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   690245篇
  免费   7346篇
  国内免费   1174篇
电工技术   12317篇
综合类   525篇
化学工业   109527篇
金属工艺   30542篇
机械仪表   22505篇
建筑科学   15192篇
矿业工程   6005篇
能源动力   16884篇
轻工业   51731篇
水利工程   9034篇
石油天然气   20029篇
武器工业   48篇
无线电   70233篇
一般工业技术   146771篇
冶金工业   112413篇
原子能技术   18895篇
自动化技术   56114篇
  2021年   6630篇
  2019年   6298篇
  2018年   11245篇
  2017年   11417篇
  2016年   11960篇
  2015年   7329篇
  2014年   12502篇
  2013年   31252篇
  2012年   19016篇
  2011年   25302篇
  2010年   20318篇
  2009年   22712篇
  2008年   23016篇
  2007年   22579篇
  2006年   19412篇
  2005年   17506篇
  2004年   16784篇
  2003年   16450篇
  2002年   15921篇
  2001年   15381篇
  2000年   14816篇
  1999年   14336篇
  1998年   32104篇
  1997年   23527篇
  1996年   18301篇
  1995年   14149篇
  1994年   12959篇
  1993年   12687篇
  1992年   9987篇
  1991年   9816篇
  1990年   9686篇
  1989年   9380篇
  1988年   9029篇
  1987年   8335篇
  1986年   8066篇
  1985年   9024篇
  1984年   8298篇
  1983年   8027篇
  1982年   7287篇
  1981年   7440篇
  1980年   7187篇
  1979年   7406篇
  1978年   7385篇
  1977年   8043篇
  1976年   9718篇
  1975年   6669篇
  1974年   6579篇
  1973年   6647篇
  1972年   5822篇
  1971年   5400篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
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   
52.
为了分析多水库系统中两座水库之间灌溉用水的分配问题,建立了基到动态规划的神经网络模型。为了研究从一座上游水库取水在下游两座之库之间进行水量分配的问题,提出了3个状态变量和4个决策变量的改进的动态规划算法。采用神经网络模型,用3个状态变量动态规划算法得出调度原则,就所研究的多水库系统实例来说,新的动态规划神经网络模型的性能很好,将该模型的性能与临时凑合的标准调度原则和以前推荐使用的约束动态规划神经网络模型进行了比较。  相似文献   
53.
54.
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   
55.
The interference issues related to ultrawideband (UWB) radio pose tight restrictions on the maximum data rate of UWB radio telecommunication systems. A possible solution is to reduce the required signal to interference ratio (SIR) that gives satisfactory performance to the UWB system. In this letter, we propose coded M-ary UWB radio communication systems. Two classes of convolutional codes, namely, low-rate superorthogonal codes and high-rate punctured codes are considered for this purpose. Simulation results on the bit error rate of the proposed system indicates that the system is capable to work in lower SIR's and therefore supports higher data transmission rates in a real interference environment compared to the previously proposed UWB communication systems.  相似文献   
56.
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   
57.
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   
58.
Learning in multiple model adaptive control switch   总被引:1,自引:0,他引:1  
Including a learning mechanism in SMMAC (switched, multiple-model adaptive control) avoids the need for a priori knowledge of the model set of the plant to control and leads to a significant performance improvement with respect to the sole inclusion of an adaptive control channel in combination with switched fixed local controllers.  相似文献   
59.
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   
60.
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   
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