全文获取类型
收费全文 | 928篇 |
免费 | 39篇 |
国内免费 | 5篇 |
专业分类
测绘学 | 25篇 |
大气科学 | 85篇 |
地球物理 | 282篇 |
地质学 | 225篇 |
海洋学 | 91篇 |
天文学 | 162篇 |
自然地理 | 102篇 |
出版年
2021年 | 8篇 |
2020年 | 10篇 |
2019年 | 10篇 |
2018年 | 13篇 |
2017年 | 13篇 |
2016年 | 24篇 |
2015年 | 16篇 |
2014年 | 20篇 |
2013年 | 42篇 |
2012年 | 23篇 |
2011年 | 40篇 |
2010年 | 39篇 |
2009年 | 52篇 |
2008年 | 35篇 |
2007年 | 36篇 |
2006年 | 51篇 |
2005年 | 44篇 |
2004年 | 48篇 |
2003年 | 40篇 |
2002年 | 29篇 |
2001年 | 34篇 |
2000年 | 22篇 |
1999年 | 17篇 |
1998年 | 24篇 |
1997年 | 18篇 |
1996年 | 13篇 |
1995年 | 13篇 |
1994年 | 18篇 |
1993年 | 13篇 |
1992年 | 22篇 |
1991年 | 8篇 |
1990年 | 15篇 |
1989年 | 8篇 |
1988年 | 8篇 |
1987年 | 14篇 |
1986年 | 11篇 |
1985年 | 14篇 |
1984年 | 9篇 |
1983年 | 16篇 |
1982年 | 13篇 |
1981年 | 13篇 |
1980年 | 10篇 |
1979年 | 7篇 |
1978年 | 7篇 |
1977年 | 9篇 |
1976年 | 3篇 |
1975年 | 5篇 |
1974年 | 3篇 |
1973年 | 5篇 |
1970年 | 2篇 |
排序方式: 共有972条查询结果,搜索用时 562 毫秒
201.
Keith Loague 《Journal of Hydrology》1990,120(1-4):405-407
202.
James W. Pengelly Keith J. Tinkler William G. Parkins Francine M. McCarthy 《Journal of Paleolimnology》1997,17(4):377-402
Over the last 12600 years, lake levels in the eastern Lake Erie basin have fluctuated dramatically, causing major changes in drainage patterns, flooding and draining ephemeral Lake Wainfleet several times and widening and narrowing the Niagara Gorge as the erosive effects of Niagara Falls waxed and waned. The control sill for Lake Erie levels was at first the Fort Erie/Buffalo sill, before the Lyell/Johnson sill in Niagara Falls took over due to isostatic rebound. This sill, in time, was eventually eroded by the recession of Niagara Falls and the Fort Erie/Buffalo sill regained control. The environmental picture is complicated by catastrophic outbursts from glacial Lake Agassiz and Lake Barlow-Ojibway, changes in outlet routes, isostatic rebound and climatic changes over the Great Lakes basins. Today, the flow of water into Lake Erie from the streams and rivers surrounding it only accounts for about 13% of the flow out of it, therefore, the importance of flow from the Upper Great Lakes, specifically the flow from Lake Huron, has a great effect on Lake Erie levels. While the changing control sills, Lyell/Johnson and Buffalo/Fort Erie would affect Lake Erie levels, overall they are mostly input driven by the amount of waters received from the Upper Great Lakes. Since Lake Erie's water level changes are so closely tied to Lake Huron's water level changes we have decided to use names assigned to Lake Huron such as the two Mattawa highstands and three Stanley lowstands rather than inflict a whole new set of names on the public. While the duration of each high and lowstand in Erie and Huron may not always be the same, they always happen within the same time frame. The datum elevations used for Lake Huron (175.8 m) and Lake Erie (173.3 m) are historically recorded averages. The Lake Erie levels proposed in this paper reflect Lake Hurons effects on Lake Erie and the levels occuring at the eastern end of the Erie Basin throughout the last 12600 years. All dates in this paper are uncorrected 14 C dates unless the date was obtained from shells, then the date has been corrected for hard-water effects. Also, all heights are given as modern day elevations and are not adjusted for isostatic rebound. 相似文献
203.
Jeffrey?W.?BookEmail author Pavel?Pistek Henry?Perkins Keith?R.?Thompson William?J.?Teague Gregg?A.?Jacobs Moon-Sik?Suk Kyung-Il?Chang Jae-Chul?Lee Byung?Ho?Choi 《Journal of Oceanography》2004,60(6):977-993
During 1999–2000, 13 bottom mounted acoustic Doppler current profilers (ADCPs) and 12 wave/tide gauges were deployed along two lines across the Korea/Tsushima Strait, providing long-term measurements of currents and bottom pressure. Tidally analyzed velocity and pressure data from the moorings are used in conjunction with other moored ADCPs, coastal tide gauge measurements, and altimeter measurements in a linear barotropic data assimilation model. The model fits the vertically averaged data to the linear shallow water equations in a least-squares sense by only adjusting the incoming gravity waves along the boundaries. Model predictions are made for the O1, P1, K1, μ2, N2, M2, S2, and K2 tides. An extensive analysis of the accuracy of the M2 surface-height predictions suggests that for broad regions near the mooring lines and in the Jeju Strait the amplitude prediction errors are less than 0.5 cm. Elsewhere, the analysis suggests that errors range from 1 to 4 cm with the exception of small regions where the tides are not well determined by the dataset. The errors in the model predictions are primarily caused by bias error in the model’s physics, numerics, and/or parameterization as opposed to random errors in the observational data. In the model predictions, the highest ranges in sea level height occur for tidal constituents M2, S2, K1, O1, and N2, with the highest magnitudes of tidal velocities occurring for M2, K1, S2, and O1. The tides exhibit a complex structure in which diurnal constituents have higher currents relative to their sea level height ranges than semi-diurnal constituents. 相似文献
204.
Fogarty Michael J.; Myers Ransom A.; Bowen Keith G. 《ICES Journal of Marine Science》2001,58(5):952-961
205.
206.
207.
Andrea Fechter David Thistle Günter Arlt Keith Suderman & Kay Vopel 《Marine Ecology》2004,25(3):217-223
Abstract. Harpacticoid copepod food is patchily distributed and individuals must episodically move to new food patches. Key questions in harpacticoid feeding ecology include how individuals detect food patches and how rapidly they move toward patches. Based on literature reports, we hypothesized that harpacticoids locate food parcels by sensing a water-borne cue. We tested this idea using individuals of Leptastacus coulli Huys, 1992 and Praeleptomesochra similis Lang, 1965 from a sandy beach in north Florida (29.948° N, 84.341° W). Individuals from both species selected seawater that had been exposed to food significantly more frequently than they selected control seawater. The rate of movement of these species was millimeters per second, which agreed with previous reports. 相似文献
208.
Chi Shing Wong Nathalie A. D. Waser Yukihiro Nojiri Wm. Keith Johnson Frank A. Whitney John S. C. Page Jiye Zeng 《Journal of Oceanography》2002,58(2):227-243
The seasonal and interannual changes in surface nutrients, dissolved inorganic carbon (DIC) and total alkalinity (TA) were
recorded in the North Pacific (30–54°N) from 1995 to 2001. This study focuses on the region north of the subarctic boundary
(∼40°N) where there was extensive monthly coverage of surface properties. The nutrient cycles showed large interannual variations
in the eastern and western subarctic gyres. In the Alaska Gyre the seasonal depletion of nitrate (ΔNO3) increased from 8–14 μmol kg−1 in 1995–1999 to 21.5 μmol kg−1 in 2000. In the western subarctic the shifts were similar in amplitude but more frequent. The large ΔNO3 levels were associated with high silicate depletions, indicating enhanced diatom production. The seasonal DIC:NO3 drawdown ratios were elevated in the eastern and central subarctic due to calcification. In the western subarctic and the
central Bering Sea calcification was significant only during 1997 and/or 1998, two El Ni?o years. Regional C/N stoichiometric
molar ratios of 5.7 to 7.0 (>40°N) were determined based on the years with negligible or no calcification. The annual new
production (NPa) based on ΔNO3 and these C/N ratios showed large interannual variations. NPa was usually higher in the western than in the eastern subarctic. However, values of 84 gC m−2yr−1 were found in the Alaska Gyre in 2000 which is similar to that in the most productive provinces of the northern North Pacific.
There were also large increases in NPa around the Alaska Peninsula in 1997 and 1998. Finally, the net removal of carbon by the biological pump was estimated as
0.72 Gt C yr−1 in the North Pacific (>30°N).
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
209.
Keith Cooper Sian Boyd Jacqueline Eggleton David Limpenny Hubert Rees Koen Vanstaen 《Estuarine, Coastal and Shelf Science》2007,75(4):547-558
The aim of this study was to investigate the effect of dredging intensity on the physical and biological recovery times of the seabed following marine aggregate dredging. Two areas of seabed, previously subject to, respectively, relatively high and lower levels of dredging intensity, were identified on the Hastings Shingle Bank. Two reference areas were also selected for comparative purposes. All four sites were monitored annually over the period 2001–2004, using a combination of acoustic, video and grab sampling techniques. Since the site was last dredged in 1996, this was intended to provide a sequence of data 5–8 years after cessation of dredging. However, an unexpected resumption of dredging within the high intensity site, during 2002 and 2003, allowed an additional assessment of the immediate effects and aftermath of renewed dredging at the seabed. The early stages of recovery could then be assessed after dredging ceased in 2003. Results from both dredged sites provide a useful insight into the early and latter stages of physical and biological recovery. A comparison of recent and historic dredge track features provided evidence of track erosion. However, tracks were still visible 8 years after the cessation of dredging. Within the high dredging intensity site, recolonisation was relatively rapid after the cessation of dredging in 2003. Rather than indicating a full recovery, we suggest that this initial ‘colonization community’ may enter a transition phase before eventually reaching equilibrium. This hypothesis is supported by results from the low intensity site, where biological recovery was judged to have taken 7 years. Further monitoring is needed in order to test this. An alternative explanation is that the rapid recovery may be explained by the settlement of large numbers of Sabellaria spinulosa. As the resumption of dredging within the high intensity site limited our assessment of longer-term recovery it is not yet possible to assume that a 7-year biological recovery period will be applicable to other, more intensively dredged areas at this or more distant locations. 相似文献
210.
Solar differential rotation for 1982–83 obtained at the double pass spectrograph of the McMath telescope at Kitt Peak, are presented for lines of Fe, Mg, Na, K, Si, and O in the wavelength interval 3820–10827. The results are analyzed by representations in Legendre polynominals and a power series. The differential rotation is very close to the result obtained by Howard and Harvey in 1966–68 at Mt. Wilson but with a slightly greater amplititude. We find a mean equatorial rate of rotation of 1.977 km s-1. Day to day variations are observed in the equatorial zone; a stable rate of rotation is observed outside of the sunspot zone.Operated by the Association of Universities for Research in Astronomy, Inc., under contract with the National Science Foundation. 相似文献