全文获取类型
收费全文 | 109篇 |
免费 | 9篇 |
专业分类
测绘学 | 1篇 |
大气科学 | 4篇 |
地球物理 | 32篇 |
地质学 | 37篇 |
海洋学 | 11篇 |
天文学 | 21篇 |
自然地理 | 12篇 |
出版年
2024年 | 1篇 |
2022年 | 2篇 |
2021年 | 2篇 |
2020年 | 5篇 |
2019年 | 1篇 |
2018年 | 3篇 |
2017年 | 3篇 |
2016年 | 1篇 |
2015年 | 5篇 |
2014年 | 4篇 |
2013年 | 3篇 |
2012年 | 7篇 |
2011年 | 4篇 |
2010年 | 5篇 |
2009年 | 6篇 |
2008年 | 8篇 |
2007年 | 4篇 |
2006年 | 7篇 |
2005年 | 3篇 |
2004年 | 3篇 |
2003年 | 2篇 |
2002年 | 2篇 |
2001年 | 1篇 |
2000年 | 2篇 |
1997年 | 1篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1991年 | 2篇 |
1990年 | 3篇 |
1988年 | 1篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1974年 | 2篇 |
1973年 | 2篇 |
1972年 | 2篇 |
1971年 | 2篇 |
1970年 | 4篇 |
1969年 | 2篇 |
1965年 | 2篇 |
排序方式: 共有118条查询结果,搜索用时 15 毫秒
61.
The European Commission has developed a set of common principles for marine spatial planning in the European Union. A critical examination of these principles in practice is undertaken through an evaluation of the Clyde Marine Spatial Planning Pilot Project. The principles are found to be lacking in specificity and somewhat inconsistent with the ecosystem based approach, which they advocate. Lessons for new marine spatial planning initiatives, relating particularly to stakeholder participation, governance, data requirements, objective setting, and skills and knowledge needs, are derived from the Clyde Pilot. 相似文献
62.
Wesley McCall Thomas M. Christy Daniel Pipp Mads Terkelsen Anders Christensen Klaus Weber Peter Engelsen 《Ground Water Monitoring & Remediation》2014,34(2):85-95
The Membrane‐Interface Probe and Hydraulic Profiling Tool (MiHpt) is a direct push probe that includes both the membrane interface probe (MIP) and hydraulic profiling tool (HPT) sensors. These direct push logging tools were previously operated as separate logging systems for subsurface investigation in unconsolidated formations. By combining these two probes into one logging system the field operator obtains useful data about the distribution of both volatile organic contaminants (VOCs) and relative formation permeability in a single boring. MiHpt logging was conducted at a chlorinated VOC contaminated site in Skuldelev, Denmark, to evaluate performance of the system. Formation cores and discrete interval slug tests are used to assess use of the HPT and electrical conductivity (EC) logs for lithologic and hydrostratigraphic interpretation. Results of soil and groundwater sample analyses are compared to the adjacent MiHpt halogen specific detector (XSD) logs to evaluate performance of the system to define contaminant distribution and relative concentrations for the observed VOCs. Groundwater profile results at moderate to highly contaminated locations were found to correlate well with the MiHpt‐XSD detector responses. In general, soil sample results corresponded with detector responses. However, the analyses of saturated coarse‐grained soils at the site proved to be unreliable as demonstrated by high RPDs for duplicate samples. The authors believe that this is due to pore water drainage observed from these cores during sampling. Additionally, a cross section of HPT pressure and MiHpt‐XSD detector logs provides insight into local hydrostratigraphy and formation control on contaminant migration. 相似文献
63.
An international wheat trade model incorporating climate variability is used to simulate different scenarios when wheat producers in the USA, Canada, and Australia adopt El Niño/Southern Oscillation (ENSO)-based climate forecasts for use in production decisions. Adoption timing and rates are varied across countries in the different scenarios. The results are consistent between the scenarios examined. Early adopters benefit the most, there is no incentive for more producers to adopt after 60 to 95% have adopted (meaning the adoption ceiling has been reached), and slower adoption corresponds to ceilings closer to 60 than 95%. When individual countries must decide whether or not to invest in ENSO technology and producer education programs to encourage adoption, results indicate the dominant strategy for each country is to invest. This is especially true if producers in other countries are adopting the use of climate forecasts. 相似文献
64.
A derivation of the luminosity function of the Kuiper belt from a broken power-law size distribution
We have derived a model of the Kuiper belt luminosity function exhibited by a broken power-law size distribution. This model allows direct comparison of the observed luminosity function to the underlying size distribution. We discuss the importance of the radial distribution model in determining the break diameter. We determine a best-fit break-diameter of the Kuiper belt size-distribution of 30<Db<90 km via a maximum-likelihood fit of our model to the observed luminosity function. We also confirm that the observed luminosity function for m(R)∼21-28 is consistent with a broken power-law size distribution, and exhibits a break at . 相似文献
65.
Case deletion diagnostics are developed for detecting observations that are influential in estimating the covariance function of a spatial random field. Diagnostics are developed within the context of universal kriging. Computational formulae are given that make the procedures feasible and the diagnostics are illustrated in an example. 相似文献
66.
Gillnet surveys from 1990 to 1992 and from 1996 to 1999 indicated a two-fold decrease in native striped bass (Morone saxatilis) populations and a concomitant two-fold increase in hybrid striped bass (Morone saxatilis × M. americana) in the Cape Fear River estuary, North Carolina. Gut content analysis indicated high diet overlap, and tagrecapture data
suggested that hybrid striped bass participate in spawning migrations. These data provide circumstantial evidence that hybrid
striped bass compete with striped bass for food and that they may compete for mates or habitat on the spawning grounds. Increasing
abundance of adult hybrid striped bass in this system elevates the likelihood of hybrid introgression. We recommend that stocking
of hybrid striped bass be terminated to preserve native striped bass populations. 相似文献
67.
Gerald Matisoff J.Berton Fisher Peter L McCall 《Geochimica et cosmochimica acta》1981,45(12):2333-2347
Rates of anaerobic decomposition of Lake Erie sediments were determined for seven depth intervals at three temperatures. Sealed sediment sections were incubated under anoxic conditions and the interstitial waters were serially sampled over a period of approximately 200 days. Concentration increases of bicarbonate, phosphate, ammonium, Ca, Mg, Fe and Mn in pore water within any given depth interval followed zero order kinetics over the sampling period and exhibited Arrhenius temperature dependency. Rates of release to the pore waters were proportional to the concentrations in the solid phases, indicating first order kinetics overall.The rates and temperature dependencies of these fermentation reactions were only slightly less than those reported from sediments undergoing sulfate reduction. The observed release rates decreased exponentially with depth in the sediment due to a corresponding decrease in the amount of metabolizable organic matter and acid hydrolyzable mineral phases.A stoichiometric model was constructed utilizing the observed release rates and assumed chemical reactions to predict the stoichiometry of the decomposing organic matter and the nature of the hydrogen buffer. The modeling indicates that 60% of the observed bicarbonate release is the direct result of organic decomposition, that 20% of the release is from the dissolution of calcium carbonate mineral phases, and that the remaining 20% of the release is from the dissolution of magnesium, iron und manganese carbonate mineral phases.Kinetic modeling of the observed production rates accurately predicts the vertical profiles of Ca, Mg, Fe and Mn, but cannot quantitatively account for all the concentration differences of the nutrient elements C, N and P. This implies that in addition to decomposition, increased depositional flux also accounts for the significant changes in concentrations of the nutrient elements in the near surface sediments. 相似文献
68.
69.
70.
The authors have visited Suswa, a complex caldera-volcano situated thirty miles north-west of Nairobi, a feature surprisingly neglected by geologists. While they do not pretend to do more than present an introductory account of the general geology of this unique volcano, they are able to augment the brief references of earlier workers, Gregory, Spink and Richard. The principal rock types are described in general terms, and are found to include unusual rhomb-porphyry types of lava, vitrophyres of phonolitic composition (closely related to the kenytes, but devoid of modal nepheline). The earliest eruptions were of quite normal lava type, phonolites of Kenya type, erupted over a wide area in central Kenya in Plio-Pleistocene times (not later than 1.7 m.y. ago), and the rhomb-porphyries are restricted to a secondary eruptive sequence, of probable Pleistocene age. There was a minor reactivation in recent times, represented by restricted, bare, fresh flows, of type at present unknown. Chemical analyses of representative specimens of the two major suites are provided, and are supported by modal analyses of related specimens. Two summit calderas have been recognised, both apparently subsidence structures related to cauldron subsidence in depth. The earlier and larger caldera covers about 40 square miles, and is interpreted as ofGlencoe type with weakly developedKrakatoan characteristics. The inner caldera covers seven square miles, and is interpreted as aGlencoe type structure: it is not a simple caldera but contains an island — block of four square miles extent — a feature which may perhaps be reasonably compared with island features within the Lake Toba cauldron, Sumatra and Nyamlagira caldera, Congo. The terminal eruptions of the first volcano seem to have largely stemmed from a ring feeder, analogous with a body reported from Crater Lake caldera, Oregon, U.S.A. The outer caldera is now partly obscured by products of later eruption, from a secondary cone eccentric to the first caldera — Ol Doinyo Nyukie — and from minor parasitic vents. Ol Doinyio Nyukie volcano possessed an axial pit-crater, nearly a mile in diameter, now transected by the boundary fault of the inner caldera: this might reasonably be regarded as a third,Kilauean, summit caldera, since it was apparently drained by low-level, adventive eruptions. Fumarolic activity is rife within Suswa at the present time: steam is being emitted, probably derived from meteoric water but charged with CO2 and probably nitrogen. Analogies between the Suswa pattern of calderas and certain lunar crater patterns are briefly mentioned. 相似文献