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   1241篇
  免费   290篇
  国内免费   523篇
测绘学   33篇
大气科学   15篇
地球物理   396篇
地质学   1357篇
海洋学   92篇
天文学   21篇
综合类   49篇
自然地理   91篇
  2024年   10篇
  2023年   28篇
  2022年   44篇
  2021年   59篇
  2020年   60篇
  2019年   91篇
  2018年   88篇
  2017年   125篇
  2016年   93篇
  2015年   79篇
  2014年   67篇
  2013年   230篇
  2012年   60篇
  2011年   66篇
  2010年   53篇
  2009年   74篇
  2008年   72篇
  2007年   68篇
  2006年   92篇
  2005年   75篇
  2004年   102篇
  2003年   75篇
  2002年   49篇
  2001年   32篇
  2000年   43篇
  1999年   38篇
  1998年   24篇
  1997年   34篇
  1996年   17篇
  1995年   20篇
  1994年   11篇
  1993年   7篇
  1992年   11篇
  1991年   9篇
  1990年   5篇
  1989年   3篇
  1988年   8篇
  1987年   10篇
  1986年   2篇
  1985年   7篇
  1984年   6篇
  1983年   2篇
  1982年   1篇
  1981年   1篇
  1980年   1篇
  1978年   1篇
  1877年   1篇
排序方式: 共有2054条查询结果,搜索用时 62 毫秒
411.
The applicability of metropolitan-derived explanations of gender differences in worktrip lengths is examined based on a sample of 435 university employees in the nonmetropolitan town of Blacksburg, VA. Women's worktrips are found to be longer than men's in contrast to metropolitan findings. This pattern results from the interaction of spatial structures of housing and employment with women's lower incomes, gender segregation of employment, and the tendency for married women to find jobs after their residence is established. Upward trends in female labor force participation rates and in nonmetropolitan growth require continued analysis of their joint impact on women's spatial behavior.  相似文献   
412.
We present radial velocity measurements proving the binary nature of all the known extremely Fe-deficient Post-ABG stars including HD 44179, the central star of the well known but poorly understood Red-Rectangle nebula. With the observed orbital parameters, it is more likely that the stars represent a particular stage in binary evolution, rather than a typical post-AGB evolutionary stage.  相似文献   
413.
BOOK REVIEWS     
Book Reviewed in this article: Unfairly Structured Cities . Blair Badcock Religion and Rural Revolt . Janos M. Bak and Gerhard Benecke The Industrial Geography of Canada . Anthony Blackbourn and Robert G. Putnam The Cuban-American Experience, Culture, Images, and Perspectives. Thomas D. Boswell and James R. Curtis Quaternary Paleoclimatology . R. S. Bradley Development and Crisis in Brazil, 1930–1983 . Luiz Bresser Pereiras Centres of Origin in Biogeography . John C. Briggs Analytical Urban Geography . Martin Cadwallader Geomorphology . Richard J. Chorley , Stanley A. Schumm, and David E. Sugden South Africa: The Impact of Past Geographies . A. J. Christopher The Geography of Underdevelopment. A Critical Survey . D. K. Forbes Health Care in Developing Countries . Wilbert M. Gesler Place to Grow Old: The Meaning of Environment in Old Age . Stephen M. Golant The Emerging Marine Economy of the Pacific . Chennat Gopalakrishnan An Introduction to Agricultural Geography . David B. Grigg The Soviet Union: A Geographical Study . G. Melvyn Howe Geographical Aspects of Health: Essays in Honour of Andrew Learmonth . N. D. Mc Glashan and J. R. Blunden Physical Geography: A Landscape Appreciation . Tom L. Mc Knight Mountain Experience. The Psychology and Sociology of Adventure. Richard G. Mitchell Jr . Systematic and Regional Biogeography. Stanley A. Morain The Economic Transformation of American Cities. T. J. Noyelle and T. M. Stanback , Jr . Normal Accidents: Living With High-Risk Technologies. Charles Perrow Vanishing Farmland: A Legal Solution for the States. Sarah E. Redfield Applied Methods of Regional Analysis: The Spatial Dimensions of Development Policy. Dennis A. Rondinelli Urbanization in Romania. A Geography of Social and Economic Change Since Independence. Per Ronnas Statistical Techniques in Geographical Analysis. Gareth Shaw and Dennis Wheeler The Granite Garden: Urban Nature and Human Design. Anne Whiston Spirn Political Geography: Recent Advances and Future Directions. Peter Taylor and John House Geographia y Medio Ambiente. Manuel Valenzuela -Rubío Nãgara and Commandery: Origins of the Southeast Asian Urban Traditions. Paul Wheatley The Common Fisheries Policy of the European Community. Mark Wise Geography and Gender. Women and Geography Study Group of the IBG Technological Hazards. D. J. Zeigler , J. H. Johnson , S. D. Brunn  相似文献   
414.
Tidal phase plays a major role in controlling sediment discharge from the Yangtze River estuary in eastern China. Direct measurements indicate that during spring tide in mid-November 1981 approximately 3 times the sediment passed down the main channel of the river as during the next neap tide, 3 days later. The estuary presumably acts as a conduit for riverine sediment during spring tide but as a sink during neap tide. Tidal phase control of sediment discharge appears to be primarily dependent upon tidal range relative to estuarine depth rather than river discharge or absolute tidal range per se.  相似文献   
415.
测试并分析了柴北缘各油气田的14个天然气样品的氦、氩稀有气体同位素比值,并进行了气源对比。研究发现,柴北缘天然气40Ar/36Ar值分布在951~1712,平均1098,多数样品40Ar/36Ar较通常认为源于侏罗系的天然气40Ar/36Ar明显偏高,研究认为本区不存在幔源高40Ar/36Ar流体的介入,储层年代效应也不可能造成天然气40Ar/36Ar明显偏高,因此柴北缘天然气40Ar/36Ar明显偏高,主要是由于源岩年代积累效应引起的。据估算,气源岩年龄分布范围为164.7~460.8Ma,平均为345.1Ma,可能多数来源于石炭系。这一认识得到了柴北缘广泛分布有石炭系源岩和已发现源于石炭系原油的支持。柴北缘石炭系天然气的发现预示了柴北缘石炭系是一个新的油气勘探层系,从而拓展了柴北缘天然气勘探领域。  相似文献   
416.
本文对四川江油马鞍塘中晚三叠世地层剖面进行了详细描述,根据岩石组合特征,结合全国岩石地层清理方案将其划分为天井山组和马鞍塘组[1].对天井山组和马鞍塘组进行了详细的沉积相及垂向变化规律研究,并将其划分为四个层序(相当于三级层序),同时讨论了各层序的体系域特征[2].  相似文献   
417.
K–Ar dating of mineral separates extracted from various granitoid rock units of the eastern Pontides and central Anatolia, Turkey, has provided some new insights unravelling various stages of the Neo-Tethyan convergence system, which evolved with northward subduction between the Eurasian plate (EP) to the north and the Tauride-Anatolide platform (TAP) to the south along the İzmir-Ankara-Erzincan suture (IAES) zone. Arc-related granitoid rocks are only encountered in the eastern Pontides and yield K–Ar cooling ages of both Early Cretaceous (138.5 ± 2.2 Ma) (early arc), and Late Cretaceous, ranging from 75.7 ± 0.0 to 66.5 ± 1.5 Ma (mature arc), respectively. The multi-sourced granitoids of the eastern Pontides, with a predominant mantle component and K–Ar ages between 40 and 50 Ma, are considered to be a part of post-collisional slab break-off magmatism accompanied by tectonic denudation of pre-Late Cretaceous granitoid rocks following juxtaposition of the EP and the TAP around 55–50 Ma in the eastern Pontides. The K–Ar cooling ages of collision-related S-, I- and A-type granitoids in central Anatolia reflect good synchronism between 80 and 65 Ma, suggesting a coeval genesis in a unique geodynamic setting but with derivation from various sources—namely, purely crustal, purely mantle and/or of mixed origin. This sort of simultaneous generation model for these S-I-A-type intrusives seems to be consistent with a post-collisional lithospheric detachment related geodynamic setting. I-type granodioritic to tonalitic intrusives with K–Ar cooling ages ranging from 40 to 48 Ma in east-central Anatolia are interpreted to have been derived from a post-collisional, within-plate, extension-related geodynamic setting following the amalgamation of the EP and the TAP in east-central Anatolia.  相似文献   
418.
地球化学的空间自相关异常信息提取方法   总被引:3,自引:0,他引:3  
针对地球化学数据存在的空间分布相关性特征,该文提出了一种基于空间自相关统计的地球化学异常提取方法。以内蒙古浩布高矿床外围的土壤地球化学数据为例,通过对Sn、Cu元素地球化学数据在不同空间间隔上的全局自相关计算,测算其空间聚集的程度,选取聚集程度最高时的间隔距离作为局部空间自相关的参数,通过局部Moran’s I值研究元素的空间分布特征,分析空间聚类和异常值,从而提取地球化学异常。结果表明,局部空间自相关分析可以揭示Sn、Cu地球化学数据的空间分布特征,能够更好地提取地球化学弱缓异常,说明空间自相关是一种有效的地球化学异常识别方法。  相似文献   
419.
宝鸡市重点景区游客满意度评价研究   总被引:2,自引:0,他引:2  
重点景区在目的地城市的旅游资源功能发挥中扮演着重要角色.构建宝鸡市重点景区期望差异理论模型,通过李克特五级量表调查游客的游前期望和游后的实际感知,对宝鸡市八大不同级别的重点旅游景区进行分析,得到游客满意度的优势和劣势因子.结果表明:游客对宝鸡旅游总体感到较为满意,旅游资源禀赋好但分布较散,难以满足多元化旅游者的需求;餐饮卫生、住宿便捷度、购物环境和种类、历史文化特色四大类因子的游客期望和实际感知差异值均为负,在景区发展中处于弱势;与法门寺相比,太白山更具有资源和观赏优势,其余景区的观赏价值虽较高,但整体满意度不均衡.针对弱势因子探讨并提出解决对策,为宝鸡市旅游业健康、快速发展提供借鉴.  相似文献   
420.
This exercise in a type of applied historiography begins by annotating aspects of reform in Western education from the 1880s to the 1930s, an interval which exhibits the responses of ‘new’ subjects to political and social demands for improved civics education, and encompasses the inauguration of a recognisably ‘academic’ geography in Australia. Designedly, since the nominated period also incorporates the early life and career of pioneering geographer Griffith Taylor, the discussion probes beneath the strata of obfuscatory generalisation to relate one individual's engagement with the vortex of change. More specifically, it extracts a few lessons from Taylor's approach to ‘Nation‐Planning’ to suggest an appropriate orientation to current reformism in Australian education. It is argued that, while this trend questions the civic utility of established disciplines, it has been badly served by a disturbing ignorance of the social and intellectual heritage of the subjects under challenge.  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