全文获取类型
收费全文 | 63266篇 |
免费 | 1154篇 |
国内免费 | 443篇 |
专业分类
测绘学 | 1407篇 |
大气科学 | 4482篇 |
地球物理 | 12535篇 |
地质学 | 23040篇 |
海洋学 | 5620篇 |
天文学 | 13780篇 |
综合类 | 146篇 |
自然地理 | 3853篇 |
出版年
2022年 | 378篇 |
2021年 | 645篇 |
2020年 | 744篇 |
2019年 | 803篇 |
2018年 | 1587篇 |
2017年 | 1579篇 |
2016年 | 1764篇 |
2015年 | 952篇 |
2014年 | 1681篇 |
2013年 | 3170篇 |
2012年 | 1947篇 |
2011年 | 2643篇 |
2010年 | 2275篇 |
2009年 | 2913篇 |
2008年 | 2571篇 |
2007年 | 2625篇 |
2006年 | 2474篇 |
2005年 | 1762篇 |
2004年 | 1764篇 |
2003年 | 1733篇 |
2002年 | 1621篇 |
2001年 | 1454篇 |
2000年 | 1377篇 |
1999年 | 1161篇 |
1998年 | 1145篇 |
1997年 | 1207篇 |
1996年 | 989篇 |
1995年 | 982篇 |
1994年 | 903篇 |
1993年 | 777篇 |
1992年 | 750篇 |
1991年 | 728篇 |
1990年 | 777篇 |
1989年 | 695篇 |
1988年 | 670篇 |
1987年 | 720篇 |
1986年 | 714篇 |
1985年 | 879篇 |
1984年 | 901篇 |
1983年 | 928篇 |
1982年 | 860篇 |
1981年 | 778篇 |
1980年 | 776篇 |
1979年 | 695篇 |
1978年 | 637篇 |
1977年 | 646篇 |
1976年 | 588篇 |
1975年 | 581篇 |
1974年 | 573篇 |
1973年 | 587篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
961.
962.
A detailed survey of a 1°×1°-square of seafloor 100 miles south-east of the Azores shows a strong correlation between directions of regional topographic and magnetic lineations. The area is dissected by the East Azores Fracture Zone at 36°55N, identified as the active Eurasian-African plate boundary, and by another large, non-active fracture zone at 36°10N. Both fracture zones strike 265° and are accompanied by large amplitude magnetic anomalies. The general strike in the area in between is 000°–015°. The skewing effect at this magnetic latitude is very sensitive to variations in strike of the magnetic contrasts. This effect was eliminated by a non-linear transformation which also gives the positions of magnetic contrasts. Some N-S contrasts were identified as sea floor spreading polarity contrasts (anomalies 31 and 32). Weak contrasts could be identified as topographic effects and gave a magnetization intensity of 5 A m-1. The identified sea floor spreading anomalies to both sides of the fracture zone at 36°10N agree very well, also quantatively, with a three-dimensional model for the fracture zone anomalies. This model describes the non-linear anomalies as end effects of the magnetic layer which is divided in blocks of alternating polarity. 相似文献
963.
Measurements of 226Ra and 210Pb in barite samples separated from different depths of a piston core from the eastern equatorial Pacific are reported. 226Ra is enriched in the barite as would be expected from the chemistries of Ra and Ba; the ratio centers around 1.5 · 1014 atoms/mole. The results suggest that barite is concentrating Ra at a rate comparable to its decay rate, viz. 5.78 · 10?3 yr?1. The gross 210Pb depletion with respect to 226Ra is indicative of 222Rn loss due to the smallness of the barite crystals. 相似文献
964.
The distribution of the colour index is considered in the region bounded by 8–11°N and 13°30–18°30W based on the results of measurements made on board vessels of the Marine Hydrophysical Institute of the Ukrainian SSR Academy of Sciences (MHI) in 1977–1985. Mean values and statistical characteristics are calculated for the colour index variability over one-degree squares. A map of its multi-yearly average distribution is plotted.Translated by M. M. Trufanov. 相似文献
965.
The problem of monitoring of the mesoscale variability of hydrophysical fields in the shelf zone is considered. The usefulness of the data available in regional information centres is discussed. The possibility of monitoring the dynamics of the oceanic fields in the tropical Atlantic encompassing separate observation sites is demonstrated using the oceanographic databank of the scientific research centre (CERESCOR) in Conakry-Rogbane as an example. The results of assimilation of the hydrophysical survey data derived on the shelf in a telescopic model of the region are given.Translated by Mikhail M. Trufanov. 相似文献
966.
The NDRE-AUV flight control system 总被引:1,自引:0,他引:1
The flight control system of an autonomous underwater vehicle (AUV) developed at the Norwegian Defence Research Establishment (NDRE) is presented. A mathematical model of the vehicle is derived and discussed. The system is separated into lightly interacting subsystems, and three autopilots are designed for steering, diving, and speed control. The design of the separate controllers is based on PID techniques. Results from extensive sea testing show robust performance and stability for the autopilot 相似文献
967.
968.
In 1980, a large earthquake caused extensive sediment failure on the shallow continental shelf off the Klamath River in northern
California. Side-scan sonography was used to complement detailed geophysical profiling in identifying specific features and
resolving modes of failure. The features include a nearly flat failure terrace mantled with sand boils, collapse craters and
sediment flows, and bounded on the seaward side by a meandering continuous toe ridge. Seaward of the terrace lies a compression
zone delineated by small pressure ridges. Our findings indicate a temporal progression of failure from lique-faction of shallow
subsurface sand to lateral spread of intact blocks to sediment collapse and flow. 相似文献
969.
Several aspects of the Maryland ridge field are pertinent to the problem of ridge genesis in response to Holocene sea-level
rise. There is a systematic morphologic change fromshoreface ridges throughnearshore ridges tooffshore ridges, which reflects the changing hydraulic regime. Grain size is 90° out of phase with topography, so that the coarsest sand
lies between the axis of each trough and the adjacent seaward ridge crest, while the finest sand lies between each ridge crest
and the axis of the adjacent seaward trough. Finally, analysis over a 43-year period on an outer ridge reveals a systematic
pattern of landward flank erosion, seaward flank deposition, and seaward crest migration.
These relationships support a model which explains the ridges as consequences of the up-current shift of maximum bottom shear
stress with respect to the crests of initial bottom irregularities. The oblique orientation of the ridges with respect to
the beach may be at least partly due to the more rapid migration rate of the ridges’ inshore ends. 相似文献
970.