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   217篇
  免费   29篇
  国内免费   27篇
  2024年   1篇
  2023年   10篇
  2022年   7篇
  2021年   14篇
  2020年   9篇
  2019年   12篇
  2018年   17篇
  2017年   14篇
  2016年   16篇
  2015年   12篇
  2014年   8篇
  2013年   25篇
  2012年   8篇
  2011年   8篇
  2010年   8篇
  2009年   12篇
  2008年   11篇
  2007年   14篇
  2006年   5篇
  2005年   10篇
  2004年   7篇
  2003年   7篇
  2002年   4篇
  2001年   3篇
  2000年   2篇
  1999年   4篇
  1998年   1篇
  1997年   2篇
  1996年   5篇
  1995年   1篇
  1994年   1篇
  1992年   2篇
  1990年   2篇
  1989年   1篇
  1988年   2篇
  1987年   2篇
  1986年   2篇
  1984年   2篇
  1982年   1篇
  1980年   1篇
排序方式: 共有273条查询结果,搜索用时 265 毫秒
1.
2.
3.
4.
5.
Systems and synthetic biology both emerged around the turn of this century as labels for new research approaches. Although their disciplinary status as well as their relation to each other is rarely discussed in depth, now and again the idea is invoked that both approaches represent ‘two sides of the same coin’. The following paper focuses on this general notion and compares it with empirical findings concerning the epistemic cultures prevalent in the two contexts. Drawing on interviews with researchers from both fields, on participatory observation in conferences and courses and on documentary analysis, this paper delineates differences and similarities, incompatibilities and blurred boundaries. By reconstructing systems and synthetic biology’s epistemic cultures, this paper argues that they represent two ‘communities of vision’, encompassing heterogeneous practices. Understanding the relation of the respective visions of understanding nature and engineering life is seen as indispensible for the characterisation of (techno)science in more general terms. Depending on the conceptualisation of understanding and construction (or: science and engineering), related practices such as in silico modelling for enhancing understanding or enabling engineering can either be seen as incommensurable or ‘two sides of one coin’.  相似文献   
6.
Conserving biodiversity in managed landscapes requires the definition of spatial conservation priorities. The systematic conservation planning tools which are used to define these conservation priorities, assess the vulnerability of different locations by combining two different elements: some measurement of the biological assets in question, and some measurement of the key processes which threaten these biological assets. For instance, in cumulative impact mapping, maps of individual human activities that impact ecosystems (hereafter referred to as ‘stressor’ for individual maps and ‘cumulative stressor’ for combined maps) are overlaid with maps of ecosystem vulnerability, in order to estimate the overall ecological impact of human activities on natural ecosystems. These tools are appealing because they are easy to use and inform regional land planning. However, given that once these spatial conservation priorities are defined they potentially have far-reaching consequences, there is a need to test their robustness and reliability. Here we propose to investigate how the uncertainties related to the estimation of a cumulative stressor layer affect the definition of spatial conservation priorities. We conduct a sensitivity analysis of the different ways of estimating major stressors related to human activities (transport, urbanization and population) with a specific focus on agriculture. We show that spatial conservation priorities are little sensitive to most of the parameters and input data used to estimate the cumulative stressor map. In particular, they are not very sensitive to changes in spatially overlapping stressors, i.e. those which overlap spatially with other stressors. However, our analyses also reveal that spatial conservation priorities are highly sensitive to how the agriculture stressor is defined. These results highlight the importance of better understanding how agricultural activities impact biodiversity and establishing how more accurate information on agricultural practices can be used to define spatial conservation priorities.  相似文献   
7.
The role of environment and the relative significance of endogenous versus exogenous selection in shaping hybrid zones have been crucial issues in the studies of hybridization. Recent advances in ecological niche modeling (ENM) offer new methodological tools, especially in combination with the genotyping of individuals in the hybrid zone. Here, we study the hybrid zone between the widely known spices Origanum onites and Origanum vulgare ssp. hirtum in Crete. We analyze the genetic structure of both parental taxa and their hybrid Origanum × intercendens using AFLP markers on 15 sympatric and 12 allopatric populations and employ ecological niche modeling and niche similarity tests to study their niche patterns. We complement these analyses with seed viability measurements. Our study revealed that the hybridizing taxa O. onites and O. vulgare ssp. hirtum and the resulting genotypic classes showed geographical and environmental niche similarities based on the predictions of ENMs and the subsequent similarity tests. The occurrence of the hybrid zone is not directly dependent on environmental factors which favor the fitness of the hybrid compared to the parental taxa, but rather on aspects such as historical factors and management practices, which may contribute to the localization and maintenance of the contact zone between parental species. Our results suggest that if a minimum required niche differentiation between genotypic classes is not achieved, environmental dependence might not have a prominent role on the outcome of the hybridization.  相似文献   
8.
9.
10.
Lee  Raymond L. M. 《Dreaming》2010,20(4):288
Why are dreams easily forgotten or difficult to remember? Dream memory is usually attributed to stored fantasies and imaginations in sleep that have distant or no relevance to waking consciousness. Lack of dream recall suggests the modern emphasis on the significance of waking realities at the expense of oneiric experiences. Yet, in the ancient West and many contemporary non-Western societies, dreaming constitutes an unbroken chain of memory to the organization of everyday life. However, reenchantment in the modern context has given new importance to dream consciousness as vital to the development of the creative self. Emphasis on dream practices or dreamwork as leading to various forms of dream control suggests a quest for mastery of inner space. In this regard, training and motivation in dream recall provide an essential tool for advancing the self's well-being. Dreams are not treated as forgotten fantasies but dynamic pathways to new meanings of the self. (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