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   95899篇
  免费   1604篇
  国内免费   1599篇
测绘学   3092篇
大气科学   7067篇
地球物理   18982篇
地质学   36553篇
海洋学   7306篇
天文学   18325篇
综合类   2346篇
自然地理   5431篇
  2022年   415篇
  2021年   706篇
  2020年   793篇
  2019年   854篇
  2018年   6351篇
  2017年   5550篇
  2016年   4724篇
  2015年   1586篇
  2014年   2349篇
  2013年   3921篇
  2012年   3247篇
  2011年   5697篇
  2010年   4557篇
  2009年   5764篇
  2008年   5082篇
  2007年   5302篇
  2006年   3052篇
  2005年   2628篇
  2004年   2740篇
  2003年   2564篇
  2002年   2214篇
  2001年   1897篇
  2000年   1817篇
  1999年   1443篇
  1998年   1545篇
  1997年   1448篇
  1996年   1150篇
  1995年   1174篇
  1994年   988篇
  1993年   913篇
  1992年   877篇
  1991年   786篇
  1990年   876篇
  1989年   739篇
  1988年   677篇
  1987年   847篇
  1986年   702篇
  1985年   889篇
  1984年   957篇
  1983年   890篇
  1982年   862篇
  1981年   754篇
  1980年   700篇
  1979年   631篇
  1978年   616篇
  1977年   567篇
  1976年   561篇
  1975年   514篇
  1974年   521篇
  1973年   486篇
排序方式: 共有10000条查询结果,搜索用时 156 毫秒
981.
982.
983.
984.
The dynamics of some characteristics of a cyclonic situation (cyclonic regime) of the northwestern Pacific cyclonic zone is studied. The characteristics that are considered are the density of cyclonic energy at a point (intensity) and the power over a given area. In the model, the intensity at a point is defined as the sum of all intensities of preceding cyclones, with consideration for their spatial and temporal separation from the given point. Power for a given moment and a given area is defined as the sum of intensities over this area. Cyclonically active seasons are considered. The dynamics of the power was estimated for areas of different size. It is shown that the point values of cyclonic intensity, at the times of their maximum, are statistically related to one another by a negative power-law dependence. Periodicity is observed in the time evolution of the power in different areas.  相似文献   
985.
This paper considers the results of numerical experiments involving POLYMODE data assimilation by a barotropic model for synoptic ocean dynamics. The model's response the data assimilation for various space-time discretenesses of assimilation is studied. Results derived from the application of optimal interpolation algorithms and modified optimal filtration algorithms are compared. Qualitative similarity to the calculations carried out through the simulation modelling technique is noted. Optimal assimilation algorithms are determined, depending on the space-time discreteness used. An optimal sampling discreteness for the POLYMODE conditions is suggested.Translated by Vladimir A. Puchkin.  相似文献   
986.
987.
Periods and amplitudes of long-term temperature fluctuations were obtained using the methods of spectral analysis and filtration of secular time series of the air temperature at 13 hydrometeorological stations in the Black Sea region. The prognostic calculations of the long-term air temperature variability are based on the results of processing of time series. The calculations of the air temperature agree with the data of observations. The possibility of the long-term air temperature variability prediction is shown.  相似文献   
988.
We describe the methodology and software developed for the numerical analysis of the characteristics of the horizontal and vertical structure of geostrophic currents. We present the results of computation of these characteristics according to the data of the summer survey of the Black Sea carried out as a part of the ComSBlack-92 program. The distinctive features of the space structure of geostrophic currents discovered as a result and the established parameters of their variability may supplement the existing data on the current field in the Black Sea.  相似文献   
989.
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   
990.
Geologic relations indicate that silica phases transformed in the Monterey Formation in two zones that persist over a narrow depth/temperature range and do not stratigraphically overlap. The wide and overlapping range of reported temperatures of these transformations is mainly a result of the many uncertainties inherent in the different methods used to estimate temperature and does not indicate that phases transform throughout these ranges. Our approach to a reliable temperature scale for silica diagenesis combines as empirical zonation of silica phases with temperature calibration from a sequence at maximum temperature and depth of burial.  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