全文获取类型
收费全文 | 6409篇 |
免费 | 343篇 |
国内免费 | 32篇 |
专业分类
测绘学 | 201篇 |
大气科学 | 447篇 |
地球物理 | 2432篇 |
地质学 | 2191篇 |
海洋学 | 315篇 |
天文学 | 911篇 |
综合类 | 34篇 |
自然地理 | 253篇 |
出版年
2022年 | 51篇 |
2021年 | 126篇 |
2020年 | 134篇 |
2019年 | 110篇 |
2018年 | 289篇 |
2017年 | 273篇 |
2016年 | 398篇 |
2015年 | 297篇 |
2014年 | 320篇 |
2013年 | 404篇 |
2012年 | 354篇 |
2011年 | 306篇 |
2010年 | 296篇 |
2009年 | 299篇 |
2008年 | 234篇 |
2007年 | 179篇 |
2006年 | 170篇 |
2005年 | 151篇 |
2004年 | 146篇 |
2003年 | 143篇 |
2002年 | 112篇 |
2001年 | 107篇 |
2000年 | 111篇 |
1999年 | 67篇 |
1998年 | 95篇 |
1997年 | 80篇 |
1996年 | 53篇 |
1995年 | 76篇 |
1994年 | 87篇 |
1993年 | 57篇 |
1992年 | 49篇 |
1991年 | 43篇 |
1990年 | 62篇 |
1989年 | 46篇 |
1988年 | 44篇 |
1987年 | 39篇 |
1986年 | 47篇 |
1985年 | 49篇 |
1984年 | 38篇 |
1983年 | 46篇 |
1982年 | 55篇 |
1981年 | 46篇 |
1980年 | 44篇 |
1979年 | 41篇 |
1978年 | 50篇 |
1977年 | 42篇 |
1975年 | 41篇 |
1974年 | 31篇 |
1973年 | 44篇 |
1971年 | 40篇 |
排序方式: 共有6784条查询结果,搜索用时 31 毫秒
51.
This paper deals with the solution of the problem of the dynamic response of the leg of a tension leg platform subjected to an axial, suddenly applied load at one end, considering a highly simplified model but taking into account several complicating factors. The problem is solved by means of a non-harmonic Fourier expansion in terms of eigenfunctions obtained from a non-regular Sturm-Liouville system. 相似文献
52.
The Maracaibo Estuary is of particular interest because of its location in the tropics, its large size (over 12,000 km2), the economic importance of its underlying hydrocarbon deposits and its increasing rate of pollution. Sediments from this estuary were studied in order to characterise their capacity to adsorb and desorb phosphorus. Considerable variability in capacity for phosphate sorption was found among the seventeen samples studied. This variability can be attributed first to the differences among the samples in total P content and, secondly, to their differences in free iron content. Also, it appears that P retention contributes to the control of P concentration in the water and therefore the sediments serve as a buffer in controlling P eutrophication in the estuary. 相似文献
53.
A spread of warm water from the first crest of the Kuroshio Extension is periodically enhanced by northward warm water intrusions from the main current. The water type in the spread area was previously found to be the same as that in the Kuroshio front at depth. In looking for the possible mechanism responsible for the northward warm water intrusions, a dynamic analysis in the Kuroshio front was carried out by using CTD, ADCP, AVHRR and ARGOS buoy data, obtained in 1996 by the R.V. Hakuho Maru. Downstream, cross-stream and vertical velocities in the Kuroshio Extension were found by using a "stream coordinate system". The velocity field in the Kuroshio front at the first crest showed a double structure with two surface velocity maxima. In the inner part of the front, relatively high cross-stream (northward) and vertical (upward) velocities were found. Thus, this study suggests that while water particles flow downstream along the first stationary meander of the Kuroshio Extension, they also experience lateral and vertical movements which allow the deeper water from an upstream location to rise to the surface layer, and in certain locations to deflect northward. By assuming isopycnal movement and conservation of potential vorticity, it was found that in those locations where anticyclonic curvature of the meander increases, warm water is more likely to deflect northward. High ageostrophic components observed in the first 300 m of the water column are probably related to the relatively high cross-stream and vertical velocities in the inner part of the front. 相似文献
54.
Baraza J. Ercilla G. Farrán M. Casamor J. L. Sorribas J. Flores J. A. Sierro F. Wersteeg W. 《Marine Geophysical Researches》1997,19(2):115-135
Multibeam bathymetric and ultra high-resolution seismic data reveal that the distal course of the Equatorial Atlantic Mid-Ocean Channel (EAMOC) extends further east and south than was previously known, and is controlled by the presence of morphologic highs related to the Fernando de Noronha Fracture Zone. Distal course of the EAMOC is buried by sediments, and does not have bathymetric expression on the seafloor. The channel fill consists of three seismic sequences, suggesting that the recent geological evolution of the channel is composed of successive phases of decreasing sedimentary activity that finally resulted in its complete burial. Tectonic and volcanic activity related to the Fernando de Noronha Fracture Zone and Ridge, together with the effect of strong pulses of the Antarctic bottom water current during the upper Pliocene are suggested to have contributed to the progressive burial and the final abandonment of the EAMOC. 相似文献
55.
Detailed structural interpretation of the recently acquired deep seismic multichannel profiles along the Iberian Atlantic Margins (IAM Project) provides new results on the geodynamic evolution of the eastern part of the Azores-Gibraltar plate boundary. Thrusting and folding of the oceanic basement and of Mesozoic and Cenozoic sedimentary cover of the Gorringe Bank region are consistent with the N–S convergence of Iberia and Africa. Compressive structures in the Gorringe Bank region are spread over a wide area. Deformation under compression took place mainly in Tertiary times, as is evidenced by a basal unconformity and several discontinuities in Tertiary sediments, although some deformation has also been recorded in Quaternary sediments. The compressive structures in the Gulf of Cadiz are E–W oriented thrusts, folds and related diapiric structures. N–S oriented transpressive deformation is likely to occur in the western Portuguese platform. There is no continuity of structures from the oceanic to the continental domain, suggesting that deformation transfers from one side to the other through a transcurrent fault zone. The fault contact between the two domains is located in the ocean-continent transition zone. 相似文献
56.
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
57.
58.
59.
A clamped square-plate is subjected to a uniform state of stress in the x-direction. The present study deals with the basic question of determining the variation of the lower natural frequencies of transverse vibration of a plate as a small diameter, central hole is made in it, introducing a stress concentration field. 相似文献
60.
R.E. Rossi P.M. Belles P.A.A. Laura S. La Malfa L. Ercoli D. Pasqua 《Ocean Engineering》1996,23(3):271-276
A numerical solution is obtained for the title problem by means of the popular finite element method. An experimental investigation of the problem is also presented for plates of square planform. The agreement between theoretical and experimental values is very good in the case of the fundamental frequency, and reasonably good when the second and third normal modes of transverse vibration are considered. It is concluded that beneficial effects are obtained in the sense that one generates a lighter structural element with higher fundamental frequency of transverse vibration. Hence, dynamic stiffening is achieved. 相似文献