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   850篇
  免费   28篇
  国内免费   36篇
测绘学   224篇
大气科学   41篇
地球物理   49篇
地质学   125篇
海洋学   60篇
天文学   8篇
综合类   73篇
自然地理   334篇
  2024年   4篇
  2023年   12篇
  2022年   40篇
  2021年   42篇
  2020年   43篇
  2019年   32篇
  2018年   32篇
  2017年   42篇
  2016年   41篇
  2015年   27篇
  2014年   46篇
  2013年   63篇
  2012年   32篇
  2011年   29篇
  2010年   30篇
  2009年   19篇
  2008年   43篇
  2007年   40篇
  2006年   35篇
  2005年   44篇
  2004年   35篇
  2003年   37篇
  2002年   21篇
  2001年   15篇
  2000年   30篇
  1999年   18篇
  1998年   17篇
  1997年   7篇
  1996年   9篇
  1995年   6篇
  1994年   7篇
  1993年   4篇
  1992年   3篇
  1991年   2篇
  1990年   1篇
  1989年   2篇
  1988年   1篇
  1986年   1篇
  1983年   1篇
  1979年   1篇
排序方式: 共有914条查询结果,搜索用时 15 毫秒
31.
Participatory research in environmental and natural resources-related fields is premised on many of the same notions that underlie participatory processes in decision making. This study examines one instance of participatory research to assess the extent to which the documented benefits of participatory decision-making hold up in the context of research. A survey of Chilean shell-fishers engaged in research with marine biologists assesses the relationships between four variables: fishers’ participation in research, fishers’ opinions of biologists, fishers’ trust in biologists, and fishers’ acquisition of knowledge from biologists. Results illuminate the multidimensionality of these variables and suggest that complex interrelationships between them make the benefits of participatory research more nuanced than those reported for participatory decision-making. For instance, participatory research may provide low benefits when participatory research outcomes differ little from those produced solely by scientists. In addition, high-cost scenarios may result when outcomes of participatory research are inferior to those produced solely by scientists. A third downside may result when participation leads participants to increase their deference to scientific knowledge, thereby defeating the corroborative purpose of their participation. A fourth effect may occur when increased trust by in scientists results from participation, decreasing participants’ perceived need to take part in research.  相似文献   
32.
粤港澳大湾区知识网络空间结构演化特征与影响机制   总被引:2,自引:0,他引:2  
高爽  王少剑  王泽宍 《热带地理》2019,39(5):678-688
以2000—2018年国内外期刊数据库合作论文数据为基础,借助社会网络分析和空间结构指数法分析了粤港澳大湾区知识空间网络结构演化特征与影响因素,结果发现:1)知识网络格局由广州的“一家独大”逐渐演变为广州、深圳、香港“齐头并进”的发展态势。香港虽然处于知识网络的核心位置,但受行政壁垒的影响,主要与广州、深圳高等级的城市建立紧密的知识合作联系。2)粤港澳大湾区知识联系网络呈现“核心—边缘”结构,西部地区知识联系远低于东部地区,虽然研究期内湾区的知识网络的极化特征得到一定的缓解,但不均衡性仍然显著。3)湾区知识活动主体的自身需求是促进城市间知识合作的内在驱动力,知识环境和知识联系通道是区域知识合作网络外在推动力,在内生作用和外生作用的共同影响下,知识合作产出得以实现,粤港澳大湾区知识网络得以发展。  相似文献   
33.
运用专家系统的知识获取和推理机设计原理与方法,探讨了ALCGEIS系统的基本结构、知识分级、知识获取过程和实现程序,推理机的基本原理和控制策略及其程序实现的算法,以及推理知识的搜索策略;论述了 AIEGEIS推理规则的设计方法及其推理算法。  相似文献   
34.
Understanding how science, technology and innovation can best help to accelerate progress in achieving sustainable development remains a grand challenge for researchers and practitioners. In the context of the global consultation process for preparing a post-2015 Sustainable Development Agenda, various science-based actor networks have emerged, aiming to translate research into political decision-making and to inform transformations towards sustainability. Over the last years, these networks seem to have taken an ever-growing role in structuring the science-policy interface in global sustainability governance. The question arises, however, how they understand and organize ‘scientific knowledge integration’ in sustainability politics.This study offers a structured comparison of twelve global science-based actor networks engaged in the implementation of the Sustainable Development Goals. It shows that these networks use two types of strategies to foster scientific knowledge integration in sustainability governance. A new framework emerges, in which each strategy corresponds to two main approaches of scientific knowledge integration: The entrepreneurial strategy generally seeks to advance advice-oriented and solution-oriented knowledge processes, while assessment-oriented and learning-oriented processes in scientific knowledge integration are mainly promoted through a mediating strategy.  相似文献   
35.
Knowledge representation structure and reasoning processes are very important issues in the knowledge-based approach of integrating multiple spatial data sets for resource exploration. An object-oriented knowledge representation structure and corresponding reasoning processes are formulated and tested in this research on the knowledge-based approach of integrating spatial exploration data. The map-based prototype expert system developed in this study has self-contained knowledge representation structure and inference mechanisms. It is important to distinguish between lack of information and information providing negative evidence for a map-based system because the spatial distribution of data sets are uneven in most cases. Error and uncertainty estimation is also an important component of any production expert system. The uncertainty propagation mechanisms developed here work well for this type of integrated exploration problem. Evidential bellef function theory provides a natural theoretical basis for representing and integrating spatially uneven geophysical and geological information. The prototype system is tested using real mineral exploration data sets from the Snow Lake area, northern Manitoba, Canada. The test results outline the favorable exploration areas successfully and show the effectiveness of the knowledge representation structure and inference mechanisms for the knowledge-based approach.  相似文献   
36.
This work reports on a method using fuzzy membership functions to construct an aggregated interaction matrix in which the summation of variables is scaled according to the way rainfall and soil variables affect water availability to plants and hence influence rangeland productivity. Aggregation of the variables gives a comprehensive value which can be used to predict production. The model increases the predicability of production to 81% compared to models using rainfall alone and a multiplicative parametric one which give predictibilities of 61 and 76% respectively. The results showed that (1) the importance of rainfall in determining production was most important at lower rainfalls i.e. <350 mm; (2) soil texture and particularly slope were important through out the rainfall range (149–700 mm) investigated; and (3) soil depth was only important at the higher >350 mm rainfalls. The aggregated interaction matrix gives a measure of land productive capability.  相似文献   
37.
38.
Pastoral production around artificial watering points in semi-arid environments affects the density and composition of plant communities. In the Kalahari desert of southwestern Africa, bush encroachment is often regarded as the major form of land degradation resulting from pastoral production around watering points. We investigated the OvaHerero pastoralists’ perceptions of the extent of vegetation change since the establishment of artificial watering points in the northern Kalahari desert of Namibia, and related this to ecological data on vegetation change. We determined the utility of woody vegetation to pastoralists’ livelihoods in terms of provision of construction material, fuel wood and browse. We quantified local knowledge of cattle browse consumption and correlated this with field data. We also assessed the purposes for which major livestock types were used. Our results showed that: (1) pastoral knowledge of bush encroachment and browse consumption was consistent with concurrently collected field data, (2) the current level of bush encroachment was perceived to be beneficial for pastoral production, and (3) cattle played an important role in the production of milk and milk by-products for domestic use, and served as a source of cash income, while sheep and goats were primarily kept for meat consumption. This result contrasts with historical studies that mainly portray cattle as a symbol of social status among OvaHerero pastoralists.  相似文献   
39.
Elana Wilson 《Area》2007,39(3):323-330
In this article, I trace the efforts of a development team working to promote a Canadian approach to natural resources management in the Russian North. These development workers used two communication strategies related to time and history to render Canadian knowledge mobile and applicable to a new location: (1) imagining today's Russian North as equivalent to the Canadian northern past and (2) reframing and idealising the Canadian past and present to make the governance export less discursively 'messy' for an outside audience. The relative failure of these communicative strategies points to the need for richer dialogue in efforts to move knowledge cross-culturally.  相似文献   
40.
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