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   11779篇
  免费   128篇
  国内免费   69篇
测绘学   246篇
大气科学   744篇
地球物理   2208篇
地质学   4604篇
海洋学   1181篇
天文学   2489篇
综合类   48篇
自然地理   456篇
  2022年   144篇
  2021年   204篇
  2020年   190篇
  2019年   227篇
  2018年   526篇
  2017年   431篇
  2016年   477篇
  2015年   188篇
  2014年   413篇
  2013年   606篇
  2012年   462篇
  2011年   562篇
  2010年   556篇
  2009年   644篇
  2008年   577篇
  2007年   573篇
  2006年   494篇
  2005年   329篇
  2004年   311篇
  2003年   281篇
  2002年   274篇
  2001年   245篇
  2000年   254篇
  1999年   169篇
  1998年   184篇
  1997年   171篇
  1996年   115篇
  1995年   131篇
  1994年   115篇
  1993年   97篇
  1992年   71篇
  1991年   98篇
  1990年   97篇
  1989年   68篇
  1988年   79篇
  1987年   99篇
  1986年   80篇
  1985年   107篇
  1984年   95篇
  1983年   104篇
  1982年   86篇
  1981年   81篇
  1980年   97篇
  1979年   88篇
  1978年   87篇
  1977年   77篇
  1976年   59篇
  1975年   63篇
  1974年   71篇
  1973年   64篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
191.
The assumption of a linearly expanding universe for the JBD-cosmological equations generates a set of solutions for the barotropic equations of statep= (=const.). These solutions turn out to be valid for closed space-except in the casep= which is for open space. The gravitational constant which is inversely proportional to the scalar field increases with time if >–1/3 and decreases for <–1/3. No solution exists for =1/3. The Brans-Dicke parameter is negative if <–1/3.  相似文献   
192.
On the basis of the experimental data on the ionospheric conductivities and field-aligned currents the electric fields and currents in the ionosphere generated by the field-aligned currents were computated for various magnetic activity conditions. The model of the ionospheric conductivities by Vanyan and Osipova (1975) was used taking into account the influence of the universal time seasons and magnetic activity. The field-aligned current patterns and their change with magnetic activity was set on the basis of the TRIAD data. It is shown that the calculated patterns of the ionospheric electric fields and currents are in agreement with the measured electric fields and the equivalent current systems of the magnetic disturbances in high latitudes. The conclusion is made that the magnetospheric field-aligned currents are the main sources of the presently known polar magnetic disturbances.  相似文献   
193.
O. Engvold 《Solar physics》1980,67(2):351-355
Observed H brightness versus size of emission substructures of quiescent prominences are compared with values predicted from thermodynamical models. The measured size of an emission element of a given brightness is substantially less than the theoretical value.Two possible causes for the discrepancy are suggested: (1) The partial filling of a recording aperture, due to the prominence fine structure, may affect the measurements seriously. Caution is therefore urged against using face values of observed brightness vs ratios in model calculations in cases of partly optically thick lines. (2) Changes of individual fine structure elements on a time scale of a few minutes implies that the prominence plasma may be in a non-stationary radiative state.  相似文献   
194.
This article is an English translation of the work cited in 46: 3092. The authors review the conclusions of Pivovarov (see 44: Title 3118) concerning the nature of the urbanization process and optimal city size in the USSR. The relationship between urbanization and the characteristics of a given socioeconomic system is examined, and the possibility of determining optimal size for cities of different functional types is evaluated  相似文献   
195.
196.
197.
198.
199.
Kopal's new iterative method for analysing partially eclipsing binary light curves in the frequency domain has been put into a form suitable for applications, and explicit forms for basic expressions developed. To facilitate the computations in practice, the required newS m -functions, which are expressed in terms ofJ , 0 -integrals, have been extensively tabulated by making use of hypergeometric series. The automated method has been tested successfully on the light curves of Persei (Algol). Short information on the system and the revised sets of elements including a new determination of the limb-darkening coefficient in the ultraviolet have been presented.  相似文献   
200.
Solar wind and interplanetary magnetic field data were obtained by the PROGNOZ 1 and PROGNOZ 2 satellites during the period following the August 4, 1972 (0621 UT) solar flare. A thermalized plasma was recorded one hour after the shock followed two hours later by the plasma piston with a bulk velocity higher than 1700 km s-1. The comparison between the PROGNOZ and PIONEER 9 solar wind data shows an attenuation of the plasma properties with the deflection from the flare's meridian.  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