全文获取类型
收费全文 | 54244篇 |
免费 | 443篇 |
国内免费 | 428篇 |
专业分类
测绘学 | 1745篇 |
大气科学 | 4041篇 |
地球物理 | 9855篇 |
地质学 | 22050篇 |
海洋学 | 3923篇 |
天文学 | 11159篇 |
综合类 | 273篇 |
自然地理 | 2069篇 |
出版年
2021年 | 283篇 |
2020年 | 279篇 |
2019年 | 335篇 |
2018年 | 3684篇 |
2017年 | 3430篇 |
2016年 | 2537篇 |
2015年 | 706篇 |
2014年 | 995篇 |
2013年 | 1702篇 |
2012年 | 2078篇 |
2011年 | 3860篇 |
2010年 | 3517篇 |
2009年 | 3869篇 |
2008年 | 3154篇 |
2007年 | 3765篇 |
2006年 | 1232篇 |
2005年 | 1467篇 |
2004年 | 1222篇 |
2003年 | 1290篇 |
2002年 | 1114篇 |
2001年 | 808篇 |
2000年 | 782篇 |
1999年 | 683篇 |
1998年 | 623篇 |
1997年 | 641篇 |
1996年 | 574篇 |
1995年 | 549篇 |
1994年 | 527篇 |
1993年 | 438篇 |
1992年 | 392篇 |
1991年 | 426篇 |
1990年 | 418篇 |
1989年 | 395篇 |
1988年 | 366篇 |
1987年 | 438篇 |
1986年 | 370篇 |
1985年 | 449篇 |
1984年 | 485篇 |
1983年 | 472篇 |
1982年 | 453篇 |
1981年 | 373篇 |
1980年 | 391篇 |
1979年 | 316篇 |
1978年 | 310篇 |
1977年 | 306篇 |
1976年 | 262篇 |
1975年 | 260篇 |
1974年 | 287篇 |
1973年 | 317篇 |
1972年 | 197篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Tiago M. Alves Vasilios Lykousis Dimitris Sakellariou Stamatina Alexandri Paraskevi Nomikou 《Geo-Marine Letters》2007,27(1):41-61
Bathymetric, 9.5-kHz long-range sidescan sonar (OKEAN), seismic reflection and sediment-core data are used in the analysis
of two tectonic troughs south of Crete, Eastern Mediterranean Sea. Here, up to 1.2 s two-way travel time (TWTT) of strata
have accumulated since the Middle Miocene in association with extension in the South Aegean region. The study area comprises
>100-km- long by >25-km-wide basins filled by sediments subdivided into two seismic units: (1) an upper Unit 1 deposited in
sub-basins which follow the present-day configuration of the southern Cretan margin; (2) a basal Unit 2, more than 500 ms
(TWTT) thick, accumulated in deeper half-graben/grabens distinct from the present-day depocentres. Both units overlap a locally
stratified Unit 3 comprising the pre-Neogene core complex of Crete and Gavdos. In this work, the interpreted seismic units
are correlated with the onshore stratigraphy, demonstrating that denudation processes occurring on Crete and Gavdos in response
to major tectonic events have been responsible for high sedimentation rates along the proximal southern Cretan margin. Consequently,
topographically confined sedimentary units have been deposited south of Crete in the last 12 Ma, including turbidites and
other mass-flow deposits fed by evolving transverse and axial channel systems. Surface processes controlling facies distribution
include the direct inflow of sediment from alluvial-fan systems and incising mountain rivers onto the Cretan slope, where
significant sediment instability processes occur at present. In this setting, seismic profiles reveal eight different types
of stratigraphic contacts on basin-margin highs, and basinal areas show evidence of halokinesis and/or fluid escape. The acquired
data also show that significant changes to the margin’s configuration occurred in association with the post-Alpine tectonic
and eustatic episodes affecting the Eastern Mediterranean. 相似文献
72.
R. K. Reed 《Journal of Oceanography》1970,26(6):331-339
After examination of the baroclinic structure below 3000 db, recent data were used to map the geopotential topography at 1000,
1500, and 2000 db (referred to 3000 db) in the Pacific Ocean. In the high-latitude regions and in the western boundary currents,
considerable relief is present at 1000 and 1500 db, and the Circumpolar Current is still well-developed at 2000 db. The geostrophic
circulation inferred is very similar to the surface circulation in these areas. Neglect of the structure below 1000 db results
in appreciable errors in estimates of the transport of these currents; direction of near-surface flow is properly shown, however,
and computed speeds are not greatly in error. In the equatorial Pacific and central North Pacific, little relief is present,
and the trends are generally unlike the surface flow. 相似文献
73.
74.
A procedure for the four-dimensional (4D) analysis of the hydrophysical fields in the Black Sea with an assimilation of the temperature and salinity (T, S) data was realized on the basis of a numerical model which involves the primitive equations of motion, and the heat and salt advection equations. Two experiments were carried out which differed by the observation data assimilation procedure. Analysis has shown that the observation data assimilation procedure realized using the energy-balanced model allows the reproduction of some synoptic features of the circulation in the Black Sea. A comparison of two computations demonstrates the efficiency of assimilating the measurement data on the basis of the 4D analysis as compared with the sequential objective analysis.Translated by Mikhail M. Trufanov. 相似文献
75.
The ability of cultured zooxanthellae to use ammonium and nitrate was tested. The zooxanthellae were initially isolated from the anemone Aiptasia pulchella. The zooxanthellae were able to grow on media supplemented with either form of dissolved inorganic nitrogen (DIN) although ammonium was inhibitory above 300 μM. In accord with the intact symbiosis and freshly isolated algae, the cultured zooxanthellae took up ammonium. In contrast, the cultured algae demonstrated nitrate uptake and utilization. This was enhanced with DIN deprivation. Nitrate reductase was found in the algae and appeared to be inducible. Within the animal host, excretory ammonium may repress this induction. 相似文献
76.
Formation of pockmarks by pore-water escape 总被引:1,自引:1,他引:1
P. K. Harrington 《Geo-Marine Letters》1985,5(3):193-197
During the course of a North Sea rig site investigation, a number of seabed depressions were observed on side-scan sonar records, some of which may be identified as pockmarks. Others are described as pits. A pockmark evolutionary series is proposed on the basis of all these features with a suggested mechanism which would favor release of pore water, but does not exclude gas escape. Acoustic voids are considered to be a related phenomenon. 相似文献
77.
Growth rate of Raia clavata in the Northeast Irish Sea 总被引:1,自引:0,他引:1
78.
79.
80.
A. G. Matul T. A. Khusid V. V. Mukhina M. P. Chekhovskaya S. A. Safarova 《Oceanology》2007,47(1):80-90
The study of diatoms and benthic foraminifers from the southeastern shelf of the Laptev Sea shows that their most diverse and abundant recent assemblages populate the peripheral underwater part of the Lena River delta representing the marginal filter of the sea. This area is characterized by an intense interaction between the fresh waters of the Siberian rivers and the basin seawater, the Atlantic one included. Local Late Holocene (~last 2300 years) environments reflect the main regional and global paleoclimatic changes, the Medieval Warm Period (~600–1100 years B.P.) and the Little Ice Age (~100–600 years B.P.) inclusive. In addition, the composition and distribution of planktonic foraminifers implies a strong influence of the Atlantic water during the Holocene optimum ~5100–6200 years B.P. 相似文献