全文获取类型
收费全文 | 66573篇 |
免费 | 1041篇 |
国内免费 | 595篇 |
专业分类
测绘学 | 1572篇 |
大气科学 | 4325篇 |
地球物理 | 12953篇 |
地质学 | 23973篇 |
海洋学 | 6103篇 |
天文学 | 15934篇 |
综合类 | 150篇 |
自然地理 | 3199篇 |
出版年
2022年 | 458篇 |
2021年 | 735篇 |
2020年 | 847篇 |
2019年 | 871篇 |
2018年 | 1875篇 |
2017年 | 1743篇 |
2016年 | 2054篇 |
2015年 | 1077篇 |
2014年 | 1947篇 |
2013年 | 3507篇 |
2012年 | 2128篇 |
2011年 | 2815篇 |
2010年 | 2506篇 |
2009年 | 3311篇 |
2008年 | 2784篇 |
2007年 | 2840篇 |
2006年 | 2649篇 |
2005年 | 1836篇 |
2004年 | 1808篇 |
2003年 | 1700篇 |
2002年 | 1661篇 |
2001年 | 1505篇 |
2000年 | 1416篇 |
1999年 | 1190篇 |
1998年 | 1227篇 |
1997年 | 1172篇 |
1996年 | 1016篇 |
1995年 | 987篇 |
1994年 | 937篇 |
1993年 | 782篇 |
1992年 | 747篇 |
1991年 | 747篇 |
1990年 | 845篇 |
1989年 | 675篇 |
1988年 | 654篇 |
1987年 | 812篇 |
1986年 | 666篇 |
1985年 | 883篇 |
1984年 | 916篇 |
1983年 | 874篇 |
1982年 | 814篇 |
1981年 | 766篇 |
1980年 | 702篇 |
1979年 | 641篇 |
1978年 | 655篇 |
1977年 | 564篇 |
1976年 | 565篇 |
1975年 | 565篇 |
1974年 | 536篇 |
1973年 | 564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.
D. Gerbal H.V. Capelato F. Durret G.B. Lima Neto I. Márquez 《Astrophysics and Space Science》2001,276(2-4):861-868
We suggest that elliptical galaxies, as stellar systems in a stage of quasi-equilibrium, may have a specific entropy. We use
the Sérsic law to describe the light profile. The specific entropy (the Boltzmann–Gibbs definition) is then calculated assuming
that the galaxy behaves as a spherical, isotropic, one-component system. We predict a relation between the three parameters
of the Sérsic law linked to the specific entropy, defining a surface in the parameter space, an ‘entropic plane’. We have
analysed a sample of simulated merging elliptical galaxies (virtual) and a sample of galaxies belonging to the Coma Cluster (real). Both virtual and realgalaxies are: 1) located in their own ‘entropic plane‘ and 2) in this plane, they are located on a straight line, indicating
constant entropy: another physical property A careful examination of the value of the specific entropy indicates a very small
increase in the specific entropy with the generation after merging (virtual sample). Although one cannot distinguish between various generations for real galaxies, the distribution of specific entropy in this sample is very similar to that in the virtual sample.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
193.
R.G. Sharp R.G. McMahon M.J. Irwin S.T. Hodgkin 《Monthly notices of the Royal Astronomical Society》2001,326(4):L45-L49
We report the first results of an observational programme designed to determine the luminosity density of high-redshift quasars quasars) using deep multicolour CCD data. We report the discovery and spectra of three high-redshift quasars, including one with . At , this is the fourth highest redshift quasar currently published. Using these preliminary results we derive an estimate of the quasar space density in the redshift range of . When completed, the survey will provide a firm constraint on the contribution to the ionizing UV background in the redshift range from quasars by determining the faint-end slope of the quasar luminosity function. The survey uses imaging data taken with the 2.5-m Isaac Newton Telescope as part of the Public Isaac Newton Group Wide Field Survey (WFS). This initial sample of objects is taken from two fields of effective area ∼12.5 deg2 from the final ∼100 deg2 . 相似文献
194.
195.
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
196.
R. T. Schilizzi W. Aldrich B. Anderson A. Bos R. M. Campbell J. Canaris R. Cappallo J. L. Casse A. Cattani J. Goodman H. J. van Langevelde A. Maccafferri R. Millenaar R. G. Noble F. Olnon S. M. Parsley C. Phillips S. V. Pogrebenko D. Smythe A. Szomoru H. Verkouter A. R. Whitney 《Experimental Astronomy》2001,12(1):49-67
197.
G. M. Karataeva V. A. Yakovleva V. A. Hagen-Thorn O. V. Mikolaichuk 《Astronomy Letters》2001,27(2):74-80
We analyze our BVR c photometry for UGC 5600, a candidate polar ring galaxy, obtained with the 6-m telescope. We have confirmed the existence of an inner polar ring and show that the outer ring-shaped structure represents spiral arms; i.e., UGC 5600 belongs to the rare class of gas-rich spiral galaxies with inner polar rings. 相似文献
198.
W. J. Chaplin G. Houdek Y. Elsworth D. O. Gough G. R. Isaak R. New 《Monthly notices of the Royal Astronomical Society》2005,360(3):859-868
We investigate the frequency dependence of the power spectral density of low-degree solar p modes by comparing measurements with the results of a stochastic-excitation model. In the past it was common practice to use the total power in such investigations. Using the maximum of the power spectral density instead provides a direct comparison with the measured mode heights in the observed power spectrum. This method permits a more careful calibration of the adjustable parameters in the excitation model, a model which we present here, for the first time, in a format that precisely and unambiguously relates the amplitudes of the modes of oscillation to the Reynolds stress in the equilibrium model. We find that errors in the theory of the linear mode damping rates, particularly at low frequency, have a dramatic impact on the predictions of the mode heights in the spectral density, whereas parameter changes in the stochastic excitation model, within a plausible domain of parameter space, have a comparatively small effect. 相似文献
199.
R. G. Langebartel 《Astrophysics and Space Science》1985,115(1):39-41
The average radial and angular velocity components are obtained for a rotating two-dimensional self-gravitating system near an equilibrium state. First-order perturbation configurations of flaring straight bars emanating from the center provide examples of such systems. In these systems the average velocity field to first order is incompressible and irrotational. The second-order effects on the product of the average velocity components with the spatial density are essentially independent of the angular coordinate. 相似文献
200.
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