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   709941篇
  免费   9380篇
  国内免费   2110篇
电工技术   13201篇
综合类   834篇
化学工业   105543篇
金属工艺   27038篇
机械仪表   20948篇
建筑科学   17279篇
矿业工程   3097篇
能源动力   19147篇
轻工业   61731篇
水利工程   7027篇
石油天然气   12009篇
武器工业   100篇
无线电   83745篇
一般工业技术   136101篇
冶金工业   138239篇
原子能技术   14065篇
自动化技术   61327篇
  2021年   6239篇
  2020年   4573篇
  2019年   5950篇
  2018年   10065篇
  2017年   9928篇
  2016年   10400篇
  2015年   7157篇
  2014年   11907篇
  2013年   32374篇
  2012年   18905篇
  2011年   26103篇
  2010年   20566篇
  2009年   23062篇
  2008年   23950篇
  2007年   23561篇
  2006年   20781篇
  2005年   19040篇
  2004年   18313篇
  2003年   18034篇
  2002年   17136篇
  2001年   17095篇
  2000年   16105篇
  1999年   16919篇
  1998年   42854篇
  1997年   30151篇
  1996年   23222篇
  1995年   17560篇
  1994年   15369篇
  1993年   15072篇
  1992年   11152篇
  1991年   10394篇
  1990年   10135篇
  1989年   9734篇
  1988年   9127篇
  1987年   8120篇
  1986年   7987篇
  1985年   8986篇
  1984年   8434篇
  1983年   7507篇
  1982年   7091篇
  1981年   7234篇
  1980年   6829篇
  1979年   6665篇
  1978年   6333篇
  1977年   7616篇
  1976年   9780篇
  1975年   5611篇
  1974年   5348篇
  1973年   5484篇
  1972年   4429篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
A series of small–capacity units has recently been constructed in regions of oil field development and crude oil and gas condensate production to satisfy the requirements for such petroleum products as naphtha, diesel fuel, kerosene, and boiler fuel and to reduce costs for delivery of these products. There are almost no data in the technical literature, particularly in periodicals, on the construction and operation of small–capacity units. We attempt to generalize the experience of Orgeneftekhimzavody Trust in this area. We hope that this experience will be useful to specialists in the development and management of small–capacity plants.  相似文献   
52.
伊朗卡尔黑多目标水利枢纽,首台机组于2002年9月投运。介绍了工程历史,并从导流系统遂洪道、渗漏控制和惟幕灌浆等方面介绍了工程的技术要求。  相似文献   
53.
This study examined reciprocal relationships between collective efficacy and team performance over a season of competition in women's intercollegiate ice hockey within weekends where the opponent was constant for 2 games. Collective efficacy beliefs within 12 teams were assessed prior to both games for at least 7 weekends. Team performance indexes produced an overall measure of performance for each game. The average influence of Saturday collective efficacy on Saturday performance was moderate and positive after controlling for Friday performance. The average influence of Friday performance on Saturday collective efficacy was small and positive after removing the influence of Friday collective efficacy from Friday performance. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
54.
The authors examined heterogeneity in symptom trajectories among youths following psychiatric crises as well as the psychosocial correlates and placement outcomes associated with identified trajectories. Using semiparametric mixture modeling with 156 youths approved for psychiatric hospitalization, the authors identified 5 trajectories based on symptoms over the 16 months following crisis: high improved, high unimproved, borderline improved, borderline unimproved, and subclinical. Membership in unimproved symptom groups was associated with less suicidality, younger age, more youth hopelessness, and more caregiver empowerment. Improved symptom group membership predicted long-term decreases in days in out-of-home placements. More important, and in contrast with general impressions from the existing literature, findings suggest that a substantive proportion of youths with serious emotional disturbance sustain high levels of symptomatology following intensive mental health services. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
55.
56.
A method of measuring and identifying the static parameters of a bipolar transistor is considered. The characteristic of the transistor, from which the parameters of the model are determined, is chosen depending on what group the calculated parameters belong to. The characteristics are measured in such a way that the equations of the model describing them can be reduced to the simplest form.  相似文献   
57.
58.
Advances in the fabrication of solid-solution single crystal relaxor ferroelectrics have made it possible to produce highly efficient piezoelectric crystals, and have attracted renewed interest in the use of these crystals for a new generation of piezoelectric transducers, actuators and sensors. Of particular interest is their incorporation into micro-electromechanical systems (MEMS). In this paper we report on the laser-induced wet chemical etching of lead zinc niobate-lead titanate (PZN-PT) in hydrochloric acid (HCl). Argon-ion laser radiation at power levels up to 4 W is focused to a spot diameter of about 15μm and results in the chemical etching of grooves at patterning speeds up to 5μm/sec. Crystal ion slicing, an ion-implant-based film separation technique, is used in combination with laser etching to form 5 to 10μm-thick patterned and freestanding films for incorporation into micro-electromechanical devices.  相似文献   
59.
Non‐isothermal processing of lignocellulosic materials in aqueous media (autohydrolysis reaction) under mild conditions leads to solutions containing valuable chemicals (oligosaccharides, sugars and acetic acid) and other, undesired, compounds (belonging to the extractive and acid‐soluble lignin fractions) which have to be removed in further purification treatments. Liquors obtained by non‐isothermal autohydrolysis of Eucalyptus globulus wood and corncobs under a variety of operational conditions were extracted with ethyl acetate in order to remove non‐saccharide components, and the suitability of the fraction dissolved in the organic phase was assayed for possible utilisation as an antioxidant. The yield and antioxidant activity of ethyl acetate extracts (measured by the α,α‐diphenyl‐β‐picrylhydrazyl (DPPH) radical scavenging capacity) showed a strong dependence on the autohydrolysis conditions. The antioxidant activity of extracts obtained under selected operational conditions compared well with synthetic antioxidants. © 2003 Society of Chemical Industry  相似文献   
60.
Si3N4 ceramic was jointed to itself using a filler alloy of Cu76.5Pd8.5Ti15, and the mechanical properties of the jointwere measured and analyzed. By using a filler alloy of Cu76.5Pd8.5Ti15, the SisN4/SisN4 joints were obtained bybrazing at 1373~1473 K f  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