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   3533篇
  免费   746篇
  国内免费   725篇
测绘学   133篇
大气科学   42篇
地球物理   435篇
地质学   3293篇
海洋学   687篇
天文学   6篇
综合类   202篇
自然地理   206篇
  2024年   8篇
  2023年   64篇
  2022年   122篇
  2021年   160篇
  2020年   138篇
  2019年   152篇
  2018年   131篇
  2017年   165篇
  2016年   195篇
  2015年   160篇
  2014年   221篇
  2013年   199篇
  2012年   238篇
  2011年   212篇
  2010年   209篇
  2009年   257篇
  2008年   239篇
  2007年   239篇
  2006年   274篇
  2005年   190篇
  2004年   170篇
  2003年   152篇
  2002年   179篇
  2001年   133篇
  2000年   154篇
  1999年   105篇
  1998年   110篇
  1997年   93篇
  1996年   62篇
  1995年   55篇
  1994年   39篇
  1993年   38篇
  1992年   30篇
  1991年   19篇
  1990年   23篇
  1989年   7篇
  1988年   18篇
  1987年   5篇
  1986年   12篇
  1985年   6篇
  1984年   8篇
  1983年   1篇
  1982年   6篇
  1981年   3篇
  1980年   1篇
  1978年   1篇
  1977年   1篇
排序方式: 共有5004条查询结果,搜索用时 31 毫秒
991.
赛汉塔拉凹陷位于二连盆地腾格尔坳陷西部,是二连盆地低熟油分布区.采用有机地球化学和生物标志物分析方法,对赛汉塔拉凹陷下白垩统腾二段低熟原油和油砂样品进行了地球化学特征和油源对比研究.赛汉塔拉凹陷腾二段低熟油具有饱和烃含量相对较低、非烃和沥青质含量相对较高的族组成特征,正构烷烃分布以前峰型为主,主峰碳为C21或C23,P...  相似文献   
992.
泥质砂岩复电阻率的频散特性实验   总被引:5,自引:0,他引:5  
不同孔隙流体特性的岩石复电阻率频散实验,是复电阻率测井资料评价水淹层和低阻油层的岩石物理基础。通过水驱水、水驱油、油驱水的岩石复电阻率频散特性的实验研究,发现泥质砂岩的复电阻率频散特性受含油饱和度的影响较大,受地层水矿化度的影响较小,尤其是异相电阻率,受地层水矿化度的影响更小;与含水泥质砂岩相比,含油泥质砂岩的相角相对较大,且随着含油饱和度的增加而增大;含水岩石和含油岩行在频散特性上存在着较大差异。实验研究结果表明,利用基于岩石频散特性发展起来的复电阻率测井技术,可以有效地识别油水层。  相似文献   
993.
张咏  杨桂君  张晖  李刚 《华南地震》2006,26(1):166-174
现代社会和生活越来越依赖于IT系统,信息系统遭到灾难和毁灭性打击将是社会公众的灾难和噩梦。美国“9.11”事件中纽约交易所成功实施了信息服务灾难恢复计划,使得全球对于“业务连续和灾难恢复”有了重新的认识。在我国,信息安全也日益成为政府部门管理层、企业和公众关注的重要话题。企业的弹性、系统的健壮性,信息系统的抗毁性与灾难恢复日益深入人心,风险管理越来越为业界所重视。地震部门在政府应急联动系统中具有重要作用,其本身的信息系统安全已逐步引起重视。  相似文献   
994.
采用物理模型试验研究了海流作用下海底输油管道溢油扩散特性。水槽中的原油从管道的泄漏点溢出,并从海底扩散到海面。采用非接触式光学测量技术,设计了图像采集与数据分析系统,研究原油泄漏机理和特性。通过该系统获得了溢油的轨迹、速度和海面上升时间。从定性和定量两个角度分析了水流和溢油量对溢油行为的影响。之后给出了特征物理量对各种因素的敏感性研究。溢油在水下主要以不同粒径的散状颗粒的形式分布。原油的上升过程可分为三个阶段:饱满、分散和聚集阶段。溢油量是影响油粒子上升时间的主要因素。在油粒子的上升过程中,原油的垂直速度主要受溢油量的影响,横向速度则更依赖于水流速度。不同水流与溢油量下,横向溢油速度的偏差远大于海面上升时间和垂直溢油速度的偏差。该研究可为溢油应急预测系统提供理论参考。  相似文献   
995.
The postdisaster landscape is replete with memorials that help communities collectively remember destructive events and recover psychologically. Although commemoration is intrinsic to all stages of recovery, little research from the disaster‐science field engages memorial texts across disasters. Meanwhile, a rich body of work on memorials and their functions exists in the cultural geographic tradition. Drawing from this literature, the current study examines a sample of U.S.‐based memorials to discern patterns within the postdisaster commemorative landscape. This research leverages discourse analysis to interrogate the meanings and mechanics of postdisaster memory work. Findings revealing that disasters catalyze remembrances that remake places, postdisaster memorial texts construct wide‐ranging degrees of intimacy, and memorials distilling survivor memories impel community recovery differently than memorials that reconstruct imagined pasts. These identified patterns in postdisaster commemoration enable further systematic exploration of memory work in the long‐term recovery process.  相似文献   
996.
Elevated wildfire activity in many regions in recent decades has increased concerns about the short- and long-term effects on water quantity, quality, and aquatic ecosystem health. Often, loss of canopy interception and transpiration, along with changes in soil structural properties, leads to elevated total annual water yields, peak flows, and low flows. Post-fire land management treatments are often used to promote forest regeneration and mitigate effects to terrestrial and aquatic ecosystems. However, few studies have investigated the longer-term effects of either wildfire or post-fire land management on catchment hydrology. Our objectives were to quantify and compare the short- and longer-term effects of both wildfire and post-fire forest management treatments on annual discharge, peak flows, low flows, and evapotranspiration (AET). We analyzed ten years of pre-fire data, along with post-fire data from 1 to 7 and 35 to 41 years after wildfire burned three experimental catchments in the Entiat Experimental Forest (EEF) in the Pacific Northwest, USA. After the fire, two of the catchments were salvage logged, aerially seeded, and fertilized, while the third catchment remained as a burned reference. We observed increases in annual discharge (150–202%), peak flows (234–283%), and low flows (42–81%), along with decreases in AET (34–45%), across all three study catchments in the first seven year period after the EEF wildfire. Comparatively, annual discharge, peak flows, lows flows, and AET had returned to pre-fire levels 35–41 years after the EEF fire in the two salvage logged and seeded catchments. Surprisingly, in the catchment that was burned but not actively managed, the annual discharge and runoff ratios remained elevated, while AET remained lower, during the period 35–41 years after the EEF fire. We posit that differences in long-term hydrologic recovery across catchments were driven by delayed vegetation recovery in the unmanaged catchment. Our study demonstrates that post-fire land management decisions have the potential to produce meaningful differences in the long-term recovery of catchment-scale ecohydrologic processes and streamflow.  相似文献   
997.
海域溢油环境敏感性评价工作是溢油应急规划的基础,有利于溢油事故的应急处理。本文对海岸线的溢油环境敏感型的主要评价方法和选取的评价指标进行了总结;在溢油环境敏感性评价中采用的方法主要包含指数法、层次分析法、德尔菲法、模糊综合评价法等;在研究中,各类方法具有不同特点,多为各种方法同时使用。目前,国内外研究中选取的各类指标可总结归为物理指标、生物指标、社会-经济指标三大类,并且针对部分指标选取的理论依据进行了论述。探讨了较为系统化的评价指标体系的构建。综述了海岸线溢油环境敏感性评价的国内外的主要研究进展。最后指出当前溢油环境敏感性评价中存在的不足,如评价体系系统性差、评价指标科学性低及评价过程主观性强等,而加强学科交叉的同时对目前研究中不足深入研究将是后续的研究重点。  相似文献   
998.
BOOK REVIEWS     
Book Reviewed in this article: Introduction to Climatology for the Tropics . J. O. Ayoade. Conservation and Management of Natural Resources in the United States . Charles F. Bennett. The Keeping of Animals: Adaptation and Social Relations in Livestock Producing Communities . Riva Berleant-Schiller and Eugenia Shanklin, ed. The Evolution of Geographic Thought in America: A Kentucky Root Wilford A. Bladen and Pradyumna P. Karan, eds. Latin America: Geographical Perspectives , 2nd ed. Harold Blakemore and Clifford T. Smith, ed. The Rural Real Estate Market. Department of Geography Publication Series, No. 18 . Chris Bryant. Urban Geomorphology in Drylands . R. U. Cooke, D. Brunsden, J. C. Doornkamp, and D. K. C. Jones with contributions by J. Griffiths, P. Knott, R. Potter, and R. Russell. Italian Geography, 1960–1980. Meeting of the Status of the Geographic Research in Italy, 1960–1980. Treated under the auspices of Consiglio Nazionale delle Ricerche and organized by Istituto di Geografia Umana della Facoltà di Lettere e Filosofia dell'Università degli Studi di Milano , Giacomo Corna Pellecrini and Carlo Brusa, eds. The Changing Fenland . H. C. Darby. The Future for the City Centre . R. L. Davies and A. G. Champion, eds. Saudi Arabia, Energy, Developmental Planning, and Industrialization . Ragaei El Mallakh, Dorothea H. El Mallakh, eds. For We Are Sold, I and My People: Women and Industry in Mexico's Frontier . Maria Patricia Fernández-Kelly. The Great Lakes Forest: An Environmental and Social History . Susan L. Flader, ed. Regional Transformation and Industrial Revolution: A Geography of the Yorkshire Woolen Industry . Derek Gregory Crime in City Politics . Anne Heinz, Herbert Jacob and Robert L. Lineberry, eds. Revitalizing Cities . H. Briavel Holcomb and Robert A. Beauregard. Cartographic Relief Presentation . Eduard Imhof. H. J. Steward, Trans. Soviet Union: A Geographical Survey . S. V. Kalesnik and V. F. Pavlenko, ed. Cognition and Environment . Stephen Kaplan and Rachel Kaplan. Environmental Protection: The International Dimension . David A. Kay and Harold K. Jacobsen, eds. Mathematical Programming Methods for Geographers and Planners , James Killen. Gentrification Amid Urban Decline: Strategies for America's Older Cities . Michael H. Lang. The North Atlantic Sulphur System . Risto Laulajainen. The Jerusalem Cathedra: Studies in the History, Archaeology, Geography and Ethnography of the Land of Israel, Vol. 2 . Lee I. Levine ed. Jerusalem and Detroit: Recreation Planning and Management . Stanely R. Lieber and Daniel R. Fesenmaier, eds. Heartland and Hinterland: A Geography of Canada . L. D. McCann, ed. Scarborough Where We Live: The Residential Districts of Minneapolis and St. Paul . Judith A. Martin and David A. Lanegran. California: The Geography of Diversity . Crane S. Miller and Richard S. Hyslop. Palo Alto The Dilemma of Amazonian Development . Emilio F. Moran, ed. Boulder Nuclear Waste: Socioeconomic Dimensions of Long-Term Storage . Steve H. Murdock, F. Larry Leistritz, and Rita R. Hamm, eds. Boulder Communism and the Politics of Inequalities . Daniel N. Nelson, ed. The Los Angeles Metropolis . Howard J. Nelson. Dubuque An Historical Geography of Urban System Development: Tidewater Virginia in the 18th Century . James O'Mara. Procedures and Standards for a Multipurpose Cadastre . East Asia: Geographical and Historical Approaches to Foreign Area Studies . Clifton W. Pannell, ed. Dubuque Mackinder: Geography as an Aid to Statecraft . W. H. Parker. Beyond the Urban Fringe: Land Use Issues of Nonmetropolitan America . Rutherford H. Platt and George Macinko, eds. Recreation Geography of the USSR . V. S. Preobrazhensky and V. M. Krivosheyev, eds. Missouri: A Geography . Milton D. Rafferty The Invisible Farmers: Women in Agricultural Production . Carolyn E. Sachs. Cayman Islands Seashore Vegetation: A Study in Comparative Biogeography . Jonathan D. Sauer. Hillslope Materials and Processes . Michael J. Selby. Housing in Britain: The Post-War Experience . John R. Short The Study of Population: Elements, Patterns and Processes . George A. Schnell and Mark Stephen Monmonier. Columbus The Soviet Union: A Systematic Geography . Leslie Symons, ed. The Ottoman Slave Trade and Its Suppression . Ehud R. Toledano. The Impact of Recession on Industry, Employment and the Regions, 1976–1981 . Alan R. Townsend. Landslides and Their Control , 2nd ed. Quido Záruba and Vojtech Mencl. Translated from the Czech by H. Zárubová and V. Mencl.  相似文献   
999.
本文从成岩磁铁矿理论出发,讨论了油气藏上方的磁异常形态,阐述了利用高精度磁测直接寻找油气田的可能性及其方法技术。文章指出,用磁测直接找油,不仅要提高磁测精度,而且关键在于要能找到并能成功提取与油气藏有关的磁异常信息的方法。文中还列举了引用本文所述方法预测油气田的效果。  相似文献   
1000.
未成熟油气是指那些埋藏深度浅于成熟门限深度的沉积有机质生成的油气.该类油气由岩石中可溶有机质直接衍生和干酪根早期热降解作用共同作用的结果。其形成条件,包括有利于有机质堆积和保存的环境、良好的有机质类型、有机质丰度高、富含有利于早期成烃的特殊组分、并长期处于低演化阶段等.  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