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   44925篇
  免费   353篇
  国内免费   276篇
测绘学   939篇
大气科学   2317篇
地球物理   8535篇
地质学   17397篇
海洋学   4285篇
天文学   10459篇
综合类   142篇
自然地理   1480篇
  2022年   531篇
  2021年   791篇
  2020年   826篇
  2019年   914篇
  2018年   1928篇
  2017年   1745篇
  2016年   1879篇
  2015年   741篇
  2014年   1651篇
  2013年   2437篇
  2012年   1866篇
  2011年   2243篇
  2010年   2077篇
  2009年   2391篇
  2008年   2106篇
  2007年   2320篇
  2006年   2008篇
  2005年   1146篇
  2004年   1067篇
  2003年   1029篇
  2002年   964篇
  2001年   939篇
  2000年   831篇
  1999年   561篇
  1998年   595篇
  1997年   619篇
  1996年   438篇
  1995年   468篇
  1994年   436篇
  1993年   366篇
  1992年   342篇
  1991年   368篇
  1990年   415篇
  1989年   335篇
  1988年   323篇
  1987年   352篇
  1986年   266篇
  1985年   395篇
  1984年   389篇
  1983年   391篇
  1982年   354篇
  1981年   325篇
  1980年   350篇
  1979年   283篇
  1978年   314篇
  1977年   270篇
  1976年   227篇
  1975年   242篇
  1974年   233篇
  1973年   264篇
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
61.
The containment property Goudas' surfaces has been studied in this paper. Physical implications of this property a consequently discussed. A general relationship is obtained, which connects the sizes of those surfaces, the magnetic moments of two stars and their mean motion.  相似文献   
62.
Quasi-steady high-temperature current sheets are an energy source during the main or hot phase of solar flares. Such sheets are shown to be stabilized with respect to the tearing instability by a small transverse component of magnetic field existing in the sheets.  相似文献   
63.
Radio astronomy experiments designed to probe the interplanetary plasma close to the Sun have been carried out at the wavelength = 2.92 m using the occultation method. The experiments are based on a modification of the occultation method by which the sources, in this case quasars, are used to measure the radial dependence of the apparent source size, the scattering angle (R). The radial dependence of this source size (R) reveals that an anomalous enhancement in the scattering appears at radial distances from about 16 to 30 R , which is associated with the solar wind transsonic region. It is shown by analysis of the theoretical equations that the radial profiles of both the source size (R) and the scintillation index m(R) are consistent in the near solar interplanetary medium (R 40 R ). Combining these two independent applications of the occultation method extends the range of the investigation and provides a powerful new diagnostic of the solar wind transsonic region.  相似文献   
64.
We present the results of the photometric observations, in theUBVRJHKLMNQ system, of CH Cyg, made in the period 1978–1987. They have shown that from 1985 to 1987 dust condensed in its circumstellar envelope have taken place the condensation of the dust matter. In 1987 its mass and temperature were about 3×10–8 M and 800 K, respectively.  相似文献   
65.
Formulae containing the elements of the variational matrix are obtained which determine the linear isoenergetic stability parameters of three-dimensional periodic orbits of the general three-boy problem. This requires the numerical integration of the variational equations but produces the stability parameters with the effective accuracy of the numerical integration. The conditions for stability, criticality, and bifurcations are briefly examined and the stability determination procedure is tested in the determination of some three-dimensional periodic orbits of low inclination bifurcating from vertical-critical coplanar orbits.  相似文献   
66.
An analysis of the effects of the mass transfer on the unsteady free-convection flow of a viscous incompressible fluid, past an impulsively started infinite porous vertical limiting surface with heat sources is presented, when the free-stream velocity and the suction velocity, are oscillating in the time about constant mean values. Approximate solutions for the coupled nonlinear equations are derived for the mean velocity, the mean temperature, the mean skin-friction, and the mean rate of heat transfer. All the above quantities are shown graphically followed, by a discussion.  相似文献   
67.
This paper is devoted to Force-Free Electromagnetic Oscillations in a constant magnetic field. A correction is made in the derivation of the basic equation. The paper confirms the predicted spectrum of frequencies, namely n = o (n + 1)1/2;n = 0, 1, 2, .... In addition it is suggested that hybrid frequency n = ( n 2 + H 2 )1/2 should be found in observational data.  相似文献   
68.
The abundances of light elements (deuterium, helium and lithium) are calculated in unconventional cosmologies in which these elements are produced by interaction of fast -particles ejected by massive pregalactic stars with a purely hydrogenous cosmological substrate. The number density and energetics of such stars needed for suitable production of light elements are estimated. It is shown that the models always lead to overproduction of lithium. The intensity of ultraviolet, X-ray, and -ray emission caused by explosions of pregalactic massive stars is calculated. The distortions of cosmic background radiation by Compton losses of electrons heated by explosive stars are also calculated.  相似文献   
69.
A simple self-consistent model of a high-temperature turbulent current sheet (HTCS) is considered. The anomalous character of plasma conductivity in a sheet is assumed to be due to gradient instabilities. The possibility of a low threshold of their excitation is demonstrated by an example of temperature-drift instability.Application of the HTCS model to the hot or main phase of a solar flare is discussed. The model consistently explains many observed properties of this phase.  相似文献   
70.
The Culgoora radioheliograph has been modified for observing at 327.4 MHz, which is in addition to the three frequencies (43.25, 80, and 160 MHz) previously available. At the new frequency the array beamwidth is 56, which represents the highest resolution yet available for metre-wavelength solar mapping.At 327.4 MHz the sources of radio emission are mainly in the lowest layers of the corona. Some preliminary four-frequency observations have been made of type I storms. It is found that the source size generally decreases with increasing observing frequency. This result confirms earlier suggestions that the sources of both type I and type III emission are contained in structures whose boundaries diverge outwards in the corona.  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