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   23291篇
  免费   1027篇
  国内免费   896篇
测绘学   988篇
大气科学   492篇
地球物理   1505篇
地质学   3237篇
海洋学   579篇
天文学   17406篇
综合类   296篇
自然地理   711篇
  2024年   61篇
  2023年   134篇
  2022年   259篇
  2021年   219篇
  2020年   223篇
  2019年   318篇
  2018年   167篇
  2017年   185篇
  2016年   238篇
  2015年   345篇
  2014年   356篇
  2013年   378篇
  2012年   464篇
  2011年   411篇
  2010年   458篇
  2009年   1825篇
  2008年   1717篇
  2007年   2025篇
  2006年   1960篇
  2005年   1809篇
  2004年   1900篇
  2003年   1662篇
  2002年   1448篇
  2001年   1258篇
  2000年   1051篇
  1999年   977篇
  1998年   1123篇
  1997年   282篇
  1996年   176篇
  1995年   327篇
  1994年   336篇
  1993年   168篇
  1992年   103篇
  1991年   122篇
  1990年   111篇
  1989年   154篇
  1988年   102篇
  1987年   95篇
  1986年   89篇
  1985年   52篇
  1984年   32篇
  1983年   30篇
  1982年   11篇
  1981年   4篇
  1980年   5篇
  1979年   3篇
  1977年   7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