全文获取类型
收费全文 | 2181篇 |
免费 | 303篇 |
国内免费 | 497篇 |
专业分类
测绘学 | 233篇 |
大气科学 | 518篇 |
地球物理 | 413篇 |
地质学 | 690篇 |
海洋学 | 218篇 |
天文学 | 530篇 |
综合类 | 112篇 |
自然地理 | 267篇 |
出版年
2024年 | 4篇 |
2023年 | 23篇 |
2022年 | 51篇 |
2021年 | 60篇 |
2020年 | 73篇 |
2019年 | 74篇 |
2018年 | 67篇 |
2017年 | 58篇 |
2016年 | 77篇 |
2015年 | 91篇 |
2014年 | 117篇 |
2013年 | 143篇 |
2012年 | 93篇 |
2011年 | 163篇 |
2010年 | 135篇 |
2009年 | 188篇 |
2008年 | 151篇 |
2007年 | 160篇 |
2006年 | 161篇 |
2005年 | 160篇 |
2004年 | 130篇 |
2003年 | 109篇 |
2002年 | 90篇 |
2001年 | 87篇 |
2000年 | 98篇 |
1999年 | 57篇 |
1998年 | 66篇 |
1997年 | 58篇 |
1996年 | 43篇 |
1995年 | 30篇 |
1994年 | 37篇 |
1993年 | 21篇 |
1992年 | 25篇 |
1991年 | 20篇 |
1990年 | 9篇 |
1989年 | 8篇 |
1988年 | 9篇 |
1987年 | 2篇 |
1986年 | 4篇 |
1985年 | 2篇 |
1984年 | 4篇 |
1983年 | 4篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1980年 | 6篇 |
1979年 | 2篇 |
1978年 | 5篇 |
1977年 | 1篇 |
排序方式: 共有2981条查询结果,搜索用时 31 毫秒
991.
The rainfall‐runoff modelling of a river basin can be divided into two processes: the production function and the transfer function. The production function determines the proportion of gross rainfall actually involved in the runoff. The transfer function spreads the net rainfall over time and space in the river basin. Such a transfer function can be modelled using the approach of the geomorphological instantaneous unit hydrograph (GIUH). The effectiveness of geomorphological models is actually revealed in rainfall‐runoff modelling, where hydrologic data are desperately lacking, just as in ungauged basins. These models make it possible to forecast the hydrograph shape and runoff variation versus time at the basin outlet. This article is an introduction to a new GIUH model that proves to be simple and analytical. Its geomorphological parameters are easily available on a map or from a digital elevation model. This model is based on general hypotheses on symmetry that provide it with multiscale versatile characteristics. After having validated the model in river basins of very different nature and size, we present an application of this model for rainfall‐runoff modelling. Since parameters are determined relying on real geomorphological data, no calibration is necessary, and it is then possible to carry out rainfall‐runoff simulations in ungauged river basins. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
992.
Recent observations of the environments of gamma-ray bursts (GRBs) favour massive stars as their progenitors, which are likely to be surrounded by gas and dust. The visibility of the optical and UV emission of a GRB is expected to depend on the characteristics of both the dust and the GRB emission itself. A reasonable distribution of surrounding dust is capable of absorbing all the optical and UV emission of the optical flash and afterglow of a GRB, unless the optical flash has a peak isotropic luminosity L peak ≳1049 erg s−1 . This means that dark bursts should exist and these bursts will have to be studied at infrared rather than optical wavelengths. In this paper details will be given about the infrared GRB dust emission. The reprocessed dust emission peaks at a rest-frame wavelength of about 8 μm. Forthcoming space telescopes, in particular the IRAC camera on board the Space Infrared Telescope Facility , could detect this emission out to a redshift of about two. However, an accurate position of the GRB afterglow must be provided for this emission to be identified, because the light curve of the reprocessed dust emission does not vary on time-scales less than several years. 相似文献
993.
994.
R. L. HAMMOND 《Journal of Metamorphic Geology》1987,5(2):195-211
Abstract Dissolution of quartz and the recryst-allization and re-equilibration of phyllosilicates produce the dark anastomosing seams that dominate microstructures of tectonic melange which occur in a low-grade, imbricated and multiply deformed, mid-Palaeozoic, intracra-tonic fiysch sequence in northeastern Australia. Seams are composed of very closely spaced or coalesced cleavage lamellae, which are very thin layers of extremely fine-grained phyllosilicates. Cleavage seams enclose lenses of silt-stone or greywacke, which formerly occurred in continuous sedimentary layers, indicating extremely heterogeneous and disruptive deformation. Microphacoids enclosed by cleavage seams have subtle shape asymmetries analogous to those of porphyroclasts. Phyllosilicate-preferred orientations within microphacoids commonly lie at a low angle to enclosing seams, and asymmetric relationships occur within seams. The shape and fabric asymmetries appear to be constant, and are regarded as analgous to S and C planes. The number and extent of seams, the amount of dissolution they indicate, and the efficiency of deformation partitioning imply some enhancement of chemical activity and substantial silica loss from the system. This, in turn, suggests the passage of large amount of silica-undersaturated fluid, and melanges may be zones of high fluid flow. However, the microstructures and the disruptive nature of the fabrics may also reflect the influence of high bulk shear strains and suggest some relationship between the shearing component of deformation and the development of cleavages and foliations. 相似文献
995.
996.
A. Peraiah 《Journal of Astrophysics and Astronomy》1980,1(1):17-23
Spectral lines formed in a rotating and expanding atmosphere have been computed in the frame of the observer at infinity.
Two kinds of velocity laws are employed: (i) a uniform radial velocity of the gas and (ii) velocity increasing with radius
(i.e. velocity gradients). The atmosphere has been assumed to be rotating with constant velocity. We have considered maximum radial
and rotational velocities to be 10 and 3 mean thermal units respectively in an atmosphere whose geometrical thickness is 10
times the stellar radius. The total radial optical depth at line centre is taken to be about 100. In all cases, Doppler profile
and a source function which is varying as 1/r
2 have been used.
Generally, the lines are broadened when rotation is introduced. However, when radial motion is also present, broadening becomes
asymmetric and the red emission and blue absorption are enhanced. 相似文献
997.
998.
999.
1000.