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   43298篇
  免费   242篇
  国内免费   192篇
测绘学   1047篇
大气科学   2684篇
地球物理   7475篇
地质学   19132篇
海洋学   3382篇
天文学   8409篇
综合类   188篇
自然地理   1415篇
  2022年   263篇
  2021年   428篇
  2020年   395篇
  2019年   462篇
  2018年   3650篇
  2017年   3362篇
  2016年   2338篇
  2015年   487篇
  2014年   795篇
  2013年   1289篇
  2012年   1880篇
  2011年   3578篇
  2010年   3277篇
  2009年   3517篇
  2008年   2832篇
  2007年   3557篇
  2006年   1108篇
  2005年   956篇
  2004年   869篇
  2003年   958篇
  2002年   812篇
  2001年   538篇
  2000年   448篇
  1999年   334篇
  1998年   321篇
  1997年   328篇
  1996年   254篇
  1995年   261篇
  1994年   236篇
  1993年   182篇
  1992年   207篇
  1991年   181篇
  1990年   195篇
  1989年   187篇
  1988年   156篇
  1987年   182篇
  1986年   170篇
  1985年   205篇
  1984年   198篇
  1983年   197篇
  1982年   188篇
  1981年   179篇
  1980年   179篇
  1979年   175篇
  1978年   157篇
  1977年   140篇
  1976年   133篇
  1975年   135篇
  1974年   124篇
  1973年   164篇
排序方式: 共有10000条查询结果,搜索用时 125 毫秒
111.
112.
an extension of the Gylden-Meshcherskii problem when the mass depends both on time and distance between two bodies is considered. certain mass loss laws as well as the Meshcherskii position vector and time transformation are used to convert the problem into the cases with equations of motion arising from integrable potentials.  相似文献   
113.
Tests and constraints on current theories of galaxy formation and evolution are presented. They are derived from observations of the Northern Hubble Deep Field with WFPC2 and NICMOS. Photometric redshifts, extinctions and spectral energy distributions are calculated for all objects in the field. The tests and constraints are derived from the output of this analysis. The tests of the predictions from hierarchical and pure luminosity evolution galaxy evolution calculations favor the hierarchical model. Constraints are provided by the current luminosity function and its evolution to a redshift of 6. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   
114.
115.
A flare of OH maser emission was discovered in W75N in 2000. Its location was determined with the Very Long Baseline Array (VLBA) to be within 110 au from one of the ultracompact H  ii regions, Very Large Array 2 (VLA2). The flare consisted of several maser spots. Four of the spots were found to form Zeeman pairs, all of them with a magnetic field strength of about 40 mG. This is the highest ever magnetic field strength found in OH masers, an order of magnitude higher than in typical OH masers. Three possible sources for the enhanced magnetic field are discussed: (i) the magnetic field of the exciting star dragged out by the stellar wind; (ii) the general interstellar field in the gas compressed by the magnetohydrodynamic shock; and (iii) the magnetic field of planets which orbit the exciting star and produce maser emission in gaseous envelopes.  相似文献   
116.
117.
118.
119.
We present the results of the preliminary study of the comet Hale-Bopp spectrum obtained April 17, 1997 by K. Churyumov and F. Mussayev with the help of the 1-meter Zeiss reflector and the echelle spectrometer (spectral resolutionλ/Δ λ ≈ 50000), CCD and the long slit, oriented along the radius-vector(“Sun-comet direction”). Energy distributions for three selected regions including the C3, C2 (0-0) and CN(Δ ν = 0) molecules emissions of the comet Hale-Bopp spectrum were built. The rotational lines of the CN(Δ ν = 0) band were identified. The nature of the high emission peak near λ 4020 Å in the C3 band is discussed. The presence of the cometary continuum of the nonsolar origin is assumed.  相似文献   
120.
The physical meaning of the terms of the potential and kinetic energy expressions, expanded by means of the density variation function for a nonuniform self-gravitating sphere, is discussed. The terms of the expansions represent the energy and the moment of inertia of the uniform sphere, the energy and the moment of inertia of the nonuniformities interacting with the uniform sphere, and the energy of the nonuniformities interacting with each other. It follows from the physical meaning of the above components of the energy structure, and also from the observational fact of the expansion of the Universe that the phase transition, notably, fusion of particles and nuclei and condensation of liquid and solid phases of the expanded matter accompanied by release of energy, must be the physical cause of initial thermal and gravitational instability of the matter. The released kinetic energy being constrained by the general motion of the expansion, develops regional and local turbulent (cyclonic) motion of the matter, which should be the second physical effect responsible for the creation of celestial bodies and their rotation.  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