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   262289篇
  免费   4329篇
  国内免费   3418篇
测绘学   7000篇
大气科学   19285篇
地球物理   54869篇
地质学   91354篇
海洋学   21741篇
天文学   56718篇
综合类   1026篇
自然地理   18043篇
  2021年   2248篇
  2020年   2621篇
  2019年   2859篇
  2018年   4020篇
  2017年   3653篇
  2016年   6003篇
  2015年   4233篇
  2014年   6949篇
  2013年   14248篇
  2012年   6662篇
  2011年   8175篇
  2010年   7184篇
  2009年   9786篇
  2008年   8660篇
  2007年   8133篇
  2006年   9697篇
  2005年   7838篇
  2004年   7739篇
  2003年   7218篇
  2002年   6791篇
  2001年   6053篇
  2000年   5975篇
  1999年   5206篇
  1998年   5245篇
  1997年   5046篇
  1996年   4684篇
  1995年   4429篇
  1994年   4118篇
  1993年   3858篇
  1992年   3644篇
  1991年   3599篇
  1990年   3763篇
  1989年   3520篇
  1988年   3303篇
  1987年   3858篇
  1986年   3422篇
  1985年   4236篇
  1984年   4742篇
  1983年   4409篇
  1982年   4319篇
  1981年   3921篇
  1980年   3646篇
  1979年   3508篇
  1978年   3487篇
  1977年   3285篇
  1976年   3055篇
  1975年   2960篇
  1974年   2917篇
  1973年   3079篇
  1972年   2024篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
992.
A statistical ensemble of microphysical parameters of the background stratospheric aerosol at altitudes of 15 to 30 km is modeled on the basis of experimental data. The aerosol attenuation coefficients (AACs) in the wavelength range 0.38–16.3 μm are calculated for all realizations of the ensemble by algorithms of the Mie theory. Analysis of correlations between the AACs and the microphysical parameters indicate that the AAC correlates most strongly with the total volume V and area S of all particles. The errors of determining the microphysical parameters from AAC measurements are analyzed via the method of linear regression. It is shown that, if the AAC is measured with an error of 5%, the errors of determining both the particle size distribution (PSD) for particles with sizes of 0.4 to 4 μm and the parameter S are an order of magnitude smaller than the prior uncertainty, whereas the error of determining V is two orders of magnitude smaller than the prior uncertainty. Schemes of AAC measurements with the SAGE III, ISAMS, CLAES, HALOE instruments and an IR interferometer in the visible and IR regions are discussed. It is shown that combining the schemes makes it possible to extend the range of particle sizes for which the PSD is retrieved with a satisfactory accuracy and to increase the accuracy of determining S and V substantially and the accuracy of determining the total number of particles N opt to a lesser extent. Examples of interpreting AAC measurements carried out simultaneously with the SAGE III and HALOE instruments within the same spatial region are presented. A systematic discrepancy between vertical profiles of S and V obtained from SAGE III and HALOE measurements is revealed.  相似文献   
993.
994.
995.
996.
997.
Within the framework of the linear theory taking into account the action of the Coriolis force, we study waves induced in a continuously stratified fluid with one thermocline by periodic variations of pressure on the free surface. The fluid fills a bounded basin of constant depth. We establish the dependences of the wave amplitudes and wave velocities on the period of disturbing pressure. The sequence of transformations of generated waves from the barotropic character of motion to baroclinic depending on changes in the period of disturbing pressure is studied in detail.  相似文献   
998.
Phytoplankton variability on the Faroe Shelf   总被引:2,自引:2,他引:2  
  相似文献   
999.
The paper considers the application of self-organizing models, specifically, the method of grouped arguments consideration (MGAC), to forecast short and non-stationary time series of observations in the ocean. A sequence of operations for the treatment of observational series is suggested. To assess its efficiency, we have used mean monthly oxygen concentration data collected in the surface and near-bottom layers of the Taganrog Bay. It is shown that the application of the MGAC model allows one to reduce by two times the root-mean-square error of that of the series prediction by five points, in comparison with the Jenkins-Box regressional model. It has been concluded that the predictors' non-linear functions may be effectively used in the treatment of short samplings. Translated by Vladimir A. Puchkin.  相似文献   
1000.
To solve problems concerning wave elements and wave propagation, an effective way is the wave energy balance equation, which is widely applied in oceanography and ocean dynamics for its simple computation. The present papaer advances wave energy balance equations considering lateral energy transmission and energy loss as the governing equation for the study of wave refraction-diffraction. For the mathematical model, numerical simulation is made by means of difference method, and the result is verified with two examples.  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