floating P+ region adjacent to the P base and the on-state MOSFET. At the turn-off stage, the interruption of the hole current to the P base due to switching off the above MOSFET occurs simultaneously with the conventional turn-off operation. The concept of this device is verified experimentally by using the fabricated lateral device with the external MOSFET. This device exhibits a better trade-off relation between the on-state voltage and the turn-off time compared uith the conventional MOS-gated thyristor  相似文献   
44.
Lubell  P. 《Spectrum, IEEE》1997,34(9):16-18
  相似文献   
45.
46.
P Le Xuan  B Hoang 《Canadian Metallurgical Quarterly》1997,181(9):1781-91; discussion 1792-3
To prevent post-transfusional hepatitis B and C, two epidemiologic studies were performed. The first, based on the frequencies distribution of hepatitis B virus serological markers versus sex and classes of age, has permitted the assessment of the profile of the infection in a population composed of 573 north vietnamese blood donors. There is no significant difference between men and women frequencies of HBs antigen (11.5%), anti-HBs antibody (70.2%) and anti-HBc antibody alone (3.8%), but a significant difference of no-marker frequencies: 7.8% and 17.9% in men and women respectively (X2 = 9.11; p = 0.010). The percentage of no-marker decreases when the mean age of each class increases. The second, using the increase of the serum alanine aminotransferase (ALAT) activity as an indirect marker of non-A, non-B hepatitis for determining in a population of more than 25,000 parisian blood donors, the percentage of donors eliminated. They are between 0.70 and 0.76 in women and 2.26 and 2.46 in men. These investigations can be applied to prevent the hepatitis B transmission in a population of 102 south vietnamese women in age to procreate or to determine the percentage of blood donors eliminated (3.12%) in a population of 2,950 Parisians composed in majority (50.9%) of new donors. The hemobiologist will have an important role to elaborate strategies for orientation of blood gifts with hepatitis B and C virus markers.  相似文献   
47.
The three-dimensional structure of glutathione S-transferase from Arabidopsis thaliana has been solved at 2.2 A resolution (Reinemer et al., 1996). The enzyme forms a dimer of two identical subunits. The structure shows a new G-site architecture and a novel and unique dimer interface. Each monomer of the protein forms a separate G-site. Therefore, the requirements on the dimer interface are reduced. As a consequence, the interactions between the monomers are weaker and residues at the dimer interface are more variable. Thus, the dimer interface looses its relevance for a classification of plant glutathione S-transferases and the formation of heterodimers becomes even more difficult to predict.  相似文献   
48.
49.
The physical widths of reference features incorporated into electrical linewidth test structures patterned in films of monocrystalline silicon have been determined from Kelvin voltage measurements. The films in which the test structures are patterned are electrically insulated from the bulk-silicon substrate by a layer of silicon dioxide provided by SIMOX (Separation by the IMplantation of OXygen) processing. The motivation is to facilitate the development of linewidth reference materials for critical-dimension (CD) metrology-instrument calibration. The selection of the (110) orientation of the starting silicon and the orientation of the structures' features relative to the crystal lattice enable a lattice-plane-selective etch to generate reference-feature properties of rectangular cross section and atomically planar sidewalls. These properties are highly desirable for CD applications in which feature widths are certified with nanometer-level uncertainty for use by a diverse range of CD instruments. End applications include the development and calibration of new generations of CD instruments directed at controlling processes for manufacturing devices having sub-quarter-micrometer features  相似文献   
50.
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