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   81487篇
  免费   1036篇
  国内免费   498篇
测绘学   1887篇
大气科学   5235篇
地球物理   15566篇
地质学   29169篇
海洋学   7283篇
天文学   19544篇
综合类   195篇
自然地理   4142篇
  2022年   586篇
  2021年   909篇
  2020年   1027篇
  2019年   1089篇
  2018年   2343篇
  2017年   2196篇
  2016年   2521篇
  2015年   1215篇
  2014年   2375篇
  2013年   4228篇
  2012年   2562篇
  2011年   3224篇
  2010年   3040篇
  2009年   3672篇
  2008年   3332篇
  2007年   3539篇
  2006年   3222篇
  2005年   2287篇
  2004年   2168篇
  2003年   2086篇
  2002年   1970篇
  2001年   1877篇
  2000年   1690篇
  1999年   1443篇
  1998年   1398篇
  1997年   1453篇
  1996年   1135篇
  1995年   1127篇
  1994年   1069篇
  1993年   968篇
  1992年   945篇
  1991年   927篇
  1990年   1057篇
  1989年   898篇
  1988年   871篇
  1987年   959篇
  1986年   783篇
  1985年   1073篇
  1984年   1208篇
  1983年   1146篇
  1982年   1077篇
  1981年   1024篇
  1980年   939篇
  1979年   871篇
  1978年   896篇
  1977年   800篇
  1976年   750篇
  1975年   674篇
  1974年   744篇
  1973年   760篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
971.
A method of determination of atmospheric dynamic characteristics from the data of remote sensing from a geostationary satellite is described. The method is based on the use of inhomogeneities in the concentration field of a conservative additive as tracers and on the application of correlation-extreme algorithms. Unlike the common methods used abroad, this method is able to determine not only the vector field of wind velocity but also the coefficient of turbulent diffusion and vorticity. Results of computations of the fields of the horizontal component of wind velocity and the effective coefficient of horizontal mesoscale turbulent diffusion from the Meteosat-8 SEVIRI water-vapor channel data are presented. It is shown that the average values of the effective coefficient of mesoscale horizontal turbulent diffusion in the areas with a predominantly turbulized air-mass motion are 1.5 times greater than in the areas where a laminar motion dominates. Specific features of the calculated values of the upper-troposphere dynamic characteristics in different stages of the North Atlantic TC Helene (September 2006) are analyzed.  相似文献   
972.
973.
Observations from a surface mooring, in a weak-flow regime over the southeastern Bering Sea shelf, were used to derive surface heat fluxes for the period May–July 1996. Changes in heat content of the water column also were determined from subsurface temperature measurements. Agreement of net surface heat flux and change in heat content was within 2%. This result provides additional evidence that heat advection and diffusion are small in this region.  相似文献   
974.
The Southeast Basin of France is the thickest onshore French sedimentary basin which contains locally as much as 10 km of Mesozoic-Cenozoic sediment. Basin development occurred in several stages between late Carboniferous and late Cretaceous times. Partial tectonic inversion took place during two compressive events, the so-called ‘Pyrenean’ and ‘Alpine’ phases of late Cretaceous-early Tertiary and late Tertiary ages respectively. They are separated by an intervening stretching event of Oligocene age, which further south resulted in the opening of the western Mediterranean oceanic basin. As a result of this complex tectonic history, structural traps were difficult to image on the seismic data shot during the first phase of exploration prior to 1980. Oil and gas natural seeps, and shows in several wells, indicate that some petroleum systems are, or have been active, at least in some places.The present erosional western margin of the basin is more or less superimposed on the initial Triassic-Jurassic margin. Margin subsidence and Tertiary inversion are discussed using regional sections on which the polyphase history of the entire basin is well shown. These sections are located on three major segments where the Mesozoic margin is either partly preserved (Ardèche), or has been partly inverted in late Tertiary times (Vercors-Chartreuse), or has been completely inverted in early Tertiary times (Corbières-eastern Pyrenees). 1-D ‘Genex’ basin modelling on the Ardèche segment, and 2-D ‘Thrustpack’ structural-maturity modelling in the Vercors-Chartreuse segment are used to further assess the remaining petroleum plays.  相似文献   
975.
976.
977.
The study of diatoms and benthic foraminifers from the southeastern shelf of the Laptev Sea shows that their most diverse and abundant recent assemblages populate the peripheral underwater part of the Lena River delta representing the marginal filter of the sea. This area is characterized by an intense interaction between the fresh waters of the Siberian rivers and the basin seawater, the Atlantic one included. Local Late Holocene (~last 2300 years) environments reflect the main regional and global paleoclimatic changes, the Medieval Warm Period (~600–1100 years B.P.) and the Little Ice Age (~100–600 years B.P.) inclusive. In addition, the composition and distribution of planktonic foraminifers implies a strong influence of the Atlantic water during the Holocene optimum ~5100–6200 years B.P.  相似文献   
978.
979.
The regular wave interaction with a twin concentric porous circular cylinder system consisting of an inner impermeable cylinder and an outer perforated cylinder was studied through physical model and numerical model studies. The experiments were carried out on the twin concentric cylinder model in a wave flume to study the wave runup and rundown at the leading and trailing edges of the perforated cylinder. It was found that the maximum wave runup on the perforated cylinder is almost same as the incident wave height. The experimental results were used to develop the predictive formulae for the wave runup and rundown on the perforated cylinder, which can be easily used for design applications. The wave runup profiles around the perforated cylinder for different values of ka and porosities were studied numerically using Green's Identity Method. The results of the numerical study are presented and compared with the experimental measurements.  相似文献   
980.
The concepts which have guided our thinking about chemical processes and interactions of organic matter in seawater are identified and their utility assessed. Some recommendations for the future are made.  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