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   61719篇
  免费   10442篇
  国内免费   16325篇
测绘学   4548篇
大气科学   7865篇
地球物理   12052篇
地质学   38076篇
海洋学   8779篇
天文学   2214篇
综合类   4206篇
自然地理   10746篇
  2024年   370篇
  2023年   983篇
  2022年   2036篇
  2021年   2182篇
  2020年   2324篇
  2019年   2661篇
  2018年   2188篇
  2017年   2432篇
  2016年   2628篇
  2015年   2805篇
  2014年   3493篇
  2013年   3429篇
  2012年   3790篇
  2011年   3936篇
  2010年   3287篇
  2009年   4008篇
  2008年   3976篇
  2007年   4336篇
  2006年   4209篇
  2005年   3714篇
  2004年   3517篇
  2003年   3334篇
  2002年   2947篇
  2001年   2563篇
  2000年   2460篇
  1999年   2208篇
  1998年   1896篇
  1997年   1788篇
  1996年   1591篇
  1995年   1327篇
  1994年   1356篇
  1993年   1127篇
  1992年   885篇
  1991年   636篇
  1990年   544篇
  1989年   451篇
  1988年   325篇
  1987年   226篇
  1986年   133篇
  1985年   93篇
  1984年   40篇
  1983年   35篇
  1982年   39篇
  1981年   27篇
  1980年   23篇
  1979年   34篇
  1978年   35篇
  1977年   24篇
  1975年   4篇
  1954年   17篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
Aimed at promoting regional coalitions and expanding the approach to economic links, this paper puts forward some new concepts such as link intensity and receiving coefficient, expounds the indexes of quantitative analysis of economic links and establishes the quantitative-analysis model of economic links. With help of the model, this paper calculates the values of the link intensities between Su-Xi-Chang (Suzhou-Wuxi-Changzhou) region and Shanghai, and analyzes the regional difference of the economic links.  相似文献   
62.
63.
Erosion of man-made, forestry drainage channels occurs when the plough cuts through the surface peat layer into the underlying erodible mineral soil. A procedure is developed, based on hydraulic considerations, which will allow the drainage engineer to design stable drainage networks in upland forestry plantations. An example design chart is given for an erodible sandy loam type soil.  相似文献   
64.
65.
本文根据大量的调查资料,采用多指标评判打分法对铜川市区滑坡逐一进行了危险性综合评价,旨在为该区滑坡的预测与防治提供可靠的依据。  相似文献   
66.
We apply the ztrace algorithm to the optical NOG and infrared PSC z galaxy catalogues to reconstruct the pattern of primordial fluctuations that have generated our local Universe. We check that the density fields traced by the two catalogues are well correlated, and consistent with a linear relation [either in δ or in  log (1 +δ)  ] with relative bias (of NOG with respect to PSC z )   b rel= 1.1 ± 0.1  . The relative bias relation is used to fill the optical zone of avoidance at  | b | < 20°  using the PSC z galaxy density field.
We perform extensive testing on simulated galaxy catalogues to optimize the reconstruction. The quality of the reconstruction is predicted to be good at large scales, up to a limiting wavenumber   k lim≃ 0.4 h Mpc−1  beyond which all information is lost. We find that the improvement arising from the denser sampling of the optical catalogue is compensated by the uncertainties connected to the larger zone of avoidance.
The initial conditions reconstructed from the NOG catalogue are found (analogously to those from the PSC z ) to be consistent with a Gaussian paradigm. We use the reconstructions to produce sets of initial conditions ready to be used for constrained simulations of our local Universe.  相似文献   
67.
Spectral analysis of the components of the relative atmospheric angular momentum vector is performed based on the series of these components for the 6 h intervals within the period of 1958–2000. These series have been computed in the Subbureau of the Atmospheric Angular Momentum of the International Earth Rotation Service using the NCEP/NCAR reanalysis of atmospheric observations. The basic harmonics of diurnal tides are determined. New results on the fortnight's and week's duration oscillations of the equatorial components of the atmospheric angular momentum are obtained. The zonal tides transformation mechanisms in the atmosphere are discussed. It is shown that the main mechanism of the zonal tides effect on the atmospheric variability is the amplitude modulation of daily oscillations of the relative atmospheric angular momentum. The effects of the atmospheric tides on the Earth rotation are discussed.  相似文献   
68.
The paper provides a new stereo‐analytical method, which is a combination of the stereographic method and analytical methods, to separate finite removable blocks from the infinite and tapered blocks in discontinuous rock masses. The methodology has applicability to both convex and concave blocks. Application of the methodology is illustrated through examples. Addition of this method to the existing block theory procedures available in the literature improves the capability of block theory in solving practical problems in rock engineering. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   
69.
70.
本文论述了保安地区火山岩的地质、岩石、副矿物、岩石化学、微量元素、稀土元素、稳定同位素、火山岩相及火山机构等特征。并对其演化规律、形成机制与成矿作用的关系,作了初步探讨。  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