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   622695篇
  免费   7980篇
  国内免费   2476篇
电工技术   11219篇
综合类   847篇
化学工业   92856篇
金属工艺   22874篇
机械仪表   18094篇
建筑科学   16240篇
矿业工程   2320篇
能源动力   16100篇
轻工业   58078篇
水利工程   5762篇
石油天然气   7382篇
武器工业   56篇
无线电   77658篇
一般工业技术   118944篇
冶金工业   116730篇
原子能技术   11865篇
自动化技术   56126篇
  2021年   4402篇
  2019年   4105篇
  2018年   6726篇
  2017年   6870篇
  2016年   7340篇
  2015年   5393篇
  2014年   9049篇
  2013年   28283篇
  2012年   15361篇
  2011年   21826篇
  2010年   16845篇
  2009年   19273篇
  2008年   20396篇
  2007年   20739篇
  2006年   18299篇
  2005年   16988篇
  2004年   16742篇
  2003年   16301篇
  2002年   15734篇
  2001年   15734篇
  2000年   14802篇
  1999年   15528篇
  1998年   36427篇
  1997年   26397篇
  1996年   20469篇
  1995年   15983篇
  1994年   14162篇
  1993年   13907篇
  1992年   10256篇
  1991年   9840篇
  1990年   9396篇
  1989年   9103篇
  1988年   8627篇
  1987年   7540篇
  1986年   7524篇
  1985年   8832篇
  1984年   8218篇
  1983年   7296篇
  1982年   6850篇
  1981年   6858篇
  1980年   6586篇
  1979年   6349篇
  1978年   6072篇
  1977年   7111篇
  1976年   9572篇
  1975年   5166篇
  1974年   4979篇
  1973年   4908篇
  1972年   4057篇
  1971年   3551篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
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   
62.
A novel monitoring method for plasma-charging damage is proposed. This method performs a quick and accurate evaluation using antenna PMOSFET. It was found that not only hot-carrier (HC) lifetime but transistor parameters such as initial gate current and substrate current were changed according to the degree of plasma-charging damage. However, the present work suggests that monitoring the shift of drain current after a few seconds of HC stress is a more accurate method to indicate plasma-charging damage. The monitoring method using the present test structure is demonstrated to be useful for realizing highly reliable devices  相似文献   
63.
Lubell  P. 《Spectrum, IEEE》1997,34(9):16-18
  相似文献   
64.
This study employed two perspectives to investigate media attention given women congressional candidates. The first perspective is that media attention may be explained by typical and normal media processes, such as focusing on incumbents. The second perspective considers a partisan explanation in which media attention is weighted more to Democratic candidates than Republican candidates. This study employs two established sources, Vanderbilt's Television News Index and Abstract and Information Access's National Newspaper Index , to examine the national media attention of Democratic and Republican women congressional candidates in 1990 and 1992. The investigation determined that media attention is related to whether the candidates are running for the Senate or House, incumbency, and state population. The results also reveal that party is a statistically significant factor associated with media attention. The investigation also determined that ethnic candidates tend to receive slightly less attention from the print media than nonethnic candidates.  相似文献   
65.
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   
66.
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   
67.
68.
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   
69.
A new commercially available diode model is described. This unified model is capable of simulating the widest range of diode technologies of any presently available. The emphasis of this paper is on describing the model's extensive features and flexibility in the different domains of operation and is of particular interest in power applications  相似文献   
70.
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