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   72201篇
  免费   820篇
  国内免费   503篇
测绘学   1595篇
大气科学   4333篇
地球物理   14048篇
地质学   26186篇
海洋学   6712篇
天文学   16996篇
综合类   160篇
自然地理   3494篇
  2022年   574篇
  2021年   934篇
  2020年   977篇
  2019年   1111篇
  2018年   2275篇
  2017年   2081篇
  2016年   2419篇
  2015年   1126篇
  2014年   2142篇
  2013年   3754篇
  2012年   2468篇
  2011年   3168篇
  2010年   2952篇
  2009年   3605篇
  2008年   3131篇
  2007年   3335篇
  2006年   3017篇
  2005年   2049篇
  2004年   1936篇
  2003年   1897篇
  2002年   1810篇
  2001年   1698篇
  2000年   1511篇
  1999年   1150篇
  1998年   1181篇
  1997年   1222篇
  1996年   956篇
  1995年   961篇
  1994年   906篇
  1993年   811篇
  1992年   776篇
  1991年   761篇
  1990年   799篇
  1989年   740篇
  1988年   705篇
  1987年   780篇
  1986年   658篇
  1985年   871篇
  1984年   927篇
  1983年   848篇
  1982年   768篇
  1981年   791篇
  1980年   702篇
  1979年   624篇
  1978年   656篇
  1977年   620篇
  1976年   551篇
  1975年   542篇
  1974年   535篇
  1973年   571篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
82.
In this paper the peculiarities of compiled oceanographic data sets, which consist primarily in the presence of some characteristic information as well as in the planned incomplete filling of the files with observations, are discussed. A number of special ways are suggested which essentially improve the packing density of computerized data without applying special archiving algorithms. The effectiveness of these methods has been tested by treating thein situ hydrological/chemical data file compiled in the Black Sea in 1988.Translated by Vladimir A. Puchkin.  相似文献   
83.
Satellite imagery and offshore magnetic data were analysed to correlate regional tectonic elements on the inner continental shelf off Konkan and the adjacent Deccan plateau. Three statistically important lineament trends—N-S, WNW-ESE and ENE-WSW—that prevail on land are correlatable well with the offshore trends. This positive correlation suggests simultaneous deformation. The major magnetic lineament observed off Jaigad Bay, west coast of India, may be the extension of onshore lineaments. The correlation of both the offshore and onshore trends indicates that the fracture pattern of the crystalline basement has also controlled the offshore structural pattern.  相似文献   
84.
85.
86.
The shadowing effects of the molecular clouds in the nearby interstellar medium on the soft x-ray background has been investigated, using ROSAT WFC data in conjunction with previous rocket B and C band surveys. Shadowing over a 5° extent occurs only for a few percent of the sky, but the mixed model of the ISM is supported.Detailed modelling of the Draco shadowing region shows little evidence for a multi-temperature, hot ISM component.  相似文献   
87.
This study considers the influence of the effects of scattering due to Langmuir turbulent pulsations in the transfer of radiation in the spectral lines. The transfer equation of radiation in spectral lines, by taking into account scattering due to Langmuir turbulent pulsations, is written in a form convenient for application by numerical methods.The profile's intensity for a plane-parallel finite isothermal slab of a turbulent plasma in the case of complete redistribution of scattering by an atom are obtained. Numerical studies show that in this case with the broadening of spectral lines and the decreasing of self-reversal, the Langmuir frequency pe is of the same order as the electronic Doppler width De. Creation of the line satellites when pe is larger than the line width is shown with the aid of numerical methods.  相似文献   
88.
The laboratory simulation experiments on volatilization from the melts formed due to micrometeoroid impacts on the lunar surface were carried out. The simulation was performed using modulated laser pulses incident on rocks and minerals in vacuum; in so doing microcraters on the targets, glass particles, condensates were formed and gases solved in the bulk of the rock and mineral grains were released. It is shown that volatilization from only the crater glass layers is negligible, which fully confirms the theoretical predictions of Nussinov and Chernyak.The volatilizations from the drops formed by the micrometeoric impacts can be noticeable. For micron-sized drops, predominant among the others after the impact, the volatilization of Na, K and other volatiles can be up to 10 to 20%. For larger-sized (d102 m) drops the volatilization should lead to the appearance of the significant gradients of the element concentrations over the particle cross-section and as a result of their normalization it leads to the surface enrichment by some elements (Si and others).The mechanism of dust formation due to the surface rocks attack by volatilizing alkaline metals (Naughtonet al.) on the Moon probably is not effective. It is the consequence of such a fact that the condensate of the target materials evaporated due to other simultaneous micrometeoric impacts and had the same (as the target has) elemental composition is the very strong background for volatilizing and condensating alkaline elements.Preliminary conclusions about a possible correlation between the composition and the sizes of dust particles in the Solar system and in the Universe (at similar initial composition) have been drawn.  相似文献   
89.
90.
We have computed the surface Green's function for linear force-free magnetic fields, where × B = B and is a constant, for application to low coronal levels of the solar atmosphere. Boundary conditions are imposed on the normal component of B on two parallel planes which delineate the force-free volume. This procedure ensures that the magnetic field energy remains bounded, and that the field lines have a smooth behavior. A simple bipolar source distribution is treated and representative field line tracings are shown.  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