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   4597篇
  免费   173篇
  国内免费   38篇
测绘学   161篇
大气科学   317篇
地球物理   1862篇
地质学   1294篇
海洋学   231篇
天文学   703篇
综合类   34篇
自然地理   206篇
  2021年   45篇
  2020年   83篇
  2019年   62篇
  2018年   120篇
  2017年   121篇
  2016年   184篇
  2015年   151篇
  2014年   169篇
  2013年   226篇
  2012年   149篇
  2011年   199篇
  2010年   195篇
  2009年   218篇
  2008年   178篇
  2007年   145篇
  2006年   133篇
  2005年   86篇
  2004年   89篇
  2003年   91篇
  2002年   96篇
  2001年   108篇
  2000年   76篇
  1999年   68篇
  1998年   71篇
  1997年   57篇
  1996年   85篇
  1995年   66篇
  1994年   68篇
  1993年   70篇
  1992年   59篇
  1991年   46篇
  1990年   57篇
  1989年   52篇
  1988年   49篇
  1987年   47篇
  1986年   55篇
  1985年   47篇
  1984年   55篇
  1983年   64篇
  1982年   58篇
  1981年   51篇
  1980年   44篇
  1979年   58篇
  1978年   55篇
  1977年   45篇
  1975年   48篇
  1974年   38篇
  1973年   46篇
  1972年   39篇
  1971年   39篇
排序方式: 共有4808条查询结果,搜索用时 31 毫秒
21.
A high resolution numerical sonagram of Pc-1 magnetic record has shown that single narrow lines of Pc-1 spectra produce lower frequency (“red-shifted”) satellite lines more than twice as often as their higher frequency (“violet”) counterparts. The violet satellites usually emerge only when at least two ancestor lines are present simultaneously.  相似文献   
22.
Spectra of accretion disks in dwarf novae and some novalike stars have been computed. Many simplifications to the general model of the nature of a cataclysmic variable are needed to make the system numerically tractable. The necessity, justification, and implications of such simplifications are discussed together with the influences of some system parameters on the disk radiation.Paper presented at the IAU Colloquium No. 93 on Cataclysmic Variables. Recent Multi-Frequency Observations and Theoretical Developments, held at Dr. Remeis-Sternwarte Bamberg, F.R.G., 16–19 June, 1986.  相似文献   
23.
The behaviour of the flare in the period of enhancement and maximum of hard X-ray, microwave and decimetric type IV continuum is analysed. The elongation of the H ribbons and microwave source disclose that the energy release site was shifting through a system of loops with a velocity less than 200 km s-1, and that the energy was carried down the field lines with a velocity of about 1000 km s-1, implying the thermal conduction front mechanism of energy transport. Several processes of energy release are considered and it is concluded that an explanation in terms of succeeding interactions of neighbouring loops, involving fast reconnection of their poloidal components is in best agreement with the observations.Proceedings of the Second CESRA Workshop on Particle Acceleration and Trapping in Solar Flares, held at Aubigny-sur-Nère (France), 23–26 June, 1986.  相似文献   
24.
Summary The estimate of the tidal long-term decrease in the angular velocity of the Earth's rotation due to the Sun is given as –(0.8±0.3)×10 –22 rad s –2. It was computed on the basis of the observed total long-term decrease in , of the observed tidal deceleration of the Moon and the observed decrease in the second-degree zonal Stokes geopotential harmonic term. Adopting the estimate given, the product of the Love number and the tidal phase lag angle due to the Sun (in degrees) comes out as 0.53±0.20.
am a z nuuu u z mu au u, az : –(0,8±0,3) 10 –22 a¶rt; –2 . ¶rt; ua n a¶rt;a u , n a¶rt;a nuu u ¶rt;z ¶rt;uu u n a¶rt;a u mz az znmuaz naama ma. u num n au, m nu¶rt;u ua a a z u ( za¶rt;a) a z nuua a (0,53±0,20).
  相似文献   
25.
Summary It has been shown that dynamically, on the basis of the distribution of angular momenta, the Jovian system cannot be considered an analogue within the Solar system. The total tidal decrease in the angular momentum of Jupiter and in its angular velocity of rotation have been estimated, as well as the loss of mechanical energy due to tidal dissipation. It has been concluded that there are no dynamical contradictions with the hypothesis of the common cosmogonic origin of Jupiter and of its eight close satellites.
aam, m ¶rt;uauu, n an¶rt;u m uma ¶rt;uu, um numa umam aayu um. a a y au ma uma ¶rt;uu numa u z mu z au u—a nuuz mu, ma a nmu au yuu um u—a ¶rt;uunauu. a au, m m ¶rt;uauu azau zunm m zuu aaa numa u z uau u nmu.
  相似文献   
26.
The relation between molecular clouds, star clusters, and the stellar component of the galactic disk is investigated. According to Elmegreen (1985) bound stellar systems, e.g., open star clusters, can be formed from molecular cloud of mass 104 M . A close encounter with a giant molecular cloud or massive black hole disrupts such stellar systems and forms superclusters. This explains why some open star clusters are so mass-deficient. Unbound stellar systems, e.g., expanding OB associations, are formed from molecular clouds of mass 105 M . When disruptive O-type stars appear the star formation is halted and the cloud is destroyed. An example of the relict of GMC disruption in the solar vicinity is Gould's belt. The velocity dispersion-versus-age relation is also investigated and explained as a consequence of gravitational scattering of stars on GMC, or massive black holes, or as due to recurrent transient spirals.Paper presented at a Workshop on The Role of Dust in Dense Regions of Interstellar Matter, held at Georgenthal, G.D.R., in March 1986.  相似文献   
27.
28.
The analytic construction of the direct periodic orbits in the circular 3-body problem is given in explicit form to the linear terms in . It is shown to be in good agreement with the numerically found orbits for large values of .  相似文献   
29.
On the coronograph spectrophotographic records taken on 31.372 UT, August 1979, some faint emission features were found which can be ascribed to Siii and Niii. These emissions were obviously a transient phenomena which were detected only 10 hr after the supposed fall of Comet 1979 XI in the Sun's photosphere. It cannot be excluded that the appearance of Si and Ni lines was triggered by the evaporation of dust particles with a high abundance of heavier elements in the solar corona. This assumption is also supported by intensity distribution of the Fex coronal line around the Sun's limb. The maximum coincide with the position angle of the projected path of the comet.  相似文献   
30.
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