全文获取类型
收费全文 | 6503篇 |
免费 | 259篇 |
国内免费 | 94篇 |
专业分类
测绘学 | 199篇 |
大气科学 | 595篇 |
地球物理 | 1615篇 |
地质学 | 2252篇 |
海洋学 | 640篇 |
天文学 | 848篇 |
综合类 | 29篇 |
自然地理 | 678篇 |
出版年
2021年 | 72篇 |
2020年 | 72篇 |
2019年 | 104篇 |
2018年 | 136篇 |
2017年 | 126篇 |
2016年 | 181篇 |
2015年 | 155篇 |
2014年 | 216篇 |
2013年 | 376篇 |
2012年 | 266篇 |
2011年 | 298篇 |
2010年 | 223篇 |
2009年 | 347篇 |
2008年 | 312篇 |
2007年 | 297篇 |
2006年 | 250篇 |
2005年 | 206篇 |
2004年 | 212篇 |
2003年 | 205篇 |
2002年 | 194篇 |
2001年 | 149篇 |
2000年 | 147篇 |
1999年 | 127篇 |
1998年 | 125篇 |
1997年 | 97篇 |
1996年 | 93篇 |
1995年 | 96篇 |
1994年 | 81篇 |
1993年 | 71篇 |
1992年 | 73篇 |
1991年 | 73篇 |
1990年 | 73篇 |
1989年 | 64篇 |
1988年 | 73篇 |
1987年 | 74篇 |
1986年 | 51篇 |
1985年 | 84篇 |
1984年 | 95篇 |
1983年 | 89篇 |
1982年 | 76篇 |
1981年 | 94篇 |
1980年 | 74篇 |
1979年 | 62篇 |
1978年 | 50篇 |
1977年 | 67篇 |
1976年 | 72篇 |
1975年 | 60篇 |
1974年 | 62篇 |
1973年 | 55篇 |
1972年 | 29篇 |
排序方式: 共有6856条查询结果,搜索用时 203 毫秒
91.
92.
An extremely simple CFD tool is used to compare the calm-water drags of a series of hull forms and to define ‘optimized’ monohull ships for which the total (friction+wave) calm-water drag is minimized. The friction drag is estimated using the classical ITTC formula. The wave drag is predicted using the zeroth-order slender-ship approximation. Comparisons of theoretical predictions and experimental measurements for a series of eight hull forms show that—despite the extreme simplicity of the method that is used here to estimate the friction drag and the wave drag—the method is able to rank the drags of a series of hull forms roughly in accordance with experimental measurements. Thus, the method may be used, with appropriate caution, as a practical hull form design and optimization tool. For purposes of illustration, optimized hull forms that have the same displacement and waterplane transverse moment of inertia as the classical Wigley hull, taken as initial hull in the optimization process, are determined for three speeds and for a speed range. 相似文献
93.
Regional variation in maturation of sandeels in the North Sea 总被引:1,自引:0,他引:1
94.
Observations of the Labrador Sea eddy field 总被引:2,自引:0,他引:2
Jonathan M. Lilly Peter B. RhinesFriedrich Schott Kara LavenderJohn Lazier Uwe SendEric D’Asaro 《Progress in Oceanography》2003,59(1):75-176
This paper is an observational study of small-scale coherent eddies in the Labrador Sea, a region of dense water formation thought to be of considerable importance to the North Atlantic overturning circulation. Numerical studies of deep convection emphasize coherent eddies as a mechanism for the lateral transport of heat, yet their small size has hindered observational progress. A large part of this paper is therefore devoted to developing new methods for identifying and describing coherent eddies in two observational platforms, current meter moorings and satellite altimetry. Details of the current and water mass structure of individual eddy events, as they are swept past by an advecting flow, can then be extracted from the mooring data. A transition is seen during mid-1997, with long-lived boundary current eddies dominating the central Labrador Sea year-round after this time, and convectively formed eddies similar to those seen in deep convection modeling studies apparent prior to this time. The TOPEX / Poseidon altimeter covers the Labrador Sea with a loose “net” of observations, through which coherent eddies can seem to appear and disappear. By concentrating on locating and describing anomalous events in individual altimeter tracks, a portrait of the spatial and temporal variability of the underlying eddy field can be constructed. The altimeter results reveal an annual “pulsation” of energy and of coherent eddies originating during the late fall at a particular location in the boundary current, pinpointing the time and place of the boundary current-type eddy formation. The interannual variability seen at the mooring is reproduced, but the mooring site is found to be within a localized region of greatly enhanced eddy activity. Notably lacking in both the annual cycle and interannual variability is a clear relationship between the eddies or eddy energy and the intensity of wintertime cooling. These eddy observations, as well as hydrographic evidence, suggest an active role for boundary current dynamics in shaping the energetics and water mass properties of the interior region. 相似文献
95.
96.
The chemical and mineralogical composition of suspended particle suites has been used to assess off-shelf transport on the West African shelves of Liberia and Sierra Leone. Using the ratios of Si/Al, Fe/Al, Mg/Al and Mn/Al as tracers, it was possible to detect shelf-derived materials in slope waters. In the majority of cases, these inputs could not have been detected using particle mass or light scattering measurements and could only be measured by using the chemical signatures of the particulate matter. At the time of sampling, the suspensate which had been moved seaward over the slope was detected adjacent to submarine canyons and highly turbid areas on the outer shelf. The chemical and mineralogical composition of the suspensates, and sediments in the adjacent eastern Atlantic basin are similar to those found in the water column seaward of the West African continental shelves and yet distinct from the Sahelian dust which is considered the major source of sedimentary material for the tropical and semi-tropical areas of the deep eastern basin. These findings suggest that materials from this shelf area could be a more important input to the deep sea than was previously realised. 相似文献
97.
A. Peter Slootweg 《Marine Geophysical Researches》1986,8(2):149-174
The multistreamer Side-Looking Seismic system presented in this paper makes a sonograph of uncovered or buried crustal topography, thus revealing the structural fabric of the oceanic basement, even when this is covered with a sedimentary layer. Major elements of the system are an airgun as a sound source, five single-channel parallel streamers and two minicomputers for signal capture and processing.The system is used simultaneously for enhanced single-channel seismic profiling and for side-looking seismics. A vertical section with an improved signal-to-noise ratio and a suppression of side-echoes is produced on a digital seismic recorder. Primary side-looking seismic output in the form of 5 profiles with different angles of incidence is obtained within 10 seconds. This part of the processing can be done in real time.In sediment-covered areas the low frequencies used cause the slanted profiles (the side beams in the primary output) to be side-looking sonar images of buried topography. The projection process yielding final side-looking output corrects for slant range deformation caused by the water column and, if necessary, for deformation caused by refraction within the sedimentary column. The result approaches a conformal map of the structure of the traversed basement. Swath width is mainly determined by water depth and refraction effects in the sediment. In Madeira abyssal plain a swath width of 8000 m was attained in a water depth of 5000 m.Within the swath, oceanic basement structures are recognized in the form of elongate more or less parallel reflectors. They are interpreted as buried spreading topography. The lack of side-echoes within fracture zones combined with typical wall signatures can be used to trace fracture zones. These features are demonstrated for an area in Madeira abyssal plain. 相似文献
98.
Anthony H. Knap Peter J. LeB. Williams Elizabeth Lysiak 《Marine environmental research》1982,7(4):235-249
The sediments of Southampton Water were analysed for petroleum hydrocarbons to determine the fate of petrochemical refinery waste in the estuary. Much of the petroleum hydrocarbons appears to be removed by adsorption onto estuarine sediments close to source. Surface sediment concentrations range from 3·1mg/g dry weight near a refinery to 0·5 mg/g dry weight at locations distant from the refinery.The absence of any change with depth in total hydrocarbon concentrations from some sediment cores and the presence of distinct ‘oil’ horizons in others suggests that mixing of sediments in the area is very random. Sedimentation rates in areas where a distinct oil horizon was observed ranged from 1 to 3cm a year. 相似文献
99.
100.
The use of a system of continuous culture of phytoplankton at constant population density, the ‘cage-culture’ turbidostat, as a monitor of the bioavailability of pollutant materials, is illustrated. In the case of proposed dredge spoils from two polluted areas, it is shown that bulk analyses for scheduled materials cannot be equated with bioavailability. Monitoring for the effect of the whole pollutant mixture on a properly chosen test population could obviate the necessity for chemical analyses for each component. 相似文献