全文获取类型
收费全文 | 101771篇 |
免费 | 1360篇 |
国内免费 | 859篇 |
专业分类
测绘学 | 2720篇 |
大气科学 | 7059篇 |
地球物理 | 19260篇 |
地质学 | 38073篇 |
海洋学 | 8610篇 |
天文学 | 23060篇 |
综合类 | 378篇 |
自然地理 | 4830篇 |
出版年
2022年 | 513篇 |
2021年 | 892篇 |
2020年 | 968篇 |
2019年 | 1005篇 |
2018年 | 4252篇 |
2017年 | 3927篇 |
2016年 | 3692篇 |
2015年 | 1530篇 |
2014年 | 2567篇 |
2013年 | 4503篇 |
2012年 | 3464篇 |
2011年 | 5439篇 |
2010年 | 4803篇 |
2009年 | 5891篇 |
2008年 | 4933篇 |
2007年 | 5437篇 |
2006年 | 3409篇 |
2005年 | 2866篇 |
2004年 | 2834篇 |
2003年 | 2710篇 |
2002年 | 2529篇 |
2001年 | 2082篇 |
2000年 | 1963篇 |
1999年 | 1628篇 |
1998年 | 1696篇 |
1997年 | 1571篇 |
1996年 | 1369篇 |
1995年 | 1330篇 |
1994年 | 1175篇 |
1993年 | 1043篇 |
1992年 | 999篇 |
1991年 | 1019篇 |
1990年 | 1102篇 |
1989年 | 908篇 |
1988年 | 883篇 |
1987年 | 1020篇 |
1986年 | 891篇 |
1985年 | 1129篇 |
1984年 | 1253篇 |
1983年 | 1145篇 |
1982年 | 1064篇 |
1981年 | 1036篇 |
1980年 | 927篇 |
1979年 | 877篇 |
1978年 | 860篇 |
1977年 | 737篇 |
1976年 | 706篇 |
1975年 | 709篇 |
1974年 | 663篇 |
1973年 | 714篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
771.
772.
A comparison of methods for the calculation of the hydrodynamic characteristics of arrays of wave power devices is presented. In particular, the plane-wave approximation and an exact multiple scattering formulation have been used to compute exciting wave forces, hydrodynamic coefficients and q factors for arrays of interacting wave power devices. The results obtained are compared with each other, and accuracy aspects of the computations are stressed and critically assessed. 相似文献
773.
S. B. Dharmadhikari E. Garcia S. Espinoza J. Dominguez J. M. Goris 《Ocean Engineering》1978,5(3):165-180
This paper describes the process of launching and joining of two sections of a product carrier of 30,500 DWT built at Dianca shipyard at Puerto Cabello, Venezuela. The specifications and characteristics of this ship are in line with the market requirements. This paper deals with the problems encountered during the decision of dividing the ship in two halves, use of syncrolift for launching and subsequent joining of two halves in the dry dock. 相似文献
774.
Considerable metal enrichments have been found in hydrothermal fluids and metalliferous sediments off the central Lesser Antilles Volcanic Arc. The elements variably enriched in the fluids as a result of the hydrothermal activity are Fe, Mn, As, Si, B, Li and in the sediments, Fe, P, Mo, As, Sb, Hg, Cu and Pb. Variations in the concentrations of these elements in both fluids and sediments along the arc result from a number of factors, the most important of which is the stage that each island's volcano has reached in its eruptive cycle. Although hydrothermal mineralization on the sea floor off the islands is only low grade, phase separation in the hydrothermal fluids at depth could be leading to higher grade stockwork mineralization below the vent fields or the discharge of metal rich brines on the lower flanks of the volcanic islands. 相似文献
775.
Integrated coastal management (ICM) is an emerging approach in East Africa for the solution of various coastal issues. This paper is intended to provide an update on the current practical aspects concerning the ICM process and related policies and strategies in Madagascar. Efforts are being made in Madagascar for the mutual integration of numerous coastal projects and activities within the Environment Program of the National Environmental Action Plan. The foundations for an ICM program, built during an ICM workshop, which took place at the end of 1996 upon existing activities, are being expanded presently. These developments concern, above all, the institutional aspects related to the formulation of an ICM program. Therefore, the actual situation sees an overgrowing collaboration of the national and international agencies involved in the implementation of coastal projects, in an expandingly integrating way, within an institutional framework that grows progressively stronger. The case of Madagascar suggests reflections on how ICM can mitigate potential sectoral conflicts as well as on, how the sometimes complex nature of the social and cultural issues may influence the development of an ICM program. The need for monitoring ICM is stressed and the role of outside partners clarified. 相似文献
776.
777.
Abstract. Survival and behaviour of the hermatypic coral Diploria strigosa was studied during 6–24 h doses with water-accomodated fractions of chemically dispersed crude oil, and for a subsequent recovery period of 1 month. Experiments utilized a flow-through laboratory dosing procedure and incorporated petroleum hydrocarbon measurements in order to simulate a major but short-term oil spill in shallow subtidal benthic reef environments. Chemically dispersed oil treatments consisted of Arabian Light Crude oil with Corexit 9527 or BP1100WD at 1–20 ppm concentrations of oil.
In general, effects observed were sub-lethal, temporary, and associated with the highest concentrations tested. Responses to the presence of dispersed oil at 20ppm for 24 h included mesenterial filament extrusion, extreme tissue contraction, tentacle retraction and localized tissue rupture. The nature and severity of reactions during the dosing phase varied between colonies and treatments, but colonies typically resumed normal behaviour within 2 h to 4 d of the recovery period. It therefore seems unlikely that observed biological effects would impair long-term viability. 相似文献
In general, effects observed were sub-lethal, temporary, and associated with the highest concentrations tested. Responses to the presence of dispersed oil at 20ppm for 24 h included mesenterial filament extrusion, extreme tissue contraction, tentacle retraction and localized tissue rupture. The nature and severity of reactions during the dosing phase varied between colonies and treatments, but colonies typically resumed normal behaviour within 2 h to 4 d of the recovery period. It therefore seems unlikely that observed biological effects would impair long-term viability. 相似文献
778.
Population structure of Haliotis rubra from South Australia inferred from nuclear and mtDNA analyses 总被引:1,自引:0,他引:1
1Introduction ThemajorityofAustralia’sabalonefisheryex ports(5.135kt,worth$216millionin2002~2003,ABARE2004)consistofblacklipabalone(HaliotisrubraLeach,1814).AssuchH.rubrais consideredasanimportantmarineresourcewithin Australia.Likemanyabalonespecieswor… 相似文献
779.
Geology of the Continental Margin of Enderby and Mac. Robertson Lands, East Antarctica: Insights from a Regional Data Set 总被引:1,自引:0,他引:1
H. M. J. Stagg J. B. Colwel N. G. Direen P. E. O’Brien G. Bernardel I. Borissova B. J. Brown T. Ishirara 《Marine Geophysical Researches》2004,25(3-4):183-219
In 2001 and 2002, Australia acquired an integrated geophysical data set over the deep-water continental margin of East Antarctica
from west of Enderby Land to offshore from Prydz Bay. The data include approximately 7700 km of high-quality, deep-seismic
data with coincident gravity, magnetic and bathymetry data, and 37 non-reversed refraction stations using expendable sonobuoys.
Integration of these data with similar quality data recorded by Japan in 1999 allows a new regional interpretation of this
sector of the Antarctic margin.
This part of the Antarctic continental margin formed during the breakup of the eastern margin of India and East Antarctica,
which culminated with the onset of seafloor spreading in the Valanginian. The geology of the Antarctic margin and the adjacent
oceanic crust can be divided into distinct east and west sectors by an interpreted crustal boundary at approximately 58° E.
Across this boundary, the continent–ocean boundary (COB), defined as the inboard edge of unequivocal oceanic crust, steps
outboard from west to east by about 100 km.
Structure in the sector west of 58° E is largely controlled by the mixed rift-transform setting. The edge of the onshore Archaean–Proterozoic
Napier Complex is downfaulted oceanwards near the shelf edge by at least 6 km and these rocks are interpreted to underlie
a rift basin beneath the continental slope. The thickness of rift and pre-rift rocks cannot be accurately determined with
the available data, but they appear to be relatively thin. The margin is overlain by a blanket of post-rift sedimentary rocks
that are up to 6 km thick beneath the lower continental slope.
The COB in this sector is interpreted from the seismic reflection data and potential field modelling to coincide with the
base of a basement depression at 8.0–8.5 s two-way time, approximately 170 km oceanwards of the shelf-edge bounding fault
system. Oceanic crust in this sector is highly variable in character, from rugged with a relief of more than 1 km over distances
of 10–20 km, to rugose with low-amplitude relief set on a long-wavelength undulating basement. The crustal velocity profile
appears unusual, with velocities of 7.6–7.95 km s−1 being recorded at several stations at a depth that gives a thickness of crust of only 4 km. If these velocities are from
mantle, then the thin crust may be due to the presence of fracture zones. Alternatively, the velocities may be coming from
a lower crust that has been heavily altered by the intrusion of mantle rocks.
The sector east of 58° E has formed in a normal rifted margin setting, with complexities in the east from the underlying structure
of the N–S trending Palaeozoic Lambert Graben. The Napier Complex is downfaulted to depths of 8–10 km beneath the upper continental
slope, and the margin rift basin is more than 300 km wide. As in the western sector, the rift-stage rocks are probably relatively
thin. This part of the margin is blanketed by post-rift sediments that are up to about 8 km thick.
The interpreted COB in the eastern sector is the most prominent boundary in deep water, and typically coincides with a prominent
oceanwards step-up in the basement level of up to 1 km. As in the west, the interpretation of this boundary is supported by
potential field modelling. The oceanic crust adjacent to the COB in this sector has a highly distinctive character, commonly
with (1) a smooth upper surface underlain by short, seaward-dipping flows; (2) a transparent upper crustal layer; (3) a lower
crust dominated by dipping high-amplitude reflections that probably reflect intruded or altered shears; (4) a strong reflection
Moho, confirmed by seismic refraction modelling; and (5) prominent landward-dipping upper mantle reflections on several adjacent
lines. A similar style of oceanic crust is also found in contemporaneous ocean basins that developed between Greater India
and Australia–Antarctica west of Bruce Rise on the Antarctic margin, and along the Cuvier margin of northwest Australia. 相似文献
780.