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   3854篇
  免费   217篇
  国内免费   2篇
电工技术   59篇
综合类   13篇
化学工业   798篇
金属工艺   155篇
机械仪表   50篇
建筑科学   185篇
矿业工程   12篇
能源动力   77篇
轻工业   328篇
水利工程   21篇
石油天然气   1篇
无线电   322篇
一般工业技术   674篇
冶金工业   703篇
原子能技术   21篇
自动化技术   654篇
  2023年   62篇
  2022年   82篇
  2021年   109篇
  2020年   91篇
  2019年   101篇
  2018年   106篇
  2017年   109篇
  2016年   106篇
  2015年   105篇
  2014年   140篇
  2013年   185篇
  2012年   199篇
  2011年   218篇
  2010年   140篇
  2009年   138篇
  2008年   151篇
  2007年   147篇
  2006年   134篇
  2005年   110篇
  2004年   77篇
  2003年   74篇
  2002年   87篇
  2001年   65篇
  2000年   46篇
  1999年   54篇
  1998年   135篇
  1997年   90篇
  1996年   80篇
  1995年   54篇
  1994年   50篇
  1993年   48篇
  1992年   41篇
  1991年   21篇
  1990年   41篇
  1989年   33篇
  1988年   29篇
  1987年   26篇
  1986年   27篇
  1985年   35篇
  1984年   29篇
  1983年   27篇
  1982年   26篇
  1981年   21篇
  1980年   24篇
  1979年   27篇
  1978年   25篇
  1977年   25篇
  1976年   47篇
  1975年   20篇
  1974年   18篇
排序方式: 共有4073条查询结果,搜索用时 0 毫秒
21.
This study of 513 Dutch farmers tested a dynamic equilibrium model of resources (an extension of the conservation of resources theory; S. E. Hobfoll, 1989, 1998, 2001). With structural equation modeling, the advantages of a 3-wave longitudinal design were comprehensively used, such as addressing bidirectional causal effects and within-individual vs. between-individual change. This allowed for a careful analysis of the management function of resources in the stress process. Results showed that well-being had stronger within-person stability than finances. Increased levels of financial problems temporarily increased psychological distress but not self-reported illness. Conversely, farmers with higher stable baselines of psychological distress also had higher baselines of self-reported illness and experienced more negative changes in their financial situation. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
22.
23.
24.
Arnold Alderman 《电子设计技术》2006,13(12):173-174,176,178-181
政府机构正在与公用事业公司合作,减少由于低效率电源所导致的功耗增长。在今天的电力供应市场上,效率是一个热门话题。增加效率曾是一个被忽视的角色,但现在却是一个全球性的重要动向。这种转变有两个主要原因。  相似文献   
25.
OBJECTIVE: To evaluate whether push enteroscopy of the small bowel (PES), undertaken after extensive previous investigations in suspected intestinal bleeding from an uncertain site, chronic diarrhoea or lymphoma of the small intestine, contributes to the diagnosis, and to ascertain the results of PES and its clinical significance. PATIENTS AND METHODS: 56 consecutive patients (29 men, 27 women; mean age 63 years) were investigated prospectively. The main indications for PES were the search for the source of intestinal bleeding in 79% of patients (group A), chronic diarrhoea or tropical sprue in 16% (group B) and search for tumour of lymphoma in 5% (group C). PES was always performed in fasting patients under sedation/analgesia using a video PES, which contrary to catheter enteroscopy provides a channel for intervention. RESULTS: In group A 27% of patients were found to have lesions, in particular angiodysplasias, or (in once case) leiomyoma. Half of these patients were successfully treated endoscopically without later surgical intervention being required (mean follow-up of six months). In the other half operation became necessary, either because the disease itself indicated it or the bleeding persisted, the source being in the more distant small intestine and thus not accessible to endoscopic intervention: only 50% of the length of the small intestine proved to be within reach of the instrument. No abnormalities were discovered in patients of groups B and C. CONCLUSION: In cases of gastrointestinal bleeding from an uncertain source PES should be performed first, because in many cases it may obviate surgical intervention. But PES seems to contribute little of diagnostic value in other indications.  相似文献   
26.
Empirical research pertaining to cardiopulmonary resuscitation (CPR), clinician behaviors related to do-not-resuscitate (DNR) orders and substituted judgment suggests potential contributions to medical ethics. Research quantifying the likelihood of surviving CPR points to the need for further philosophical analysis of the limitations of the patient autonomy in decision making, the nature and definition of medical futility, and the relationship between futility and professional standards. Research on DNR orders has identified barriers to the goal of patient involvement in these life and death discussions. The initial data on surrogate decision making also points to the need for a reexamination of the moral basis for substituted judgment, the moral authority of proxy decision making and the second-order status of the best interests standard. These examples of empirical research suggest that an interplay between empirical research, ethical analysis and policy development may represent a new form of interdisciplinary scholarship to improve clinical medicine.  相似文献   
27.
An efficient sampling scheme called Updated Latin Hypercube Sampling is presented. The proposed method is an improved variant of Latin Hypercube Sampling. It uses specially modified tables of independent random permutations of rank numbers which form the strategy of generating input samples for a simulation procedure. The method is presented in order to obtain these specially modified tables. The aim of this paper is to compare estimates of certain widely used statistical parameters obtained by Updated Latin Hypercube Sampling, Latin Hypercube Sampling and Simple Random Sampling. It is shown that Updated Latin Hypercube Sampling usually results in a substantial decrease of the variance in the estimates of commonly used statistical parameters and that the bias is quite small for a moderate number of simulations. This sampling technique seems to be generally very useful, efficient and superior to other methods especially in the case of statistical, sensitivity and probability analyses of complex analytical models with random input variables.  相似文献   
28.
29.
The use of computer models offers a general and flexible framework that can help to deal with some of the complexities and difficulties associated with the development of water management plans as prescribed by the Water Framework Directive. However, despite the advantages modelling presents, the integration of information derived from models into policy is far away from being trivial or the norm. Part of the difficulties of this integration is rooted in the lack of confidence policy makers have on the incorporation of modelling information into policy formulation. In this paper we examine the reasons for this apparent lack of confidence and explore how some tools, presently in use, address this problem. We conclude that public confidence in models is highly dependent on the way uncertainties are addressed and suggest possible directions of action to improve the current situation. Four real case studies illustrate how computer models have been used in The Netherlands for carrying out management plans at regional and national scale. We suggest that the solution to integrate modelling information into policy formulation lies on both the modelling and the policy-making communities.  相似文献   
30.
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