全文获取类型
收费全文 | 37058篇 |
免费 | 727篇 |
国内免费 | 581篇 |
专业分类
测绘学 | 961篇 |
大气科学 | 3078篇 |
地球物理 | 7420篇 |
地质学 | 12293篇 |
海洋学 | 3365篇 |
天文学 | 8720篇 |
综合类 | 127篇 |
自然地理 | 2402篇 |
出版年
2021年 | 200篇 |
2020年 | 262篇 |
2019年 | 259篇 |
2018年 | 622篇 |
2017年 | 576篇 |
2016年 | 890篇 |
2015年 | 629篇 |
2014年 | 855篇 |
2013年 | 1898篇 |
2012年 | 1042篇 |
2011年 | 1459篇 |
2010年 | 1200篇 |
2009年 | 1778篇 |
2008年 | 1580篇 |
2007年 | 1499篇 |
2006年 | 1412篇 |
2005年 | 1289篇 |
2004年 | 1211篇 |
2003年 | 1172篇 |
2002年 | 1094篇 |
2001年 | 977篇 |
2000年 | 987篇 |
1999年 | 919篇 |
1998年 | 835篇 |
1997年 | 842篇 |
1996年 | 723篇 |
1995年 | 649篇 |
1994年 | 563篇 |
1993年 | 514篇 |
1992年 | 508篇 |
1991年 | 484篇 |
1990年 | 479篇 |
1989年 | 419篇 |
1988年 | 404篇 |
1987年 | 455篇 |
1986年 | 437篇 |
1985年 | 523篇 |
1984年 | 585篇 |
1983年 | 560篇 |
1982年 | 521篇 |
1981年 | 467篇 |
1980年 | 436篇 |
1979年 | 399篇 |
1978年 | 413篇 |
1977年 | 359篇 |
1976年 | 323篇 |
1975年 | 337篇 |
1974年 | 336篇 |
1973年 | 338篇 |
1972年 | 203篇 |
排序方式: 共有10000条查询结果,搜索用时 187 毫秒
591.
The Blake Outer Ridge is a 480–kilometer long linear sedimentary drift ridge striking perpendicular to the North American
coastline. By modeling free-air gravity anomalies we tested for the presence of a crustal feature that may control the location
and orientation of the Blake Outer Ridge. Most of our crustal density models that match observed gravity anomalies require
an increase in oceanic crustal thickness of 1–3 km on the southwest side of the Blake Outer Ridge relative to the northeast
side. Most of these models also require 1–4 km of crustal thinning in zone 20–30 km southwest of the crest of the Blake Outer
Ridge. Although these features are consistent with the structure of oceanic fracture zones, the Blake Outer Ridge is not parallel
to adjacent known fracture zones. Magnetic anomalies suggest that the ocean crust beneath this feature formed during a period
of mid-ocean ridge reorganization, and that the Blake Outer Ridge may be built upon the bathymetric expression of an oblique
extensional feature associated with ridge propagation. It is likely that the orientation of this trough acted as a catalyst
for sediment deposition with the start of the Western Boundary Undercurrent in the mid-Oligocene. 相似文献
592.
593.
Hydrodynamic implications of large offshore mussel farms 总被引:2,自引:0,他引:2
Plew D.R. Stevens C.L. Spigel R.H. Hartstein N.D. 《Oceanic Engineering, IEEE Journal of》2005,30(1):95-108
594.
A numerical model to compute wave field is developed. It is based on the Berkhoff diffraction-refraction equation, in which an energy dissipation term is added, to take into account the breaking and the bottom friction phenomena. The energy dissipation function, by breaking and by bottom friction, is introduced in the Berkhoff equation to obtain a new equation of propagation.The resolution is done with the hybrid finite element method, where lagrangians elements are used. 相似文献
595.
In this study, the dynamic stresses within the seabed induced by non-linear progressive waves were explored through a series of hydraulic model tests on a movable bed within a wave flume. By comparing Stokes’ 2nd-order wave theory with the theory of wave-induced dynamic stresses within the seabed as proposed by Yamamoto et al. [1978. On the response of a poro-elastic bed to water waves. Journal of Fluid Mechanics 87 (1), 193–206.] and Hsu and Jeng [1994. Wane-induced soil response in an unsaturated anisotropic seabed of finite thickness. International Journal for Numerical and Analytical Methods in Geomechanics 18, 785–807], the experimental results show that the pressure on the seabed surface, the pore water pressure within the seabed as well as the vertical and the horizontal stresses are all smaller than their theoretical values. If we were to obtain the characteristics of seabed soil, the analytical solution of Hsu and Jeng [1994. Wane-induced soil response in an unsaturated anisotropic seabed of finite thickness. International Journal for Numerical and Analytical Methods in Geomechanics 18, 785–807] might agree to the simulation of the wave-induced effective stresses and shear stress in the sandy seabed. A different phase shift exists among all the three soil stresses. Their influences on the three dynamic stresses within seabed soil are important for seabed stability, and can be used in the verification of numerical models. In the whole, the non-linear progressive waves and the naturally deposited seabed are found to have a strong interaction, and the behavior of the induced dynamic stresses within the seabed is very complicated, and should be investigated integrally. 相似文献
596.
The highest short-crested waves have been studied analytically and numerically by several workers, but without a conclusive view. An efficient numerical scheme is proposed in this paper which retains the water-surface elevations in an implicit form in the governing equations, rather than using a series approximation, thus improving the accuracy of the numerical results. Convergence of the numerical scheme is verified. The almost highest short-crested waves in deep water are then evaluated, which are defined for the condition with the largest wave energies. It is found that the critical angle for wave frequency reversal also demarcates the wave characteristics near breaking, for either kinematic or dynamic prominence. The known results available for the limiting two-dimensional cases of standing and progressive waves are compared favourably. 相似文献
597.
J. -M. Auzende L. Géli H. Ondréas J. -Y. Collot Y. Lafoy J. -P. Eissen E. Gracia M. B. Larue C. Olisukulu D. Tolia N. Biliki 《Geo-Marine Letters》1994,14(4):232-237
During the SOPACMAPS 2 crusie carried out by IFREMER (Institut Français de Recherche pour l'Exploitation de la Mer) and ORSTOM (Institut Français de Recherche Scientifique pour le dévelopement en Coopération) on theR/V L'Atalante, in the Central Solomon Arc area, multibeam bathymetric and imagery data and single-channel seismic reflection profiles were collected from an area of about 3500 km2, to evaluate regional tectonics. Structural data geophysical profiles interpretation provide evidence for left-lateral transtensional tectonics on the southern edge of the Central Solomon Trough. This transtensional deformation is represented by faulting, block tilting, and rhombohedral deformation. The regional geology and the analysis of the sedimentary cover allow us to demonstrate that this tectonic occurred in two different phases during Oligocene to Miocene and Pliocene to Pleistocene times. 相似文献
598.
An instrumented tetrapod was deployed for three weeks on the Dry Tortugas Bank at a depth of 26 m in February 1995. Bottom
roughness was dominated by shrimp burrows and worm mounds with rms roughness amplitudes ranging from 0.47 to 1.75 cm. Logarithmic
velocity profiles show apparent total roughness heights ranging from 0.30 to 1.45 cm, values consistent with observed biological
roughness. The bed sediments were weakly bound by an algal crust at the sediment–water interface. When this bound layer was
scraped away by a mooring that was accidentally dragged, sharp-crested wave-induced ripples appeared within the resulting
swath. We conclude that physically induced roughness is biologically suppressed, but if dominant, would be significantly higher
than the prevailing biological roughness. 相似文献
599.
600.
Whether or not there are extensional detachment faults in the Alboran basement can be tested directly because a part of the Alboran Basin is now emerged. These detachments, related to crustal thinning beneath the Alboran Basin, occurred from the Aquitanian to Tortonian. The resulting extensional geometries can be described in general terms. During the Serravalian a considerable southwest extension of the basin took place, accompanied by south-southeast extension in the northern Gibraltar Arc. Other detachments affected by Serravalian extension can be found. The spreading of the Alboran was nearly coeval with roughly westward migration of the Gibraltar mountain front. 相似文献