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91.
Understanding the interactions of vegetation and soil water under varying hydrological conditions is crucial to aid quantitative assessment of land-use sustainability for maintaining water supply for humans and plants. Isolating and estimating the volume and ages of water stored within different compartments of the critical zone, and the associated fluxes of evaporation, transpiration, and groundwater recharge, facilitates quantification of these soil–plant-water interactions and the response of ecohydrological fluxes to wet and dry periods. We used the tracer-aided ecohydrological model EcH2O-iso to examine the response of water ages of soil water storage, groundwater recharge, evaporation, and root-uptake at a mixed land use site, in northeastern Germany during the drought of 2018 and in the following winter months. The approach applied uses a dynamic vegetation routine which constrains water use by ecological mechanisms. Two sites with regionally typical land-use types were investigated: a forested site with sandy soils and a deep rooting zone and a grassland site, with loamier soils and shallower rooting zone. This results in much younger water ages (<1 year) through the soil profile in the forest compared to the grass, coupled with younger groundwater recharge. The higher water use in the forest resulted in a more pronounced annual cycle of water ages compared to the more consistent water age in the loamier soil of the grasslands. The deeper rooting zone of the forested site also resulted in older root-uptake water usage relative to soil evaporation, while the grassland site root-uptake was similar to that of soil evaporation. Besides more dynamic water ages in the forest, replenishment of younger soil waters to soil storage was within 6 months following the drought (cf. >8 months in the grassland). The temporal evaluation of the responsiveness of soil and vegetation interactions in hydrologic extremes such as 2018 is essential to understand changes in hydrological processes and the resilience of the landscape to the longer and more severe summer droughts predicted under future climate change. 相似文献
92.
Natalia Hauser Wolf Uwe Reimold Aaron J. Cavosie Alvaro P. Crsta Winfried H. Schwarz Mario Trieloff Carolinna Da Silva Maia de Souza Luciana A. Pereira Eduardo N. Rodrigues Matthews Brown 《Meteoritics & planetary science》2019,54(10):2286-2311
A silicious impact melt rock from polymict impact breccia of the northern part of the alkali granite core of the Araguainha impact structure, central Brazil, has been investigated. The melt rock is thought to represent a large mass of impact‐generated melt in suevite. In particular, a diverse population of zircon grains, with different impact‐induced microstructures, has been analyzed for U‐Pb isotopic systematics. Backscattered electron and cathodoluminescence images reveal heterogeneous intragrain domains with vesicular, granular, vesicular plus granular, and vesicular plus (presumably) baddeleyite textures, among others. The small likely baddeleyite inclusions are not only preferentially located along grain margins but also occur locally within grain interiors. LA‐ICP‐MS U‐Pb data from different domains yield lower intercept ages of 220, 240, and 260 Ma, a result difficult to reconcile with the previous “best age” estimate for the impact event at 254.7 ± 2.7 Ma. SIMS U‐Pb data, too, show a relatively large range of ages from 245 to 262 Ma. A subset of granular grains that yielded concordant SIMS ages were analyzed for crystallographic orientation by EBSD. Orientation mapping shows that this population consists of approximately micrometer‐sized neoblasts that preserve systematic orientation evidence for the former presence of the high‐pressure polymorph reidite. In one partially granular grain (#36), the neoblasts occur in linear arrays that likely represent former reidite lamellae. Such grains are referred to as FRIGN zircon. The best estimate for the age of the Araguainha impact event from our data set from a previously not analyzed type of impact melt rock is based on concordant SIMS data from FRIGN zircon grains. This age is 251.5 ± 2.9 Ma (2σ, MSWD = 0.45, p = 0.50, n = 4 analyses on three grains), indistinguishable from previous estimates based on zircon and monazite from other impact melt lithologies at Araguainha. Our work provides a new example of how FRIGN zircon can be combined with in situ U‐Pb geochronology to extract an accurate age for an impact event. 相似文献
93.
Marco Langbroek Peter Jenniskens Leo M. Kriegsman Henk Nieuwenhuis Niek De Kort Jacob Kuiper Wim Van Westrenen Michael E. Zolensky Karen Ziegler Qing‐Zhu Yin Matthew E. Sanborn Josh Wimpenny Akane Yamakawa Sebastiaan J. De Vet Matthias M. M. Meier Kees C. Welten Kunihiko Nishiizumi Marc W. Caffee Aaron S. Burton Jason P. Dworkin Daniel P. Glavin Qinghao Wu Richard N. Zare Alexander Ruf Mourad Harir Philippe Schmitt‐Kopplin 《Meteoritics & planetary science》2019,54(7):1431-1461
A carbonaceous chondrite was recovered immediately after the fall near the village of Diepenveen in the Netherlands on October 27, 1873, but came to light only in 2012. Analysis of sodium and poly‐aromatic hydrocarbon content suggests little contamination from handling. Diepenveen is a regolith breccia with an overall petrology consistent with a CM classification. Unlike most other CM chondrites, the bulk oxygen isotopes are extremely 16O rich, apparently dominated by the signature of anhydrous minerals, distributed on a steep slope pointing to the domain of intrinsic CM water. A small subset plots closer to the normal CM regime, on a parallel line 2 ‰ lower in δ17O. Different lithologies in Diepenveen experienced varying levels of aqueous alteration processing, being less aqueously altered at places rather than more heated. The presence of an agglutinate grain and the properties of methanol‐soluble organic compounds point to active impact processing of some of the clasts. Diepenveen belongs to a CM clan with ~5 Ma CRE age, longer than most other CM chondrites, and has a relatively young K‐Ar resetting age of ~1.5 Ga. As a CM chondrite, Diepenveen may be representative of samples soon to be returned from the surface of asteroid (162173) Ryugu by the Hayabusa2 spacecraft. 相似文献
94.
Lukas P. Loose Jens Lange Aaron Budde Barbara Herbstritt Nicola Fohrer Uta Ulrich 《水文研究》2024,38(1):e15058
The protection of the globally widespread lentic small water bodies (LSWB) must be based on detailed knowledge about their hydrological connectivity and water balance. The study aimed to identify and quantify water balance components as well as surface-groundwater interaction of two LSWB in a characteristic lowland region with a combination of different methods. This includes the collection of hydrological data and the use of bromide and water stable isotopes (δ2H and δ18O) as tracers. With their help, mixing models were established, and daily water balances were assessed. The results show a strong bidirectional interaction of both LSWB systems with shallow groundwater. Bromide and stable isotope tracers allowed for the identification of the most relevant in- and outflow sources and pathways. Thereby, isotope data revealed isotopic enrichment typical for open-water bodies and only minor precipitation inputs mainly relevant at the end of the dry season. Water balance calculations suggested accentuated seasonal dynamics that were strongly influenced by shallow groundwater, which represented large inputs into both LSWB. By that, different phases could be identified, with high inflow rates in winter and spring and decreasing fluxes in summer. In one LSWB, a drainage system was found to have a major impact next to the shallow groundwater interaction. The findings of this research provide detailed insights into the influence and importance of shallow groundwater for LSWB in lowland regions. This impacts the diffuse input of agricultural pollutants into these ecologically important landscape features. 相似文献
95.
Knowledge of groundwater seepage to and from lakes can be an important component of scientific investigations involving water and geochemical budgets. Measurements of groundwater seepage at Lake Anna, a man-made lake in central Virginia, show that inflow to the lake occurs even under dry summer conditions. Seepage rates were found to be correlated with the elevation of the near-shore water table, which responded rapidly to rainfall events in the fractured rock terrane in which Lake Anna is located. Seepage rates did not decline uniformly with distance offshore. This result contrasts with those for lakes underlain by relatively homogeneous porous media where measurements generally confirm the prediction that seepage rates drop off exponentially with distance from shore. The along shore variability of seepage rates in Lake Anna was related to a topographic index that is used to describe drainage from hillslopes. This suggests that seepage in impoundments such as Lake Anna may be strongly controlled by drainage pathways that pre-date the lake. 相似文献
96.
Ernst Zinner Sachiko Amari Cristine Jennings Aaron F. Mertz Ann N. Nguyen Roberto Gallino Maria Lugaro Roy S. Lewis 《Geochimica et cosmochimica acta》2007,71(19):4786-4813
We report isotopic ratio measurements of small SiC and Si3N4 grains, with special emphasis on presolar SiC grains of type Z, and new nucleosynthesis models for 26Al/27Al and the Ti isotopic ratios in asymptotic giant branch (AGB) stars. With the NanoSIMS we analyzed 310 SiC grains from Murchison (carbonaceous CM2 chondrite) separate KJB (diameters 0.25-0.45 μm) and 153 SiC grains from KJG (diameters 1.8-3.7 μm), 154 SiC and 23 Si3N4 grains from Indarch (enstatite EH4 chondrite) separate IH6 (diameters 0.25-0.65 μm) for their C and N isotopic compositions, 549 SiC and 142 Si3N4 grains from IH6 for their C and Si isotopic compositions, 13 SiC grains from Murchison and 66 from Indarch for their Al-Mg compositions, and eight SiC grains from Murchison and 10 from Indarch for their Ti isotopic compositions. One of the original objectives of this effort was to compare isotopic analyses with the NanoSIMS with analyses previously obtained with the Cameca IMS 3f ion microprobe. Many of the Si3N4 grains from Indarch have isotopic anomalies but most of these apparently originate from adjacent SiC grains. Only one Si3N4 grain, with 13C and 14N excesses, has a likely AGB origin. The C, N, and Si isotopic data show that the percentage of SiC grains of type Y and Z increase with decreasing grain size (from ∼1% for grains >2 μm to ∼5-7% for grains of 0.5 μm), providing an opportunity for isotopic analyses in these rare grains. Our measurements expand the number of Al-Mg analyses on SiC Z grains from 4 to 23 and the number of Ti analyses on Z grains from 2 to 11. Inferred26Al/27Al ratios of Z grains are in the range found in mainstream and Y grains and do not exceed those predicted by models of AGB nucleosynthesis. Cool bottom processing (CBP) has been invoked to explain the low 12C/13C ratios of Z grains, but this process apparently does not lead to increased 26Al production in the parent stars of these grains. This finding is in contrast to presolar oxide grains where CBP is needed to explain their high 26Al/27Al ratios. The low 46,47,49Ti/48Ti ratios found in Z grains and their correlation with low 29Si/28Si ratios extend the trend seen in mainstream grains and confirm an origin in low-metallicity AGB stars. The relatively large excesses in 30Si and 50Ti in Z grains are predicted by our models to be the result of increased production of these isotopes by neutron-capture nucleosynthesis in low-metallicity AGB stars. However, the predicted excesses in 50Ti (and 49Ti) are much larger than those found. Even lowering the strength of the 13C pocket cannot solve this discrepancy in a consistent way. 相似文献
97.
In the classical view of fine sediment transport and deposition in streams, particles are expected to be removed from flowing water simply by direct sedimentation onto the streambed. However, recent research has demonstrated that fine sediments can propagate into pore spaces in the streambed due to hyporheic exchange and be removed by a combination of physical and chemical processes. This behaviour can significantly alter fine sediment size distributions during in-stream sediment transport because the physical transport of fine particles and their attachment to bed sediment grains are both a function of the particle size. Herein, we present model simulations for deposition of suspended sediments with a bimodal size distribution. We also applied this approach to analyse the results of laboratory flume observations of suspended sediment deposition. Results from model simulations and flume experiments clearly show that the rate of particle deposition increases with increasing particle size. Thus, the larger particles are preferentially removed from mixtures and there is a fining of the mixed suspensions over time. Both particle deposition mechanisms, i.e. particle sedimentation and filtration, contribute to the fining of the mixed fine particle suspensions over time, and their effects are clearly demonstrated using the fundamental process-based model. These results clearly demonstrate the effects of stream-subsurface exchange on the temporal evolution of the suspended fine sediment size distribution in downstream transport. 相似文献
98.
Harold E. Brooks Aaron R. Anderson Kathrin Riemann Irina Ebbers Heather Flachs 《Atmospheric Research》2007,83(2-4):294-305
Annual cycles of convectively important atmospheric parameters have been computed for a variety of from the National Center for Atmospheric Research (NCAR)/National Centers for Environmental Prediction (NCEP) global reanalysis, using 7 years of reanalysis data. Regions in the central United States show stronger seasonality in combinations of thermodynamic parameters than found elsewhere in North America or Europe. As a result, there is a period of time in spring and early summer when climatological mean conditions are supportive of severe thunderstorms.The annual cycles help in understanding the large-scale processes that lead to the combination of atmospheric ingredients necessary for strong convection. This, in turn, lays groundwork for possible changes in distribution of the environments associated with possible global climate change. 相似文献
99.
Aaron Kingsbury 《Geoforum》2006,37(4):596-609
Business associations (BAs) represent a widely prevalent institution contingent upon a plethora of regional and industrial contexts around the world. Although their role in local development is rarely highlighted this paper argues that analysis of the structure and strategies of BAs reveals important insights into the problematic nature of external economies, typically based on the willingness of highly independent small firms to share and possibly fund some common service(s). BAs illustrate cooperative behaviour and their fragmentation indicates limits to cooperation and thereby to the contested nature of this particular external economy. Conceptually, the paper interprets BAs as institutional expressions of local cooperation and theorizes their strategy and structure in terms of a ‘logic of exchange’ model. This model defines the relationships between BAs, their members (organizational domains) and governments in terms of the logics of ‘membership’ and ‘influence’ that help understand the opportunities afforded and tensions imposed by the rationale and dynamics of cooperation. Empirically, the paper examines the formation and performance of BAs in the restructuring of the Okanagan’s wine industry that was stimulated by the Free Trade Agreement (FTA) between the US and Canada in 1989 and the North American Free Trade Agreement (NAFTA) of 1991. In the Okanagan wine industry, a newly formed BA was vital in helping firms overcome the crisis generated by free trade. However, subsequent fragmentation that arose out of member disenchantment with logics of influence and membership, indicated limits to local cooperation that may constitute a significant diseconomy in a future crisis. 相似文献
100.
Aaron J. Adams R. Kirby Wolfe William E. Pine Bridget L. Thornton 《Estuaries and Coasts》2006,29(2):311-317
Many marine fishes use spatially distinct habitats as juveniles and adults. Determining which juvenile habitats are most important
to sustaining adult populations (i.e., which habitats are nurseries) has proven difficult, in part due to challenges in estimating
survival of juveniles in putative nursery habitats. Recent technological advances have made largescale tagging efforts a viable
approach to estimating survival of juvenile fishes by increasing recapture rates and enabling the use of individual-identification
tags. These techniques, using Passive Integrated transponder (PIT) tags and autonomous antenna detection systems (antenna),
have been successfully applied in freshwater environments. This paper reports the adaptation of these techniques to estuarine
mangrove creeks (salinity: 2–28‰) for research of the juvenile life stage on an estuarine-dependent marine fish,Centropomus undecimalis. Retention rate of PIT tags in juveniles >120 mm standard length was 100%, with no mortality. The antenna detection field
covered 48% of the creek water column, and the antenna was experimentally determined to detect approximately 67% of tagged
fish that swam through. Overall recapture rate of tagged fish by the antenna was >40%. This recapture rate is higher than
the sparse data typical of traditional tag-recapture studies. A time-dependent Jolly-Seber model was fit to the data, providing
estimates of capture probability (0.8) and weekly apparent survival (0.41) that will be invaluable in comparing juvenile habitats
of different quality (e.g., natural versus anthropogenically degraded). This research demonstrates the viability of this approach
to fish research in estuarine habitats. 相似文献