全文获取类型
收费全文 | 452篇 |
免费 | 26篇 |
国内免费 | 4篇 |
专业分类
测绘学 | 14篇 |
大气科学 | 46篇 |
地球物理 | 114篇 |
地质学 | 172篇 |
海洋学 | 33篇 |
天文学 | 68篇 |
自然地理 | 35篇 |
出版年
2021年 | 6篇 |
2020年 | 7篇 |
2019年 | 9篇 |
2018年 | 9篇 |
2017年 | 18篇 |
2016年 | 21篇 |
2015年 | 8篇 |
2014年 | 25篇 |
2013年 | 27篇 |
2012年 | 20篇 |
2011年 | 21篇 |
2010年 | 17篇 |
2009年 | 22篇 |
2008年 | 13篇 |
2007年 | 19篇 |
2006年 | 17篇 |
2005年 | 13篇 |
2004年 | 15篇 |
2003年 | 12篇 |
2002年 | 11篇 |
2001年 | 8篇 |
2000年 | 9篇 |
1999年 | 11篇 |
1998年 | 9篇 |
1997年 | 5篇 |
1996年 | 9篇 |
1995年 | 3篇 |
1994年 | 3篇 |
1993年 | 6篇 |
1992年 | 7篇 |
1991年 | 13篇 |
1990年 | 9篇 |
1988年 | 2篇 |
1987年 | 5篇 |
1986年 | 5篇 |
1985年 | 7篇 |
1984年 | 8篇 |
1983年 | 7篇 |
1982年 | 4篇 |
1981年 | 6篇 |
1979年 | 4篇 |
1978年 | 3篇 |
1977年 | 5篇 |
1976年 | 4篇 |
1975年 | 5篇 |
1974年 | 3篇 |
1967年 | 2篇 |
1964年 | 1篇 |
1940年 | 1篇 |
1938年 | 2篇 |
排序方式: 共有482条查询结果,搜索用时 15 毫秒
41.
David A.T. Harper 《Geological Journal》2014,49(3):330-330
42.
Describing the spatial variability of heterogeneous snowpacks at a watershed or mountain‐front scale is important for improvements in large‐scale snowmelt modelling. Snowmelt depletion curves, which relate fractional decreases in snow‐covered area (SCA) against normalized decreases in snow water equivalent (SWE), are a common approach to scale‐up snowmelt models. Unfortunately, the kinds of ground‐based observations that are used to develop depletion curves are expensive to gather and impractical for large areas. We describe an approach incorporating remotely sensed fractional SCA (FSCA) data with coinciding daily snowmelt SWE outputs during ablation to quantify the shape of a depletion curve. We joined melt estimates from the Utah Energy Balance Snow Accumulation and Melt Model (UEB) with FSCA data calculated from a normalized difference snow index snow algorithm using NASA's moderate resolution imaging spectroradiometer (MODIS) visible (0·545–0·565 µm) and shortwave infrared (1·628–1·652 µm) reflectance data. We tested the approach at three 500 m2 study sites, one in central Idaho and the other two on the North Slope in the Alaskan arctic. The UEB‐MODIS‐derived depletion curves were evaluated against depletion curves derived from ground‐based snow surveys. Comparisons showed strong agreement between the independent estimates. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
43.
Joel A. Eaton 《Astrophysics and Space Science》1991,186(1):7-20
Observations of V535 Ara obtained with IUE define the light curve of this long-period W UMa binary in the ultraviolet and let us estimate its gravity darkening. This star was chosen as a contact binary near the high-T
eff limit for convection. The ultraviolet colours and spectral type correspond to (B–V)0=0.24, or A8V, and imply the star should have very little residual convection in its envelope. The gravity darkening thus ought to be large, as in a radiative star, unless it is modified by circulation in the common envelope, or unless all stars this warm are convective. The light-curve analysis is complicated by a long-term wave that depresses the orbital phases before and after secondary eclipse. We have obtained four solutions to a combination of optical and ultraviolet light curves, two for high, radiative gravity darkening and two for low, convective gravity darkening. For each value of the gravity-darkening exponent, we let the larger, more massive binary component either (a) have a dark spot in its back side or (b) have an excessively hot side facing its companion. The light curves were fitted equally well in all four cases; however, in all but the one with low-gravity darkening and a hot inner face there was a rather large global temperature difference between the two stars. The primary component of this system appears to be significantly undermassive for its spectral type, more so than the primary in AW UMa, but this probably results simply from systematic errors in a radial-velocity solution by Schöffel. It is suggested that the W UMa binaries are found only at spectral types later than about A8 because their outer envelopes must be convective to transfer luminosity. 相似文献
44.
45.
Alexander Deutsch Christian Koeberl Joel D. Blum Bevan M. French Billy P. Glass Richard Grieve Peter Horn Elmar K. Jessberger Gero Kurat Wolf Uwe Reimold Jan Smit Dieter Stöffler Stuart Ross Taylor 《地学学报》1994,6(6):644-650
In a recent article in Terra Nova, Kristan-Tollmann and Tollmann (1994) suggested that the Biblical Flood can be explained by seven fragments of a comet that impacted the ocean at seven locations on Earth at 03.00h (C.E.T.) on 23 September, 9545 yr BP. We demonstrate that all the ‘geological proofs’ that allegedly support their conclusions are not supported by the available data on impact cratering. Their hypothesis is based on insufficient and ambiguous data, selective citation, and incomplete comprehension of previous research. 相似文献
46.
The climate-population nexus in the East African Horn: Emerging degradation trends in rangeland and pastoral livelihood zones 总被引:1,自引:0,他引:1
Narcisa G. Pricope Gregory Husak David Lopez-Carr Christopher Funk Joel Michaelsen 《Global Environmental Change》2013,23(6):1525-1541
Increasing climate variability and extreme weather conditions along with declining trends in both rainfall and temperature represent major risk factors affecting agricultural production and food security in many regions of the world. The rangelands of Ethiopia, Kenya, and Somalia in the East African Horn remain one of the world's most food insecure regions, yet have substantially increasing human populations predominantly dependent on pastoralist and agro-pastoralist livelihoods. We identify regions where substantial rainfall decrease between two periods interrupted by the 1998 El Nino event (1981–2012) in the East African Horn is coupled with human population density increases. Vegetation in this region is characterized by a variable mosaic of land covers, generally dominated by grasslands necessary for agro-pastoralism, interspersed by woody vegetation. Recent assessments indicate that vegetation degradation is occurring, adversely impacting fragile ecosystems and human livelihoods. Using AVHRR and MODIS vegetation products from 1981 to 2012, we observe changes in vegetation patterns and productivity over the last decade across the East African Horn. We observe vegetation browning trends in areas experiencing reduced main-growing season precipitation; these areas are also concurrently experiencing increasing population pressures. We also found that the drying precipitation patterns only partially statistically explain the vegetation browning trends, indicating that other factors such as population pressures and land use changes might be responsible for the observed declining vegetation condition. Furthermore, we show that the general vegetation browning trends persist even during years with normal rainfall conditions such as 2012, pointing to potential long-term degradation of rangelands on which approximately 10 million people depend. These findings may have implications for current and future regional food security monitoring and forecasting as well as for mitigation and adaptation strategies in a region where population is expected to continue increasing against a backdrop of drying climate trends and increased climatic variability. 相似文献
47.
Climate change and mental health: an exploratory case study from Rigolet, Nunatsiavut, Canada 总被引:1,自引:0,他引:1
Ashlee Cunsolo Willox Sherilee L. Harper James D. Ford Victoria L. Edge Karen Landman Karen Houle Sarah Blake Charlotte Wolfrey 《Climatic change》2013,121(2):255-270
As the impacts from anthropogenic climate change are increasing globally, people are experiencing dramatic shifts in weather, temperature, wildlife and vegetation patterns, and water and food quality and availability. These changes impact human health and well-being, and resultantly, climate change has been identified as the biggest global health threat of the 21st Century. Recently, research is beginning to indicate that changes in climate, and the subsequent disruption to the social, economic, and environmental determinants of health, may cause increased incidences and prevalence of mental health issues, emotional responses, and large-scale sociopsychological changes. Through a multi-year, community-led, exploratory case study conducted in Rigolet, Nunatsiavut, Labrador, Canada, this research qualitatively explores the impacts of climate change on mental health and well-being in an Inuit context. Drawing from 67 in-depth interviews conducted between January 2010 and October 2010 with community members and local and regional health professionals, participants reported that changes in weather, snow and ice stability and extent, and wildlife and vegetation patterns attributed to climate change were negatively impacting mental health and well-being due to disruptions in land-based activities and a loss of place-based solace and cultural identity. Participants reported that changes in climate and environment increased family stress, enhanced the possibility of increased drug and alcohol usage, amplified previous traumas and mental health stressors, and were implicated in increased potential for suicide ideation. While a preliminary case study, these exploratory findings indicate that climate change is becoming an additional mental health stressor for resource-dependent communities and provide a baseline for further research. 相似文献
48.
Catherine Heymans Ludovic Van Waerbeke David Bacon Joel Berge Gary Bernstein Emmanuel Bertin Sarah Bridle Michael L. Brown Douglas Clowe Håkon Dahle Thomas Erben Meghan Gray Marco Hetterscheidt Henk Hoekstra Patrick Hudelot Mike Jarvis Konrad Kuijken Vera Margoniner Richard Massey Yannick Mellier Reiko Nakajima Alexandre Refregier Jason Rhodes Tim Schrabback David Wittman 《Monthly notices of the Royal Astronomical Society》2006,368(3):1323-1339
49.
Brian A. Ebel Benjamin B. Mirus Christopher S. Heppner Joel E. VanderKwaak Keith Loague 《水文研究》2009,23(13):1949-1959
Distributed hydrologic models capable of simulating fully‐coupled surface water and groundwater flow are increasingly used to examine problems in the hydrologic sciences. Several techniques are currently available to couple the surface and subsurface; the two most frequently employed approaches are first‐order exchange coefficients (a.k.a., the surface conductance method) and enforced continuity of pressure and flux at the surface‐subsurface boundary condition. The effort reported here examines the parameter sensitivity of simulated hydrologic response for the first‐order exchange coefficients at a well‐characterized field site using the fully coupled Integrated Hydrology Model (InHM). This investigation demonstrates that the first‐order exchange coefficients can be selected such that the simulated hydrologic response is insensitive to the parameter choice, while simulation time is considerably reduced. Alternatively, the ability to choose a first‐order exchange coefficient that intentionally decouples the surface and subsurface facilitates concept‐development simulations to examine real‐world situations where the surface‐subsurface exchange is impaired. While the parameters comprising the first‐order exchange coefficient cannot be directly estimated or measured, the insensitivity of the simulated flow system to these parameters (when chosen appropriately) combined with the ability to mimic actual physical processes suggests that the first‐order exchange coefficient approach can be consistent with a physics‐based framework. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
50.