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   91481篇
  免费   1078篇
  国内免费   759篇
测绘学   2363篇
大气科学   5968篇
地球物理   17063篇
地质学   35047篇
海洋学   7876篇
天文学   20785篇
综合类   379篇
自然地理   3837篇
  2022年   666篇
  2021年   1034篇
  2020年   1124篇
  2019年   1219篇
  2018年   4337篇
  2017年   3914篇
  2016年   3787篇
  2015年   1488篇
  2014年   2702篇
  2013年   4184篇
  2012年   3483篇
  2011年   5225篇
  2010年   4561篇
  2009年   5452篇
  2008年   4648篇
  2007年   5191篇
  2006年   3402篇
  2005年   2453篇
  2004年   2424篇
  2003年   2361篇
  2002年   2202篇
  2001年   1876篇
  2000年   1726篇
  1999年   1298篇
  1998年   1340篇
  1997年   1288篇
  1996年   1064篇
  1995年   1066篇
  1994年   936篇
  1993年   811篇
  1992年   806篇
  1991年   815篇
  1990年   877篇
  1989年   689篇
  1988年   712篇
  1987年   733篇
  1986年   640篇
  1985年   844篇
  1984年   910篇
  1983年   807篇
  1982年   773篇
  1981年   696篇
  1980年   700篇
  1979年   618篇
  1978年   646篇
  1977年   526篇
  1976年   491篇
  1975年   502篇
  1974年   443篇
  1973年   507篇
排序方式: 共有10000条查询结果,搜索用时 921 毫秒
991.
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   
992.
993.
This paper studies the influence of shelf tidal flows on the structure of surface and near-bottom turbulent boundary layers.Translated by Vladimir A. Puchkin.  相似文献   
994.
995.
Traditional methods for determining spatial distributions of planktonic taxa involve net, pump, and bottle collections followed by the tedious and time-consuming task of plankton sample analysis. Thus, plankton ecologists often require months or even years to process samples from a single study. In this paper, we present a method that allows rapid visualization of the distribution of planktonic taxa while at sea. Rapid characterization of plankton distributions is essential in the dynamic physical environment, where biological and physical patterns can change quickly. Such a “sample-and-observe” capability is necessary for mapping ephemeral features (such as patches, eddies, jets, plumes) and determining appropriate locations to conduct more localized sampling, including in situ observational studies. We describe the techniques used in imaging the plankton, analyzing the video, and visualizing the data. We present an example of at-sea data analysis conducted aboard R.V. Columbus Iselin on Georges Bank in May 1994 and visualizations of the 3-dimensional distribution of selected planktonic taxa in a 2 × 2 km × 90 m volume of seawater. A video of the image processing and visualization is included on the CD-ROM accompanying this volume and is an essential part of this paper.  相似文献   
996.
997.
998.
999.
The basic relations of the classical dyamic method have been complemented with the condition allowing for the non-monotonicity of the vertical kinematic structure. The elements of the multi-layered system of geostrophic currents have been found to correlate over depth with seawater density and hydrostatic pressure distribution. An example of the analysis of the vertical structure of currents, involving specific hydrological data, is given. Translated by Vladimir A. Puchkin.  相似文献   
1000.
The sway, heave and roll added masses of three uniform cylinders with semi-circular, rectangular and triangular cross-sectional shapes in shallow and narrow water are numerically analysed. The method is based on simulation of the potential flow induced by the cylinder's mode of motion. The effects of shallow and narrow water on added mass are analysed and presented. It is concluded that the shallow and narrow water effects on added mass depend on the different cross-section shapes of the cylinders. In particular, the water depth effect on sway added mass is stronger than that on heave added mass while the narrow water effect on sway is weaker than that on heave. The shallow water effect on added mass tends to weaken the narrow water effect. Lastly the effect of shallow and narrow water on added mass on a rectangular cylinder is the strongest while that on a triangular cylinder is the weakest.  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