全文获取类型
收费全文 | 78271篇 |
免费 | 1435篇 |
国内免费 | 743篇 |
专业分类
测绘学 | 2050篇 |
大气科学 | 5656篇 |
地球物理 | 15917篇 |
地质学 | 27891篇 |
海洋学 | 6686篇 |
天文学 | 17865篇 |
综合类 | 250篇 |
自然地理 | 4134篇 |
出版年
2022年 | 455篇 |
2021年 | 817篇 |
2020年 | 884篇 |
2019年 | 932篇 |
2018年 | 2119篇 |
2017年 | 2022篇 |
2016年 | 2565篇 |
2015年 | 1479篇 |
2014年 | 2410篇 |
2013年 | 4093篇 |
2012年 | 2609篇 |
2011年 | 3317篇 |
2010年 | 2906篇 |
2009年 | 3780篇 |
2008年 | 3205篇 |
2007年 | 3236篇 |
2006年 | 3046篇 |
2005年 | 2326篇 |
2004年 | 2362篇 |
2003年 | 2240篇 |
2002年 | 2086篇 |
2001年 | 1891篇 |
2000年 | 1804篇 |
1999年 | 1480篇 |
1998年 | 1545篇 |
1997年 | 1450篇 |
1996年 | 1214篇 |
1995年 | 1190篇 |
1994年 | 1077篇 |
1993年 | 924篇 |
1992年 | 894篇 |
1991年 | 852篇 |
1990年 | 914篇 |
1989年 | 763篇 |
1988年 | 732篇 |
1987年 | 823篇 |
1986年 | 740篇 |
1985年 | 934篇 |
1984年 | 1037篇 |
1983年 | 960篇 |
1982年 | 893篇 |
1981年 | 820篇 |
1980年 | 786篇 |
1979年 | 763篇 |
1978年 | 781篇 |
1977年 | 643篇 |
1976年 | 607篇 |
1975年 | 645篇 |
1974年 | 559篇 |
1973年 | 598篇 |
排序方式: 共有10000条查询结果,搜索用时 140 毫秒
271.
Wimbush M. Chiswell S.M. Lukas R. Donohue K.A. 《Oceanic Engineering, IEEE Journal of》1990,15(4):380-383
A four-year record from an inverted echo sounder deployed near Palmyra Island at 6°N in the central Pacific Ocean is compared with a simultaneous record of subsurface pressure from this island lagoon. A factor m , converting round-trip acoustic travel time to surface dynamic height relative to a deep pressure level, was estimated from the ratio of the spectra of the two records in the energetic synoptic oscillation band. Year-to-year variation in m was not statistically significant. For the overall record, m was found to be -70±8 dynamic m/s, where the error bounds represent a 90% confidence interval. This is consistent with first-baroclinic-mode excitation 相似文献
272.
273.
274.
275.
We have used Monte Carlo simulations to investigate the capabilities of a giant air shower observatory designed to detect showers initiated by cosmic rays with energies exceeding 1019 eV. The observatory is to consist of an array of detectors that will characterise the air shower at ground level, and optical detectors to measure the fluorescence light emitted by the shower in the atmosphere. Using these detectors together in a ‘hybrid’ configuration, we find that precise geometrical reconstruction of the shower axis is possible, leading to excellent resolution in energy. The technique is also shown to provide very good reconstruction below 1019 eV, at energies where the ground array is not fully efficient. 相似文献
276.
The equation of transfer for the case of non-coherent scattering (Hummer, 1968; Ivanov, 1973; McCormick and Siewert, 1970) has been considered. The correspondingX- andY-functions have been derived by a combination of eigenfunction method developed by Case, and from the principle of invariance as developed by Chandrasekhar (1960). 相似文献
277.
Current plate motions 总被引:57,自引:0,他引:57
278.
The process of non-linear ambipolar diffusion in the region overlying the solar surface can be an effective mechanism for producing sharp magnetic structures and current sheets. These may be the sites responsible for the occurrence of connectivity of magnetic field lines, and the subsequent explosive input of energy for heating of some of the features in the atmosphere of the Sun.. 相似文献
279.
A.G.G.M. Tielens L.B.F.M. Waters F.J. Molster K. Justtanont 《Astrophysics and Space Science》1997,255(1-2):415-426
This paper reviews spectra obtained with the SWS on board of ISO of dust shells around O-rich objects. These spectra reveal
the presence of many new emission features between 10 and 45 μm. These bands are generally much narrower than the well-known
10 and 20 μm silicates features. The strength of these features relative to the underlying broad continuum varies from source
to source (≅ 5-50%). The 10 μm region shows evidence for the presence of Al2O3 grains. At longer wavelength, the spectra are
dominated by features due to crystalline olivine and pyroxene. The exact peak position of these features shows that the emitting
grains consist of the Mg-rich end-members of these minerals with an Fe-content of < 10%. The underlying continuum is attributed
to amorphous silicate grains.
These observations of aluminum-rich and magnesium-rich compounds compare well with the thermodynamic condensation sequence
of minerals expected for O-rich outflows. The observations also imply that freeze out (ie., kinetics) of this condensation
sequence at different temperatures is an important characteristic of dust formation in these objects. It is suggested that
the absence of Fe-rich silicates is a natural consequence of the low temperature at which gaseous Fe reacts with Mg-rich silicates
in these outflows, resulting in amorphous grains with little characterizing spectral detail.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
280.
Exact solutions of the semi-classical Einstein equations for conformally invariant free quantum fields in an homogeneous and
isotropic space-time, with cosmological constant and containing a classical scalar field, dust matter, an unquantised Dirac
field and electromagnetic radiation are found. The initial behaviour of the semiclassical models is investigated. Some of
the solutions found avoid the singularity and do not have particle horizons.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献