全文获取类型
收费全文 | 4284篇 |
免费 | 176篇 |
国内免费 | 91篇 |
专业分类
测绘学 | 157篇 |
大气科学 | 296篇 |
地球物理 | 1120篇 |
地质学 | 1517篇 |
海洋学 | 378篇 |
天文学 | 702篇 |
综合类 | 20篇 |
自然地理 | 361篇 |
出版年
2022年 | 30篇 |
2021年 | 46篇 |
2020年 | 47篇 |
2019年 | 63篇 |
2018年 | 85篇 |
2017年 | 105篇 |
2016年 | 120篇 |
2015年 | 110篇 |
2014年 | 136篇 |
2013年 | 258篇 |
2012年 | 130篇 |
2011年 | 232篇 |
2010年 | 164篇 |
2009年 | 226篇 |
2008年 | 237篇 |
2007年 | 208篇 |
2006年 | 192篇 |
2005年 | 173篇 |
2004年 | 136篇 |
2003年 | 164篇 |
2002年 | 136篇 |
2001年 | 84篇 |
2000年 | 88篇 |
1999年 | 63篇 |
1998年 | 69篇 |
1997年 | 56篇 |
1996年 | 65篇 |
1995年 | 53篇 |
1994年 | 55篇 |
1993年 | 42篇 |
1992年 | 48篇 |
1991年 | 42篇 |
1990年 | 35篇 |
1989年 | 37篇 |
1988年 | 38篇 |
1987年 | 40篇 |
1986年 | 44篇 |
1985年 | 57篇 |
1984年 | 47篇 |
1983年 | 50篇 |
1982年 | 52篇 |
1981年 | 57篇 |
1980年 | 48篇 |
1979年 | 40篇 |
1978年 | 49篇 |
1977年 | 28篇 |
1976年 | 30篇 |
1975年 | 24篇 |
1974年 | 31篇 |
1973年 | 29篇 |
排序方式: 共有4551条查询结果,搜索用时 15 毫秒
41.
The Kimmeridge Clay is considered a major oil source rock for the North Sea hydrocarbon province. The formation is also developed onshore in an organic-rich mudstone facies. This paper examines the possibility of onshore oil generation from the Kimmeridge Clay. Geochemically, onshore basin margin sediments contain rich, potential source horizons with mainly Type l/Type ll oil-prone kerogen, but are immature. Some deeper Cleveland Basin sediments have reached marginal maturity. Burial history reconstruction suggests significant formation palaeoburial depths in central areas of the Cleveland and Wessex Basins. Computed vitrinite isoreflectance contours show the Wealden and Isle of Wight Kimmeridge Clay to be thermally mature. Basin modelling suggests an early Palaeogene onset of oil generation in parts of the Cleveland Basin, while maximum oil generation could have been reached by the formation base in the Isle of Wight area during the late Cretaceous. Although basin subsidence ceased in the Neogene, in the Weald and Isle of Wight, where the formation is still deeply buried, oil generation probably continued for some time during uplift. Thus significant quantities of oil could have been generated. Whether or not this oil is present today however, would depend on the correct timing of suitable migration and trap structures. 相似文献
42.
Toshiro Saino Alexander Bychkov Chen-Tung Arthur Chen Paul J. Harrison 《Journal of Oceanography》2004,60(1):1-4
This special issue is comprised of 13 papers, including this overview, and focuses on the synthesis of the Joint Global Ocean
Flux Study (JGOFS) in the North Pacific which took place from 1997 through 2003. The effort was led by the JGOFS North Pacific
Synthesis Group, with the aim of quantifying CO2 drawdown by physical and biological pumps in the North Pacific by identifying and studying the regional, seasonal to inter-annual
variations in the key processes, and understanding their regulating mechanisms. Emphasis was placed on the similarities and
differences of the biogeochemical regimes in the eastern and western subarctic Pacific. Effort was also made to address the
future research directions which arose from the scientific findings during the North Pacific JGOFS process study. A brief
overview of the papers from view points of CO2 drawdown by physical and biological pumps, spatial variability, and temporal variability from seasonal to decadal scales
is made, followed by suggestions for the directions of future research.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
43.
Sidescan-sonar surveys were performed on a 2×4 km area of seafloor in the southern Baltic Sea (Pomeranian Bight) in 1996 and 1998. Overlapping sub-areas of the individual surveys showing characteristic details were processed into geographically referenced mosaics. Sediment types were identified from echo characteristics and by comparison with granulometric data. The sea bottom covered by the mosaics consists predominantly of sand, with subordinate lag sediments with stones and small ripple fields consisting of coarse sand to fine gravel. A comparison of the two mosaics did not reveal any significant changes of the sea bottom over the 2-year period. Characteristic sedimentary features remained almost unchanged over this period on detailed sonar images of smaller sub-areas. Substantial transport of sandy sediments can thus be excluded in the course of the observation period. Grid files of advective velocity components and orbital velocity of wave motion of a three-dimensional hydrodynamical model for the period from September 1996 to October 1997 were used to estimate the current regime in the study area for the interval between the two sidescan surveys. Comparing critical velocities for the dominant sediment types with the results of the numerical bottom current simulations and the observations from sidescan images, it is apparent that strong current events during the modelled time interval were still too weak to resuspend and transport sand of any grain size, even though maximum current velocities of 30 cm/s at the seafloor were modelled. Only a few patches of newly accumulated (acoustically soft) material (mud, fluff and/or soft plant remnants), with a horizontal extension of about 10 m at a terrain step feature, were recognised in the 1998 mosaic. Our results imply that sand deposits in the southern Baltic Sea can remain stationary over time periods of several years, and that the transport of organic material, nutrients and associated pollutants to depositional areas in deeper water is predominantly accomplished by the movement of material finer than sand. A significant portion of this fine material is evidently transported in the bottom boundary layer under conditions of moderate hydrodynamical forcing. 相似文献
44.
A 3-year program, to determine spatial and temporal trends in sediment concentrations of hydrocarbons and metals from oil and gas exploration and development activities, was conducted in the US Beaufort Sea. Concentrations of saturated and aromatic hydrocarbons in sediments from the Beaufort Sea were elevated in comparison to non-polluted shelf-sediments from other regions of the US coast. Potential natural sources for hydrocarbons that were examined included riverine sediments and coastal peat. Significant quantities of fossil hydrocarbons characterize the surface sediments from the entire region. Sediment inputs from river discharges appear to account for this observation. The use of source-diagnostic ratios has allowed the differentiation of various sources in an area with high naturally-occurring hydrocarbon concentrations where effects due to oil and gas exploration and development activities may be obscured. 相似文献
45.
46.
Interannual variability in Nordic seas primary production 总被引:1,自引:0,他引:1
47.
48.
49.
50.