全文获取类型
收费全文 | 395篇 |
免费 | 12篇 |
国内免费 | 6篇 |
专业分类
测绘学 | 10篇 |
大气科学 | 63篇 |
地球物理 | 105篇 |
地质学 | 123篇 |
海洋学 | 52篇 |
天文学 | 32篇 |
综合类 | 1篇 |
自然地理 | 27篇 |
出版年
2023年 | 5篇 |
2022年 | 3篇 |
2021年 | 7篇 |
2020年 | 8篇 |
2019年 | 8篇 |
2018年 | 9篇 |
2017年 | 19篇 |
2016年 | 24篇 |
2015年 | 12篇 |
2014年 | 26篇 |
2013年 | 25篇 |
2012年 | 19篇 |
2011年 | 25篇 |
2010年 | 21篇 |
2009年 | 30篇 |
2008年 | 32篇 |
2007年 | 15篇 |
2006年 | 18篇 |
2005年 | 21篇 |
2004年 | 18篇 |
2003年 | 12篇 |
2002年 | 8篇 |
2001年 | 11篇 |
2000年 | 5篇 |
1999年 | 5篇 |
1998年 | 5篇 |
1997年 | 6篇 |
1996年 | 2篇 |
1995年 | 2篇 |
1994年 | 1篇 |
1993年 | 3篇 |
1992年 | 1篇 |
1991年 | 3篇 |
1985年 | 1篇 |
1983年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
排序方式: 共有413条查询结果,搜索用时 15 毫秒
371.
Natural Hazards - The Río de la Plata (RdP) Estuary is affected by significant surges several times per year. This phenomenon has historically caused catastrophic water-level enlargements of... 相似文献
372.
Claudia Baldwin Graham Marshall Helen Ross Jim Cavaye Janet Stephenson Lyn Carter 《社会与自然资源》2019,32(5):566-587
Neoliberalism is frequently blamed for challenges in achieving sustainable development; consequently some also question if sustainability is still a useful concept. Neoliberal influence on natural resource management has evolved over the last 30?years to a hybrid form that seeks to compensate for its negative social and environmental externalities. Through review of literature and critical analysis of three case studies of resource development in Australia and New Zealand, we argue that, in spite of modifications under hybrid approaches, neoliberalism still tests achievement of sustainability goals, due to privileging industry and shifting risk and costs to future generations, through inadequate regulation, neglect of public consultation, lack of transparency, and weak impact assessment. We suggest that while neoliberal approaches bring both benefits and disadvantages, sustainability principles must continue to be kept at the forefront of legislation, regulation and management. 相似文献
373.
Benjamin R. Tanner Maria E. Uhle Claudia I. Mora Joseph T. Kelley Patrick J. Schuneman Chad S. Lane Evan S. Allen 《Estuarine, Coastal and Shelf Science》2010
Sources of sedimentary organic matter to a Morse River, Maine (USA) salt marsh over the last 3390 ± 60 RCYBP (Radiocarbon Years Before Present) are determined using distribution patterns of n-alkanes, bulk carbon isotopic analysis, and compound-specific carbon isotopic analysis. Marsh foraminiferal counts suggest a ubiquitous presence of high marsh and higher-high marsh deposits (dominated by Trochammina macrescens forma macrescens, Trochammina comprimata, and Trochammina inflata), implying deposition from ∼0.2 m to 0.5 m above mean high water. Distributions of n-alkanes show a primary contribution from higher plants, confirmed by an average chain length value of 27.5 for the core sediments, and carbon preference index values all >3. Many sample depths are dominated by the C25 alkane. Salicornia depressa and Ruppia maritima have similar n-alkane distributions to many of the salt marsh sediments, and we suggest that one or both of these plants is either an important source to the biomass of the marsh through time, or that another unidentified higher plant source is contributing heavily to the sediment pool. Bacterial degradation or algal inputs to the marsh sediments appear to be minor. Compound-specific carbon isotopic analyses of the C27 alkane are on average 7.2‰ depleted relative to bulk values, but the two records are strongly correlated (R2 = 0.89), suggesting that marsh plants dominate the bulk carbon isotopic signal. Our study underscores the importance of using caution when applying mixing models of plant species to salt marsh sediments, especially when relatively few plants are included in the model. 相似文献
374.
Marwan A. Hassan Matteo Saletti Chendi Zhang Carles Ferrer-Boix Joel P.L. Johnson Tobias Müller Claudia von Flotow 《地球表面变化过程与地形》2020,45(4):948-961
We use flume experiments to better understand how gravel-bed channels maintain bed surface stability in response to pulses of sediment supply. Bed elevations and surface imagery at high spatial resolutions were used to quantify the co-evolution of surface grain-size distribution (GSD), bed roughness statistics, and bed surface structures (clusters, cells and transverse features). Using a new semi-automated method, we identified individual stone structures over a 2 m × 1 m area throughout the experiments. After an initial coarsening, surface GSD and armouring ratio remained nearly stable as sediment pulses caused net bed aggradation. In contrast, individual grain structures continued to form, increase or decrease in size, and disappear throughout the experiments. The response of the bed to sediment pulses depended on the history of surface roughness evolution and bed surface structure development, as these factors changed much more in response to supply perturbations earlier in the experiments compared to later, even as the bed continued to aggrade. We interpret that the dynamic production and destruction of bed surface structures can act as a ‘buffer’ to sediment supply pulses, maintaining a stable bed surface during aggradation with minimal change in grain size or armouring. © 2019 John Wiley & Sons, Ltd. 相似文献
375.
Cloud-to-ground (CG) lightning observations for the warm seasons (May-September) of 1989 and 1990 were analyzed for the Great Lakes region in order to assess the diurnal variations in the lightning characteristics. Several parameters, including flash rate, the spatial extent of lightning activity, first stroke peak current, and the percentage of positive flashes, varied markedly over the course of the day. In contrast, other parameters, such as the frequency of lightning periods and the multiplicity of both negative and positive CG flashes, displayed little diurnal variation. A large degree of intraseasonal (i.e., month-to-month) variation was observed in the diurnal patterns for several of the lightning parameters. 相似文献
376.
We present an efficient algorithm using a complex variables formulation for the computation of the gravity effect of 2D polygonal bodies having densities varying both laterally and with depth. The first derivatives of the gravity effect are also provided in order to enable the computation of the Jacobian matrix, which is necessary for linear inverse gravity problems. A geophysical example based on numerical assumptions about the density contrast on a well-studied basin area shows the applicability of the algorithm. 相似文献
377.
James T. Waples Claudia Benitez-Nelson Nicolas Savoye Michiel Rutgers van der Loeff Mark Baskaran
rjan Gustafsson 《Marine Chemistry》2006,100(3-4):166
234Th is an extremely useful radiotracer of particle dynamics in aquatic systems. Its utility, however, has yet to be realized by many within the aquatic science community. The reasons for this may in part be due to a lack of knowledge of how this nuclide has been used in the past as well as how and where 234Th might be profitably applied in future research. The purpose of this paper, then, is to examine the variety of 234Th applications that have been used to understand natural aquatic processes in four major areas: vertical transport, particle cycling, horizontal transport, and sediment dynamics. We provide a general overview of the possible applications of 234Th in the hopes of provoking an increased interest in the inherent potential and future application of 234Th in these systems. We end this paper with a discussion of future research avenues in the context of three specific regimes: (i) the upper 1000 m of the open ocean, (ii) coastal sediment/water processes and (iii) large freshwater lakes. 相似文献
378.
Claudia Benitez-Nelson Ken O. Buesseler David M. Karl John Andrews 《Deep Sea Research Part I: Oceanographic Research Papers》2001,48(12)
Depth profiles of total 234Th (dissolved+particulate) were collected at Station ALOHA (22°45N, 158°00W) in the North Pacific Subtropical Gyre during 9 cruises from April 1999 to March 2000. Samples were collected and processed by a new 2 L technique that enables more detailed depth resolution then previous 234Th studies. Significant zones of particle export (234Th deficiency) and particle remineralization (234Th excess) were measured both temporally and with depth. 234Th derived particulate carbon (PC) and nitrogen (PN) fluxes were determined with steady-state and non-steady-state models and PC/234Th and PN/234Th ratios measured with both in situ pumps and free-drifting particle interceptor traps deployed at 150 m. 234Th based export estimates of 4.0±2.3 mmol C m−2 d−1 and 0.53±0.19 mmol N m−2 d−1, were approximately 60% higher than those measured in PIT style sediment traps from the same time period, 2.4±0.2 mmol C m−2 d−1 and 0.32±0.08 mmol N m−2 d−1. Most of this difference is attributable to two large export events that occurred during October and December 1999, when traps undercollected for 234Th by a factor of 2 to 4. 234Th export (ThE) ratios based on 234Th derived PC flux/14C based primary production ranged from 4% to 22% (average=8.8%). Our results confirm the recent estimates of C export by Emerson et al. (Nature 389 (1997) 951) and Sonnerup et al. (Deep-Sea Research I 46 (1999) 777) and indicate that C export from the oligotrophic ocean must be considered when discussing C sequestration in global climate change. 相似文献
379.
Claudia Terzi Franco Ricci Lucchi Gian Battista Vai Paul Aharon 《Geo-Marine Letters》1994,14(2-3):177-184
Over 20 occurrences of discontinuous limestone blocks, locally called calcari aLucina, were mapped in the Tuscan—Romagna region of the northern Italian Apennines. The limestones, consisting of a variable mixture of authigenic carbonates (calcite, dolomite, and aragonite), sulfides (primarily pyrite), and allogenic silicates, occur in association with turbidite and hemipelagite units that were deposited in foredeep basins during early to late Miocene times. The limestone blocks are interpreted to represent relicts of carbonate buildups formed around methane-rich fluid vents on the basis of their (1) striking petrographic similarities to carbonates from cold vents in the modern oceans; (2) unique chemosynthetic-like fauna, and (3) anomalously negative
13C values (
13C = – 16 to – 58 PDB). The contemporaneous tectonism of the Apennine orogeny is likely to be the primary cause for the expulsion of the methane-rich fluids to the seabed in a manner analogous to the fluid-flow processes occurring at modern accretionary prisms. 相似文献
380.
Michiel Rutgers van der Loeff Manmohan M. Sarin Mark Baskaran Claudia Benitez-Nelson Ken O. Buesseler Matt Charette Minhan Dai
rjan Gustafsson Pere Masque Paul J. Morris Kent Orlandini Alessia Rodriguez y Baena Nicolas Savoye Sabine Schmidt Robert Turnewitsch Ingrid Vge James T. Waples 《Marine Chemistry》2006,100(3-4):190
The short-lived thorium isotope 234Th (half-life 24.1 days) has been used as a tracer for a variety of transport processes in aquatic systems. Its use as a tracer of oceanic export via sinking particles has stimulated a rapidly increasing number of studies that require analyses of 234Th in both marine and freshwater systems. The original 234Th method is labor intensive. Thus, there has been a quest for simpler techniques that require smaller sample volumes. Here, we review current methodologies in the collection and analysis of 234Th from the water column, discuss their individual strengths and weaknesses, and provide an outlook on possible further improvements and future challenges. Also included in this review are recommendations on calibration procedures and the production of standard reference materials as well as a flow chart designed to help researchers find the most appropriate 234Th analytical technique for a specific aquatic regime and known sampling constraints. 相似文献