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   71162篇
  免费   879篇
  国内免费   600篇
测绘学   1943篇
大气科学   5125篇
地球物理   12723篇
地质学   27835篇
海洋学   6035篇
天文学   15592篇
综合类   308篇
自然地理   3080篇
  2022年   365篇
  2021年   616篇
  2020年   658篇
  2019年   704篇
  2018年   3943篇
  2017年   3650篇
  2016年   3108篇
  2015年   1076篇
  2014年   1774篇
  2013年   2868篇
  2012年   2720篇
  2011年   4609篇
  2010年   4081篇
  2009年   4775篇
  2008年   3939篇
  2007年   4577篇
  2006年   2227篇
  2005年   2012篇
  2004年   1941篇
  2003年   1886篇
  2002年   1694篇
  2001年   1316篇
  2000年   1195篇
  1999年   924篇
  1998年   977篇
  1997年   885篇
  1996年   739篇
  1995年   774篇
  1994年   673篇
  1993年   597篇
  1992年   578篇
  1991年   585篇
  1990年   613篇
  1989年   477篇
  1988年   494篇
  1987年   519篇
  1986年   476篇
  1985年   602篇
  1984年   666篇
  1983年   584篇
  1982年   552篇
  1981年   508篇
  1980年   484篇
  1979年   469篇
  1978年   456篇
  1977年   366篇
  1976年   344篇
  1975年   356篇
  1974年   301篇
  1973年   342篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Geomagnetism and Aeronomy - It is possible that the radially independent, spatial-spectral components of the energy and power of the potential part of the main geomagnetic field were determined and...  相似文献   
42.
Mathematical Geosciences - A robust, high order modeling approach is introduced, based on the finite difference-based radial basis functions method, for solving the groundwater flow equation in the...  相似文献   
43.
Izvestiya, Atmospheric and Oceanic Physics - Gravimetric data obtained by the GOCE spacecraft contributes to the development of global models of the deep structure of the Earth’s crust and...  相似文献   
44.
Catchments have highly variable yields of runoff and soil erosion. The size, land use and the surface cover play a significant role and influence the catchment response and parameter values of simulation models. Two experimental basins—the Cariri basins—were equipped in a semi-arid region of Brazil, for obtaining runoff and sediment yield at different catchment scales, as well as, to evaluate the influence of the land use and surface cover. In the first basin, located in the municipality of Sumé, the field studies were carried out at two different scales: four micro-catchments with an area of around 0.5 ha and nine standard Wischmeier-type erosion plots of 100 m2. The experimental units had varied vegetation and management. They were subjected only to natural rainfall events, and were monitored from 1982 to 1991. The total runoff and total sediment yield were determined for each of the events. The installations in the second basin, in the municipality of São João do Cariri, from 1999, include two erosion plots, three micro-catchments, and two sub-catchments of a small basin. These basins are still being monitored for runoff and sediment production. Among the micro-catchments two are nested to detect any scale effect at the micro-catchment level. Nearly 600 events of precipitation, that produced runoff in at least one of the experimental units, have been registered. These data have been used to evaluate the influence of various factors, including cultivation practices and to calibrate hydrological models for plots and micro-catchments. Parameters have been tested by means of cross validations among micro-catchments and sub-catchments. The data sets are made available to all the catchment hydrology researchers and others at https://doi.org/10.5281/zenodo.4690886 .  相似文献   
45.
The existence and linear stability of the planar equilibrium points for photogravitational elliptical restricted three body problem is investigated in this paper. Assuming that the primaries, one of which is radiating are rotating in an elliptical orbit around their common center of mass. The effect of the radiation pressure, forces due to stellar wind and Poynting–Robertson drag on the dust particles are considered. The location of the five equilibrium points are found using analytical methods. It is observed that the collinear equilibrium points L1, L2 and L3 do not lie on the line joining the primaries but are shifted along the y-coordinate. The instability of the libration points due to the presence of the drag forces is demonstrated by Lyapunov’s first method of stability.  相似文献   
46.
47.
48.
The IZMIRAN database of Forbush effects and interplanetary disturbances was used to study features of the action of high-speed solar wind streams from coronal holes on cosmic rays. Three hundred and fifty Forbush effects created by coronal holes without other actions were distinguished. The mean values and distributions have been found for different characteristics of events from this group and compared with all Forbush effects and Forbush effects caused by coronal ejections. Despite the great differences in high-speed streams from coronal holes, this group turned out to be more compact and uniform as compared to events related to coronal ejections. Regression dependences and correlation relations between different parameters of events for the studied groups have been obtained. It has been shown that Forbush effects caused by coronal ejections depend considerably more strongly on the characteristics of interplanetary disturbances as compared to Forbush effects related to coronal holes. This suggests a significant difference between the modulation mechanisms of Forbush effects of different types and corroborates earlier conclusions based on indirect data.  相似文献   
49.
The effects of atmospheric nonequilibrium in the generation of wave perturbations due to the solar radiation flux are studied. Equations of nonequilibrium thermodynamics are used to perform an assessment of the channels of solar energy transformation into the atmosphere for different altitudes. As a result of calculations of the dispersion relation for a nonequilibrium atmosphere, we consider how the flux of solar radiation changes the spectrum of natural atmospheric oscillations at different altitudes and for different solar activities. A qualitative relation between the results of wave spectra calculations and the data of ionosphere dynamics observations for different intensities of the solar radiation flux has been established.  相似文献   
50.
During the prolonged and deep minimum of solar activity between cycles 23 and 24, an unusual behavior of the heliospheric characteristics and increased intensity of galactic cosmic rays (GCRs) near the Earth’s orbit were observed. The maximum of the current solar cycle 24 is lower than the previous one, and the decline in solar and, therefore, heliospheric activity is expected to continue in the next cycle. In these conditions, it is important for an understanding of the process of GCR modulation in the heliosphere, as well as for applied purposes (evaluation of the radiation safety of planned space flights, etc.), to estimate quantitatively the possible GCR characteristics near the Earth in the upcoming solar minimum (~2019–2020). Our estimation is based on the prediction of the heliospheric characteristics that are important for cosmic ray modulation, as well as on numeric calculations of GCR intensity. Additionally, we consider the distribution of the intensity and other GCR characteristics in the heliosphere and discuss the intercycle variations in the GCR characteristics that are integral for the whole heliosphere (total energy, mean energy, and charge).  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