全文获取类型
收费全文 | 132228篇 |
免费 | 1936篇 |
国内免费 | 942篇 |
专业分类
测绘学 | 3043篇 |
大气科学 | 9223篇 |
地球物理 | 26285篇 |
地质学 | 46454篇 |
海洋学 | 11914篇 |
天文学 | 29587篇 |
综合类 | 329篇 |
自然地理 | 8271篇 |
出版年
2021年 | 1285篇 |
2020年 | 1470篇 |
2019年 | 1606篇 |
2018年 | 3191篇 |
2017年 | 2993篇 |
2016年 | 3669篇 |
2015年 | 2076篇 |
2014年 | 3569篇 |
2013年 | 6814篇 |
2012年 | 3839篇 |
2011年 | 5207篇 |
2010年 | 4683篇 |
2009年 | 6153篇 |
2008年 | 5425篇 |
2007年 | 5329篇 |
2006年 | 5130篇 |
2005年 | 3928篇 |
2004年 | 3899篇 |
2003年 | 3671篇 |
2002年 | 3578篇 |
2001年 | 3136篇 |
2000年 | 3086篇 |
1999年 | 2563篇 |
1998年 | 2588篇 |
1997年 | 2439篇 |
1996年 | 2159篇 |
1995年 | 2105篇 |
1994年 | 1841篇 |
1993年 | 1741篇 |
1992年 | 1636篇 |
1991年 | 1559篇 |
1990年 | 1682篇 |
1989年 | 1483篇 |
1988年 | 1327篇 |
1987年 | 1603篇 |
1986年 | 1414篇 |
1985年 | 1728篇 |
1984年 | 2002篇 |
1983年 | 1906篇 |
1982年 | 1743篇 |
1981年 | 1648篇 |
1980年 | 1438篇 |
1979年 | 1400篇 |
1978年 | 1409篇 |
1977年 | 1262篇 |
1976年 | 1215篇 |
1975年 | 1183篇 |
1974年 | 1166篇 |
1973年 | 1217篇 |
1972年 | 747篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
211.
212.
A non-steady, two-dimensional, compressible mathematical model of a fluid with constant viscosity and thermal conductivity is given in order to represent a thin atmospheric layer located at 60 km height, as a function of a known initial vertical distribution of temperature, chemical concentrations of minor components and assumed free boundary conditions.The purpose of this paper is to determine the influence of convective laminar processes in the vertical distribution of minor constituents in a thermal interface. Only three minor components are considered, atomic oxygen, molecular oxygen and ozone. Numerical solutions of the stated timedependent convection problem for different Rayleigh numbers show a marked influence of the established flow pattern upon the distribution of minor constituents. In all cases, an enhancement of mean concentration gradients in relatively small regions adjacent to the warmer and colder boundaries was observed. 相似文献
213.
214.
A. S. Trew 《Astrophysics and Space Science》1982,82(1):223-228
The possible correlation noted between the intrinsic quasar luminosity and the absorption line expulsion velocity is re-examined using homogeneous data sets for metal and L only line systems. The method of analysis is chosen to enable any reasonable form of correlation to be found. No correlation is detected at a confidence level >10%. 相似文献
215.
The authors attempt to provide a comprehensive review of urbanization in three Melanesian countries (Papua New Guinea, the Solomon Islands, and Vanuatu) and in Fiji. The focus of the paper is on the development and perpetuation of various forms of inequality exemplified by Melanesian urbanization and its colonial origins. 相似文献
216.
J. Perdang 《Astrophysics and Space Science》1981,74(1):149-156
A preliminary numerical analysis of the power spectrum of solar oscillations of the SCLERA group suggests that this curve can be characterized by a Hausdorff-Besicovich dimension close to 3/2 near the present observational resolution (0.03 mHz). We show that this result is not inconsistent with the presence of a component due to non-linear, turbulent-like motions, which, in addition to linear oscillation modes, is shaping the observed spectral distribution.On leave of absence from Institut d'Astrophysique, Cointe-Ougrée, Belgium. 相似文献
217.
218.
219.
220.
The spreading angle of a number of light and dark Martian streaks is determined from selected Mariner 9 images. The resulting frequency distributions of spreading half-angles have maxima at ~5° for light, and ~7° for dark streaks; however the dark streaks have a secondary maximum spreading angle at ~14°. The smaller values, which include most streaks, are interpreted as crater-wake spreading phenomena. The larger value, found in only a few dark streaks or “tails,” may result from atmospheric diffusion and subsequent deposition of material from isolated sources such as vents or blowouts. An atmospheric diffusion-deposition analysis is presented, assuming this streak origin, from which it is possible to deduce the eddy diffusivity, K, in Mars' boudary layer. Calculated K values are found to agree with various theoretical estimates. They lie in the range 107 and 109 cm2 sec?1 and exhibit the proper scale dependence. Thus it appears that, in addition to streak-derived wind direction patterns and speed information, it is possible in a few cases to derive information on Mars' boundary-layer turbulence from streak-spreading measurements. 相似文献