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   1894篇
  免费   353篇
  国内免费   480篇
测绘学   267篇
大气科学   417篇
地球物理   390篇
地质学   880篇
海洋学   233篇
天文学   66篇
综合类   216篇
自然地理   258篇
  2024年   17篇
  2023年   53篇
  2022年   145篇
  2021年   148篇
  2020年   116篇
  2019年   111篇
  2018年   144篇
  2017年   125篇
  2016年   121篇
  2015年   110篇
  2014年   116篇
  2013年   124篇
  2012年   105篇
  2011年   110篇
  2010年   96篇
  2009年   79篇
  2008年   72篇
  2007年   74篇
  2006年   67篇
  2005年   63篇
  2004年   46篇
  2003年   36篇
  2002年   54篇
  2001年   50篇
  2000年   48篇
  1999年   84篇
  1998年   72篇
  1997年   76篇
  1996年   51篇
  1995年   30篇
  1994年   25篇
  1993年   38篇
  1992年   28篇
  1991年   24篇
  1990年   11篇
  1989年   14篇
  1988年   5篇
  1987年   10篇
  1986年   9篇
  1985年   2篇
  1984年   5篇
  1983年   2篇
  1982年   1篇
  1981年   5篇
  1980年   1篇
  1979年   1篇
  1977年   1篇
  1958年   2篇
排序方式: 共有2727条查询结果,搜索用时 15 毫秒
971.
自2005年国家出台新地震应急预案以来,根据预案制定要"纵向到底,横向到边"的精神要求,上至国家地震主管部门,下至基层地震单位,以及横向到与地震应急有关的部门和单位大都制定了地震应急预案.这些预案的法律、法规的依据是1997年颁布的<中华人民共和国防震减灾法>,1995年制定的<破坏性地震应急条例>和2005年制定的<国家突发公共事件总体应急预案>.  相似文献   
972.
The Anninghe fault is an important active fault along the eastern boundary of Sichuan-Yunnan active tectonic block, and the study of its surface deformation and rupture behavior during strong earthquake in the late Quaternary is of fundamental importance for understanding the future seismic risk of the fault zone or even the entire western Sichuan region. Using the methods of detailed geomorphic and geological survey, digital image analysis, total station instrument survey, excavation of combined trench and dating, we analyze the geomorphologic sequences of the offset strata at several sites where the late Quaternary deformation remnants are fairly well preserved and obtain some new results as follows: Strong earthquake events with left-lateral displacements of about 3 m occurred at the two sites of Zimakua and Yejitong at 1634-1811, 1030-1050 and 280-550 a BP, respectively, and the recurrence interval is 520-660 a; The youngest event in the area of Dahaizi-Ganhaizi should be the earthquake of 1536, other events are at 1768-1826, 2755-4108 and 4108-6593 a BP, respectively, with a recurrence interval of 1300-1900 a. The strong earthquake activity shows a clustering character. The possibility of occurrence of a strong earthquake exists on the north segment of the Anninghe fault sometime in the future.  相似文献   
973.
The abundance curves derived from area proportions of brachiopods and Girvanella in the thin sections from the Yangdi section, South China, exhibits complex relationships during the Late Devonian Frasnian-Famennian transition. The living activity of brachiopods such as grazing and borrowing did great damage to the growth of Girvanella. However, there was more to just a mere a survival competing relationship between them, Girvanella actually improved marine environments by oxygenating the dysoxic ambient sea-water through photosynthesis in the lower Kellwasser Horizon. Profited from this improvement brachiopods’ abundance increased subsequently and suppressed Girvanella again. Nonetheless, without Girvanella’s photosynthesis, brachiopods were wiped out by the farther anoxic environments in the upper Kellwasser Horizon. The complex relationships between Girvanella and brachiopods may be a key to unlocking the relationships between geomicrobes and metazoans in the geological overturn periods. Supported by NSFC Innovation Research Group Program (Grant No. 40621002), MOE Innovative Research Team Program (Grant No. IRT0546), the National Natural Science Foundation of China (Grant Nos. 40472020, 40730209, 40802005 and 40872001) and SINOPEC Project (Grant No. G0800-06-ZS-319)  相似文献   
974.
INTRODUCTIoNTheprocessesandratesoffluidflowsinsedimentarybasinsareakeyforunderstandingdiagenesis,thermalconvec-tionandpetroleumaccumu1ationanddistribution.Therearemorethan18ooverpressuredbasinsintheworld(Hunt,l996,l99o).Episodicexpulsionisbelievedbymanyinvesti-gatorstobethemainprocessesforprimaryhydrocarbonmi-grationinoverpressuredsourcerocks.However,littlehasbeenknownaboutthenatureoffluidinjectionandpetroleumaccumulationinoverpressuredbasins.TheYinggehaibasinisoneofthefourmajorTertiaryb…  相似文献   
975.
Dijkstra 最短路径算法的一种高效率实现   总被引:14,自引:1,他引:13  
在已存在的一些最短路径算法测试总结的基础上,根据GIS中网络计算的实际情况,从网络结构的拓扑表示以及Dijkstra 算法中快速搜索技术的实现入手,提出了一种Dijkstra 最短路径算法的高效率实现方法。  相似文献   
976.
阐述了用数字高程模型的理论去解决自动确定最佳观察位置的思想及算法。考虑到实际问题的复杂性,提出了从GIS数据库中获取知识,以解求更为复杂的最佳位置的定位问题。实例验证了基于GIS的最佳位置的自动确定算法的正确性。  相似文献   
977.
本文介绍了测绘运筹学参数线性规划的实用意义,并就如何应用参数线性规划为测绘生产管理提供量化决策依据进行了讨论。  相似文献   
978.
广西五圩锑矿床的水锑铅矿及其物种归属   总被引:1,自引:0,他引:1  
Bindheimite is a secondary antimony oxide minera l and a weathering product of jamesonite. It is reported that bindheimite occurr in an antimony deposit at the surface of the earth′s crust in Wuxu,Guangxi, China.  相似文献   
979.
Polygonal object is a fundamental type of geometric data in vector GIS. The key step of cleaning topological relationship after data collection of polygonal layer is to build polygonal objects from digital arcs. The raw digital arcs may intersect with each other. The algorithm for building polygonal objects after the raw arcs have been split at all intersections is presented. The build-up of polygonal objects in this paper is designed to be implemented by two steps. The first step is to extract all the polygons needed for build-up of polygonal objects from arcs. The second step is to organize polygonal objects from these polygons. For the first step, a tracing algorithm is proposed. The algorithm merely extracts the polygons needed for the build-up of polygonal objects, which is a subset of all the possible polygons that can be induced from the arcs. For the second step, an algorithm based on a specially designed order of polygons is advanced. All the topological relationships among the polygons are sho  相似文献   
980.
城市环境下的水土作用对土强度的影响   总被引:11,自引:1,他引:10  
在对南宁市水化学场进行历史分析的基础上,对南宁市天然水化学场进行模拟,以模拟溶液作为土体的浸渍液,研究变异后的水化学场对土体强度的影响。  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