全文获取类型
收费全文 | 36868篇 |
免费 | 700篇 |
国内免费 | 579篇 |
专业分类
测绘学 | 933篇 |
大气科学 | 3066篇 |
地球物理 | 7395篇 |
地质学 | 12195篇 |
海洋学 | 3358篇 |
天文学 | 8693篇 |
综合类 | 120篇 |
自然地理 | 2387篇 |
出版年
2021年 | 198篇 |
2020年 | 257篇 |
2019年 | 255篇 |
2018年 | 611篇 |
2017年 | 563篇 |
2016年 | 878篇 |
2015年 | 619篇 |
2014年 | 846篇 |
2013年 | 1882篇 |
2012年 | 1032篇 |
2011年 | 1448篇 |
2010年 | 1190篇 |
2009年 | 1770篇 |
2008年 | 1568篇 |
2007年 | 1490篇 |
2006年 | 1404篇 |
2005年 | 1284篇 |
2004年 | 1206篇 |
2003年 | 1166篇 |
2002年 | 1090篇 |
2001年 | 975篇 |
2000年 | 983篇 |
1999年 | 917篇 |
1998年 | 834篇 |
1997年 | 841篇 |
1996年 | 720篇 |
1995年 | 645篇 |
1994年 | 561篇 |
1993年 | 514篇 |
1992年 | 510篇 |
1991年 | 480篇 |
1990年 | 476篇 |
1989年 | 418篇 |
1988年 | 402篇 |
1987年 | 449篇 |
1986年 | 433篇 |
1985年 | 522篇 |
1984年 | 582篇 |
1983年 | 558篇 |
1982年 | 519篇 |
1981年 | 462篇 |
1980年 | 435篇 |
1979年 | 397篇 |
1978年 | 412篇 |
1977年 | 358篇 |
1976年 | 323篇 |
1975年 | 336篇 |
1974年 | 336篇 |
1973年 | 338篇 |
1972年 | 201篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
381.
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
382.
383.
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
384.
William C. Schwab Elazar Uchupi Robert D. Ballard Thomas K. Dettweiler 《Geo-Marine Letters》1989,9(3):171-178
SeaMARC side-scan sonographs and Argo video and photographic data suggest that the recent sedimentary environment of the floor
of the Tongue of the Ocean is controlled by an interplay of turbidity current flow from the south, sediment spill-over from
the carbonate platform to the east (windward side), and rock falls from the west carbonate escarpment (lee side). The spill-over
forms a sandy sedimentary deposit that acts as a topographic obstruction to the turbidity current flow from the south. This
obstruction is expressed by the westward migration of a northwest-southeast oriented turbidity-current-cut channel. 相似文献
385.
F. E. Grousset J. L. Joron P. E. Biscaye C. Latouche M. Treuil N. Maillet J. C. Faugères E. Gonthier 《Geo-Marine Letters》1988,8(1):25-34
Data obtained from mineralogical and geochemical analyses of piston and gravity cores, recovered from an area off Lisbon (Portugal) to the Alboran Sea (Mediterranean), serve as a basis for better understanding the past 18,000 years of hydrological exchanges at Gibraltar. Tracers used in this study are smectite, kaolinite, Ta, Th, La. One of the primary sources of particles both into and out of the Mediterranean is the Guadalquivir River. These particles are transported back into the Atlantic in the Mediterranean outflow water, and deposited along the Iberian slope. No evidence for reversal of this outflow current was found in those cores, since 18,000 years B.P. 相似文献
386.
387.
C. Kranenburg 《Applied Ocean Research》1984,6(1):23-30
The rupture of a submarine oil pipeline starts various mechanisms leading to an oil spill. Among these mechanisms the leakage of oil driven by the difference in specific gravities of oil and sea-water is difficult to estimate. A simple mathematical model has been developed and laboratory experiments have been carried out to obtain an insight into the density-driven exchange flow and to determine the leak rate. The mathematical model is predictive and takes account of the effects of friction, inclination of the pipeline, and inertia of the fluid. The experiments were done in a horizontal model pipeline. Theoretical and experimental results are in satisfactory agreement. 相似文献
388.
From July, 1975 to November, 1976 mussels from the Laguna Veneta, north-east Italy, and the adjacent Adriatic Sea were collected bimonthly at ten stations and analysed for 3,4-benzopyrene (BaP) and perylene (Pe) content. Mean concentrations were in the range 12·0–135·1 μg/kg dry weight for BaP and 1·5–16·9 μg/kg for Pe, but values as high as 327 μg/kg for BaP and 71 μg/kg for Pe have been measured. The distribution of BaP and Pe closely matches previous results on petroleum hydrocarbon contamination in mussels from this area and indicates that the major portion of BaP and Pe in these bivalves is due principally to human activities. 相似文献
389.
390.