全文获取类型
收费全文 | 71117篇 |
免费 | 1316篇 |
国内免费 | 864篇 |
专业分类
测绘学 | 2041篇 |
大气科学 | 5449篇 |
地球物理 | 14522篇 |
地质学 | 23951篇 |
海洋学 | 6333篇 |
天文学 | 16573篇 |
综合类 | 224篇 |
自然地理 | 4204篇 |
出版年
2021年 | 490篇 |
2020年 | 575篇 |
2019年 | 667篇 |
2018年 | 1462篇 |
2017年 | 1348篇 |
2016年 | 1881篇 |
2015年 | 1164篇 |
2014年 | 1761篇 |
2013年 | 3586篇 |
2012年 | 2005篇 |
2011年 | 2747篇 |
2010年 | 2428篇 |
2009年 | 3381篇 |
2008年 | 2974篇 |
2007年 | 2925篇 |
2006年 | 2760篇 |
2005年 | 2243篇 |
2004年 | 2235篇 |
2003年 | 2098篇 |
2002年 | 2063篇 |
2001年 | 1835篇 |
2000年 | 1788篇 |
1999年 | 1604篇 |
1998年 | 1532篇 |
1997年 | 1522篇 |
1996年 | 1274篇 |
1995年 | 1182篇 |
1994年 | 1087篇 |
1993年 | 964篇 |
1992年 | 890篇 |
1991年 | 888篇 |
1990年 | 873篇 |
1989年 | 837篇 |
1988年 | 770篇 |
1987年 | 862篇 |
1986年 | 809篇 |
1985年 | 980篇 |
1984年 | 1153篇 |
1983年 | 1030篇 |
1982年 | 990篇 |
1981年 | 897篇 |
1980年 | 825篇 |
1979年 | 767篇 |
1978年 | 784篇 |
1977年 | 684篇 |
1976年 | 627篇 |
1975年 | 642篇 |
1974年 | 615篇 |
1973年 | 652篇 |
1972年 | 428篇 |
排序方式: 共有10000条查询结果,搜索用时 843 毫秒
191.
We develop a general formalism for analysing parameter information from non-Gaussian cosmic fields. The method can be adapted to include the non-linear effects in galaxy redshift surveys, weak lensing surveys and cosmic velocity field surveys as part of parameter estimation. It can also be used as a test of non-Gaussianity of the cosmic microwave background. Generalizing maximum-likelihood analysis to second order, we calculate the non-linear Fisher information matrix and likelihood surfaces in parameter space. To this order we find that the information content is always increased by including non-linearity. Our methods are applied to a realistic model of a galaxy redshift survey, including non-linear evolution, galaxy bias, shot-noise and redshift-space distortions to second order. We find that including non-linearities allows all of the degeneracies between parameters to be lifted. Marginalized parameter uncertainties of a few per cent will then be obtainable using forthcoming galaxy redshift surveys. 相似文献
192.
A. Greco G. Zimbardo P. Veltri A.L. Taktakishvili L.M. Zelenyi 《Astrophysics and Space Science》2001,277(1-2):35-38
We study the ion dynamics in a magnetic field reversal with a constant electric field and with a model of three dimensional
magnetic turbulence. By computing the mean square displacements in the plane of the current sheet we find superdiffusive and
superballistic transport regimes. Since velocity increases with the length of the free path, we have accelerated Lévyflights.
The possibility to generate power law velocity distribution functions is pointed out, as well as the long memory effects and
non local properties of ion transport.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
193.
194.
K. Nagamine † M. Fukugita R. Cen J.P. Ostriker 《Monthly notices of the Royal Astronomical Society》2001,327(1):L10-L14
The luminosity function of galaxies is derived from a cosmological hydrodynamic simulation of a Λ cold dark matter universe with the aid of a stellar population synthesis model. At , the resulting B -band luminosity function has a flat faint-end slope of with the characteristic luminosity and the normalization in fair agreement with observations, while the dark matter halo mass function is steep with a slope of . The colour distribution of galaxies also agrees well with local observations. We also discuss the evolution of the luminosity function, and the colour distribution of galaxies from to 5. A large evolution of the characteristic mass in the stellar mass function as a result of number evolution is compensated by luminosity evolution; the characteristic luminosity increases only by 0.8 mag from to 2, and then declines towards higher redshift, while the B -band luminosity density continues to increase from to 5 (but only slowly at . 相似文献
195.
We report on SWS and LWS observations of the circumstellar disks of young stars of a few solar masses. The ISO spectra of
these objects present a diversity of emission features of carbon-rich and oxygen-rich grains. The similarity of the forsterite
spectra observed for Comet Hale-Bopp and the Haebe star HD100546 is particularly striking and provides a new argument that
huge comet swarms are formed in the disks surrounding young stars. While the data suggest that the formation of crystalline
silicates in the dust disks essentially occurs when a Haebe star has already reached the main sequence, no clear correlation
with stellar age only is apparent.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
196.
J. M. Gregory J. A. Church G. J. Boer K. W. Dixon G. M. Flato D. R. Jackett J. A. Lowe S. P. O'Farrell E. Roeckner G. L. Russell R. J. Stouffer M. Winton 《Climate Dynamics》2001,18(3-4):225-240
Sea-level rise is an important aspect of climate change because of its impact on society and ecosystems. Here we present
an intercomparison of results from ten coupled atmosphere-ocean general circulation models (AOGCMs) for sea-level changes
simulated for the twentieth century and projected to occur during the twenty first century in experiments following scenario
IS92a for greenhouse gases and sulphate aerosols. The model results suggest that the rate of sea-level rise due to thermal
expansion of sea water has increased during the twentieth century, but the small set of tide gauges with long records might
not be adequate to detect this acceleration. The rate of sea-level rise due to thermal expansion continues to increase throughout
the twenty first century, and the projected total is consequently larger than in the twentieth century; for 1990–2090 it amounts
to 0.20–0.37 m. This wide range results from systematic uncertainty in modelling of climate change and of heat uptake by the
ocean. The AOGCMs agree that sea-level rise is expected to be geographically non-uniform, with some regions experiencing as
much as twice the global average, and others practically zero, but they do not agree about the geographical pattern. The lack
of agreement indicates that we cannot currently have confidence in projections of local sea-level changes, and reveals a need
for detailed analysis and intercomparison in order to understand and reduce the disagreements.
Received: 1 September 2000 / Accepted: 20 April 2001 相似文献
197.
198.
This paper presents a method that incorporates a non‐associated flow rule into the limit analysis to investigate the influence of the dilatancy angle on the factor of safety for the slope stability analysis. The proposed method retain's the advantage of the upper bound method, which is simple and has no stress involvement in the calculation of the energy dissipation and the factor of safety. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
199.
The Etna volcano is located in an apparently anomalous position on the hinge zone of the Apennines subduction and its Na-alkaline geochemistry does not favour a magma source from the deep slab as indicated for the Aeolian K-alkaline magmatism. The steeper dip of the regional foreland monocline at the front of the Apennines in the Ionian Sea than in Sicily, implies a larger rollback of the subduction hinge in the Ionian Sea. Moreover, the lengthening of the Apennines arc needs extension parallel to the arc. Therefore, the larger southeastward subduction rollback of the Ionian lithosphere with respect to the Hyblean plateau in Sicily, should kinematically produce right-lateral transtension and a sort of vertical 'slab window' which might explain (i) the Plio-Pleistocene alkaline magmatism of eastern Sicily (e.g. the Etna volcano) and (ii) the late Pliocene to present right lateral transtensional tectonics and seismicity of eastern Sicily. The area of transfer of different dip and rollback occurs along the inherited Mesozoic passive continental margin between Sicily and the oceanic Ionian Sea, i.e. the Malta escarpment. 相似文献
200.
Historical Changes in the Flood Hazard at Khartoum, Sudan: Lessons and Warnings for the Future 总被引:1,自引:0,他引:1
The 1988 floods at Khartoum were frequently described as "unprecedented". However, an examination of evidence for floods caused by the Nile and rain storms during the nineteenth and twentieth centuries leads to the conclusion that neither the Nile flood nor the rain storms nor their coincidence in one season were unprecedented and that similar situations will recur.We argue that most problems were created by complacency, lack of planning and mismanagement. We conclude with some simple suggestions for flood amelioration in the future and warn that complacency is the single most important phenomenon likely to recur to the detriment of Greater Khartoum in the future. 相似文献