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   17568篇
  免费   2098篇
  国内免费   1422篇
电工技术   1932篇
技术理论   2篇
综合类   1523篇
化学工业   1301篇
金属工艺   395篇
机械仪表   897篇
建筑科学   1535篇
矿业工程   665篇
能源动力   381篇
轻工业   784篇
水利工程   656篇
石油天然气   665篇
武器工业   107篇
无线电   1874篇
一般工业技术   1112篇
冶金工业   726篇
原子能技术   48篇
自动化技术   6485篇
  2024年   95篇
  2023年   250篇
  2022年   523篇
  2021年   527篇
  2020年   593篇
  2019年   502篇
  2018年   482篇
  2017年   583篇
  2016年   644篇
  2015年   764篇
  2014年   1312篇
  2013年   1201篇
  2012年   1533篇
  2011年   1621篇
  2010年   1245篇
  2009年   1192篇
  2008年   1165篇
  2007年   1263篇
  2006年   1020篇
  2005年   846篇
  2004年   705篇
  2003年   589篇
  2002年   526篇
  2001年   400篇
  2000年   295篇
  1999年   223篇
  1998年   151篇
  1997年   135篇
  1996年   128篇
  1995年   91篇
  1994年   82篇
  1993年   62篇
  1992年   41篇
  1991年   32篇
  1990年   23篇
  1989年   23篇
  1988年   17篇
  1987年   12篇
  1986年   10篇
  1985年   23篇
  1984年   13篇
  1983年   13篇
  1982年   13篇
  1981年   10篇
  1980年   9篇
  1979年   7篇
  1965年   13篇
  1963年   9篇
  1955年   11篇
  1954年   5篇
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
51.
调节阀的闪蒸和气蚀   总被引:1,自引:0,他引:1  
针对调节阀的闪蒸和气蚀问题,介绍了调节阀在选型和使用中的要点。  相似文献   
52.
The aim of this study was to bring to the surface the strategic use of imitative processes in the context of a 2-route model: (a) direct imitation, used in reproducing new, meaningless actions, and (b) imitation based on stored semantic knowledge of familiar meaningful actions. Three experiments were carried out with healthy participants who reproduced meaningful and meaningless actions within an established time limit. The study investigated 3 factors that could potentially affect the selection of processes used for imitation: (a) the composition of the experimental list (blocked or mixed presentation), (b) the presence-absence of instructions (Experiments 1 and 2), and (c) the relative proportions of the stimuli (Experiment 3). Overall, the results suggest that each of these factors influences the selection of imitative strategies in healthy individuals with temporarily reduced capacities, as happens in the case of brain-damaged patients. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
53.
改进的BP神经网络在大坝安全监控中的应用   总被引:7,自引:5,他引:2  
针对经典BP神经网络运行中存在的缺陷,提出了改进的BP神经网络,不仅解决了经典BP网络易陷入局部最小的弊端,而且应用的0.618分割选取法能使网络快速找到较优隐含层节点数,初始权值的自相关修正进一步提高了网络的稳定性。实际应用证明,改进的BP神经网络有效提高了网络质量,适合大型网络的构建与训练。  相似文献   
54.
The cumulative survival of Japanese hemodialysis patients is more than 2.5 times better than that of dialysis patients in the United States (U.S.). The difference is particularly pronounced in older patients, being 4 times better in patients over the age of 50 years. The mortality in U.S. patients has increased from 10 to 25% over the last three decades, but has remained stable at around 10% in Japan.
There is no obvious difference in patient selection. The Japanese accept almost as high a proportion of diabetic patients as does the United States, and the mean age of incident patients is higher in Japan.
Renal transplantation, virtually absent in Japan, should increase mortality in U.S. dialysis patients by removing patients with the highest probability of survival, but even if one adds surviving transplant patients and studies prevalent populations, the survival rate is much better in Japan. Genetic factors are unlikely to explain differences in mortality, as older Americans live much longer than older Japanese.
We speculate that the difference lies in the practice of dialysis. Patients in the United States are generally treated by much faster and shorter dialysis than in Japan. This puts a severe burden on the cardiovascular system of older patients, leading to the poorer survival rate. Japanese physicians also appear to be better trained in dialysis and to spend more time with their patients. The nursing shortage in the United States may also contribute to the increased mortality. Whatever the explanations, the U.S. dialysis community must work to equal and, hopefully, surpass the now superior survival of Japanese dialysis patients.  相似文献   
55.
Two experiments examined the disruption of feature-based selection in triple-conjunction search at multiple target transfers. In Experiment 1, after 10 training sessions, a new target possessing previous distractor features was introduced. This produced disruption in RT and fixation number, but no disruption in feature-based selection. Specifically, there was a tendency to fixate objects sharing the target's contrast polarity and shape and this did not change even upon transfer to the new target. In Experiment 2, 30 training sessions were provided with three target transfers. At the first transfer, the results replicated Experiment 1. Subsequent transfers did not produce disruption on any measure. These findings are discussed in terms of strength theory, Guided Search, rule-based approaches to perceptual learning, and the area activation model. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
56.
Gene expression microarray is a rapidly maturing technology that provides the opportunity to assay the expression levels of thousands or tens of thousands of genes in a single experiment. We present a new heuristic to select relevant gene subsets in order to further use them for the classification task. Our method is based on the statistical significance of adding a gene from a ranked-list to the final subset. The efficiency and effectiveness of our technique is demonstrated through extensive comparisons with other representative heuristics. Our approach shows an excellent performance, not only at identifying relevant genes, but also with respect to the computational cost.  相似文献   
57.
周玉莲 《大氮肥》1995,18(3):218-220
介绍了美国C.F布朗公司大型合成氨装置根据操作条件和介质腐蚀程度不同,如何选择管道和设备材料,并对其用材进行逐一剖析。  相似文献   
58.
The problem addressed in this paper is the template selection and update in biometrics based on clustering. Template selection is a reliable method to reduce the number of templates used in a biometric system to account for variations observed in a person's biometric data. An efficient method based on clustering with automatic selection of the number of clusters is proposed in this work for finding subgroups of similar templates which are used for prototype selection.Experimental results confirm the advantage of the new method and the importance of adopting a procedure to perform template selection.  相似文献   
59.
. A knowledge-based expert system was developed to aid in the selection of the type of dam. The dam type selector expert system (DTSA ES) was designed to determine the type of dam on the alluvium foundations. Detailed expert knowledge is required to estimate the type of dam and to develop an expert system. The DTSA ES utilizes rules of thumb used by an expert for determining the selection of the type of dam. The DTSA ES was developed using a shell program. The expert system was tested on several dam sites in order to validate the decision obtained. The use of this expert system, containing knowledge about the selection of dam type, can be helpful to students, potential owners or contractors in selecting dam types. The current prototype always needs additional parameters for more detailed analyses of new developments. However, the current DTSA ES is designed to include existing information about dam types.  相似文献   
60.
Decision routines unburden the cognitive capacity of the decision maker. In changing environments, however, routines may become maladaptive. In 2 experiments with a hypothetical stock market game (n = 241), the authors tested whether decision routines tend to persist at the level of decision strategies rather than at the level of options in strategy selection. The payoff structure of the task was changed after 80 decision trials, rendering a new strategy optimal with respect to expected payoff. Whereas most participants detected the appropriate strategy at the beginning of the task, they tended to retain it even when it was no longer optimal. A hint about a possible change had only a small influence on this maladaptive routine; a monetary incentive had none. Switching to a similar but not identical task relaxed the routine, but not much. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  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