全文获取类型
收费全文 | 64787篇 |
免费 | 1136篇 |
国内免费 | 645篇 |
专业分类
测绘学 | 1756篇 |
大气科学 | 4540篇 |
地球物理 | 12775篇 |
地质学 | 22824篇 |
海洋学 | 5953篇 |
天文学 | 15379篇 |
综合类 | 174篇 |
自然地理 | 3167篇 |
出版年
2022年 | 416篇 |
2021年 | 683篇 |
2020年 | 788篇 |
2019年 | 886篇 |
2018年 | 1855篇 |
2017年 | 1710篇 |
2016年 | 2059篇 |
2015年 | 1113篇 |
2014年 | 1934篇 |
2013年 | 3387篇 |
2012年 | 2130篇 |
2011年 | 2733篇 |
2010年 | 2466篇 |
2009年 | 3198篇 |
2008年 | 2802篇 |
2007年 | 2874篇 |
2006年 | 2679篇 |
2005年 | 1852篇 |
2004年 | 1835篇 |
2003年 | 1715篇 |
2002年 | 1746篇 |
2001年 | 1564篇 |
2000年 | 1455篇 |
1999年 | 1255篇 |
1998年 | 1264篇 |
1997年 | 1236篇 |
1996年 | 1037篇 |
1995年 | 966篇 |
1994年 | 926篇 |
1993年 | 782篇 |
1992年 | 711篇 |
1991年 | 708篇 |
1990年 | 740篇 |
1989年 | 667篇 |
1988年 | 618篇 |
1987年 | 725篇 |
1986年 | 631篇 |
1985年 | 797篇 |
1984年 | 886篇 |
1983年 | 777篇 |
1982年 | 776篇 |
1981年 | 673篇 |
1980年 | 646篇 |
1979年 | 599篇 |
1978年 | 612篇 |
1977年 | 524篇 |
1976年 | 487篇 |
1975年 | 493篇 |
1974年 | 472篇 |
1973年 | 505篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
191.
Summary
Atmospheric backscattering from aerosol particulates has been measured over the Atlantic at 10.6 μm wavelength with an airborne,
coherent heterodyne, lidar, and corresponding air mass back trajectories have been calculated. These back trajectories (usually
extended up to 10 days prior to the backscatter measurement) have shown very diverse origins for the air parcels at different
altitudes. In many cases it has been possible to attribute the observed levels of scattering to these origins over oceanic,
arctic, continental, industrial etc. regions. This is illustrated by 6 flight records: out of Ascension Island in the South
Atlantic; over the Azores in the mid North Atlantic; over the UK and the North Sea; and in the Arctic along 71° North. In
each of these regions the profiles of backscatter versus altitude show highly variable features; remarkably different origins
for air masses at different altitudes are evident from the corresponding back trajectory analyses. It is thus possible for
the first time to present probable explanations for the different levels of scattering observed at different altitudes.
Received July 14, 2000 Revised May 14, 2001 相似文献
192.
193.
C.J. Mooney W.R.J. Rolleston F.P. Keenan P.L. Dufton D.L. Pollacco H.R. Magee 《Monthly notices of the Royal Astronomical Society》2001,326(3):1101-1109
We present a model-atmosphere analysis for the bright ( V ∼13) star ZNG-1, in the globular cluster M10. From high-resolution ( R ∼40 000) optical spectra we confirm ZNG-1 to be a post-asymptotic giant branch (post-AGB) star. The derived atmospheric parameters are T eff =26 500±1000 K and log g =3.6±0.2 dex . A differential abundance analysis reveals a chemical composition typical of hot post-AGB objects, with ZNG-1 being generally metal poor, although helium is approximately solar. The most interesting feature is the large carbon underabundance of more than 1.3 dex. This carbon deficiency, along with an observed nitrogen enhancement relative to other elements, may suggest that ZNG-1 evolved off the AGB before the third dredge-up occurred. Also, iron depletions observed in other similar stars suggest that gas–dust fractionation in the AGB progenitor could be responsible for the observed composition of these objects. However, we need not invoke either scenario since the chemical composition of ZNG-1 is in good agreement with abundances found for a Population II star of the same metallicity. 相似文献
194.
R. A.Street KeithHorne T. A.Lister A.Penny Y.Tsapras A.Quirrenbach N.Safizadeh J.Cooke D.Mitchell A.Collier Cameron 《Monthly notices of the Royal Astronomical Society》2002,330(3):737-754
We report on the discovery of 25 variable stars plus 13 suspected variables found in the field of the open cluster NGC 6819. The stars were identified from time-series photometric data obtained on the Isaac Newton Telescope, La Palma, during two observing runs covering the 19 nights between 1999 June 22–30 and 1999 July 22–31 . The variables found include 12 eclipsing binaries with an additional three suspected, nine BY Draconis systems, plus four variables of other types, including one star believed to be a Cepheid. Three of the 15 eclipsing binaries are believed to be cluster members. Details of a further 10 suspected variable stars are also included. 相似文献
195.
196.
Profiles of spectral lines emitted from an accretion ring around an object with strong gravitational field should be affected by Doppler shift, gravitational redshift, and deflection of light. Taking these effects into account, precise line profile of a Keplerian ring around a Kerr black hole for a distant observer is obtained by solving the kinetic equation of photons. 相似文献
197.
P. G. Niarchos 《Astrophysics and Space Science》2005,296(1-4):359-370
A new method for the determination of the proximity effects and gravity darkening exponents in contact binaries of W UMa type
is presented. The method is based on Kopal’s method of Fourier analysis of the light changes of eclipsing variables in the
Frequency Domain. The method was applied to 36 W UMa systems for which geometric and photometric elements have been derived
by the most powerful techniques. The derived values are very close to those predicted by the existing theory of radiative
transfer or convective equilibrium. 相似文献
198.
K.A. MAASCH P.A. MAYEWSKI E.J. ROHLING J.C. STAGER W. KARLEN L.D. MEEKER E.A. MEYERSON 《Geografiska Annaler: Series A, Physical Geography》2005,87(1):7-15
ABSTRACT. Although considerable attention has been paid to the record of temperature change over the last few centuries, the range and rate of change of atmospheric circulation and hydrology remain elusive. Here, eight latitudinally well-distributed (pole-equator-pole), highly resolved (annual to decadal) climate proxy records are presented that demonstrate major changes in these variables over the last 2000 years. A comparison between atmospheric 14 C and these changes in climate demonstrates a first-order relationship between a variable Sun and climate. The relationship is seen on a global scale. 相似文献
199.
200.