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   686篇
  免费   94篇
  国内免费   74篇
测绘学   32篇
大气科学   122篇
地球物理   50篇
地质学   292篇
海洋学   67篇
天文学   2篇
综合类   32篇
自然地理   257篇
  2023年   7篇
  2022年   19篇
  2021年   29篇
  2020年   15篇
  2019年   18篇
  2018年   10篇
  2017年   21篇
  2016年   23篇
  2015年   17篇
  2014年   29篇
  2013年   57篇
  2012年   17篇
  2011年   43篇
  2010年   23篇
  2009年   18篇
  2008年   40篇
  2007年   38篇
  2006年   28篇
  2005年   37篇
  2004年   31篇
  2003年   36篇
  2002年   33篇
  2001年   33篇
  2000年   45篇
  1999年   32篇
  1998年   20篇
  1997年   26篇
  1996年   29篇
  1995年   18篇
  1994年   23篇
  1993年   10篇
  1992年   4篇
  1991年   10篇
  1990年   4篇
  1989年   5篇
  1987年   1篇
  1985年   1篇
  1984年   1篇
  1983年   1篇
  1982年   1篇
  1978年   1篇
排序方式: 共有854条查询结果,搜索用时 156 毫秒
851.
试论江苏地质遗迹保护和利用   总被引:2,自引:0,他引:2  
地质遗迹是地球46亿年演化留给人类的宝贵财富,基于对江苏省地质遗迹的鉴评,提出申报建设地质公园与地质遗迹保护区,推行“科学在公园”计划,建立地球科学野外露天教室,开拓地学知性之旅等作为保护和利用地质遗迹的举措与相关建议。  相似文献   
852.
Global sustainability governance is marked by a highly fragmented system of distinct clusters of international organizations, along with states and other actors. Enhancing inter-organizational coordination and cooperation is thus often recognized as an important reform challenge in global sustainability governance. The 17 Sustainable Development Goals, agreed by the United Nations in 2015, thus explicitly aim at advancing policy coherence and institutional integration among the myriad international institutions. Yet, have these goals been effective in this regard? We assess here the impact of the Sustainable Development Goals on the network structure of 276 international organizations in the period 2012–2019, that is, four years before and four years after the launch of the Sustainable Development Goals. The network structure was approximated by analyzing data from the websites of these 276 international organizations that were joined by more than 1.5 million hyperlinks, which we collected using a custom-made web crawler. Our findings are contrary to what is widely expected from the Sustainable Development Goals: we find that fragmentation has in fact increased after the Sustainable Development Goals came into effect. In addition, silos are increasing around the 17 SDGs as well as around the social, economic, and environmental dimensions of sustainable development.  相似文献   
853.
Scaling up national climate adaptation under the Paris Agreement is critical not only to reduce risk, but also to contribute to a nation’s development. Traditional adaptation assessments are aimed at evaluating adaptation to cost-effectively reduce risk and do not capture the far-reaching benefits of adaptation in the context of development and the global Sustainable Development Goals (SDGs). By grounding adaptation planning in an SDG vision, we propose and demonstrate a methodological process that for the first time allows national decision-makers to: i) quantify the adaptation that is needed to safeguard SDG target progress, and ii) evaluate strategies of stakeholder-driven adaptation options to meet those needs whilst delivering additional SDG target co-benefits. This methodological process is spatially applied to a national adaptation assessment in Ghana. In the face of the country’s risk from floods and landslides, this analysis identifies which energy and transport assets to prioritise in order to make the greatest contribution to safeguarding development progress. Three strategies (‘built’, ‘nature-based’, ‘combined SDG strategy’) were formulated through a multi-stakeholder partnership involving government, the private sector, and academia as a means to protect Ghana’s prioritised assets against climate risk. Evaluating these adaptation strategies in terms of their ability to deliver on SDG targets, we find that the combined SDG strategy maximises SDG co-benefits across 116 targets. The proposed methodological process for integrating SDG targets in adaptation assessments is transferable to other climate-vulnerable nations, and can provide decision-makers with spatially-explicit evidence for implementing sustainable adaptation in alignment with the global agendas.  相似文献   
854.
绿海龟(Chelonia mydas)血细胞发育过程的观察   总被引:1,自引:0,他引:1       下载免费PDF全文
采用Wright's液染色方法,对绿海龟的外周血、骨髓、脾脏和肝脏等几种组织的印片和涂片进行观察研究.结果表明,骨髓和脾脏是绿海龟的主要造血器官,红血细胞、粒细胞、单核细胞等血细胞主要在骨髓中发生,淋巴细胞主要在脾脏中发生;脾脏中可以发现晚幼红血细胞,脾脏可能是红血细胞的成熟场所;肝脏中无原始型的血细胞,可能不是其造血器官.红血细胞的发育经历了5个阶段:原红血细胞、早幼红血细胞、中幼红细胞、晚幼红血细胞和红血细胞等阶段,其胞体体积经历了由小到大,由大到小、再到大的发育过程;粒细胞的发育经历了5个阶段:原粒细胞、早幼粒细胞、中幼白细胞、晚幼白血细胞和白细胞等阶段,胞体体积均由大到小变化,核分叶可能是粒细胞的衰老的标志;淋巴细胞和单核细胞的发育各经历了3个阶段.各细胞发育均经历了由有细胞核仁到无细胞核仁的变化过程.原血细胞和幼血细胞在造血器官中可以进行有丝分裂,部分成熟的红血细胞可以在外周血中进行直接分裂.  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