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   10445篇
  免费   2232篇
  国内免费   2924篇
测绘学   1198篇
大气科学   1642篇
地球物理   2251篇
地质学   6060篇
海洋学   1578篇
天文学   404篇
综合类   1084篇
自然地理   1384篇
  2024年   83篇
  2023年   239篇
  2022年   710篇
  2021年   762篇
  2020年   639篇
  2019年   694篇
  2018年   761篇
  2017年   664篇
  2016年   751篇
  2015年   684篇
  2014年   719篇
  2013年   756篇
  2012年   677篇
  2011年   684篇
  2010年   677篇
  2009年   600篇
  2008年   541篇
  2007年   498篇
  2006年   445篇
  2005年   370篇
  2004年   311篇
  2003年   318篇
  2002年   428篇
  2001年   356篇
  2000年   319篇
  1999年   361篇
  1998年   226篇
  1997年   196篇
  1996年   168篇
  1995年   167篇
  1994年   151篇
  1993年   131篇
  1992年   112篇
  1991年   66篇
  1990年   64篇
  1989年   55篇
  1988年   34篇
  1987年   29篇
  1986年   36篇
  1985年   35篇
  1984年   15篇
  1983年   9篇
  1982年   15篇
  1981年   7篇
  1980年   10篇
  1979年   5篇
  1978年   4篇
  1958年   7篇
  1957年   2篇
  1954年   7篇
排序方式: 共有10000条查询结果,搜索用时 289 毫秒
11.
通过对影响能见度的因素的分析,提出了一种能见度预报方法-综合分析法,极大地提高了能见度的预报准确率。  相似文献   
12.
本文报告一种用半导体激光器作光源,用子脉冲宽度100ns,长度为511的周期伪随机码对半导体激光器的输出作幅度调制;APD作光电检测器,高速数字信号处理器TMS320C25作信号处理的激光雷达组成方案和试作样机的实验结果。  相似文献   
13.
In this paper the tidal phenomena on the Earth are concisely specified, including solid tides, ocean tides and atmospheric tides due to the luni-solar tide-generating force, and the Earth pole tide due to the motion of the Earth's rotation axis (polar motion); as well as their effects on the Earth rotation. The outcomes of scientific researches of Chinese astronomers on these topics are described in some detail. These researches deal with the mechanisms responsible for tidal effects on the earth rotation, and on the measurements of the Earth rotation parameters. Finally, the effects discovered by Chinese researchers on the measurements of the period and change in period of pulsars are discussed. These effects are very small in magnitude but not negligible.  相似文献   
14.
地倾斜台站数字化、模拟观测数据频率特性研究   总被引:2,自引:2,他引:0  
分析了四川、云南的部分地倾斜数字化观测与模拟观测资料的特性,从频率范围,周期10天以上的FFT谱特性,固体潮波振幅,相位特征值等方面,论述了地倾斜数字化资料较模拟记录资料的信息组成变化,并对资料的分析与应用进行了初步探讨。  相似文献   
15.
16.
本文叙述南天区 5GHzVLBI普查中新发现的视超光速射电源 ,0 4 2 0— 0 1 4,1 334—1 2 7和 2 345— 1 67,这些结果尚待进一步的观测加以证实  相似文献   
17.
The Changjiang River (Yangtze) is one of the fastest growth areas of container transportation in Chi-na. Rail, road and water transportation have competed against each other for container transportation in the Chang-jiang River main line and its delta area. It is of significance to assess these different transportation modes scientifi-cally in order to organize container transportation efficiently in this area and make decision for integral plan and construction of transportation system in this area. This paper outlines application of fuzzy comprehensive evaluation to appraise different modes of typical direction of containers. Twelve assessment indexes were decided. Membership functions were formulated. Evaluation results indicated that road transportation was optimal mode in the Changjiang River delta area, however water transportation was the primary way in the Changjiang River main line.  相似文献   
18.

Study is made on a 45 km-long artificial ecosystem without irrigation in Tengger desert on the basis of long-term ecological monitoring and ecohydrological fundamentals. Changes in water allocation, utilization, cycle and balance patterns in more than 40-year evolution of the soil-plant system are analyzed. The formation of a drought horizon in shrub rhizosphere and its effect, ecohydrological function of the crust and its effect on the soil-plant system change are discussed. Driven by water self-regulation and water stress, the soil-plant system is going to develop towards the steppe desert to ensure more effective use and optimum collocation of water resource.

  相似文献   
19.
Free radical scavenging abilities of polypeptide from Chlamys farreri   总被引:1,自引:0,他引:1  
1 INTRODUCTION Active oxygen free radicals can damage cell structure, even kill the cells, causing aging and cer- tain serious diseases (Bors et al., 1989). Usually, the production and scavenging of active oxygen free radicals are in balance in healthy hu…  相似文献   
20.
In this paper, the neutrino mass has been determined from SN1987a observation in a manner that the simultaneity of neutrino emission is not regarded as the starting point, but is itself defined through the analysis by Monte-Carlo simulation. The result is that the neutrino mass lies in 3–4 eV, possiblym v 3.6 eV. Neutrino luminosity variation and neutrino spectrum are also obtained. Comparison with theories gives further support to the mass determination, and also predicts the mass of progenitor star of SN1987a to be in the range of 12–25M .The project supported by the National Natural Science Foundation of China.  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