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   2323篇
  免费   321篇
  国内免费   365篇
测绘学   166篇
大气科学   201篇
地球物理   345篇
地质学   956篇
海洋学   277篇
天文学   20篇
综合类   135篇
自然地理   909篇
  2024年   8篇
  2023年   27篇
  2022年   84篇
  2021年   101篇
  2020年   95篇
  2019年   130篇
  2018年   83篇
  2017年   103篇
  2016年   108篇
  2015年   99篇
  2014年   119篇
  2013年   149篇
  2012年   153篇
  2011年   155篇
  2010年   126篇
  2009年   117篇
  2008年   113篇
  2007年   125篇
  2006年   157篇
  2005年   157篇
  2004年   130篇
  2003年   113篇
  2002年   90篇
  2001年   63篇
  2000年   60篇
  1999年   68篇
  1998年   44篇
  1997年   45篇
  1996年   36篇
  1995年   35篇
  1994年   33篇
  1993年   23篇
  1992年   15篇
  1991年   8篇
  1990年   3篇
  1989年   5篇
  1988年   6篇
  1987年   7篇
  1986年   7篇
  1984年   3篇
  1983年   3篇
  1982年   1篇
  1980年   1篇
  1972年   1篇
排序方式: 共有3009条查询结果,搜索用时 281 毫秒
981.
This article traces the ways in which the field emerges and becomes emplaced among three groups of people by presenting an inclusive reading of fieldwork in postconflict Vietnam. It employs a heuristic device called spaces of association to illustrate the different yet interrelated socio-spatial fields that surface when conducting fieldwork in an environment known for violence. In shedding light on the field's ability to extend beyond the territorially defined “field site,” this article speaks to debates surrounding the socio-spatial production of multiple and overlapping fields, describes the audiences engaged with and implicated in research, and contributes to understandings of ethical research engagement with postconflict field sites.  相似文献   
982.

Research traditions exert a powerful influence over the thinking of academic researchers. In population geography an entrenched empiricism and a reluctance to engage in wider debates on theory and method within human geography have resulted in a degree of separate development. Such methodological complacency has, until recently, threatened to undermine population geography's role within the discipline as a whole. Thus the discussion of multi-method research designs is of particular significance because it offers population geographers an opportunity to break out from the confines of a dominant research tradition and participate with other human geographers in an important methodological debate. This paper seeks not only to provide a critical overview of the current debate within population geography (as represented in the preceding papers in this Focus section) but also to extend that debate by raising issues of much more general concern. I argue that there are dangers in drawing the terms of the debate too narrowly. If we are to understand the nature and potential of multi-method research, we must first pose fundamental questions about the interrelationships among methods, data, and research problems. Pragmatic views on the choice of research method are inadequate because they fail to recognise the theory-driven nature of research. Only once we have achieved a better understanding of the philosophical grounding of research strategies will the opportunities afforded by multi-method research be fully realised.  相似文献   
983.
For qualitative researchers, selecting appropriate sites in which to conduct interviews may seem to be a relatively simple research design issue. In fact it is a complicated decision with wide-reaching implications. In this paper, we argue that the interview site itself embodies and constitutes multiple scales of spatial relations and meaning, which construct the power and positionality of participants in relation to the people, places, and interactions discussed in the interview. We illustrate how observation and analysis of interview sites can offer new insights with respect to research questions, help researchers understand and interpret interview material, and highlight particular ethical considerations that researchers need to address.  相似文献   
984.

The Young Geographers, an informal organization of American geographers, flourished from 1936 to 1943. One of its projects in 1940 and 1941 was the compilation and publication of lists of contemplated research by some 170 Young Geographers. Their listed research interests were relatively narrow in subject and geographical area. The successor of the Young Geographers was the American Society for Professional Geographers which merged with the Association of American Geographers in 1948 under a democratic constitution which assured that young geographers and their research would be recognized.  相似文献   
985.

The expansion of the Internet and e-mail access around the globe, especially into less-developed areas, raises the question of how geographers might use this technology for research purposes and the development of appropriate methodologies. This paper identifies three ways in which the use of e-mail surveys for geographic research differs from traditional mail surveys. First, there are substantial differences in selecting an appropriate sample population. Second, electronic medium considerations such as alphabet character translation, survey format, and receiving end conditions pose unique data collection challenges. Third, ascertaining that e-mail addresses to be included in a survey are operative is discussed as a useful means of maximizing the potential of an e-mail survey. Examples from an e-mail survey of environmentalists in Russia illustrate these points.  相似文献   
986.
Through a long-term summary of highway construction in the permafrost regions of Qinghai Province, the formation conditions and distribution characteristics of permafrost and their impact on transporta...  相似文献   
987.
花岗岩研究进展   总被引:2,自引:0,他引:2  
花岗岩的起源、形成的物理化学过程、结晶和分异、矿物-化学成分多样性、时空演变等是当前花岗岩研究的主题.矿物微区原位同位素分析,特别是锆石原位微区U-Pb和Hf-O同位素分析,以及岩浆作用的物理过程实验模拟是重要的研究手段.近年来,不同类型花岗岩起源和演化过程认识的深入,得益于对与花岗岩及其伴生的其它相关岩石研究的突破,以及锆石原位U-Pb和Hf-O同位素分析技术的应用.本文结合国内外花岗岩研究进展,综述了我国东南部华夏陆块上花岗岩研究中的一些问题.  相似文献   
988.
疏松质石笋碳酸盐的精确微区取样   总被引:2,自引:1,他引:1  
高分辨率极端气候事件是古气候研究中的一个热点。作为重要的古气候信息载体之一的石笋,以其每年几十到几百微米的生长速率,为提取高分辨率古气候代用指标提供了可能。而可靠的微区取样则是石笋高分辨率分析的重要前提。本文利用美国New Wave微区取样装置,对微区取样技术在石笋碳酸盐中的应用进行了探讨。在年层并非平直的疏松质石笋表面,于40 μm取样步长内,成功获得了平均质量约为100 μg的石笋微区分析样品。所获得的年内分辨率样品可同时提供微量元素分析和稳定同位素分析。重点讨论了石笋微区取样过程中必须注意的样品固定和取样参数设置等关键问题,提供了有效收集石笋微区样品和避免样品交叉污染的方法。  相似文献   
989.
动力地貌过程是河口与海岸滩涂研究的基础和关键。从动力地貌作用过程、数值模拟技术应用、遥感技术应用等方面综述了近年来河口与海岸滩涂动力地貌过程研究的主要进展,并强调采用先进仪器进行现场原型观测、加强人类活动与全球变暖协同作用下的滩涂动力地貌过程及灾害研究、加强当前滩涂开发已移至中低滩背景下的滩涂动力地貌过程演变趋势研究、加强不同因素综合影响下的滩涂区域粘性泥沙运动特性的基础理论研究和重视国内外滩涂动力地貌过程的对比研究为未来进一步研究的方向。  相似文献   
990.
国家自然科学基金申请项目数量可以较为可靠地反映基础研究队伍情况。2001—2011年地质学科基金申请数量不断增加,显示基础研究队伍得到新生力量的补充,从事地质学基础研究的单位也在不断增加。进一步分析揭示,目前地质学基础研究队伍结构存在如下主要问题:①地质学科基础研究队伍青年人才比例相对偏低,青年人才的补充滞后;②地质学人才队伍年龄结构连续性差,具有明显分段特征,可能会导致在某个时期科研资源和岗位竞争加剧,或是缺少特定层次的人才,引发科研工作的"瓶颈效应";③地质学申请项目增长在专业上不均衡,反映目前地质学科研队伍向侧重于地质资源和地质环境方面转移的趋势,长远发展不利于基础科学的源头创新和知识积累。分析了上状现象的原因,并初步提出一些改善建议。  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