全文获取类型
收费全文 | 4702篇 |
免费 | 252篇 |
国内免费 | 63篇 |
专业分类
测绘学 | 141篇 |
大气科学 | 365篇 |
地球物理 | 1087篇 |
地质学 | 1639篇 |
海洋学 | 434篇 |
天文学 | 759篇 |
综合类 | 19篇 |
自然地理 | 573篇 |
出版年
2023年 | 18篇 |
2022年 | 15篇 |
2021年 | 88篇 |
2020年 | 94篇 |
2019年 | 117篇 |
2018年 | 134篇 |
2017年 | 138篇 |
2016年 | 178篇 |
2015年 | 162篇 |
2014年 | 165篇 |
2013年 | 332篇 |
2012年 | 214篇 |
2011年 | 297篇 |
2010年 | 240篇 |
2009年 | 286篇 |
2008年 | 252篇 |
2007年 | 257篇 |
2006年 | 229篇 |
2005年 | 181篇 |
2004年 | 187篇 |
2003年 | 163篇 |
2002年 | 135篇 |
2001年 | 99篇 |
2000年 | 87篇 |
1999年 | 84篇 |
1998年 | 74篇 |
1997年 | 48篇 |
1996年 | 60篇 |
1995年 | 42篇 |
1994年 | 47篇 |
1993年 | 41篇 |
1992年 | 39篇 |
1991年 | 37篇 |
1990年 | 36篇 |
1989年 | 35篇 |
1988年 | 34篇 |
1987年 | 36篇 |
1986年 | 25篇 |
1985年 | 44篇 |
1984年 | 44篇 |
1983年 | 34篇 |
1982年 | 39篇 |
1981年 | 33篇 |
1980年 | 22篇 |
1979年 | 22篇 |
1978年 | 18篇 |
1977年 | 13篇 |
1974年 | 8篇 |
1973年 | 6篇 |
1972年 | 6篇 |
排序方式: 共有5017条查询结果,搜索用时 15 毫秒
1.
Tomoki Oda Tomohiro Egusa Nobuhito Ohte Norifumi Hotta Nobuaki Tanaka Mark B. Green Masakazu Suzuki 《水文研究》2021,35(5):e14177
Understanding changes in evapotranspiration during forest regrowth is essential to predict changes of stream runoff and recovery after forest cutting. Canopy interception (Ic) is an important component of evapotranspiration, however Ic changes and the impact on stream runoff during regrowth after cutting remains unclear due to limited observations. The objective of this study was to examine the effects of Ic changes on long-term stream runoff in a regrowth Japanese cedar and Japanese cypress forest following clear-cutting. This study was conducted in two 1-ha paired headwater catchments at Fukuroyamasawa Experimental Watershed in Japan. The catchments were 100% covered by Japanese coniferous plantation forest, one of which was 100% clear-cut in 1999 when the forest was 70 years old. In the treated catchment, annual runoff increased by 301 mm/year (14% of precipitation) the year following clear-cutting, and remained 185 mm/year (7.9% of precipitation) higher in the young regrowth forest for 12–14 years compared to the estimated runoff assuming no clear-cutting. The Ic change was −358 mm/year (17% of precipitation) after cutting and was −168 mm/year (6.7% of precipitation) in the 12–14 years old regrowth forest compared to the observed Ic during the pre-cutting period. Stream runoff increased in all seasons, and the Ic change was the main fraction of evapotranspiration change in all seasons throughout the observation period. These results suggest that the change in Ic accounted for most of the runoff response following forest cutting and the subsequent runoff recovery in this coniferous forest. 相似文献
2.
Sherri L. Johnson Don Henshaw Greg Downing Steve Wondzell Mark Schulze Adam Kennedy Greg Cohn Stephanie A. Schmidt Julia A. Jones 《水文研究》2021,35(5):e14187
The H. J. Andrews Experimental Forest (HJA) encompasses the 6400 ha Lookout Creek watershed in western Oregon, USA. Hydrologic, chemistry and precipitation data have been collected, curated, and archived for up to 70 years. The HJA was established in 1948 to study the effects of harvest of old-growth conifer forest and logging-road construction on water quality, quantity and vegetation succession. Over time, research questions have expanded to include terrestrial and aquatic species, communities and ecosystem dynamics. There are nine small experimental watersheds and 10 gaging stations in the HJA, including both reference and experimentally treated watersheds. Gaged watershed areas range from 8.5 to 6242 ha. All gaging stations record stage height, water conductivity, water temperature and above-stream air temperature. At nine of the gage sites, flow-proportional water samples are collected and composited over 3-week intervals for chemical analysis. Analysis of stream and precipitation chemistry began in 1968. Analytes include dissolved and particulate species of nitrogen and phosphorus, dissolved organic carbon, pH, specific conductance, suspended sediment, alkalinity, and major cations and anions. Supporting climate measurements began in the 1950s in association with the first small watershed experiments. Over time, and following the initiation of the Long Term Ecological Research (LTER) grant in 1980, infrastructure expanded to include a set of benchmark and secondary meteorological stations located in clearings spanning the elevation range within the Lookout Creek watershed, as well as a large number of forest understory temperature stations. Extensive metadata on sensor configurations, changes in methods over time, sensor accuracy and precision, and data quality control flags are associated with the HJA data. 相似文献
3.
Luca Collanega Katherine Siuda Christopher A.‐L. Jackson Rebecca E. Bell Alexander J. Coleman Antje Lenhart Craig Magee Anna Breda 《Basin Research》2019,31(4):659-687
Reactivation of pre‐existing intra‐basement structures can influence the evolution of rift basins, yet the detailed kinematic relationship between these structures and overlying rift‐related faults remains poorly understood. Understanding the kinematic as well as geometric relationship between intra‐basement structures and rift‐related fault networks is important, with the extension direction in many rifted provinces typically thought to lie normal to fault strike. We here investigate this problem using a borehole‐constrained, 3D seismic reflection dataset from the Taranaki Basin, offshore New Zealand. Excellent imaging of intra‐basement structures and a relatively weakly deformed, stratigraphically simple sedimentary cover allow us to: (a) identify a range of interaction styles between intra‐basement structures and overlying, Plio‐Pleistocene rift‐related normal faults; and (b) examine the cover fault kinematics associated with each interaction style. Some of the normal faults parallel and are physically connected to intra‐basement reflections, which are interpreted as mylonitic reverse faults formed during Mesozoic subduction and basement terrane accretion. These geometric relationships indicate pre‐existing intra‐basement structures locally controlled the position and attitude of Plio‐Pleistocene rift‐related normal faults. However, through detailed 3D kinematic analysis of selected normal faults, we show that: (a) normal faults only nucleated above intra‐basement structures that experienced late Miocene compressional reactivation, (b) despite playing an important role during subsequent rifting, intra‐basement structures have not been significantly extensionally reactivated, and (c) preferential nucleation and propagation of normal faults within late Miocene reverse faults and folds appears to be the key genetic relationship between contractionally reactivated intra‐basement structures and rift‐related normal faults. Our analysis shows that km‐scale, intra‐basement structures can control the nucleation and development of newly formed, rift‐related normal faults, most likely due to a local perturbation of the regional stress field. Because of this, simply inverting fault strike for causal extension direction may be incorrect, especially in provinces where pre‐existing, intra‐basement structures occur. We also show that a detailed kinematic analysis is key to deciphering the temporal as well as simply the spatial or geometric relationship between structures developed at multiple structural levels. 相似文献
4.
Michael J. Steventon Christopher A.‐L. Jackson David M. Hodgson Howard D. Johnson 《Basin Research》2019,31(3):600-620
Strain style, magnitude and distribution within mass‐transport complexes (MTCs) are important for understanding the process evolution of submarine mass flows and for estimating their runout distances. Structural restoration and quantification of strain in gravitationally driven passive margins have been shown to approximately balance between updip extensional and downdip contractional domains; such an exercise has not yet been attempted for MTCs. We here interpret and structurally restore a shallowly buried (c. 1,500 mbsf) and well‐imaged MTC, offshore Uruguay using a high‐resolution (12.5 m vertical and 15 × 12.5 m horizontal resolution) three‐dimensional seismic‐reflection survey. This allows us to characterise and quantify vertical and lateral strain distribution within the deposit. Detailed seismic mapping and attribute analysis shows that the MTC is characterised by a complicated array of kinematic indicators, which vary spatially in style and concentration. Seismic‐attribute extractions reveal several previously undocumented fabrics preserved in the MTC, including internal shearing in the form of sub‐orthogonal shear zones, and fold‐thrust systems within the basal shear zone beneath rafted‐blocks. These features suggest multiple transport directions and phases of flow during emplacement. The MTC is characterised by a broadly tripartite strain distribution, with extensional (e.g. normal faults), translational and contractional (e.g. folds and thrusts) domains, along with a radial frontally emergent zone. We also show how strain is preferentially concentrated around intra‐MTC rafted‐blocks due to their kinematic interactions with the underlying basal shear zone. Overall, and even when volume loss within the frontally emergent zone is included, a strain difference between extension (1.6–1.9 km) and contraction (6.7–7.3 km) is calculated. We attribute this to a combination of distributed, sub‐seismic, ‘cryptic’ strain, likely related to de‐watering, grain‐scale deformation and related changes in bulk sediment volume. This work has implications for assessing MTCs strain distribution and provides a practical approach for evaluating structural interpretations within such deposits. 相似文献
5.
Mark Williams Toshifumi Komatsu Phong Nguyen Duc Tom Harvey Thijs Vandenbroucke 《Geology Today》2019,35(6):217-220
To the north of Hanoi, about a day's drive by car, lies Ha Giang Province, the northernmost region of Vietnam. Ha Giang is remote from the hustle and bustle of daily life, and beyond its eponymous provincial capital towards the border with China, mountains rise quickly to Quan Ba, ‘Heaven's Gate’. The mountains form an uneven landscape of steep‐sided karst rising from deep river‐cut gorges and form a formidable barrier on the northern frontier of Vietnam. Beyond ‘Heaven's Gate’ lies the little travelled region of Dong Van, with its majestic mountains of Palaeozoic strata rising precipitously to the sky. Here, a century ago, the French geologists Henri Mansuy and Jacques Deprat documented early finds of fossils from lower Palaeozoic strata on the border with China. 相似文献
6.
Philipp R. Heck Christopher Herd Jeffrey N. Grossman Dmitry Badjukov Audrey Bouvier Emma Bullock Hasnaa Chennaoui‐Aoudjehane Vinciane Debaille Tasha L. Dunn Denton S. Ebel Ludovic Ferrire Laurence Garvie Jrme Gattacceca Matthieu Gounelle Richard Herd Trevor Ireland Emmanuel Jacquet Robert J. Macke Tim McCoy Francis M. McCubbin Takashi Mikouchi Knut Metzler Mathieu Roskosz Caroline Smith Meenakshi Wadhwa Linda Welzenbach‐Fries Toru Yada Akira Yamaguchi Ryan A. Zeigler Michael Zolensky 《Meteoritics & planetary science》2019,54(7):1397-1400
7.
Christopher Airriess 《Singapore journal of tropical geography》2020,41(1):6-22
The tropical fruit durian in Southeast and East Asia has witnessed a surge in popularity in the past two decades to assume the rank of a fetishized commodity. This research investigates the construction of the multidimensional concept of terroir as applied to the durian economy of Penang, Malaysia based on personal interviews with orchard owners and state government officials to strategically embed the local in the global through the promotion of agritourism. While environmental terroir is a contingent dimension, the construction of a place bound cultural terror is anchored in a strong cultivation tradition, cultivar diversity, and a historical sense of community. This research deepens the cultural terroir dimension in two ways. First, it injects the otherwise aspatial concept of refinement to the cultural terroir narratives of orchard owners allowing the on-farm tourist consumption experience to be more geographically rooted. Second, it conceptually links cultural terroir to the marketing terroir instrument of the Balik Pulau geographical indication; while functioning as a governance tool to prevent fraud and to construct a place bound product valorization and differentiation within an expanding and larger scale durian economy, it also indirectly assists in preserving agro-diversity and local identity. 相似文献
8.
The formal opportunity to learn geography in the United States is unevenly distributed across space, creating possible geography deserts. Data on the number of exams taken in Advanced Placement Human Geography (APHG) and bachelor’s degrees earned in geography are mapped at the state and regional scales. Normalized rates are ranked and grouped into quintiles. For APHG exams, states in the southeastern region of the United States are in the uppermost quintiles while states in the northeastern region are in the lowermost quintiles. The pattern for bachelor’s degrees in geography is somewhat the spatial inverse of that for APHG. 相似文献
9.
Christopher M. U. Neale Maria P. Gonzalez-Dugo Angelica Serrano-Perez Isidro Campos Luciano Mateos 《水文研究》2021,35(6):e14162
Evapotranspiration (ET) is an important parameter in hydrologic processes and modelling. In agricultural watersheds with competing uses of fresh water including irrigated agriculture, estimating crop evapotranspiration (ETc) accurately is critical for improving irrigation system and basin water management. The use of remote sensing-based basal crop coefficients is becoming a common method for estimating crop evapotranspiration for multiple crops over large areas. The Normalized Difference Vegetation Index (NDVI) and the Soil Adjusted Vegetation Index (SAVI), based on reflectance in the red and near-infrared bands, are commonly used for this purpose. In this paper, we examine the effects of row crop orientation and soil background darkening due to shading and soil surface wetness on these two vegetation indices through modelling, coupled with a field experiment where canopy reflectance of a cotton crop at different solar zenith angles, was measured with a portable radiometer. The results show that the NDVI is significantly more affected than the SAVI by background shading and soil surface wetness, especially in north–south oriented rows at higher latitudes and could lead to a potential overestimation of crop evapotranspiration and irrigation water demand if used for basal crop coefficient estimation. Relationships between the analysed vegetation indices and canopy biophysical parameters such as crop height, fraction of cover and leaf area index also were developed for both indices. 相似文献
10.
Garett Pignotti Indrajeet Chaubey Keith Cherkauer Mark Williams Melba Crawford 《水文研究》2021,35(3):e14034
Soil water dynamics are central in linking and regulating natural cycles in ecohydrology, however, mathematical representation of soil water processes in models is challenging given the complexity of these interactions. To assess the impacts of soil water simulation approaches on various model outputs, the Soil and Water Assessment Tool was modified to accommodate an alternative soil water percolation method and tested at two geographically and climatically distinct, instrumented watersheds in the United States. Soil water was evaluated at the site scale via measured observations, and hydrologic and biophysical outputs were analysed at the watershed scale. Results demonstrated an improved Kling–Gupta Efficiency of up to 0.3 and a reduction in percent bias from 5 to 25% at the site scale, when soil water percolation was changed from a threshold, bucket-based approach to an alternative approach based on variable hydraulic conductivity. The primary difference between the approaches was attributed to the ability to simulate soil water content above field capacity for successive days; however, regardless of the approach, a lack of site-specific characterization of soil properties by the soils database at the site scale was found to severely limit the analysis. Differences in approach led to a regime shift in percolation from a few, high magnitude events to frequent, low magnitude events. At the watershed scale, the variable hydraulic conductivity-based approach reduced average annual percolation by 20–50 mm, directly impacting the water balance and subsequently biophysical predictions. For instance, annual denitrification increased by 14–24 kg/ha for the new approach. Overall, the study demonstrates the need for continued efforts to enhance soil water model representation for improving biophysical process simulations. 相似文献