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   73953篇
  免费   1030篇
  国内免费   837篇
测绘学   1857篇
大气科学   5110篇
地球物理   13800篇
地质学   26834篇
海洋学   6983篇
天文学   17522篇
综合类   245篇
自然地理   3469篇
  2022年   541篇
  2021年   900篇
  2020年   993篇
  2019年   1043篇
  2018年   2257篇
  2017年   2165篇
  2016年   2586篇
  2015年   1372篇
  2014年   2424篇
  2013年   4010篇
  2012年   2591篇
  2011年   3333篇
  2010年   2930篇
  2009年   3733篇
  2008年   3191篇
  2007年   3273篇
  2006年   3050篇
  2005年   2142篇
  2004年   2162篇
  2003年   2025篇
  2002年   1969篇
  2001年   1751篇
  2000年   1643篇
  1999年   1312篇
  1998年   1388篇
  1997年   1279篇
  1996年   1110篇
  1995年   1039篇
  1994年   971篇
  1993年   830篇
  1992年   812篇
  1991年   809篇
  1990年   867篇
  1989年   672篇
  1988年   674篇
  1987年   739篇
  1986年   641篇
  1985年   861篇
  1984年   898篇
  1983年   796篇
  1982年   778篇
  1981年   653篇
  1980年   664篇
  1979年   631篇
  1978年   628篇
  1977年   503篇
  1976年   485篇
  1975年   499篇
  1974年   448篇
  1973年   480篇
排序方式: 共有10000条查询结果,搜索用时 11 毫秒
971.
We have made an analysis of the observed equivalent widths of the lines of Lyman and Werner bands by Smith. The H2 column densities of 3×1019 to 1020 and the excitation temperature of 80 to 150 K satisfy the observations. This temperature refers to the kinetic temperature. We have also discussed the importance of getting the excitation temperature from lines of H2 and other heteronuclear diatomic molecules for the same star and from different regions of space.  相似文献   
972.
Energy transport in a hot flare plasma is examined with particular reference to the influence of fluid motion. On the basis of dimensional considerations the dynamical timescale of the flare plasma is shown to be comparable to the timescale for energy loss by conduction and radiation. It is argued that mass motion is likely to have a profound influence on the evolution of the flare.The detailed response of a flare filament to a localized injection of energy is then analyzed. Radiative, conductive and all dynamical terms are included in the energy equation. Apart from greatly enhancing the rate of propagation of the thermal disturbance through space, mass motion is found to be significant in transferring energy through the moving fluid.Finally the predicted thermal structure is discussed and it is concluded that the presence of mass motions in the flare may be inferred from the form of the soft X-ray differential emission measure.  相似文献   
973.
Preliminary investigations have been made on two separate pieces from the Aïoun el Atrouss meteorite that fell on April 17, 1974 in southeast Mauritania. The major portion of the meteorite is a brecciated hypersthene achondrite with orthopyroxene (En74) as the major phase. Clasts of eucrite, up to 7 percent in volume within a single slice, occur within the hypersthene achondrite host. No evidence has been found of reaction between the two meteorite types, nor of the presence of any materials intermediate in composition.  相似文献   
974.
975.
N. Gopalswamy 《Solar physics》1987,110(2):327-335
The pulsed electron acceleration and release from the energy release volume in solar flares implies that there is a possibility of interaction between a group of electrons reflected from the foot of a bipolar flux tube with a newly injected beam. It is shown that interaction can lead to the stoppage of the synchrotron maser instability caused by the loss cone distribution and hence can produce further millisecond fine structures in the solar microwave bursts.  相似文献   
976.
977.
It is shown that the Hori auxiliary system for the motion of two planets, whose motions around the Sun have commensurable periods in the ratio 2 : 1, is completely integrable and, an intermediate orbit that includes the effects of the resonance is obtained. The difficulties of classifying some solutions as librations or circulations are discussed.  相似文献   
978.
Tidal effects of a Schmidt (1965) model galaxy on a typical globular cluster moving in an orbit along the axis of symmetry of the spheroid is studied under the impulsive approximation. Ann-body simulation is made for comparison. Results show that in both cases, a high concentration cluster gains enough energy to be totally dissolved within a distance of 2 kpc. A significant mass loss occurs as the cluster approaches the Roche distance.  相似文献   
979.
In this work, the history of the development of the Turali area (the Dagestan coast of the Caspian Sea) in the Late Holocene is under consideration. The analysis of the geological structure of the bay bar that separates the Bolshoy Turali lagoon from the sea, the granulometric analysis of the coastal deposits, and the data of geo-radar profiles make it possible to assert that the large eolian relief forms were formed during the New Caspian (Novokaspiyskoe) transgression of the Caspian Sea.  相似文献   
980.
This review contains the most significant results of Russian studies in the field of atmospheric electricity in 2011–2014. It is part of the Russian National Report on Meteorology and Atmospheric Sciences to the International Association of Meteorology and Atmospheric Sciences (IAMAS). The report was presented and approved at the XXVI General Assembly of the International Union of Geodesy and Geophysics (IUGG).1 The review is followed by a list of the main published works on the studies of atmospheric electricity of Russian scientists in 2011–2014.  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