全文获取类型
收费全文 | 911篇 |
免费 | 52篇 |
国内免费 | 4篇 |
专业分类
测绘学 | 20篇 |
大气科学 | 73篇 |
地球物理 | 258篇 |
地质学 | 312篇 |
海洋学 | 137篇 |
天文学 | 103篇 |
综合类 | 5篇 |
自然地理 | 59篇 |
出版年
2023年 | 2篇 |
2022年 | 7篇 |
2021年 | 20篇 |
2020年 | 18篇 |
2019年 | 21篇 |
2018年 | 41篇 |
2017年 | 38篇 |
2016年 | 59篇 |
2015年 | 43篇 |
2014年 | 53篇 |
2013年 | 52篇 |
2012年 | 46篇 |
2011年 | 82篇 |
2010年 | 60篇 |
2009年 | 61篇 |
2008年 | 63篇 |
2007年 | 40篇 |
2006年 | 39篇 |
2005年 | 30篇 |
2004年 | 36篇 |
2003年 | 23篇 |
2002年 | 23篇 |
2001年 | 18篇 |
2000年 | 12篇 |
1999年 | 10篇 |
1998年 | 11篇 |
1997年 | 10篇 |
1996年 | 3篇 |
1995年 | 4篇 |
1994年 | 3篇 |
1993年 | 3篇 |
1992年 | 2篇 |
1991年 | 5篇 |
1990年 | 6篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1977年 | 1篇 |
1975年 | 1篇 |
1974年 | 3篇 |
1973年 | 1篇 |
1971年 | 1篇 |
1970年 | 1篇 |
1969年 | 2篇 |
排序方式: 共有967条查询结果,搜索用时 0 毫秒
961.
Ernesto Martínez Alfonso Aranda Yolanda Díaz-De-Mera Ana Rodríguez Diana Rodríguez Alberto Notario 《Journal of Atmospheric Chemistry》2004,48(3):283-299
The reaction of Cl with cyclohexanone (1) was investigated, for the first time, as a function of temperature (273–333 K) and at a low total pressure (1 Torr) with helium as a carrier gas using a discharge flow-mass spectrometry technique (DF-MS). The resulting Arrhenius expression is proposed, k
1= (7.7 ± 4.1) × 10–10 exp[–(540 ± 169)/T]. We also report a mechanistic study with the quantitative determination of the products of the reaction of Cl with cyclohexanone. The absolute rate constant derived from this study at 1 Torr of total pressure and room temperature is (1.3 ± 0.2) × 10–10 cm3 molecule–1 s–1. A yield of 0.94 ± 0.10 was found for the H-abstraction channel giving HCl. In relative studies, using a newly constructed relative rate system, the decay of cyclohexanone was followed by gas chromatography coupled with flame-ionisation detection. These relative measurements were performed at atmospheric pressure with synthetic air and room temperature. Rate constant measured using the relative method for reaction (1) is: (1.7 ± 0.3) × 10–10 cm3 molecule–1 s–1. Finally, results and atmospheric implications are discussed and compared with the reactivity with OH radicals. 相似文献
962.
The Gibraltar Strait is the very narrow neck which connects the Atlantic Ocean and the Mediterranean Sea. The causes and mode
of its opening at the end of the Messinian Salinity Crisis are still a matter of debate, and models based on eustatic rise
and/or topographic lowering due to either erosion or faulting are generally evoked. We investigated the presence of faults
based on a morphological and structural analysis of the Camarinal Sill, the shallowest passage in the Gibraltar Strait (<100 m
water depth in places). This sill connects the Spanish and Moroccan shelves, and probably represents a structural high inherited
from the Miocene compressive tectonics which took place in the external zones of the Betic-Rif orogenic arc. Our high-resolution
bathymetric data enabled us to identify and interpret the origin of major morphological features in the area, including canyons,
channels and a landslide, which we name the Tarifa landslide. Topographic arguments suggest that the Camarinal Sill is crossed
by two main E-W- to ENE-WSW-directed fault zones which bound areas with different distribution, orientation and slopes of
both scarps and crests. We name these the Hercules and Tarik fault zones, north and south of the sill respectively. The Hercules
fault zone probably incorporates a normal movement component, whereas kinematic indicators are poor along the Tarik fault
zone. The age of faulting is poorly constrained in both cases. Together with existing evidence of faults onland, the presence
of these fault zones implies that they could be responsible for, or have contributed to, the opening of the Gibraltar Strait. 相似文献
963.
Paula Camus Fernando J. Méndez Inigo J. Losada Melisa Menéndez Antonio Espejo Jorge Pérez Ana Rueda Yanira Guanche 《Ocean Dynamics》2014,64(7):1025-1038
In this study, a method to obtain local wave predictor indices that take into account the wave generation process is described and applied to several locations. The method is based on a statistical model that relates significant wave height with an atmospheric predictor, defined by sea level pressure fields. The predictor is composed of a local and a regional part, representing the sea and the swell wave components, respectively. The spatial domain of the predictor is determined using the Evaluation of Source and Travel-time of wave Energy reaching a Local Area (ESTELA) method. The regional component of the predictor includes the recent historical atmospheric conditions responsible for the swell wave component at the target point. The regional predictor component has a historical temporal coverage (n-days) different to the local predictor component (daily coverage). Principal component analysis is applied to the daily predictor in order to detect the dominant variability patterns and their temporal coefficients. Multivariate regression model, fitted at daily scale for different n-days of the regional predictor, determines the optimum historical coverage. The monthly wave predictor indices are selected applying a regression model using the monthly values of the principal components of the daily predictor, with the optimum temporal coverage for the regional predictor. The daily predictor can be used in wave climate projections, while the monthly predictor can help to understand wave climate variability or long-term coastal morphodynamic anomalies. 相似文献
964.
Ana Maria Rodrigues Adília PiresSónia Mendo Victor Quintino 《Estuarine, Coastal and Shelf Science》2009
This paper reports the presence of Diopatra marocensis in European waters, for which Diopatra neapolitana was the only species recognized until recently. Both species coexist in transitional waters, where D. marocensis may be mistaken for young specimens of D. neapolitana. The population of D. marocensis studied in the coastal shelf can be traced back to 1997 and is increasing in density, apparently benefiting from a local anthropogenic organic enrichment source. 相似文献
965.
Physically based models are useful frameworks for testing intervention strategies designed to reduce elevated sediment loads in agricultural catchments. Evaluating the success of these strategies depends on model accuracy, generally established by a calibration and evaluation process. In this contribution, the physically based SHETRAN model was assessed in two similar U.K. agricultural catchments. The model was calibrated on the Blackwater catchment (18 km2) and evaluated in the adjacent Kit Brook catchment (22 km2) using 4 years of 15 min discharge and suspended sediment flux data. Model sensitivity to changes in single and multiple combinations of parameters and sensitivity to changes in digital elevation model resolution were assessed. Model flow performance was reasonably accurate with a Nash–Sutcliffe efficiency coefficient of 0.78 in Blackwater and 0.60 in Kit Brook. In terms of event prediction, the mean of the absolute percentage of difference (μAbsdiff) between measured and simulated flow volume (Qv), peak discharge (Qp), sediment yield (Sy), and peak sediment flux (Sp) showed larger values in Kit Brook (48% [Qv], 66% [Qp], 298% [Sy], and 438% [Sp]) compared with the Blackwater catchment (30% [Qv], 41% [Qp], 106% [Sy], and 86% [Sp]). Results indicate that SHETRAN can produce reasonable flow prediction but performs less well in estimation of sediment flux, despite reasonably similar hydrosedimentary behaviour between catchments. The sensitivity index showed flow volume sensitive to saturated hydraulic conductivity and peak discharge to the Strickler coefficient; sediment yield was sensitive to the overland flow erodibility coefficient and peak sediment flux to raindrop/leaf soil erodibility coefficient. The multiparameter sensitivity analysis showed that different combinations of parameters produced similar model responses. Model sensitivity to grid resolution presented similar flow volumes for different digital elevation model resolutions, whereas event peak and duration (for both flow and sediment flux) were highly sensitive to changes in grid size. 相似文献
966.
Ana M Abarzúa 《Quaternary Research》2004,62(1):49-59
Palynologic and stratigraphic data from Laguna Tahui (42°50′S, 73°30′W) indicate cool-temperate and humid conditions there between 14,000 and 10,000 14C yr B.P., followed by warmer and drier-than-present conditions between 10,000 and 7000 14C yr B.P., and subsequent cooling and rise in precipitation over the last 5800 14C yr. The thermophilous Valdivian trees Eucryphia cordifolia and Caldcluvia paniculata reached their maximum abundance during the early Holocene warm-dry phase (10,000-7000 14C yr B.P.), followed by a rise in lake levels and reexpansion of North Patagonian conifers starting at 7000 and 5800 14C yr B.P., respectively. Variations in the stratigraphic and geographic distribution of temperate rainforests in southern Chile suggest multimillennial trends in temperature and westerly activity, which are spatially and temporally coherent with paleoclimate records from neighboring regions. Climate variability at millennial and submillennial time scales may account for the establishment and persistence of fine-scale mosaics of Valdivian and North Patagonian rainforest species in low- to mid-elevation communities since ∼5800 14C yr B.P. 相似文献
967.