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911.
912.
Heidy M. E. Van Kaam-Peters Stefan Schouten Jan W. De Leeuw Jaap S. Sinninghe Damst 《Organic Geochemistry》1997,27(7-8)
Structures and carbon isotopic compositions of biomarkers and kerogen pyrolysis products of a dolomite, a bituminous shale and an oil shale of the Kimmeridge Clay Formation (KCF) in Dorset were studied in order to gain insight into (i) the type and extent of water column anoxia and (ii) changes in the concentration and isotopic composition of dissolved inorganic carbon (DIC) in the palaeowater column. The samples studied fit into the curve of increasing δ13C of the kerogen (δ13CTOC) with increasing TOC, reported by Huc et al. (1992). Their hypothesis, that the positive correlation between TOC and δ13CTOC is the result of differing degrees of organic matter (OM) mineralisation in the water column, was tested by measuring the δ13C values of primary production markers. These δ13C values were found to differ on average by only 1‰ among the samples, implying that differences in the extent of OM mineralisation cannot fully account for the 3‰ difference in δ13CTOC. The extractable OM in the oil shale differs from that in the other sediments due to both differences in maturity, and differences in the planktonic community. These differences, however, are not likely to have significantly influenced δ13CTOC either. All three sediments contain abundant derivatives of isorenieratene, indicating that periodically euxinia was extending into the photic zone. The sediments are rich in organic sulfur, as revealed by the abundant sulfur compounds in the pyrolysates. The prominence of C1-C3 alkylated thiophenes over n-alkanes and n-alkenes is most pronounced in the pyrolysate of the sediment richest in TOC. This suggests that sulfurisation of OM may have played an important role in determining the TOC-δ13CTOC relationship reported by Huc et al. (1992). 相似文献
913.
In this paper the first fluid-inclusion data are presented from Late Archaean Scourian granulites of the Lewisian complex of mainland northwest Scotland. Pure CO2 or CO2-dominated fluid inclusions are moderately abundant in pristine granulites. These inclusions show homogenization temperatures ranging from − 54 to + 10 °C with a very prominent histogram peak at − 16 to − 32 °C. Isochores corresponding to this main histogram peak agree with P-T estimates for granulite-facies recrystallization during the Badcallian (750–800 °C, 7–8 kbar) as well as with Inverian P-T conditions (550–600 °C, 5 kbar). The maximum densities encountered could correspond to fluids trapped during an early, higher P-T phase of the Badcallian metamorphism (900–1000 °C, 11–12 kbar). Homogenization temperatures substantially higher than the main histogram peak may represent Laxfordian reworking (≤ 500 °C, < 4 kbar). In the pristine granulites, aqueous fluid inclusions are of very subordinate importance and occur only along late secondary healed fractures. In rocks which have been retrograded to amphibolite facies from Inverian and/or Laxfordian shear zones, CO2 inclusions are conspicuously absent; only secondary aqueous inclusions are present, presumably related to post-granulite hydration processes. These data illustrate the importance of CO2-rich fluids for the petrogenesis of Late Archaean granulites, and demonstrate that early fluid inclusions may survive subsequent metamorphic processes as long as no new fluid is introduced into the system. 相似文献
914.
The natural abundance15N/14N method was used to estimate the influence of silvicultural and P fertilization treatments on N accretion, N2fixation and N partitioning among tissues in a mature mesquiteProsopis glandulosavar.glandulosastand in Texas. The silvicultural treatments consisted of understory removal, herbicide treatment of brushy resprouts, thinning trees to single stems and 100 kg ha−1P fertilization. The trees had a mean basal diameter of 17·8 cm with 8 to 35 cm range. The stand was slow growing with the increase in dry matter ranging from 0·465 Mg ha−1year−1to 0·701 Mg ha−1year−1for the 8 years after the treatments were applied. N accretion after 8 years ranged from 3·1 kg ha−1year−1to 4·4 kg ha−1year−1.Due to the range in δ15N of the leaves, twigs, branches and trunk, we used the weighted (by biomass) average δ15N per tree in calculations of the percent N derived from N2fixation (%Ndfa). There was considerable variability in δ15N of the reference plants, i.e. from 3·3 to 5·9. In contrast there was low variability in the background δ15N of nearby soils (7·0±1·0). As the total above-ground biomass δ15N of a grass grown outside the influence of mesquite (7·8±0·58) had the same δ15N as the soil (7·5±1·0), we used the grass outside the influence of mesquite and the weighted tree mean δ15N to calculate % of N derived from N2fixation.The decrease in intraspecific competition by thinning multistemed trees to single stemmed trees was the only treatment that significantly (p= 0·0001) increased growth. Interspecific competition, i.e. understory removal, did not increase growth. There were no significant differences in total N production or N fixation among treatment means. The most striking result was the highly positive correlation between tree δ15N and total N per tree and biomass per tree (R2= 0·90,F= 164·4, df. = 18, mean square error (MSE) = 0·155,p= 0·0001). This implies that the younger trees colonizing infertile soils relied more heavily on N2fixation than larger trees which accumulated 1200 kg ha−1more N under their canopies. The percentage N derived from N2fixation ranged from 63 to 73% in the various treatments. Despite the high percentage of N derived from N2fixation, the N2fixation of the stand was very low, i.e. 1·98 to 2·80 kg N ha−1year−1, due to the low growth of the stand. We believe that comparisons of the whole tree weighted δ15N to background soil δ15N provides a more reasonable approach to estimate % N2fixation than comparisons of leaves of fixers and reference plants. 相似文献
915.
Increases in the number of large-scale land transactions (LSLTs), commonly known as ‘land grabbing’ or ‘global land rush,’ have occurred throughout the lower- and middle-income world over the past two decades. Despite substantial and continuing concerns about the negative socio-environmental impacts of LSLTs, trade-off analysis on boosting crop yield and minimizing climate-related effects remains limited. Our study makes use of a global dataset on LSLTs for agricultural production to estimate potential carbon emissions based on different scenarios of land cover change and fertilizer use, as well as potential value of agricultural production on transacted land. We show that, if fully implemented on ∼ 38 M ha of transacted land, 2.51 GtC will be emitted during land conversion, with another 24.2 MtC/year emitted from fertilizer use, assuming farming technology of investors’ origin is adopted on transacted land. Comparison of different combinations of forest protection policies and agricultural intensification levels reveals that enforcing strict deforestation regulation while promoting fertilizer use rate improves the carbon efficiency of agricultural production. Additionally, positive spillovers of investors’ farming technology on existing arable lands of host countries can potentially double their crop yield. Our analyses thus suggest that fostering agricultural intensification and technology spillovers under strict regulation on land allocation to investors to protect forests would allow for boosting agricultural yield while minimizing carbon emissions. 相似文献
916.
In order to address the pressing challenge of climate change, countries are now submitting long-term climate strategies to the United Nations Framework Convention on Climate Change (UNFCCC) process. These strategies include within them potential future use of ‘negative emissions technologies’ (NETs). NETs are interventions that remove carbon from the atmosphere, ranging from large-scale terrestrial carbon sequestration in forests, wetlands and soils, to use of carbon capture and storage technologies. We assess here how NETs are discussed in 29 long-term climate strategies, in order to ascertain the risk that including the promise of future NETs may delay the taking of short-term mitigation actions. Our analysis shows that almost all countries plan to rely on NETs, particularly enhanced use of natural carbon sinks, even as a wide array of challenges and trade-offs in doing so are highlighted. Many strategies call for improved accounting systems and market incentives in realizing future NETs. While no strategy explicitly suggests that NETs can be a substitute for short-term mitigation, most estimate substantial potential for future use of NETs even in the face of acknowledged uncertainties. This, we suggest, may have the consequence of resulting in what we describe here as ‘a spiral of delay’ characterized by the promise of future NET options juxtaposed with the simultaneous uncertainty around these future options. Our analysis highlights that this inter-connected delaying dynamic may be intrinsic to what we term ‘governing-by-aspiration’ within global climate politics, wherein the voicing of lofty future ambition risks replacing current action and accountability. 相似文献
917.
As the low-carbon transition accelerates, loans to and investments in carbon-intensive assets, firms and sectors are at risk of not generating the anticipated returns, with implications for individual financial institutions as well as financial markets more broadly. However, research on this topic has largely been focused on high- and upper-middle income economies to date. In this paper, we explore the salience of this issue in India – one of the world’s largest emitters and economies – by asking: (1) how extensive is financial-sector exposure to transition risks? And: (2) are finance professionals and financial institutions taking sufficient action to manage those transition risks? Our findings reveal that India’s financial sector is much more heavily exposed to low-carbon transition risks than standard borrowing classifications might suggest. For example, our granular assessment of individual loans and bonds finds that three-fifths of lending to the ‘mining’ sector is for oil and gas extraction, while one-fifth of ‘manufacturing’ debt is for petroleum refining and related industries. We also find that electricity production – by far the largest source of emissions – accounts for 5.2% of outstanding credit, but that only 17.5% of this lending is to pureplay renewables. Yet our survey of India’s largest financial institutions suggests that there have been limited efforts to identify, measure or manage low-carbon transition risks. Fewer than half of the 154 finance professionals surveyed were familiar with environmental issues including climate change mitigation and adaption, greenhouse gas emissions or transition risks. Only four of the ten major financial institutions surveyed collect information on ESG risks, and these firms do not systematically incorporate that data into business continuity planning, internal capital adequacy assessment processes, credit risk assessments, enterprise risk management frameworks or loan product pricing. Given extensive financial-sector exposure to low-carbon transition risks coupled with the absence of bottom-up action to manage those risks, our findings suggest that financiers, regulators and policymakers in emerging and developing economies should be acting swiftly to ensure an orderly transition to net-zero. 相似文献
918.
Carbon taxes raise the costs of carbon-intensive products to penalize their consumption. Policymakers can decide whether the carbon tax is hidden or indicated explicitly as a component of the retail price. This policy design decision has effects on demand that have been overlooked. Here we show that salient carbon taxes are less effective than hidden taxes in reducing demand because being aware of paying a carbon tax activates a moral licensing process that encourages consumption. Across four experimental studies and two pilot experiments, we found that participants’ purchase intention was consistently higher when the carbon tax was salient. This effect remained robust with different products, carbon tax levels, and additional carbon footprint labels. Salient carbon taxes had a stronger effect on the purchase intention of the climate change concerned and less conservative individuals because they were more susceptible to a boost in moral self-concept triggered by paying the carbon tax. 相似文献
919.
交通运输行业是温室气体排放的主要来源之一。“双碳”目标对交通领域碳减排工作提出了更高的要求。我国交通运输行业能源消耗统计和温室气体排放测算的统计数据基础较为薄弱,目前国家层面尚未公布统一的交通运输温室气体核算方法,温室气体排放存在底数不清的问题,其核算边界、范围、方法都有待进一步明确。文中通过梳理国内外交通运输领域温室气体核算边界及测算方法,提出了适用于我国交通运输不同子领域温室气体的测算研究思路。并针对我国交通运输温室气体核算工作现存问题,从健全行业能耗与排放核算方法体系、建立交通运输能耗与碳排放数据共享机制、加强交通能耗与碳排放核算方法培训、强化数据质量管理等方面提出相应的政策建议,为我国交通运输行业温室气体排放核算工作的持续开展提供参考。 相似文献
920.
Complexity, land-use modeling, and the human dimension: Fundamental challenges for mapping unknown outcome spaces 总被引:2,自引:0,他引:2
Land-use systems are characterized by complex interactions between human decision-makers and their biophysical environment. Mismatches between the scale of human drivers and the impacts of human decisions potentially threaten the ecological sustainability of these systems. This article reviews sources of complexity in land-use systems, moving from the human decision level to human interactions to effects over space, time and scale. Selected challenges in modeling such systems and potential resolutions are discussed, including strategies to empiricize complex models and methods for linking models across human and natural systems. Illustrative examples from published literature and an ongoing research project focused on timber harvest and carbon sequestration are used throughout the paper. The paper concludes with a brief discussion of remaining challenges to modeling indirect and cross-scale linkages and of the potential utility of complex models of land systems. 相似文献