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   63045篇
  免费   10555篇
  国内免费   14631篇
测绘学   5220篇
大气科学   7247篇
地球物理   11550篇
地质学   37196篇
海洋学   10469篇
天文学   2303篇
综合类   4255篇
自然地理   9991篇
  2024年   380篇
  2023年   967篇
  2022年   1941篇
  2021年   2201篇
  2020年   2320篇
  2019年   2611篇
  2018年   2150篇
  2017年   2483篇
  2016年   2724篇
  2015年   2787篇
  2014年   3405篇
  2013年   3334篇
  2012年   3745篇
  2011年   3903篇
  2010年   3351篇
  2009年   4055篇
  2008年   3909篇
  2007年   4373篇
  2006年   4219篇
  2005年   3796篇
  2004年   3520篇
  2003年   3336篇
  2002年   3026篇
  2001年   2579篇
  2000年   2385篇
  1999年   2221篇
  1998年   1867篇
  1997年   1673篇
  1996年   1557篇
  1995年   1285篇
  1994年   1318篇
  1993年   1118篇
  1992年   895篇
  1991年   652篇
  1990年   541篇
  1989年   470篇
  1988年   331篇
  1987年   229篇
  1986年   144篇
  1985年   102篇
  1984年   43篇
  1983年   42篇
  1982年   43篇
  1981年   28篇
  1980年   36篇
  1979年   35篇
  1978年   41篇
  1977年   24篇
  1975年   4篇
  1954年   15篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
951.
In this study,a 3D virtual reality and visualization engine for rendering the ocean,named VV-Ocean,is designed for marine applications.The design goals of VV-Ocean aim at high fidelity simulation of ocean environment,visualization of massive and multidimensional marine data,and imitation of marine lives.VV-Ocean is composed of five modules,i.e.memory management module,resources management module,scene management module,rendering process management module and interaction management module.There are three core functions in VV-Ocean:reconstructing vivid virtual ocean scenes,visualizing real data dynamically in real time,imitating and simulating marine lives intuitively.Based on VV-Ocean,we establish a sea-land integration platform which can reproduce drifting and diffusion processes of oil spilling from sea bottom to surface.Environment factors such as ocean current and wind field have been considered in this simulation.On this platform oil spilling process can be abstracted as movements of abundant oil particles.The result shows that oil particles blend with water well and the platform meets the requirement for real-time and interactive rendering.VV-Ocean can be widely used in ocean applications such as demonstrating marine operations,facilitating maritime communications,developing ocean games,reducing marine hazards,forecasting the weather over oceans,serving marine tourism,and so on.Finally,further technological improvements of VV-Ocean are discussed.  相似文献   
952.
???360???????????????????????????????????????????????·???????????в???????????????????????YCbCr???????????????????????????????????????????Ч??????????????????????????????????????????????????????????????????????????????????Ч?????????????????÷????????360?????????е??????????????????????????????????????????????Ч?????????á?  相似文献   
953.
在2维交通网络逻辑数据模型基础上,讨论了概念化的楼层网络,进行了室内连通的3维网络模型的研究。基于ArcGIS的交通网络模型建立了试验区的室内3维网络模型,并给出分析结果,该方法为室内3维网络模型研究提供了技术支持。  相似文献   
954.
The Kungurian-Capitanian ( Permian) Zhesi branchiopod fauna is mainly composed of cold-water typed taxa with high diversity and abundance. This fauna is similar with the coeval brachiopod faunas from Timan-Pechora,Svalbard,and Queen Elizabeth Islands of the Boreal Realm,with no real"warm-water"species. Zhesi brachiopod fauna is a cold-water fauna and should be assigned to the Boreal Realm. Considering the paleogeographic characteristics of this fauna and the basic rationale of paleobiogeographic provinces being controlled by latitude-temperate,and that the above areas were located at 50°N 70°N in the global paleoclimate reconstruction map compiled by Boucot et al. ,the paleo-latitude of the southern margin of Jiamusi-Mongolia Block,where developed the Zhesi brachiopod fauna,is suggested ranging from 40°N to 60°N. Zhesi brachiopod fauna is an endemic fauna,containing more than 75% endemic species and self-grouped as a biogeographic province,termed Inner Mongolia Province. These characteristics indicate that this area was closed or semiclosed at that time. On the Jiamusi-Mongolia Block,the Herlen-Jiamusi Old-land as an obvious "continental barrier"hindered the northward migration of the Zhesi brachiopod fauna and the immigration of brachiopod species from other areas. The Tarim plate has collided with the Kazakhstan plate and the western part of South Tianshan-Beishan-Xar Moron Ocean has been closed. At the same time,the western margin of Jiamusi-Mongolia Block was joined with the Tarim plate. The Xar Moron Ocean in south of Jiamusi-Mongolia Block was wide enough and the ocean temperature rose gradually southward,so that it is not suitable for the cold-water brachiopods to survive and thrive on the northern margin of the North China plate. Thus,the ocean with large width and high temperature formed another natural barrier for the southward migration of the cold-water brachiopods.  相似文献   
955.
北京五里营井水温每天都有24次锯齿状畸变,有很好的规律性,经分析认为是气氡观测对水温造成影响.将气氡和水温供电分离,并在水温地线和地网之间增加一个电感,以阻挡其他干扰信号由地线反馈到观测仪器,改造后水温脉冲干扰彻底消除,观测质量明显提高.  相似文献   
956.
In China, many scenic and tourism areas are suffering from the urbanization that results from physical development of tourism projects, leading to the removal of the vegetative cover, the creation of areas impermeable to water, in-stream modifications, and other problems. In this paper, the risk of soil erosion and its ecological risks in the West Lake Scenic Spots (WLSS) area were quantitatively evaluated by integrating the revised universal soil loss equation (RUSLE) with a digital elevation model (DEM) and geographical information system (GIS) software. The standard RUSLE factors were modified to account for local climatic and topographic characteristics reflected in the DEM maps, and for the soil types and vegetation cover types. An interface was created between the Areinfo software and RUSLE so that the level of soil erosion and its ecological risk in the WLSS area could be mapped immediately once the model factors were defined for the area. The results from an analysis using the Areinfo-RUSLE interface showed that the risk value in 93 % of the expanding western part of the WLSS area was moderate or more severe and the soil erosion risk in this area was thus large compared with that in the rest of the area. This paper mainly aimed to increase the awareness of the soil erosion risk in urbanizing areas and suggest that the local governments should consider the probable ecological risk resulting from soil erosion when enlarging and developing tourism areas.  相似文献   
957.
?????????г???????????????????????????????????????????????????????????????????????????α?????????黯???α?????????????????????????????????α?????????????????????????????????????е????????????,??????????α???????????  相似文献   
958.
研究了贵州省三板溪水库蓄水前后的地震活动特征与地震成因类型, 认为三板溪水库蓄水后出现的地震成因类型可划分为水库诱发构造型和地壳表层卸荷型。  相似文献   
959.
地质调查信息网格平台是基于网格GIS技术,空间数据库具有开放性、集成性,可以对地质调查信息化成果进行多样式、海量数据的组织集成与分布、网络共享服务。结点是平台系统中实现数据资源无缝集成与共享的中间件,是其核心部分。该文叙述地质调查信息网格平台山东结点建设中应用的技术方法。  相似文献   
960.
采用五态连续提取法(SEP)对雷州半岛高桥红树林群落内外不同深度的沉积物砷含量进行测定.结果表明,高桥红树林湿地0~60cm深处沉积物中除Al-结合态砷和Ca-结合态砷含量低,难以检出外,交换态砷、残渣态砷、Fe-结合态砷皆可检出,沉积物砷积累以残渣态砷和 Fe-结合态砷为主,总砷测定含量为7.34±0.39~10.32±0.48 mg/kg,其中以20~40cm深处沉积物总砷测含量最多;不同深度沉积物砷含量中林内与林区外裸滩呈现不同的分布规律,林外裸滩-林缘-林内的表土总砷含量的分布呈波浪式分布,以林缘为最高,总砷达9.97±1.29 mg/kg,林内显著大于林外裸滩(p值<0.05),林内沉积物对砷的吸附强度较林外裸滩高  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