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   1006篇
  免费   176篇
  国内免费   205篇
测绘学   85篇
大气科学   85篇
地球物理   273篇
地质学   558篇
海洋学   90篇
天文学   6篇
综合类   118篇
自然地理   172篇
  2024年   1篇
  2023年   12篇
  2022年   40篇
  2021年   36篇
  2020年   44篇
  2019年   45篇
  2018年   39篇
  2017年   34篇
  2016年   47篇
  2015年   42篇
  2014年   56篇
  2013年   67篇
  2012年   58篇
  2011年   54篇
  2010年   66篇
  2009年   76篇
  2008年   52篇
  2007年   64篇
  2006年   64篇
  2005年   38篇
  2004年   53篇
  2003年   42篇
  2002年   58篇
  2001年   54篇
  2000年   33篇
  1999年   43篇
  1998年   24篇
  1997年   17篇
  1996年   20篇
  1995年   24篇
  1994年   18篇
  1993年   8篇
  1992年   12篇
  1991年   9篇
  1990年   6篇
  1989年   8篇
  1988年   3篇
  1987年   2篇
  1986年   5篇
  1985年   4篇
  1984年   3篇
  1983年   2篇
  1982年   3篇
  1976年   1篇
排序方式: 共有1387条查询结果,搜索用时 46 毫秒
61.
淮南矿区潘三矿构造发育规律定量研究   总被引:1,自引:0,他引:1  
本文采用煤层构造形态空间分析、断裂要素数理统计分析等方法,并引入断裂分形维数指标作为刻划断裂构造发育强度的指标之一,对准南矿区潘三矿地质构造进行了定性—定量分析,揭示了矿井地质构造发育的南北分带性和东西分区性特征。  相似文献   
62.
论证“熵气象学”就是应用热力学第二定律的动力气象,是不足是统计出来的规律,所以它是气象学的发展。  相似文献   
63.
内蒙古胜利煤田锗矿床赋存规律及找矿方向   总被引:5,自引:0,他引:5  
胜利煤田首次发现全国最大的锗矿床,其储量占全国30%以上,且赋存条件好,宜于大型露天开采。研究了其赋存规律,指明了今后找矿方向。  相似文献   
64.
呼伦贝尔盟北部地区由于新构造运动含金地质体长期风化剥蚀,促使金的活化。河流及其2-3级支流发育,流域广,水流充足,有利于砂金矿的迁移、富集。现代的乐山丘陵、宽阔沟谷有利于砂金的保存。该区已发现数十个砂金矿,多为河谷型,主要含金层为含粘土砂层或砂砾层。砂金富集与河谷地貌关系密切,河床弯曲的凸岸、变异部位、关门咀、迎门山等地貌是砂金富集有利部位。该区金直接来源于加里东和华力西花岗岩。结合金的来源、矿床的分布特征和富集规律,指出了该区今后砂金找矿方向。  相似文献   
65.
八家子银多金融矿矿田成矿规律与成矿预测   总被引:3,自引:0,他引:3  
潘厚满 《矿产与地质》2001,15(5):320-323
八家子矿田由NW、NE向两组断裂带与孤形推覆构造交织,控制构成银铅锌、银铁矿床成矿系列,基成矿组份具有组合分带特征。预测东山-冰沟银、铅、锌、炉沟钼和冰沟里银多金属找矿区,经验证,获得找矿成效。  相似文献   
66.
IntroductiontoanInvariantQuantityMethodLiuGuifu(刘桂复)(NamingInstituteofMeteorology,Naming210044ReceivedMarch11.1995,revisedJun...  相似文献   
67.
A diffusion approximation for a network of continuous time reservoirs with power law release rules is examined. Under a mild assumption on the inflow processes, we show that for physically reasonable values of the power law constants, the system of processes converges to a multi-dimensional Gaussian diffusion process. We also illustrate how the limiting Gaussian process may be used to compute approximations to the original system of reservoirs. In addition, we study the quality of our approximations by comparing them to results obtained by simulations of the original watershed model. The simulations offer support for the use of the approximation developed here.  相似文献   
68.
Although organic compounds typically constitute a substantial fraction of the fine particulate matter (PM) in the atmosphere, their molecular composition remains poorly characterized. This is largely because atmospheric particles contain a myriad of diverse organic compounds, not all of which extract in a single solvent or elute through a gas chromatograph; therefore, a substantial portion typically remains unanalyzed. Most often the chemical analysis is performed on a fraction that extracts in organic solvents such as benzene, ether or hexane; consequently, information on the molecular composition of the water-soluble fraction is particularly sparse and incomplete.This paper investigates theoretically the characteristics of the water-soluble fraction by splicing together various strands of information from the literature. We identify specific compounds that are likely to contribute to the water-soluble fraction by juxtaposing observations regarding the extraction characteristics and the molecular composition of atmospheric particulate organics with compound-specific solubility and condensibility for a wide variety of organics. The results show that water-soluble organics, which constitute a substantial fraction of the total organic mass, include C2 to C7 multifunctional compounds (e.g., diacids, polyols, amino acids). The importance of diacids is already recognized; our results provide an impetus for new experiments to establish the atmospheric concentrations and sources of polyols, amino acids and other oxygenated multifunctional compounds.  相似文献   
69.
Many observations and studies indicate that pore fluid pressure in the crustal rocks plays an important role in deformation, faulting, and earthquake processes. Conventional models of pore pressure effects often assume isotropic porous rocks and yield the nondeviatoric pressure effects which seem insufficient to explain diverse phenomena related to pore pressure variation, such as fluid-extraction induced seismicity and crustal weak faults. We derive the anisotropic effective stress law especially for transversely-isotropic and orthotropic rocks, and propose that the deviatoric effects of pore fluid pressure in anisotropic rocks not only affect rock effective strength but also cause variation of shear stresses. Such shear stress variations induced by either pore pressure buildup or pore pressure decline may lead to faulting instability and trigger earthquakes, and provide mechanisms for the failure of crustal weak faults with low level of shear stresses. We believe that the deviatoric effects of pore fluid pressure in anisotropic rocks are of wide application in studies of earthquake precursors and aftershocks, oil and gas reservoir characterization, enhanced oil recovery, and hydraulic fracturing.  相似文献   
70.
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