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   38292篇
  免费   1048篇
  国内免费   522篇
测绘学   1488篇
大气科学   3114篇
地球物理   8393篇
地质学   13858篇
海洋学   2864篇
天文学   8151篇
综合类   327篇
自然地理   1667篇
  2021年   292篇
  2020年   281篇
  2019年   334篇
  2018年   1482篇
  2017年   1347篇
  2016年   1315篇
  2015年   769篇
  2014年   1088篇
  2013年   1807篇
  2012年   1693篇
  2011年   1699篇
  2010年   1195篇
  2009年   1519篇
  2008年   1337篇
  2007年   1273篇
  2006年   1305篇
  2005年   1949篇
  2004年   2037篇
  2003年   1688篇
  2002年   1033篇
  2001年   839篇
  2000年   783篇
  1999年   686篇
  1998年   622篇
  1997年   645篇
  1996年   577篇
  1995年   534篇
  1994年   507篇
  1993年   425篇
  1992年   384篇
  1991年   418篇
  1990年   414篇
  1989年   390篇
  1988年   360篇
  1987年   436篇
  1986年   361篇
  1985年   445篇
  1984年   478篇
  1983年   462篇
  1982年   444篇
  1981年   357篇
  1980年   360篇
  1979年   311篇
  1978年   307篇
  1977年   296篇
  1976年   261篇
  1975年   258篇
  1974年   281篇
  1973年   306篇
  1972年   194篇
排序方式: 共有10000条查询结果,搜索用时 406 毫秒
911.
As climate is one factor determining the potential range of malaria, climate change may work with or against efforts to bring malaria under control. We developed a model of future climate suitability for stable Plasmodium falciparum malaria transmission in Zimbabwe. Current climate suitability for stable malaria transmission is based on the MARA/ARMA model of climatic constraints on the survival and development of the Anopheles vector and the Plasmodium falciparum malaria parasite. We explored potential future geographic distributions of malaria using sixteen projections of climate in 2100. The results suggest that, assuming no future human-imposed constraints on malaria transmission, changes in temperature and precipitation could alter the geographic distribution of malaria in Zimbabwe, with previously unsuitable areas of dense human population becoming suitable for transmission. Among all scenarios, the highlands become more suitable for transmission, while the lowveld and areas currently limited by precipitation show varying degrees of change, depending on climate sensitivity and greenhouse gas emission stabilization scenarios, and depending on the general circulation model used. The methods employed can be used within or across other African countries. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   
912.
Post-earthquake field investigations of landslide occurrence have provided a basis for understanding, evaluating, and mapping the hazard and risk associated withearthquake-induced landslides. This paper traces thehistorical development of knowledge derived from these investigations. Before 1783, historical accounts of the occurrence of landslides in earthquakes are typically so incomplete and vague that conclusions based on these accounts are of limited usefulness. For example, the number of landslides triggered by a given event is almost always greatly underestimated. The first formal, scientific post-earthquake investigation that included systematic documentation of the landslides was undertaken in the Calabria region of Italy after the 1783 earthquake swarm. From then until the mid-twentieth century, the best information on earthquake-induced landslides came from a succession ofpost-earthquake investigations largely carried out by formal commissions that undertook extensive ground-based field studies. Beginning in the mid-twentieth century, when the use of aerial photography became widespread, comprehensive inventories of landslide occurrence have been made for several earthquakes in the United States, Peru, Guatemala, Italy, El Salvador, Japan, and Taiwan. Techniques have also been developed for performing ``retrospective' analyses years or decades after an earthquake that attempt to reconstruct the distribution of landslides triggered by the event. The additional use of Geographic Information System (GIS) processing and digital mapping since about 1989 has greatly facilitated the level of analysis that can applied to mapped distributions of landslides. Beginning in 1984, syntheses of worldwide and national data on earthquake-induced landslides have defined their general characteristics and relations between their occurrence and various geologic and seismic parameters. However, the number of comprehensive post-earthquake studies of landslides is still relatively small, and one of the most pressing needs in this area of research is for the complete documentation of landslides triggered by many more earthquakes in a wider variety of environments.  相似文献   
913.
Smoothing the Marmousi Model   总被引:1,自引:0,他引:1  
  相似文献   
914.
3-D Viscoelastic FEM Modeling of Crustal Deformation in Northeast Japan   总被引:1,自引:0,他引:1  
-- As a first step toward establishing a standard earthquake cycle model in Japan, we simulate the crustal deformation during the past 100 years in northeast Japan, using a 3-D FEM based on the kinematic model. Then, we compare the computed results with the observed long-term leveling data and the recent GPS data. On the whole, although the effect of the subducting PAC is dominant, coseismic deformation of the interplate earthquakes can be clearly seen in the inland. Moreover, the postseismic deformation of the earthquakes due to the viscoelastic upper mantle seriously affects the inland movements, and continues for a few decades. Our modeling, including the effects of the interplate earthquakes and the three-dimensional viscoelastic inhomogeneity, reasonably explains the observed movement. Finally, we stress that the viscoelastic effect should be taken into consideration in the analyses, even if no earthquakes occur in the analyzed period.  相似文献   
915.
—?Microseismicity (M?M?M?M??6 were also monitored at a crustal movement monitoring station located several hundred meters from the veins. It was found that the opening of the vertical ore veins primary led to significant strain and tilt, but not to seismicity, because the delay and the longer duration of the seismicity were significant. Most seismic events involve thrusting mechanisms that are consistent with the present stress state of E-W-oriented tectonic compression, but are not consistent with the opening of the deepest ore vein. Interstingly, all the events within a few months of the heavy rainfall occurred near the faults that offset the deepest ore veins, wheareas all those events located away from the deepest ore veins occurred many months after the heavy rainfall. Consequently, the delayed diffusion of water appears to have played a dominant role in reducing rock strength, which led to seismicity in the Ikuno mine.  相似文献   
916.
新时期我国区域经济地理学发展问题初探   总被引:4,自引:0,他引:4  
我国新时期的区域经济地理学在取得全面发展的同时,在理论体系,研究方法和实践领域等方面还需要进一步的发展,文章根据学习和实践区域经济地理学的体会,初步提出基础理论和应用理论,思维方法和技术方法等方面发展见解,并指出区域创新系统和国际经济技术合作等学科应注意拓展的重要实践领域,最后提出我国区域经济地理学科发展的建议。  相似文献   
917.
文章以广东省新兴县为例,从凉果资源分布与加工能力的匹配关系角度对华南地区凉果资源的分布,凉果加工业的分布与布局,凉果市场分布与竞争力,凉果加工业与资源的匹配关系等进行了分析,并针对华南地区凉果加工业面临的主要问题提供了一些建议。  相似文献   
918.
成都市民消费结构与休闲活动关系研究   总被引:6,自引:0,他引:6  
城市居民消费水平,消费结构会影响其休闲消费能力,消费意愿,消费方式,消费态度和休闲时空结构,文章以成都市7个城区歌舞,茶棋牌,电影及城市公园休闲活动调查为基础,探讨了城市居民消费结构及其变化与休闲活动特征的关系。研究结果表明,城市居民消费结构的改变对歌舞,茶棋牌娱乐活动影响最大。  相似文献   
919.
南水北调中线工程建设与河南水资源可持续利用   总被引:2,自引:0,他引:2  
文章通过对河南省水资源开发利用现状,存在的主要问题,水资源供需平衡以及南水北调工程对河南省水资源利用的影响论述,提出了在拟定南水北调工程供水方案中,应通过强化节水,加强水资源保护,严格控制地下水开采,将水资源作为商品等措施,促进河南省水资源的可持续开发利用。  相似文献   
920.
区域视觉形象识别系统设计的理论与实践   总被引:6,自引:0,他引:6  
目前,全国各地正在兴起区域形象设计与建设的浪潮,但如何把区域形象信息系统地传递出去,这方面的理论研究大大落后于实践。文章就区域形象信息传递的有效工具-区域视觉识别系统设计的主要内容,设计的原则,设计的基本流程等在理论与实践上作了较为详细的探讨,并就区域视觉识别系统设计方案的经济学论证作了一些有益探讨。  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