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   20622篇
  免费   533篇
  国内免费   199篇
测绘学   452篇
大气科学   203篇
地球物理   540篇
地质学   1856篇
海洋学   267篇
天文学   17421篇
综合类   95篇
自然地理   520篇
  2024年   47篇
  2023年   76篇
  2022年   158篇
  2021年   96篇
  2020年   95篇
  2019年   163篇
  2018年   58篇
  2017年   44篇
  2016年   76篇
  2015年   180篇
  2014年   162篇
  2013年   157篇
  2012年   251篇
  2011年   239篇
  2010年   299篇
  2009年   1620篇
  2008年   1561篇
  2007年   1845篇
  2006年   1842篇
  2005年   1696篇
  2004年   1791篇
  2003年   1542篇
  2002年   1346篇
  2001年   1164篇
  2000年   950篇
  1999年   893篇
  1998年   1061篇
  1997年   241篇
  1996年   111篇
  1995年   300篇
  1994年   307篇
  1993年   130篇
  1992年   77篇
  1991年   93篇
  1990年   92篇
  1989年   146篇
  1988年   97篇
  1987年   97篇
  1986年   79篇
  1985年   45篇
  1984年   31篇
  1983年   28篇
  1982年   14篇
  1981年   10篇
  1980年   5篇
  1979年   3篇
  1977年   6篇
  1905年   3篇
  1900年   3篇
  1897年   7篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
We present a study of the relationship between integral area and corresponding total magnetic flux for solar active regions. It is shown that some of these relationships are satisfied to simple power laws. Fractal examination showed that some of these power laws can not be justified inside the simple models of stationary magnetic flux tube aggregation. All magnetic fluxes and corresponding areas were calculated using the data measured with the Solar Magnetic Field Telescope of the Huairou Solar Observing Station in Beijing.  相似文献   
72.
Wavelet Analysis of Space Solar Telescope Images   总被引:1,自引:0,他引:1  
The scientific satellite SST (Space Solar Telescope) is an important research project strongly supported by the Chinese Academy of Sciences. Every day, SST acquires 50 GB of data (after processing) but only 10GB can be transmitted to the ground because of limited time of satellite passage and limited channel volume. Therefore, the data must be compressed before transmission. Wavelets analysis is a new technique developed over the last 10 years, with great potential of application. We start with a brief introduction to the essential principles of wavelet analysis, and then describe the main idea of embedded zerotree wavelet coding, used for compressing the SST images. The results show that this coding is adequate for the job.  相似文献   
73.
We present the preliminary results of a study of how small stellar systems merge to form larger ones. As we display the families of galaxies in the μe - Re plane (effective surface brightness versus effective radius) we realize that different morphological types occupy different loci, evidencing the different physical mechanisms operating in each family. As proposed by Capaccioli et al. (1992) this diagram is the logical equivalent of the HR diagram for stars. Here we take some initial steps in understanding of how we can establish the evolutionary tracks, solely due to dynamical processes, in the μe - Re plane, ultimately making a dwarf elliptical to turn into a normal elliptical galaxy. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   
74.
75.
76.
77.
78.
Photographic spectra of SN1987A in the LMC have been obtained from 1987 February 25 to 1988 June 30. Microdensitometer tracings of these have been reduced to intensity and corrections for instrumental response have been applied to the spectra. This paper presents these data in an atlas format, discusses the reduction procedures in detail, and presents radial velocity measurements of selected lines in the spectra  相似文献   
79.
Observations of the brightness, color, and polarization of the fuor V1057 Cyg over more than 30 years are presented and briefly discussed. Variability of the linear polarization was found.  相似文献   
80.
bdAbstract The open cluster NGC 2818 containing a planetary nebula has been observed inVRI bands using the CCD system at prime focus of the 2.3-metre Vainu Bappu Telescope. The study extending to starsV ∼ 21 magnitude establishes the distance modulus as(m-M) 0 = 12.9 ±0.1 for the cluster. Based on the fitting of theoretical isochrones computed for solar metallicity, an age of 5(±1) × 108 years has been assigned to the cluster. Association of the planetary nebula with the cluster indicates that the progenitor mass of the planetary nebula on the main sequence is ≥2.5M Based on observations obtained with the Vainu Bappu Telescope.  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