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31.
32.
Judith B. Moody 《Lithos》1976,9(2):125-138
The common alteration assemblage produced by serpentinization of ultramafic rocks is: lizardite, chrysotile, magnetite±brucite±antigorite. Lizardite-chrysotile serpentinites are more common than antigorite; the presence of antigorite indicates that the serpentinite has undergone prograde metamorphism or that the periootite was serpentinized in a higher P,T regime than lizardite and chrysotile. The iron subsitution into serpentine minerals and brucite is a function of temperature at low fO2, with increased temperature enhancing magnetite formation. The presence of awaruite and native Fe are strong evidence for a locally very reducing environment. Isotopic studies have shown a wide variety of origins for the fluids involved in serpentinization. The increased boron content of serpentinized rocks when compared to boron contents of the parent ultramafic body indicates a possible sea water origin for the fluids. Serpentinization takes place under both constant volume and constant chemical composition conditions. The factors in evaluating the importance of the two processes for an individual serpentinite are: (1) determination of the mineral assemblage and its paragenesis, (2) the structural and tectonic relationship of the ultramafic body to its country rock, (3) fluid access to the rock in duration and amount, and (4) timing of serpentinization - before, during or after emplacement into the crust. 相似文献
33.
Judith M. Capuzzo Joel C. Goldman John A. Davidson Sarah A. Lawrence 《Marine pollution bulletin》1977,8(7):161-163
The effects of free chlorine and chloramine on stage I lobster larvae and juvenile killifish were investigated in continuous flow bioassay units. In comparing mortality and changes in standard respiration rates during and after exposure to either chlorine form, significant respiratory stress was observed with exposure to sublethal levels. Sublethal responses to free and combined chlorine should be considered when establishing regulations for chlorine residuals in cooling waters. 相似文献
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Human arrival in Sahul – Pleistocene Australia and New Guinea – has long been argued as the catalyst in the decline and disappearance of a suite of extinct animals referred to as megafauna. The debate concerning causality in Sahul is highly polarised, with climate change often cited as the alternative explanatory model. On continental Australia, there are few datasets available with which to explore the likely processes leading to the extinction events. At the present time, there is one site in New Guinea (Nombe Rockshelter) and one on continental Australia (Cuddie Springs) where the coexistence and temporal overlap of humans and megafauna has been identified. The Cuddie Springs Pleistocene archaeological site in southeastern Australia contains an association of fossil extinct and extant fauna with an archaeological record through two sequential stratigraphic units dating from c. 36 to c. 30 ka ago. A taphonomic study of the fossil fauna has revealed an accumulation of bone in a primary depositional context, consistent with a waterhole death assemblage. Overall the faunal assemblage studied here (n: 8146; NISP: 1355) has yielded little direct evidence of carnivore damage or human activities. Post depositional factors such as physical destruction incurred by trampling, compaction of sediments, and/or the hydrological status of the lake at that time have played important roles. As the only known site on continental Australia where megafauna and humans co-occur, the Cuddie Springs faunal assemblage yields equivocal evidence for a significant human role in the accumulation of the fauna here. At the present time there is no evidential basis to the argument that humans had a primary role in the extinction of the Australian megafauna. The first colonisers are likely to have preyed upon those few species known to have persisted to this time, but their impact may have been restricted to the tail end of a process that had been underway for millennia prior to human arrival. 相似文献
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Real-time multi-model decadal climate predictions 总被引:1,自引:1,他引:0
Doug M. Smith Adam A. Scaife George J. Boer Mihaela Caian Francisco J. Doblas-Reyes Virginie Guemas Ed Hawkins Wilco Hazeleger Leon Hermanson Chun Kit Ho Masayoshi Ishii Viatcheslav Kharin Masahide Kimoto Ben Kirtman Judith Lean Daniela Matei William J. Merryfield Wolfgang A. Müller Holger Pohlmann Anthony Rosati Bert Wouters Klaus Wyser 《Climate Dynamics》2013,41(11-12):2875-2888
We present the first climate prediction of the coming decade made with multiple models, initialized with prior observations. This prediction accrues from an international activity to exchange decadal predictions in near real-time, in order to assess differences and similarities, provide a consensus view to prevent over-confidence in forecasts from any single model, and establish current collective capability. We stress that the forecast is experimental, since the skill of the multi-model system is as yet unknown. Nevertheless, the forecast systems used here are based on models that have undergone rigorous evaluation and individually have been evaluated for forecast skill. Moreover, it is important to publish forecasts to enable open evaluation, and to provide a focus on climate change in the coming decade. Initialized forecasts of the year 2011 agree well with observations, with a pattern correlation of 0.62 compared to 0.31 for uninitialized projections. In particular, the forecast correctly predicted La Niña in the Pacific, and warm conditions in the north Atlantic and USA. A similar pattern is predicted for 2012 but with a weaker La Niña. Indices of Atlantic multi-decadal variability and Pacific decadal variability show no signal beyond climatology after 2015, while temperature in the Niño3 region is predicted to warm slightly by about 0.5 °C over the coming decade. However, uncertainties are large for individual years and initialization has little impact beyond the first 4 years in most regions. Relative to uninitialized forecasts, initialized forecasts are significantly warmer in the north Atlantic sub-polar gyre and cooler in the north Pacific throughout the decade. They are also significantly cooler in the global average and over most land and ocean regions out to several years ahead. However, in the absence of volcanic eruptions, global temperature is predicted to continue to rise, with each year from 2013 onwards having a 50 % chance of exceeding the current observed record. Verification of these forecasts will provide an important opportunity to test the performance of models and our understanding and knowledge of the drivers of climate change. 相似文献
38.
Marjolijn Haasnoot Jan H. Kwakkel Warren E. Walker Judith ter Maat 《Global Environmental Change》2013,23(2):485-498
A new paradigm for planning under conditions of deep uncertainty has emerged in the literature. According to this paradigm, a planner should create a strategic vision of the future, commit to short-term actions, and establish a framework to guide future actions. A plan that embodies these ideas allows for its dynamic adaptation over time to meet changing circumstances. We propose a method for decisionmaking under uncertain global and regional changes called ‘Dynamic Adaptive Policy Pathways’. We base our approach on two complementary approaches for designing adaptive plans: ‘Adaptive Policymaking’ and ‘Adaptation Pathways’. Adaptive Policymaking is a theoretical approach describing a planning process with different types of actions (e.g. ‘mitigating actions’ and ‘hedging actions’) and signposts to monitor to see if adaptation is needed. In contrast, Adaptation Pathways provides an analytical approach for exploring and sequencing a set of possible actions based on alternative external developments over time. We illustrate the Dynamic Adaptive Policy Pathways approach by producing an adaptive plan for long-term water management of the Rhine Delta in the Netherlands that takes into account the deep uncertainties about the future arising from social, political, technological, economic, and climate changes. The results suggest that it is worthwhile to further test and use the approach. 相似文献
39.
There are compelling reasons for policy makers to be interested in the low-carbon agenda. More than half of the world's population lives in, and more than half of the world's economic output comes from, cities. Up to 70% of global carbon emissions can also be attributed to consumption that takes place in cities. Recent research has shown that cost-effective investments in low-carbon options could deliver a 40% reduction in GHG emissions from cities by 2020, while also providing wider economic benefits such as enhanced competitiveness and increased employment. As yet, however, investments in low-carbon cities have not been made at scale due mainly to the scale of the finance required, local government budgetary constraints, and perceptions about their costs and benefits. With a focus on the UK, a contemporary account is provided of what local authorities see as the major financial risks associated with funding low-carbon cities. Practical proposals – which also have more general relevance to the future financing of low-carbon cities around the world – are offered on how local authorities, in conjunction with central government, the private sector, and institutional investors, can effectively manage these risks. Policy relevance Cities house more than half of the world's population, generate more than half of the world's economic output, and produce between 40% and 70% of all anthropogenic GHG emissions. In the UK, 70% of such emissions are under the influence of its local authorities. Thus, one of the key public policy challenges for the low-carbon transition is how it should be financed. There are several obstacles and related risks to this transition, including financial and legal obstacles and the differing views and perceptions of stakeholders. These can be attenuated, somewhat, by national government support at scale, local authority leadership, and cooperation between other authorities and the private sector, and the development of tools and guidance to reduce transaction costs. 相似文献
40.
Polar coronal holes (PCHs) trace the magnetic variability of the Sun throughout the solar cycle. Their size and evolution have been studied as proxies for the global magnetic field. We present measurements of the PCH areas from 1996 through 2010, derived from an updated perimeter-tracing method and two synoptic-map methods. The perimeter-tracing method detects PCH boundaries along the solar limb, using full-disk images from the SOlar and Heliospheric Observatory/Extreme ultraviolet Imaging Telescope (SOHO/EIT). One synoptic-map method uses the line-of-sight magnetic field from the SOHO/Michelson Doppler Imager (MDI) to determine the unipolarity boundaries near the poles. The other method applies thresholding techniques to synoptic maps created from EUV image data from EIT. The results from all three methods suggest that the solar maxima and minima of the two hemispheres are out of phase. The maximum PCH area, averaged over the methods in each hemisphere, is approximately 6 % during both solar minima spanned by the data (between Solar Cycles 22/23 and 23/24). The northern PCH area began a declining trend in 2010, suggesting a downturn toward the maximum of Solar Cycle 24 in that hemisphere, while the southern hole remained large throughout 2010. 相似文献