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   3421篇
  免费   27篇
  国内免费   27篇
系统科学   76篇
丛书文集   2篇
教育与普及   11篇
理论与方法论   56篇
现状及发展   798篇
研究方法   405篇
综合类   1974篇
自然研究   153篇
  2021年   16篇
  2020年   15篇
  2019年   13篇
  2018年   47篇
  2017年   37篇
  2016年   56篇
  2015年   49篇
  2014年   39篇
  2013年   64篇
  2012年   229篇
  2011年   408篇
  2010年   94篇
  2009年   17篇
  2008年   246篇
  2007年   256篇
  2006年   244篇
  2005年   268篇
  2004年   274篇
  2003年   213篇
  2002年   263篇
  2001年   16篇
  2000年   28篇
  1999年   22篇
  1997年   11篇
  1996年   13篇
  1995年   11篇
  1993年   15篇
  1992年   17篇
  1989年   10篇
  1985年   9篇
  1984年   11篇
  1983年   12篇
  1982年   20篇
  1981年   21篇
  1979年   35篇
  1978年   26篇
  1977年   24篇
  1976年   19篇
  1975年   11篇
  1974年   17篇
  1973年   27篇
  1972年   14篇
  1971年   18篇
  1970年   27篇
  1969年   22篇
  1968年   22篇
  1967年   19篇
  1966年   13篇
  1965年   10篇
  1964年   10篇
排序方式: 共有3475条查询结果,搜索用时 9 毫秒
1.

This article presents a community learning model formulated by Engineers Without Borders Colombia with the aim of providing communities with tools to create sustainable productive solutions which have relevancy for members and for potential customers. The goal of this formulation is to promote learning processes that are guided by decisions made by community members to propose sustainable and replicable initiatives. The model applicability is evidenced through a case study devoted to strengthening community-led green businesses in the Guavio Province, Colombia by collecting lessons and conclusions. Ultimately, this collection will prove useful in replicating the learning model in other similar rural communities.

  相似文献   
2.
国际空间站和欧洲核子中心的大型强子对撞机 (LHC)计划目前都面临资金上的窘境 ;……除了对项目 (尤其是耗资巨大的项目 )预算的科学化 ,管理的科学化在其中尤显重要  相似文献   
3.
Duhem’s concept of ‘good sense’ is central to his philosophy of science, given that it is what allows scientists to decide between competing theories. Scientists must use good sense and have intellectual and moral virtues in order to be neutral arbiters of scientific theories, especially when choosing between empirically adequate theories. I discuss the parallels in Duhem’s views to those of virtue epistemologists, who understand justified belief as that arrived at by a cognitive agent with intellectual and moral virtues, showing how consideration of Duhem as a virtue epistemologist offers insights into his views, as well as providing possible answers to some puzzles about virtue epistemology. The extent to which Duhem holds that the intellectual and moral virtues of the scientist determine scientific knowledge has not been generally noticed.  相似文献   
4.
Linear models are invariant under non-singular, scale-preserving linear transformations, whereas mean square forecast errors (MSFEs) are not. Different rankings may result across models or methods from choosing alternative yet isomorphic representations of a process. One approach can dominate others for comparisons in levels, yet lose to another for differences, to a second for cointegrating vectors and to a third for combinations of variables. The potential for switches in ranking is related to criticisms of the inadequacy of MSFE against encompassing criteria, which are invariant under linear transforms and entail MSFE dominance. An invariant evaluation criterion which avoids misleading outcomes is examined in a Monte Carlo study of forecasting methods.  相似文献   
5.
We identified three distinct mutations and six mutant alleles in GDAP1 in three families with axonal Charcot-Marie-Tooth (CMT) neuropathy and vocal cord paresis, which were previously linked to the CMT4A locus on chromosome 8q21.1. These results establish the molecular etiology of CMT4A (MIM 214400) and suggest that it may be associated with both axonal and demyelinating phenotypes.  相似文献   
6.
Vermillion has been shown to be useful in preserving human bones from 5000 years ago. Remarkably well-preserved human bones have been found in the dolmenic burial La Velilla in Osorno (Palencia, Spain), carefully covered by pulverized cinnabar (vermillion) which ensured their preservation even in non-favorable climatic conditions. We believe the red powder was deliberately deposited for preservative use because no cinnabar mine is to be found within 160 km, because of the large amount (hundreds of kilograms) used, and because its composition, red mercuric sulphide, is similar to that of preparations used in technical embalming. This finding pushes back the data of the use of mercury ore for preservation by four millennia in South America, and by at least one millennium in the Old World. Chemical and thermal analyses of vermillion in La Velilla have demonstrated its great purity and shown that the cinnabar was pulverized and washed (but not heated), producing a bright red-orange tone.  相似文献   
7.
美东地区的罗德河流域遭受着严重的酸沉降侵蚀.在酸性条件下,铝从土壤中大量溶解并迁移到水环境中.地表水中升高的铝浓度对鱼类产生毒害,监测地表水和土壤水中的铝形态及浓度变化已成为问题的关键.本文报导了用化学平衡模式计算法分析美东地区罗德河流域地下水中的铝形态分布,获得了有价值的结论  相似文献   
8.
9.
10.
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