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   5863篇
  免费   171篇
  国内免费   18篇
电工技术   66篇
综合类   16篇
化学工业   899篇
金属工艺   86篇
机械仪表   115篇
建筑科学   247篇
矿业工程   42篇
能源动力   180篇
轻工业   568篇
水利工程   51篇
石油天然气   19篇
无线电   691篇
一般工业技术   805篇
冶金工业   1472篇
原子能技术   43篇
自动化技术   752篇
  2023年   20篇
  2022年   38篇
  2021年   76篇
  2020年   76篇
  2019年   72篇
  2018年   96篇
  2017年   107篇
  2016年   109篇
  2015年   91篇
  2014年   123篇
  2013年   341篇
  2012年   207篇
  2011年   259篇
  2010年   233篇
  2009年   232篇
  2008年   257篇
  2007年   254篇
  2006年   217篇
  2005年   160篇
  2004年   168篇
  2003年   169篇
  2002年   140篇
  2001年   112篇
  2000年   102篇
  1999年   126篇
  1998年   443篇
  1997年   256篇
  1996年   202篇
  1995年   122篇
  1994年   105篇
  1993年   115篇
  1992年   67篇
  1991年   60篇
  1990年   54篇
  1989年   56篇
  1988年   41篇
  1987年   57篇
  1986年   61篇
  1985年   67篇
  1984年   60篇
  1983年   44篇
  1982年   43篇
  1981年   42篇
  1980年   34篇
  1979年   24篇
  1978年   27篇
  1977年   49篇
  1976年   77篇
  1975年   18篇
  1973年   27篇
排序方式: 共有6052条查询结果,搜索用时 0 毫秒
991.
This study demonstrates palladium membranes can be electrolessly plated on aluminum oxide-modified porous Hastelloy with hydrazine using an EDTA-free bath. The plating bath temperature affected the membrane surface morphology, with the palladium grain size increasing with increasing temperature. A 7.5 μm thick membrane plating was obtained at room temperature. Helium leak testing confirmed that the membrane was free of defects. Hydrogen permeation test showed that the membrane had a hydrogen permeation flux of 3.3 × 10−1 mol m−2 s−1 at a temperature of 823 K and at a pressure difference of 100 kPa. There was no measurable interdiffusion between the membrane film and the porous Hastalloy substrate at 823 K. This room temperature membrane plating method provides several advantages such as very high selectivity, stability, favorable energy efficiency and simplicity.  相似文献   
992.
Teachers are in a very real sense the embodiment of leadership, providing direction, guidance, and feedback to their students in addition to acting as role models. Teachers may well thus benefit from developmental coaching that draws on theories of leadership. This study was both an experimental (randomly assigned conditions) and a quasi-experimental (pre–post) study. A randomized controlled design was used to explore the impact of coaching on goal attainment, mental health, workplace well-being, and resilience, and a quasi-experimental (pre–post) design was used to explore the impact of coaching on leadership styles. Forty-four high school teachers were randomly assigned to either coaching or a waitlist control group. The coaching used a cognitive–behavioral, solution-focused approach and was informed by theories of self-leadership and transformational leadership. Participants in the coaching group received multirater feedback on their leadership style and undertook 10 coaching sessions conducted by professional coaches over a 20-week period. Compared with randomly allocated controls, participation in coaching was associated with increased goal attainment, reduced stress, and enhanced workplace well-being and resilience. Pre–post analyses for the coaching group indicated that coaching enhanced self-reported achievement and humanistic–encouraging components of constructive leadership styles and reduced self-reported aggressive/defensive and passive/defensive leadership styles. Findings suggest that coaching, as a professional development methodology, has great potential to contribute to the development and well-being of society beyond the corporate and organizational settings with which leadership coaching and executive coaching are normally associated. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
993.
Reports an error in "Minding one’s emotions: Mindfulness training alters the neural expression of sadness" by Norman A. S. Farb, Adam K. Anderson, Helen Mayberg, Jim Bean, Deborah McKeon and Zindel V. Segal (Emotion, 2010[Feb], Vol 10[1], 25-33). The DOI printed in the article was incorrect. The correct DOI is presented in the erratum. (The following abstract of the original article appeared in record 2010-01983-008.) Recovery from emotional challenge and increased tolerance of negative affect are both hallmarks of mental health. Mindfulness training (MT) has been shown to facilitate these outcomes, yet little is known about its mechanisms of action. The present study employed functional MRI (fMRI) to compare neural reactivity to sadness provocation in participants completing 8 weeks of MT and wait-listed controls. Sadness resulted in widespread recruitment of regions associated with self-referential processes along the cortical midline. Despite equivalent self-reported sadness, MT participants demonstrated a distinct neural response, with greater right-lateralized recruitment, including visceral and somatosensory areas associated with body sensation. The greater somatic recruitment observed in the MT group during evoked sadness was associated with decreased depression scores. Restoring balance between affective and sensory neural networks—supporting conceptual and body based representations of emotion—could be one path through which mindfulness reduces vulnerability to dysphoric reactivity. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
994.
995.
996.
997.
998.
999.
1000.
Saline-sodic shale overburden associated with oil sand mining is a potential source of salt release to surface water and groundwater and can lead to salinization and/or sodification of reclamation covers. Weathering of shale overburden due to oxidation of sulphide minerals within the shale leads to sulphate (SO4 2?) production and increased salinity. The controls on the rates of weathering of a shale overburden dump in the oil sands region of northern Alberta were determined from soil chemistry sampling and in situ monitoring of pore gases (O2, CO2, CH4) in three shallow profiles (1.9–4.45 m deep) and one deep (25 m deep) profile under reclamation covers of varying thickness. Oxidation, defined by the depth over which O2 concentrations were depleted, reached depths of approximately 1.1 m under the reclamation soil covers over a 6 year period after dump placement. Calculations of SO4 2? production rates and weathering depths were consistent with numerical simulations of the diffusion and subsequent consumption of atmospheric O2 in the overburden. The rate of SO4 2? production during the 6 year weathering period estimated from direct measurements of solids chemistry ranged from 0.70 to 8.3 g m?2 day?1. The rates calculated from the oxygen diffusion models were within that same range, between 1.6 and 4.1 g m?2 day?1.  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