全文获取类型
收费全文 | 37675篇 |
免费 | 561篇 |
国内免费 | 432篇 |
专业分类
测绘学 | 1339篇 |
大气科学 | 2902篇 |
地球物理 | 7495篇 |
地质学 | 13168篇 |
海洋学 | 3047篇 |
天文学 | 8533篇 |
综合类 | 156篇 |
自然地理 | 2028篇 |
出版年
2021年 | 324篇 |
2020年 | 339篇 |
2019年 | 390篇 |
2018年 | 920篇 |
2017年 | 887篇 |
2016年 | 1144篇 |
2015年 | 687篇 |
2014年 | 1082篇 |
2013年 | 1988篇 |
2012年 | 1202篇 |
2011年 | 1525篇 |
2010年 | 1298篇 |
2009年 | 1615篇 |
2008年 | 1426篇 |
2007年 | 1352篇 |
2006年 | 1389篇 |
2005年 | 1159篇 |
2004年 | 1044篇 |
2003年 | 1020篇 |
2002年 | 1013篇 |
2001年 | 879篇 |
2000年 | 839篇 |
1999年 | 766篇 |
1998年 | 707篇 |
1997年 | 706篇 |
1996年 | 649篇 |
1995年 | 619篇 |
1994年 | 586篇 |
1993年 | 501篇 |
1992年 | 467篇 |
1991年 | 480篇 |
1990年 | 505篇 |
1989年 | 465篇 |
1988年 | 432篇 |
1987年 | 520篇 |
1986年 | 432篇 |
1985年 | 537篇 |
1984年 | 603篇 |
1983年 | 558篇 |
1982年 | 539篇 |
1981年 | 452篇 |
1980年 | 444篇 |
1979年 | 407篇 |
1978年 | 372篇 |
1977年 | 378篇 |
1976年 | 324篇 |
1975年 | 322篇 |
1974年 | 334篇 |
1973年 | 365篇 |
1972年 | 228篇 |
排序方式: 共有10000条查询结果,搜索用时 10 毫秒
921.
922.
Single-channel seismic reflection profiles show evidence for areas of significant gas accumulation at the head of the Cape Fear Slide on the continental rise off North Carolina. Gas accumulation appears to occur beneath a gas hydrate seal in landward-dipping strata and in domed strata associated with diapirism. In addition, gas venting may have occurred near diapirs located at the head of the slide. 相似文献
923.
C.H.K. Williamson 《Applied Ocean Research》1985,7(2):97-106
The most widely used mathematical model to represent flow-induced in-line forces on structures is based on the Morison1 equation. The present paper investigates the validity of using an extension of Morison's equation for non-stationary structures, by comparing predictions with results from a simple laboratory experiment. An elastically-mounted circular cylinder is placed in the sinusoidal flow of a U-tube, and responds in-line with the flow. Cylinder forces and responses are recorded over a range of Keulegan Carpenter numbers up to 35. An equation of motion is solved simply by using relative coordinates and by employing equivalent linearisation. The linear results are compared over a wide variation of parameters with solutions using the full nonlinear equation. Thereafter experimental results are compared with linear predictions. 相似文献
924.
925.
Consideration of the oasis analogy for chemosynthetic communities at Gulf of Mexico hydrocarbon vents 总被引:4,自引:0,他引:4
Robert S. Carney 《Geo-Marine Letters》1994,14(2-3):149-159
The analogy between desert oasis and deep-sea chemosynthetic community arose from the biomass contrast between vents and the relatively depauperate background benthic fauna. Fully developed, the analogy helps pose questions about interactions with the background fauna with respect to resources, colonization, and persistence. The chemosynthetic sites of the Gulf of Mexico provide an opportunity to consider possible interactions between vent and nonvent fauna over a 3000-m depth range. It is postulated that deep chemosynthetic communities require the operation of geochemical transporting and concentrating processes to overcome low levels of in situ methane and sulfide production. Clathrate reservoirs may serve these functions. A few chemosynthetic species at the Gulf of Mexico upper slope sites are related to shallow-water sulfide species, but it can be speculated that the dominant chemosynthetic fauna may have originated in a wide spread deep sulfide biome of the Cretaceous. Generic endemism of consumers is low in Gulf of Mexico sites, suggesting a high level of colonization from the surrounding benthos. Chemosynthetic communities may avoid excessive colonization by predators in spite of the apparent food limitation of the surrounding benthos due to toxicity or an evolutionary mechanism selecting against specialized predators. The abundance of large predators is related to the composition of the surrounding benthos and is high at the Gulf of Mexico upper slope sites. Exclusion of chemosyntheic communities from shallower depths may be due to excessive predation by generalists. 相似文献
926.
From 1988 to 1993, 23 satellite-tracked drifting buoys entered the Kamchatka Current. The buoy trajectories showed a well-formed, high-speed current that originated near Shirshov Ridge, and flowed southward through Kamchatka Strait. During some years, the buoys turned eastward at 50°N, while in other years they were transported as far south as Japan (40°N). Only one buoy entered the Sea of Okhotsk. Eddies were evident in many of the buoy trajectories. Greatest maximum daily velocities (>100 cm s–1) were observed south of Kamchatka Strait, with 50–60 cm s–1 being more common. 相似文献
927.
928.
Water surface profiles and horizontal and vertical water particle velocity components have been measured to investigate the properties of intermediate depth waves generated in the laboratory. The data has been compared with linear wave theory. It was found that linear theory predicted the attenuation of velocity field with depth successfully and that it overestimates both components of velocity slightly. 相似文献
929.
Large deposits of marine clays are encountered all along the Indian coastal belt. These clays are pleistocene to recent in origin, are considered to be young, and were deposited in a salt or brackish environment. These clays are very soft in consistency with low in-situ strength and high compressibility. The properties of these soil deposits depend mainly on the clay minerals present. In the present investigation, the mineralogical studies of some Cochin marine clays were carried out using XRD technique. The physical and chemical properties of these deposits were also reported. The test results were compared with some earlier reported works on marine clays. 相似文献
930.
Hübscher C. Breitzke M. Michels K. Kudrass H. R. Spiess V. Wiedicke M. 《Marine Geophysical Researches》1998,20(1):57-71
An ultra-high-resolution seismic study of the eastern Bengal Shelf with the parametric narrow-beam echosounder Parasound allows the interpretation of late Quaternary depositional patterns in terms of seismic stratigraphy. Accommodation space was still present on the outer shelf during the last lowstand, where a prograding delta developed in the western survey area. Oolitic beach ridges were later formed on top of this lowstand delta. Farther east, large parts of the shelf were exposed to subaerial erosion and a river system extended seaward across the area. A subaqueous highstand delta prograded southwards following the maximum transgression about 7,000 years ago. Its foreset beds exhibit acoustic voids very likely generated by sediment liquefaction, possibly caused by episodic energetic events such as major cyclones and/or earthquakes. Bottomset sediments extend seaward close to the shelf break in the west, whereas no Holocene sediments cover the outer shelf in the east. 相似文献