全文获取类型
收费全文 | 736篇 |
免费 | 32篇 |
专业分类
测绘学 | 8篇 |
大气科学 | 33篇 |
地球物理 | 159篇 |
地质学 | 212篇 |
海洋学 | 67篇 |
天文学 | 203篇 |
综合类 | 4篇 |
自然地理 | 82篇 |
出版年
2021年 | 9篇 |
2020年 | 11篇 |
2019年 | 8篇 |
2018年 | 11篇 |
2017年 | 13篇 |
2016年 | 27篇 |
2015年 | 23篇 |
2014年 | 12篇 |
2013年 | 35篇 |
2012年 | 29篇 |
2011年 | 19篇 |
2010年 | 28篇 |
2009年 | 32篇 |
2008年 | 21篇 |
2007年 | 26篇 |
2006年 | 24篇 |
2005年 | 28篇 |
2004年 | 42篇 |
2003年 | 22篇 |
2002年 | 29篇 |
2001年 | 22篇 |
2000年 | 18篇 |
1999年 | 10篇 |
1998年 | 16篇 |
1997年 | 13篇 |
1996年 | 10篇 |
1995年 | 16篇 |
1994年 | 9篇 |
1993年 | 6篇 |
1992年 | 11篇 |
1991年 | 7篇 |
1990年 | 10篇 |
1989年 | 7篇 |
1987年 | 5篇 |
1985年 | 8篇 |
1984年 | 11篇 |
1983年 | 9篇 |
1982年 | 9篇 |
1981年 | 11篇 |
1980年 | 11篇 |
1979年 | 13篇 |
1978年 | 13篇 |
1977年 | 7篇 |
1975年 | 7篇 |
1974年 | 8篇 |
1973年 | 6篇 |
1972年 | 6篇 |
1971年 | 4篇 |
1968年 | 6篇 |
1966年 | 3篇 |
排序方式: 共有768条查询结果,搜索用时 843 毫秒
561.
K. B. Lewis 《Geo-Marine Letters》1994,14(1):19-28
The Hikurangi Channel, east of New Zealand, is one of the earth's major, active, sediment conduits between rising mountains and ocean basin. About 1500 km long, it uniquely incorporates most variations of canyon—channel systems worldwide. An apical canyon feeds a meandering, aggradational, trench-axis channel. This diverts, 800 km from the source, across an oceanic plateau. There, an oceanic-type channel has become incised over 500 m at the plateau-edge scarp. Beyond the scarp, distributary fan channels supply sediment to the Pacific's Deep Western Boundary Current and one distributary merges into a boundary channel. 相似文献
562.
Seasonal abundance, distribution and recruitment of mud crabs (Scylla spp.) in replanted mangroves 总被引:3,自引:0,他引:3
Mark E. Walton Lewis Le Vay Junemie H. Lebata Joseph Binas Jurgenne H. Primavera 《Estuarine, Coastal and Shelf Science》2006,66(3-4):493-500
The abundance and distribution of mud crabs were studied in a replanted mangrove forest in Buswang, Aklan, Philippines. Two fishing gears, lift nets and bamboo traps, were used to monitor relative abundance of Scylla spp. populations from March 2002 to December 2003 inside the mangrove forest. A third gear, a stakenet set across a creek, was used to monitor crabs migrating out of the mangroves during the ebb tide. Scylla olivacea formed 99.3% and 70.3% of the catch in the mangrove and the stakenet, respectively. The percentage of Scylla tranquebarica increased from <1% in the mangrove catches to 29% in the stakenet. Scylla serrata was present at very low levels in both catches. The lack of modal progression in the size–frequency plots and the year-round catch rate of gravid females suggested that recruitment was constant throughout the year. Even though relative abundance decreased over the study period indicating that the stock is being over-exploited, mud crab production is more than equivalent to that of most natural mangroves. 相似文献
563.
564.
565.
Lewis S. Incze Peter Aas Terri Ainaire 《Deep Sea Research Part II: Topical Studies in Oceanography》1996,43(7-8)
The vertical distributions of copecod nauplii and water properties were sampled at well-mixed and stratified sites on Georges Bank using a pumping system, CTD and in vivo fluorometer during a four day period in late May 1992. At each stratified station at least one sample was taken within the thermocline and the fluorescence maximum, which usually co-occurred. Well-mixed sites had low average concentrations of nauplii, ca 41−1, and showed little variation of abundance with depth. Stratified sites had from 4 to 16 times the integrated (0–50 m) abundance of nauplii compared to well-mixed sites and showed strong vertical patterns of distribution. Maximum concentrations of nauplii, up to 1601−1, were associated with the thermocline at 7 of the 9 stratified stations. At the two remaining stratified sites the naupliar maximum was in the upper mixed layer, sampled at 5 m depth. The encounter rate between early feeding cod (Gadus morhua) larvae and their naupliar prey was calculated with and without turbulence. Turbulence was estimated from two sources: wind stress in the upper layer (calculated from wind observations during our cruise) and tidal shear in the lower layer (estimated initially from a tidal mixing equation). We ultimately replaced the lower layer estimates with turbulence data from a series of measurements made in 1995. The latter are more robust and had the advantage of providing dissipation rates for the pycnocline as well as the lower layer. Theory predicts an increase in encounters between a predator and its prey with the addition of turbulence parameters into standard models of encounter. We combined turbulence profiles with the vertical distribution of nauplii to examine the potential contribution of turbulent kinetic energy to predator-prey encounter rates at various depths in stratified and mixed water columns. Our calculations suggest the following increases due to turbulence at stratified sites on Georges Bank during our cruise: from 34 to 219% in the upper mixed layer, depending on wind speed and depth; approximately 8% in the pycnocline; and approximately 110% below the pycnocline. Mixed sites experience increases of at least 110% (tide only), but greater increases (118–192% in this study) occur when the wind blows because of the combined (spatially overlapped) effects of wind and tidal mixing at these sites. The absolute values for encounter rates and their modification by turbulence are sensitive to a number of assumptions in the models. We used a series of stated assumptions to generate estimates that range from 0.6 to 26.5 prey h−1, depending on geographical location, physical forcing and depth. 相似文献
566.
567.
568.
Laboratory experiments indicate that colloidal Fe is aggregated in estuarine waters by a second-order kinetic mechanism. The corresponding rate coefficient is proportional to the square of the salinity. A simple theoretical formulation is presented to describe the distribution of Fe in an estuary, based on observed second-order kinetics. The distribution depends on a single parameter whose value may be determined from measurements of the physical characteristics of the estuary. The theoretical expression accurately predicts observed distributions of Fe in a variety of estuaries, suggesting general applicability. 相似文献
569.
Sixteen amorphous carbon (lampblack) samples that had been exposed to Xe127 and pumped for >9 hrs to remove the most labile gas were examined by etching with HNO3, for comparison with the release pattern of meteoritic xenon. Samples originally exposed at 100–200°C lost 90% of their Xe very readily, when the surface had been etched to a mean depth of only ~0.2 Å. This suggests that the Xe is adsorbed mainly at rare sites that are unusually reactive to HNO3. The adsorbed Xe survived several months' storage in vacuum, but on exposure to air, part of it was lost within a few hours, while the remainder persisted without measurable exchange. Samples exposed at 800–1000°C had a similar adsorbed component, as well as a second, tightly bound component extending to a mean depth of up to 30 Å; this component had apparently diffused into the carbon during exposure. The (microscopic) diffusion coefficient for graphitic crystallites is 5 × 10?20 cm2/sec at 1000°C.PVDC carbon lost its adsorbed Xe at about the same rate as lampblack on exposure to air or HNO3, though it differs from lampblack in being non-graphitizable and more porous. It had only a small diffused component, however.The most tightly bound part of the Xe adsorbed on lampblack resembles planetary Xe in most characteristics: surface siting, etchability, persistence in vacuum, and lack of exchange with atmospheric Xe. The Xe concentrations—if interpreted as equilibrium distribution coefficients—are some 106× too small to account for meteoritic Xe, but it appears that equilibrium had not been reached by any of the samples, even after 1 day's exposure to Xe. If the uptake of Xe is controlled by rate rather than equilibrium, then the high noble gas concentrations in meteorites may simply reflect the much longer uptake times in the solar nebula. It seems likely that the trapping mechanisms discussed here can also explain two other features: elemental fractionations of noble gases, and the close correlation between planetary Xe and CCFXe. 相似文献
570.