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   8057篇
  免费   618篇
  国内免费   208篇
测绘学   517篇
大气科学   882篇
地球物理   2439篇
地质学   3440篇
海洋学   395篇
天文学   674篇
综合类   233篇
自然地理   303篇
  2023年   19篇
  2022年   62篇
  2021年   76篇
  2020年   69篇
  2019年   80篇
  2018年   679篇
  2017年   599篇
  2016年   471篇
  2015年   283篇
  2014年   312篇
  2013年   374篇
  2012年   811篇
  2011年   582篇
  2010年   258篇
  2009年   279篇
  2008年   238篇
  2007年   188篇
  2006年   202篇
  2005年   871篇
  2004年   911篇
  2003年   682篇
  2002年   196篇
  2001年   89篇
  2000年   70篇
  1999年   38篇
  1998年   22篇
  1997年   37篇
  1996年   22篇
  1995年   12篇
  1994年   22篇
  1993年   15篇
  1992年   7篇
  1991年   36篇
  1990年   27篇
  1989年   21篇
  1988年   13篇
  1987年   23篇
  1986年   15篇
  1985年   16篇
  1984年   14篇
  1982年   7篇
  1980年   9篇
  1979年   9篇
  1978年   9篇
  1975年   10篇
  1974年   11篇
  1973年   7篇
  1972年   8篇
  1971年   7篇
  1969年   8篇
排序方式: 共有8883条查询结果,搜索用时 15 毫秒
1.
Geometric and kinematic models reveal that rotation of layers during thrusting or development of drag folds produced by movement along listric thrust faults results in the formation of dilation space at the junction of the thrust ramp with the basal decollement. This is accompanied by upwarping of the basement to occupy the available space thereby producing an antiformal structure, which restricts the thrust displacement. The structure is termed a decollement upwarp and examples are cited from the foothill belt of the Himalaya.  相似文献   
2.
3.
4.
The present work applies the method of characteristics to study the behaviour of planar and cylindrical wave-heads propagating through a perfectly electrically conducting and thermally radiating inviscid gas under the optically thin limit in the presence of a transverse magnetic field. The true nonlinear progress of the flow variable gradients at the wavefront is predicted and the critical distance at which the characteristics pile up at the wavefront to form a shock wave is obtained. It is investigated as to how the effects of radiative flux, the magnetic field strength and the specific heat ratio influence the process of steepening or flattening of the characteristic wavefront.  相似文献   
5.
The oscillatory, conjugate and asymptotic behaviours of the principal and non-principal solutions of the Blasius and corresponding heat transfer equations governing the compressible laminar boundary-layer flow over a semi-infinite flat plate with heat flux have been studied; the results of the discussion being based on the asymptotic integrations of second-order linear differential equations.  相似文献   
6.
7.
The sub-iron-iron flux ratio in cosmic rays at an atmospheric depth of 9.8 g cm–2 has been estimated using a balloon-borne CR-39 (HCB) stack launched from Alice Springs for 32 hours. The recovered and chemically etched plates were analysed optically and the measured etch pit diameters yielded the sub-iron-iron flux ratio at the flight altitude. The sub-iron-iron flux ratio has been corrected for the top of the atmosphere by considering the loss of heavy ions due to nuclear interaction and fragmentation. The present result has been compared with the result expected from the source composition derived by Protheroeet al. as well as other authors.  相似文献   
8.
9.
Introducing a concept of equivalent mass depth of flow, this study describes the phenomenon of non‐point source pollutant (metal) transport for pavement (or overland) flow in analogy with wave propagation in wide open channels. Hysteretic and normal mass rating curves are developed for runoff rate and mass of 12 dissolved and particulate‐bound metal elements (pollutants) using the rainfall‐runoff and water quality data of the 15 × 20 m2 instrumented pavement in Cincinnati, USA. Normal mass rating curves developed for easy computation of pollutant load are found to be of a form similar to Manning's, which is valid for open channel flows. Based on the hysteresis analysis, wave types for dissolution and mixing of particulate‐bound metals are identified. The analysis finds that the second‐order partial‐differential equation normally used for metal transport does not have the efficacy to describe fully the strong non‐linear phenomena such as is described for various metal elements by dynamic waves. In addition, the proportionality concept of the popular SCS‐CN concept is extended for determining the potential maximum metal mass Mp of all the 12 elements transported by a rain storm and related to the antecedent dry period (ADP). For the primary metal zinc element, Mp is found to increase with the ADP and vice versa. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   
10.
Introduction The Himalaya is considered to be the youngest mountains on the earth, and is tectonically very active, and hence inherently (geologically) vulnerable to hazards. Extreme rainfall events, landslides, debris flows, torrents and flash floods due…  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