全文获取类型
收费全文 | 25396篇 |
免费 | 350篇 |
国内免费 | 312篇 |
专业分类
测绘学 | 716篇 |
大气科学 | 1790篇 |
地球物理 | 4867篇 |
地质学 | 8744篇 |
海洋学 | 2289篇 |
天文学 | 6295篇 |
综合类 | 52篇 |
自然地理 | 1305篇 |
出版年
2021年 | 200篇 |
2020年 | 237篇 |
2019年 | 297篇 |
2018年 | 605篇 |
2017年 | 587篇 |
2016年 | 724篇 |
2015年 | 408篇 |
2014年 | 696篇 |
2013年 | 1299篇 |
2012年 | 795篇 |
2011年 | 1037篇 |
2010年 | 954篇 |
2009年 | 1253篇 |
2008年 | 1126篇 |
2007年 | 1151篇 |
2006年 | 1124篇 |
2005年 | 838篇 |
2004年 | 835篇 |
2003年 | 759篇 |
2002年 | 718篇 |
2001年 | 616篇 |
2000年 | 638篇 |
1999年 | 562篇 |
1998年 | 555篇 |
1997年 | 526篇 |
1996年 | 396篇 |
1995年 | 396篇 |
1994年 | 408篇 |
1993年 | 313篇 |
1992年 | 309篇 |
1991年 | 258篇 |
1990年 | 311篇 |
1989年 | 271篇 |
1988年 | 254篇 |
1987年 | 279篇 |
1986年 | 237篇 |
1985年 | 317篇 |
1984年 | 339篇 |
1983年 | 329篇 |
1982年 | 313篇 |
1981年 | 249篇 |
1980年 | 267篇 |
1979年 | 216篇 |
1978年 | 206篇 |
1977年 | 215篇 |
1976年 | 179篇 |
1975年 | 190篇 |
1974年 | 177篇 |
1973年 | 167篇 |
1972年 | 114篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
The Cryogenian succession of the Northern Flinders Ranges reveals a complex sedimentary record between the Sturtian and Marinoan glacial deposits. A major unconformity separates the Sturtian and Marinoan-aged sedimentary successions in the area. This forms a subaerial erosion surface with terrestrial and marginal marine infill directly above the Angepena and Balcanoona Formations in their respective localities. This exposure surface is here correlated with the previously documented submarine unconformity between the Yankaninna Formation and the underlying deep marine Tapley Hill Formation. This erosional event provides a chronostratigraphic marker horizon that coincides approximately with thepreviously defined Sturtian–Marinoan Time Series boundary in the Northern Flinders Ranges. These stratigraphic relationships also constrain lateral facies relationships between the Oodnaminta ReefComplex (Balcanoona Formation) and the Angepena Formation. Similarly, the shallow-water Weetootla Dolomite is correlated with the deeper water carbonates of the Yankaninna Formation. 相似文献
82.
83.
In this paper we compute the rate of solar EUV heating in the upper atmosphere by photo-dissociation and photo-ionization, taking care to include properly the effects of oblique incidence of solar flux, sphericity of the atmosphere and ellipticity of the Earth's orbit. The time and latitudinal variations of the computed heat function are revealed by numerical Fourier analysis of the heat function into harmonics of the yearly cycle. It is shown that EUV absorption contains a ‘latitude independent’ semi-annual component of heating with the ‘proper phase’ to account for the semi-annual density variations. Further, the annual component of the heat function predicts the existence of ‘summer polar’ density increases in the northern and southern hemispheres. 相似文献
84.
85.
The banded structures observed on the surfaces of the gas giants are associated with strong zonal winds alternating in direction with latitude. We use three-dimensional numerical simulations of compressible convection in the anelastic approximation to explore the properties of zonal winds in rapidly rotating spherical shells. Since the model is restricted to the electrically insulating outer envelope, we therefore neglect magnetic effects.A systematic parametric study for various density scaleheights and Rayleigh numbers allows to explore the dependence of convection and zonal jets on these parameters and to derive scaling laws.While the density stratification affects the local flow amplitude and the convective scales, global quantities and zonal jets properties remain fairly independent of the density stratification. The zonal jets are maintained by Reynolds stresses, which rely on the correlation between zonal and cylindrically radial flow components. The gradual loss of this correlation with increasing supercriticality hampers all our simulations and explains why the additional compressional source of vorticity hardly affects zonal flows.All these common features may explain why previous Boussinesq models were already successful in reproducing the morphology of zonal jets in gas giants. 相似文献
86.
Chashei I. V. Lebedeva T. O. Tyul’bashev S. A. Subaev I. A. 《Astronomy Reports》2021,65(11):1150-1169
Astronomy Reports - A joint analysis of the monitoring data of interplanetary scintillations with solar and geophysical data showed that at the descending phase of the 24 solar activity cycle, the... 相似文献
87.
T. A. Shatilina G. Sh. Tsitsiashvili T. V. Radchenkova 《Russian Meteorology and Hydrology》2010,35(11):740-743
Peculiarities are investigated of the air temperature variation tendencies at some stations of the Far East in 1976–2005.
The estimate of linear trend equation coefficients is computed according to the air temperature observation data using the
least squares method. It is demonstrated that the air temperature trend in northern regions possesses a small probability
at small values of residual variability. In the southern regions, the trend significance increases for almost all seasons
at small values of residual variability. At midlatitude stations, the trend significance in January and February decreases
considerably due to the large values of residual variability. 相似文献
88.
Vasil’ev D. Yu. Vodopyanov V. V. Zayzeva G. S. Zakirzyanov Sh. I. Semenov V. A. Sivokhip Zh. T. Chibilev A. A. 《Doklady Earth Sciences》2019,486(2):724-727
Doklady Earth Sciences - The results of long-term forecasting of the spring runoff in the Belaya River basin based on the water-balance model are presented. The structure and parameters of the... 相似文献
89.
The aim of this paper is to evaluate current knowledge and uncertainties associated with the impact of increasing greenhouse
gas and aerosol concentrations on the West African monsoon. For this purpose, coupled and time-slice simulations are used.
A global measure of the monsoon changes is defined in order to avoid regional biases and to try and obtain significant results.
The position and width of the monsoon in latitude are the main focuses. There is almost no agreement between the Coupled General
Circulation models from the Coupled models Inter-Comparison project—Phase II in regard to the impact of climate change on
the monsoon. Moreover, very simple discriminations between the models seem inappropriate to get a better signal. The role
of the different forcings in time-slice simulations is then investigated. The sea surface temperature (SST) and particularly
the pattern of the SST are shown to be the most important forcing. This accounts for the diversity of the results either from
the coupled or the forced simulations with different SST changes. With a fixed SST, but of a smaller magnitude in AMJ, there
are still uncertainties, coming first from the Atmospheric General Circulation models and the way they balance greenhouse
gas and global SST increase. Finally the uncertainty due to the Land Surface models (LSMs) is not negligible. The greenhouse
gas and the LSMs are shown to have more impact in August, when the monsoon is at its highest latitude on the continent. 相似文献