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   47509篇
  免费   8096篇
  国内免费   10123篇
测绘学   4519篇
大气科学   6085篇
地球物理   7906篇
地质学   25480篇
海洋学   6201篇
天文学   3578篇
综合类   3319篇
自然地理   8640篇
  2024年   184篇
  2023年   543篇
  2022年   1537篇
  2021年   1810篇
  2020年   1688篇
  2019年   2154篇
  2018年   1607篇
  2017年   1854篇
  2016年   1904篇
  2015年   2110篇
  2014年   2676篇
  2013年   2570篇
  2012年   2885篇
  2011年   3012篇
  2010年   2592篇
  2009年   3241篇
  2008年   3113篇
  2007年   3365篇
  2006年   3322篇
  2005年   3132篇
  2004年   2763篇
  2003年   2622篇
  2002年   2259篇
  2001年   1928篇
  2000年   1824篇
  1999年   1623篇
  1998年   1388篇
  1997年   1061篇
  1996年   926篇
  1995年   794篇
  1994年   714篇
  1993年   601篇
  1992年   467篇
  1991年   396篇
  1990年   258篇
  1989年   266篇
  1988年   165篇
  1987年   100篇
  1986年   62篇
  1985年   47篇
  1984年   24篇
  1983年   22篇
  1982年   15篇
  1981年   10篇
  1980年   10篇
  1979年   13篇
  1978年   19篇
  1977年   8篇
  1976年   5篇
  1954年   9篇
排序方式: 共有10000条查询结果,搜索用时 203 毫秒
91.
92.
In the article the author looks back the hard development course and great progress in earth quake science and technology in China during the last near a half of century and expounds the following 3 aspects: (1) The strong desire of the whole society to mitigate seismic disasters and reduce the effect of earthquakes on social-economic live is a great driving force to push forward the development of earthquake science and technology in China; (2) To better ensure people‘ s life and property, sustainable economic development, and social stability is an essential purpose to drive the development of earthquake science and technology in China; and (3) To insist on the dialectical connection of setup of technical system for seismic monitoring with the scientific research of earthquakes and to better handle the relation between crucial task, current scientif ic level, and the feasibility are the important principles to advance the earthquake science and technology in China. Some success and many setbacks in earthquake disaster mitigation consistently enrich our knowledge regarding the complexity of the conditions for earthquake occurrence and the process of earthquake preparation, promote the reconstruction and modernization of technical system for earthquake monitoring, and deepen the scientific research of earthquakes. During the last 5 years, the improvement and modernization of technical system for earthquake monitoring have clearly provided the technical support to study and practice of earthquake prediction and pre caution, give prominence to key problems and broaden the field of scientific research of earth quakes. These have enabled us to get some new recognition of the conditions for earthquake oc currence and process of earthquake preparation, characteristics of seismic disaster, and mecha nism for earthquake generation in China‘s continent. The progress we have made not only en courages us to enhance the effectiveness of earthquake disaster mitigation, but also provides a basis for accelerating further development of earthquake science and technology in China in the new century, especially in the 10th five-year plan. Based on the history reviewed, the author sets forth a general requirement for develop ment of earthquake science and technology in China and brings out 10 aspects to be stressed and strengthened at present and in the future. These are: upgrade and setup of the network of digitized seismic observation; upgrade and setup of the network for observation of seismic pre cursors; setup of the network for observation of strong motion; setup of the laboratories for ex periment on seismic regime; establishment of technical system for seismic information, emer gency command and urgent rescue; research on short-term and imminent earthquake predic tion; research on intermediate- and long-term earthquake prediction; research on attenuation of seismic ground motion, mechanism for seismic disaster, and control on seismic disaster; ba sic research fields related to seismology and geoscience. We expect that these efforts will signifi cantly elevate the level of earthquake science and technology in China to the advanced interna tional level, improve theories, techniques, and methods for earthquake precaution and predic tion, and enhance the effectiveness of earthquake disaster mitigation.  相似文献   
93.
94.
We investigate the morphological relation between the orbits of the central family of periodic orbits ( x 1 family) and the bar itself using models of test particles moving in a barred potential. We show that different bar morphologies may have as a backbone the same set of x 1 periodic orbits. We point out that by populating initially axisymmetric stellar discs exponentially with test particles in circular, or almost circular motion, we may end up with a response bar which reveals a shape different in crucial details from that of the individual stable x 1 orbits. For example, a bar model in which the x 1 orbits are pure ellipses may have a much more complicated response morphology. This depends on the particular invariant curves around x 1, which are populated in each model.  相似文献   
95.
国家重大科学工程项目LAMOST总控系统的程序设计是一个庞大的软件工程.其总控系统下共包括8个既相互独立又互有关联的子系统.如何通过良好的软件设计方法来处理好这8个子系统之间的关系使其协调运转,以及如何确保软件开发的可维护性、可持续性是研究重点.  相似文献   
96.
97.
98.
99.
企鹅珍珠贝人工苗生长的初步观察   总被引:3,自引:0,他引:3  
为了解企鹅珍珠贝生长规律,观察了壳高2.5~5.0mm的出池幼苗,按月测量其生长参数和成活率,以及环境因子。结果表明,企鹅珍珠贝生长最快的月份为7~11月和次年4~6月,壳长,壳高和壳宽月均增加量分别为3.8~13.0mm、4.7~11.2mm、2.3~3.8mm,月成活率97.8%~98.6%。企鹅珍珠贝生长最慢月份是11月至次年3月。  相似文献   
100.
We compare theoretical stellar models for main sequence (MS) stars with the Hipparcos data base for the Hyades cluster to give a warning against the uncritical use of available theoretical scenarios and to show how formal MS fittings can be fortuitous if not fictitious. Moreover, we find that none of the current theoretical scenarios appears able to account for an observed mismatch between theoretical predictions and observations of the coolest Hyades MS stars. Finally, we show that current theoretical models probably give too faint He burning luminosities unlike the case of less massive He burning models, with degenerate progenitors, which have been suggested to suffer the opposite discrepancy.  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