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   3587篇
  免费   134篇
  国内免费   31篇
测绘学   117篇
大气科学   390篇
地球物理   740篇
地质学   1203篇
海洋学   361篇
天文学   674篇
综合类   4篇
自然地理   263篇
  2022年   11篇
  2021年   36篇
  2020年   43篇
  2019年   51篇
  2018年   94篇
  2017年   69篇
  2016年   127篇
  2015年   77篇
  2014年   107篇
  2013年   185篇
  2012年   139篇
  2011年   182篇
  2010年   148篇
  2009年   227篇
  2008年   204篇
  2007年   178篇
  2006年   167篇
  2005年   143篇
  2004年   149篇
  2003年   123篇
  2002年   137篇
  2001年   103篇
  2000年   100篇
  1999年   78篇
  1998年   90篇
  1997年   55篇
  1996年   57篇
  1995年   40篇
  1994年   34篇
  1993年   40篇
  1992年   27篇
  1991年   39篇
  1990年   29篇
  1989年   32篇
  1988年   10篇
  1987年   37篇
  1986年   16篇
  1985年   27篇
  1984年   40篇
  1983年   24篇
  1982年   23篇
  1981年   15篇
  1980年   16篇
  1979年   19篇
  1978年   19篇
  1977年   16篇
  1976年   17篇
  1975年   21篇
  1974年   17篇
  1971年   11篇
排序方式: 共有3752条查询结果,搜索用时 234 毫秒
101.
102.
. Three transgressive–regressive 2nd-order cycles were identified in the Upper Aptian–Albian fluvial and marine deposits of the Lusitanian Basin. Its widespread nature, probably including eustatic origin, allows correlation between the southern package, with precise stratigraphic positioning, and the northern series with a poorly constrained age. The main unconformities can be related to the onset of an oceanic crust, in the western margin of Galicia during the Late Aptian, in the bay of Biscay during the Early Albian, and, to the northwest of the Galicia triple point, during the Middle to Late Albian transition, and, at the Albian–Cenomanian boundary, to a probable compressive event with Africa due to the rotation of Iberia. To cite this article: J. Dinis et al., C. R. Geoscience 334 (2002) 757–764.  相似文献   
103.
We analyse longitudinal river profiles in southwestern Taiwan. As all necessary data are not available, a physical modelling of river erosion would be subject to large uncertainties. We thus shortcut this modelling and adopt simple empirical exponential equations giving riverbed elevation as a function of downstream distance. We identify a positive altimetric anomaly, which reveals active uplift of an anticline at the front of the fold-and-thrust belt. To cite this article: J. Angelier, R.-F. Chen, C. R. Geoscience 334 (2002) 1103–1111.  相似文献   
104.
105.
Pore‐ice sublimation is a prerequisite for aeolian activity in cold environments where surface sediments hold significant amounts of frozen water. Few quantitative studies have defined the rate of grain release from cemented surfaces by pore‐ice sublimation. In 1996–1997, controlled field experiments at Presqu'ile Beach, Ontario, were implemented to measure sediment release from frozen surfaces. The release rates were compared to the local wind regime, ambient temperature and humidity. In additional field experiments, the effect of sediment water content on grain release by sublimation was examined. From the experimental results, an equation which predicts grain release based on local wind speed, ground temperature, humidity, and surface water content is proposed. Predicted release rates show reasonable agreement with natural deflation measured on the beach at Presqu'ile Provincial Park.  相似文献   
106.
107.
108.
109.
Military training activities reduce vegetation cover, disturb crusts, and degrade soil aggregates, making the land more vulnerable to wind erosion. The objective of this study was to quantify wind erosion rates for typical conditions at the Marine Corps Air Ground Combat Center, Twentynine Palms, CA, U.S.A. Five Big Spring Number Eight (BSNE) sampler stations were installed at each of five sites. Each BSNE station consisted of five BSNE samplers with the lowest sampler at 0·05 m and the highest sampler at 1·0 m above the soil surface. Once a month, sediment was collected from the samplers for analysis. Occurrence of saltating soil aggregates was recorded every hour using Sensits, one at each site. The site with the most erosion had a sediment discharge of 311 kg m−1 over a period of 17 months. Other sites eroded much less because of significant rock cover or the presence of a crust. Hourly sediment discharge was estimated combining hourly Sensit count and monthly sediment discharge measured using BSNE samplers. More simultaneously measured data are needed to better characterize the relationship between these two and reconstruct a detailed time-series of wind erosion. This measured time-series can then be used for comparison with simulation results from process-based wind erosion models such as the Wind Erosion Prediction System (WEPS), once it has been adapted to the unique aspects of military lands.  相似文献   
110.
We compare two geophysical survey measurements of the same type made at different times in order to characterize the change in the geological medium during the elapsed time. The aim of this study is to develop a strategy using a full non-linear inversion algorithm as the interpretation tool. In this way, not only the location and the form of the changes are recovered, but also the changes in the material parameters of the geological medium can be estimated. In order to solve this fully non-linear problem, the so-called ‘multiplicative regularized contrast source inversion’ (MR-CSI) method is employed. The unique property of this iterative method is that it does not solve the forward problem at each iterative step. This makes it possible to use the non-linear inversion algorithm for large-scale computation problems. The numerical results show that by taking into account the non-linear nature of the problem, interpretation of the time-lapse data can be significantly improved, compared with that obtained using linear inversion.  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