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   51254篇
  免费   9339篇
  国内免费   12261篇
测绘学   4165篇
大气科学   5171篇
地球物理   9937篇
地质学   34802篇
海洋学   5491篇
天文学   2232篇
综合类   3600篇
自然地理   7456篇
  2024年   205篇
  2023年   536篇
  2022年   1462篇
  2021年   1653篇
  2020年   1705篇
  2019年   2086篇
  2018年   1632篇
  2017年   1847篇
  2016年   2062篇
  2015年   2207篇
  2014年   2774篇
  2013年   2746篇
  2012年   3066篇
  2011年   3363篇
  2010年   2845篇
  2009年   3388篇
  2008年   3349篇
  2007年   3677篇
  2006年   3615篇
  2005年   3218篇
  2004年   2998篇
  2003年   2833篇
  2002年   2523篇
  2001年   2219篇
  2000年   2078篇
  1999年   1898篇
  1998年   1685篇
  1997年   1507篇
  1996年   1348篇
  1995年   1117篇
  1994年   1149篇
  1993年   962篇
  1992年   757篇
  1991年   524篇
  1990年   464篇
  1989年   366篇
  1988年   290篇
  1987年   181篇
  1986年   134篇
  1985年   99篇
  1984年   42篇
  1983年   32篇
  1982年   32篇
  1981年   21篇
  1980年   25篇
  1979年   30篇
  1978年   40篇
  1977年   29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 171 毫秒
951.
鄂尔多斯盆地上古生界高分辨率层序地层分析   总被引:35,自引:1,他引:35  
按基准面旋回原理,将鄂尔多斯盆地上古生界本溪组(C2b)、太原组(P1t)、山西组(P1s)和下石盒子组(P1xs)划分为3个超长期、8个长期、19个中期和62个短期旋回层序:较为详细地介绍了各级别层序的结构类型、叠加样式和沉积演化序列;建立以长期旋回层序为年代地层框架,中期旋回层序为等时地层对比单元的层序的地层格架;并讨论高分辨率层序地层与天然气藏的关系。  相似文献   
952.
张箭 《矿物岩石》2002,22(4):83-86
气藏评价尚未结束之前,开发的早期部署工作非常困难。针对洛带气田蓬莱镇组气藏的开发部署工作,利用目前许多新方法对开发层系划分、采气规模、开发规划、合理配产和井网部署等进行了优化研究,对气藏开发提出了指导性意见,且对类似气藏也具有参考意义。  相似文献   
953.
饶玉学 《矿产与地质》2002,16(6):327-331
详细研究了燕山东段地区花岗岩类的侵入时代、产出形式和成因类型 ,指出该区与花岗岩有关的三个金属成矿系列。  相似文献   
954.
回顾了中国科学院国家知识创新试点工程实施以来特别是启动阶段3年里固体地球科学知识创新工程试点各项工作的进展情况,包括项目与经费、创新成果、人才吸引、科研竞争力提升、院地合作推进等方面,分析和总结了中国科学院固体地球科学知识创新工程现状,并展望了固体地球科学知识创新工程若干重要发展态势。  相似文献   
955.
Groundwater-flow modeling in the Yucatan karstic aquifer, Mexico   总被引:1,自引:0,他引:1  
The current conceptual model of the unconfined karstic aquifer in the Yucatan Peninsula, Mexico, is that a fresh-water lens floats above denser saline water that penetrates more than 40 km inland. The transmissivity of the aquifer is very high so the hydraulic gradient is very low, ranging from 7–10 mm/km through most of the northern part of the peninsula. The computer modeling program AQUIFER was used to investigate the regional groundwater flow in the aquifer. The karstified zone was modeled using the assumption that it acts hydraulically similar to a granular, porous medium. As part of the calibration, the following hypotheses were tested: (1) karstic features play an important role in the groundwater-flow system; (2) a ring or belt of sinkholes in the area is a manifestation of a zone of high transmissivity that facilitates the channeling of groundwater toward the Gulf of Mexico; and (3) the geologic features in the southern part of Yucatan influence the groundwater-flow system. The model shows that the Sierrita de Ticul fault, in the southwestern part of the study area, acts as a flow barrier and head values decline toward the northeast. The modeling also shows that the regional flow-system dynamics have not been altered despite the large number of pumping wells because the volume of water pumped is small compared with the volume of recharge, and the well-developed karst system of the region has a very high hydraulic conductivity. Electronic Publication  相似文献   
956.
The application of variations in the earth's gravity in groundwater exploration on a regional scale, especially in sedimentary basins, metamorphic terrains, valley fills, and for buried alluvial channels, is well established. However, its use in hard crystalline rocks is little known. In granite, for example, the upper weathered layer is a potential primary aquifer, and the underlying fractured rock can form a secondary aquifer. Fracturing and weathering increases the porosity of a rock, thereby reducing the bulk density. Changes in gravity anomalies of 0.1–0.7 mGal for granites, due to weathering or variations in lithology, can be detected. To test the use of gravity as a groundwater exploration tool for crystalline rocks, a gravity survey of the peninsular shield granites underlying Osmania University Campus, Hyderabad, India, was undertaken. At the site, gravity anomalies reflect variations in the lithology and in the thickness of weathered zones. These anomalies also define the position of intrusives and lineaments. Areas of more deeply weathered granite that contain wells of higher groundwater yield are represented by negative gravity values. In the weathered zone, well yield has an inverse relation to the magnitudes of residual gravity. The study confirms the feasibility of gravity as a tool for groundwater exploration in crystalline rocks. Electronic Publication  相似文献   
957.
The composition of quartz inclusions and trace elements in ore indicate that gold-bearing fluid in the Xiadian gold deposit,Shandong Province,stemmed from both mantle and magma,belonging to a composite origin.Based on theoretical analysis and high temperature and high pressure experimental studies,gold-bearing fluid initiative localization mechanism and the forming environment of ore-host rocks are discussed in the present paper.The composite fluid extracted gold from rocks because of its expanding and injecting forces and injecting forces and flew through ore-conducive structures,leading to the breakup of rocks.The generation of ore-host faults and the precipitation of gold-bearing fluid occurred almost simultaneously.This study provides fur-ther information about the relationships between gold ore veins and basic-ultrabasic vein rocks and intermediate vein rocks,the spatial distribution of gold ore veins and the rules governing the migration of ore fluids.  相似文献   
958.
SK setV4.0是中国地质科学院岩溶地质研究所GIS中心2001年4月开发成功的、具有自主板权的专业GIS平台软件。它集成了现今较为先进的组件、控件重用,面向对象编程等技术,并以美国Inprise公司的BorladnC^ Builder编译软件为开发平台,提供了全中文菜单环境,不仅具有基本信息和多图层查询、相关分析动态监测、多因子分析、图斑编辑、自动演示、系统维护等功能,而且还具有快速响应的工具条、友好的对话框和较强的纠错机制,很适合缺乏专业GIS人才的县市级政府管理部门使用。文中还以贵州省沿河县资源遥感信息系统为例,对SK setV4.0的功能和使用方法进行了具体的介绍。  相似文献   
959.
Considering the existing problems of the petroleum system, this paper brings forward the concept of natural gas accumulation system and presents the dividing principles. Then detailed statistics on the accumulation factors of the 32 typical natural gas accumulation systems in China and studies on the laws controlling distribution of gas are collected. The research shows that the petroleum accumulation system is the basic unit controlling petroleum generation, migration and accumulation. Generating intensity, generating amount, accumulating efficiency and migration distance plays an important role in the distribution of natural gas. Through analysis on results of resources evaluation, discovered reserves and residual reserves, potential areas in middle-scaled petroliferous basins in China are forecasted in this paper. Ordos, Sichuan, Tarim and Qaidam basins are found out to be the main basins developing and enriching gas accumulation systems.  相似文献   
960.
The Gulf of Corinth in central Greece is an active normal fault zone with particularly clear evidence of isostatic footwall uplift, constrained by Quaternary marine terraces, and hanging-wall subsidence and sedimentation. It is bounded to the south by a Pliocene to Early Pleistocene sedimentary basin, which is now eroding into the Gulf. Previous work has suggested that the relief across this region has increased dramatically since the Early Pleistocene, due to the isostatic response to increased rates of footwall erosion and hanging-wall sedimentation. It is indeed assumed here that incision accompanying the draw-down of global sea-level at 0.9 Ma, during the first major Pleistocene glaciation, initiated the erosion of the basin south of the Gulf of Corinth and so abruptly increased the sedimentation rate in the Gulf. The resulting transient thermal and isostatic response to these changes is modelled, with the subsiding depocentre and eroding sediment source coupled by flow in the lower continental crust. The subsequent enhancement of relief, involving an increase in bathymetry from near zero to 900 m and 500 m of uplift of the eroding land surface in the sediment source, is shown to be a direct consequence of this change. The model is sensitive to the effective viscosity of the lower crust, and can thus resolve this parameter by matching observations. A value of 6×1019 Pa s is indicated, suggesting a viscosity at the Moho no greater than 1018 Pa s. Similar transient topographic effects caused by increased rates of sedimentation and erosion are likely to be widespread within the geological record, suggesting that this coupling process involving flow in the weak lower crust may be of major geological and geomorphological importance.  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