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   201314篇
  免费   2348篇
  国内免费   608篇
电工技术   3524篇
综合类   154篇
化学工业   29379篇
金属工艺   8070篇
机械仪表   6090篇
建筑科学   4878篇
矿业工程   1311篇
能源动力   5173篇
轻工业   17330篇
水利工程   2318篇
石油天然气   4046篇
武器工业   8篇
无线电   23160篇
一般工业技术   40305篇
冶金工业   37442篇
原子能技术   5101篇
自动化技术   15981篇
  2021年   1686篇
  2019年   1580篇
  2018年   2584篇
  2017年   2657篇
  2016年   2789篇
  2015年   1815篇
  2014年   3084篇
  2013年   8994篇
  2012年   5083篇
  2011年   7070篇
  2010年   5619篇
  2009年   6381篇
  2008年   6496篇
  2007年   6535篇
  2006年   5604篇
  2005年   5249篇
  2004年   5026篇
  2003年   4912篇
  2002年   4544篇
  2001年   4688篇
  2000年   4603篇
  1999年   4743篇
  1998年   11429篇
  1997年   8162篇
  1996年   6442篇
  1995年   4702篇
  1994年   4303篇
  1993年   4092篇
  1992年   3250篇
  1991年   3093篇
  1990年   2879篇
  1989年   2966篇
  1988年   2847篇
  1987年   2412篇
  1986年   2323篇
  1985年   2731篇
  1984年   2523篇
  1983年   2356篇
  1982年   2107篇
  1981年   2216篇
  1980年   2046篇
  1979年   2140篇
  1978年   2135篇
  1977年   2396篇
  1976年   3215篇
  1975年   1838篇
  1974年   1784篇
  1973年   1790篇
  1972年   1460篇
  1971年   1353篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
A method is developed, based on word-searching, which provides a rapid test for the statistical significance of DNA sequence similarities for use in databank searching. The method makes allowance for the lengths and dinucleotide compositions of the sequences being compared. A way is also described to calculate the power of the test, i.e. the probability of detecting a given similarity as being statistically significant. The effects on the power of the test of the scoring method, word length, sequence length, and sequence composition are examined. A novel scoring method is shown to be superior to the method currently used in most word-searching algorithms.  相似文献   
72.
73.
This article presents the development of a ceramic micro heat exchanger. Starting from its geometrical design, results obtained from a simplified simulation of the heat exchanger efficiency will be given. The alumina microcomponents were manufactured by a rapid prototyping process chain. Here, stereolithography was combined with a low‐pressure injection molding process for the rapid and precise manufacturing of ceramic components down to the micrometer range. A micro heat exchanger, joined from sintered components using a glass solder, was applied as a prototype and checked for its performance at a system pressure of 8 bar.  相似文献   
74.
There are four ecologically important river catchments that contain candidate Special Areas of Conservation (cSACs) under the Habitats Directive in the Lake District National Park located in the North of England. These are the rivers Ehen, Kent, Derwent and Eden. For each cSAC, there are defined ecological criteria that include water quality targets to protect the designated species. Stretches of the riverine cSACs in each catchment are failing to meet these and other water quality targets. The Environment Agency commissioned a study of each catchment to provide the underpinning scientific knowledge to allow it to deliver its statutory obligations under the Habitats Directive. SIMCAT river water quality models were produced and used to predict the water quality impacts resulting from a number of water quality planning scenarios aimed at achieving full compliance with the Habitats Directive and other national and EEC water quality targets. The results indicated that further controls on effluent discharges will allow the majority of targets to be met but other sources of pollution will also need to be controlled. The outcome of the study also recognised that water quality improvements alone will not necessarily produce the required improvement to the ecological interest features in each cSAC.  相似文献   
75.
76.
77.
78.
Hydroelectric generators of less than 20 kilowatts can be in remote areas served only by a single-phase line. For high efficiency and low cost, a three-phase induction generator should be used. This three-phase generator can operate with balanced voltages and currents when the ``phase-splitting' circuit uses two capacitors connetted to two different single-phase voltage sources.  相似文献   
79.
This paper presents results of reliability investigation of 20 V N-Drift MOS transistor in 0.13 μm CMOS technology. Due to high performances required for CMOS applications, adding high voltage devices becomes a big challenge to guarantee the reliability criteria. In this context, new reliability approaches are needed. Safe Operating Area are defined for switch, Vds limited and Vgs limited applications in order to improve circuit designs. For Vds limited applications, deep doping dose effects in drift area are investigated in correlation to lifetime evaluations based on device parameter shifts under hot carrier stressing. To further determine the amount and locations of hot carriers injections, accurate 2D technological and electrical simulations are performed and permit to select the best compromise between performance and reliability for N-Drift MOS transistor.  相似文献   
80.
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