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   780177篇
  免费   15666篇
  国内免费   5553篇
电工技术   18341篇
技术理论   2篇
综合类   6362篇
化学工业   122326篇
金属工艺   33589篇
机械仪表   27372篇
建筑科学   22077篇
矿业工程   7192篇
能源动力   20333篇
轻工业   61412篇
水利工程   10398篇
石油天然气   21812篇
武器工业   727篇
无线电   85844篇
一般工业技术   153443篇
冶金工业   122886篇
原子能技术   18429篇
自动化技术   68851篇
  2022年   7047篇
  2021年   10168篇
  2020年   7355篇
  2019年   8388篇
  2018年   13189篇
  2017年   13794篇
  2016年   14079篇
  2015年   10682篇
  2014年   16755篇
  2013年   37207篇
  2012年   25033篇
  2011年   32099篇
  2010年   26067篇
  2009年   28372篇
  2008年   28537篇
  2007年   27937篇
  2006年   24763篇
  2005年   22018篇
  2004年   19797篇
  2003年   18884篇
  2002年   18327篇
  2001年   17622篇
  2000年   16847篇
  1999年   16680篇
  1998年   36864篇
  1997年   26672篇
  1996年   20918篇
  1995年   16065篇
  1994年   14302篇
  1993年   13974篇
  1992年   10776篇
  1991年   10340篇
  1990年   10029篇
  1989年   9688篇
  1988年   9378篇
  1987年   8353篇
  1986年   8162篇
  1985年   9214篇
  1984年   8327篇
  1983年   7989篇
  1982年   7188篇
  1981年   7242篇
  1980年   7024篇
  1979年   7119篇
  1978年   6995篇
  1977年   7686篇
  1976年   9488篇
  1975年   6273篇
  1974年   6016篇
  1973年   6149篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
Mössbauer effect measurements and physicochemical analysis demonstrate that annealing of amorphous Fe–P–Mn alloys leads to the formation of a nanocrystalline structure.  相似文献   
42.
This paper considers several aspects of the sequential prediction problem for unbounded, nonstationary processes under pth power loss /spl lscr//sub p/(u,v)=|u-v|/sup p/, 1相似文献   
43.
44.
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   
45.
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   
46.
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   
47.
Exposure to ammonia (NH3) increases the dark current (DC) in nanocrystalline silicon. Light soaking (LS) for short periods also enhances the dark current, which remains at a high value for a long time. Pumping alone is unable to restore the initial annealed state, but annealing brings it back. The final state obtained by LS and NH3 exposure depends on the order in which they are performed. Evaporated selenium (Se) deposited on nanocrystalline silicon decreases the DC. These effects cannot be explained entirely by the presence of a-Si : H alone, in our sample. DC and photoluminescence (PL) measurements indicate the presence of two types of center in our sample, which behave differently when exposed to NH3.  相似文献   
48.
The effects of parameter uncertainty on optimal policy have been a matter of interest for academics, and even for some policymakers, for a long time. Two lines of literature have developed analytical results on this matter. The first line uses static models and the second dynamic models. In this dynamic line most of the results are confined to models with a single state and a single control variable. In this paper we want to encourage the analysis of more general dynamic cases. To do so, the results in the dynamic line are extended from one-state and one-control finite horizon models to models with a pair of control variables. We then discuss some of the hurdles which must be surmounted for the results to be made more general and suggests some lines for further research. JEL classification: C61; E61  相似文献   
49.
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   
50.
The magneto-optical Kerr effect for red (628 nm) and green (532 nm) light is used to study magnetization processes in 2D magnonic crystals obtained by etching pits with the diameter D ≈ 32 μm to a depth of t ≤ 2 μm in a 16.1-μm-thick film of yttrium iron garnet (YIG). Hysteresis loops obtained in the case of the inplane crystal magnetization at 628 nm are characterized by lower saturation fields H s and higher remanent magnetizations than those obtained at 532 nm, a result that is attributed to different absorption coefficients of the YIG film at these wavelengths. This difference between the magnetization curves reflects the fact that the magnonic-crystal surface probed with the green light makes a greater contribution to the magneto-optical Kerr effect. Therefore, the green light is more sensitive to the demagnetizing fields, which govern magnetization processes in the magnonic crystals.  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