全文获取类型
收费全文 | 294篇 |
免费 | 25篇 |
国内免费 | 3篇 |
专业分类
测绘学 | 4篇 |
大气科学 | 35篇 |
地球物理 | 88篇 |
地质学 | 99篇 |
海洋学 | 25篇 |
天文学 | 37篇 |
综合类 | 3篇 |
自然地理 | 31篇 |
出版年
2022年 | 4篇 |
2021年 | 3篇 |
2020年 | 9篇 |
2019年 | 9篇 |
2018年 | 17篇 |
2017年 | 6篇 |
2016年 | 11篇 |
2015年 | 15篇 |
2014年 | 11篇 |
2013年 | 31篇 |
2012年 | 19篇 |
2011年 | 18篇 |
2010年 | 17篇 |
2009年 | 16篇 |
2008年 | 11篇 |
2007年 | 14篇 |
2006年 | 13篇 |
2005年 | 4篇 |
2004年 | 6篇 |
2003年 | 7篇 |
2002年 | 11篇 |
2001年 | 1篇 |
2000年 | 5篇 |
1999年 | 8篇 |
1998年 | 4篇 |
1997年 | 3篇 |
1996年 | 2篇 |
1995年 | 2篇 |
1994年 | 2篇 |
1992年 | 3篇 |
1991年 | 1篇 |
1990年 | 2篇 |
1987年 | 2篇 |
1985年 | 1篇 |
1984年 | 4篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1976年 | 1篇 |
1971年 | 1篇 |
1967年 | 1篇 |
1966年 | 4篇 |
1965年 | 2篇 |
1964年 | 7篇 |
1963年 | 6篇 |
1956年 | 1篇 |
排序方式: 共有322条查询结果,搜索用时 15 毫秒
31.
Nathan D. Sheldon Ramananda Chakrabarti Gregory J. Retallack Roger M. H. Smith 《Sedimentology》2014,61(6):1812-1829
The end of the Palaeozoic is marked by two mass‐extinction events during the Middle Permian (Capitanian) and the Late Permian (Changhsingian). Given similarities between the two events in geochemical signatures, such as large magnitude negative δ13C anomalies, sedimentological signatures such as claystone breccias, and the approximate contemporaneous emplacement of large igneous provinces, many authors have sought a common causal mechanism. Here, a new high‐resolution continental record of the Capitanian event from Portal Mountain, Antarctica, is compared with previously published Changhsingian records of geochemical signatures of weathering intensity and palaeoclimatic change. Geochemical means of discriminating sedimentary provenance (Ti/Al, U/Th and La/Ce ratios) all indicate a common provenance for the Portal Mountain sediments and associated palaeosols, so changes spanning the Capitanian extinction represent changes in weathering intensity rather than sediment source. Proxies for weathering intensity chemical index of alteration, ?W and rare earth element accumulation all decline across the Capitanian extinction event at Portal Mountain, which is in contrast to the increased weathering recorded globally at the Late Permian extinction. Furthermore, palaeoclimatic proxies are consistent with unchanging or cooler climatic conditions throughout the Capitanian event, which contrasts with Changhsingian records that all indicate a significant syn‐extinction and post‐extinction series of greenhouse warming events. Although both the Capitanian and Changhsingian event records indicate significant redox shifts, palaeosol geochemistry of the Changhsingian event indicates more reducing conditions, whereas the new Capitanian record of reduced trace metal abundances (Cr, Cu, Ni and Ce) indicates more oxidizing conditions. Taken together, the differences in weathering intensity, redox and the lack of evidence for significant climatic change in the new record suggest that the Capitanian mass extinction was not triggered by dyke injection of coal‐beds, as in the Changhsingian extinction, and may instead have been triggered directly by the Emeishan large igneous province or by the interaction of Emeishan basalts with platform carbonates. 相似文献
32.
Nathan Gale Reginald G. Golledge William C. Halperin Helen Couclelis 《The Professional geographer》1990,42(3):299-313
Spatial familiarity is a natural language concept that has no well-defined technical interpretation. We explore here some possible dimensions of the concept, provide subjective measurements of the dimensions, and evaluate their independence. The four dimensions examined are locational knowledge, visual recognition, name identification, and interaction frequency. We suggest that both cognitive and behavioral dimensions are embedded in the concept of spatial familiarity and must be part of the meaning of the concept and of any attempt to make it operational. 相似文献
33.
Young Nathan L. Lemieux Jean-Michel Locat Pascal Demers Denis Delottier Hugo Mony Laura 《Hydrogeology Journal》2022,30(4):1337-1344
Hydrogeology Journal - An extensive network of multilevel vibrating-wire piezometers (VWP) was recently created to monitor the spatial and temporal variation of pore pressure (and hydraulic head)... 相似文献
34.
Kayje Booker Lynn Huntsinger James W. Bartolome Nathan F. Sayre William Stewart 《Global Environmental Change》2013,23(1):240-251
Scientific interest in carbon sequestration on rangelands is largely driven by their extent, while the interest of ranchers in the United States centers on opportunities to enhance revenue streams. Rangelands cover approximately 30% of the earth's ice-free land surface and hold an equivalent amount of the world's terrestrial carbon. Rangelands are grasslands, shrublands, and savannas and cover 312 million hectares in the United States. On the arid and semi-arid sites typical of rangelands annual fluxes are small and unpredictable over time and space, varying primarily with precipitation, but also with soils and vegetation. There is broad scientific consensus that non-equilibrium ecological models better explain the dynamics of such rangelands than equilibrium models, yet current and proposed carbon sequestration policies and associated grazing management recommendations in the United States often do not incorporate this developing scientific understanding of rangeland dynamics. Carbon uptake on arid and semi-arid rangelands is most often controlled by abiotic factors not easily changed by management of grazing or vegetation. Additionality may be impossible to achieve consistently through management on rangelands near the more xeric end of a rangeland climatic gradient. This point is illustrated by a preliminary examination of efforts to develop voluntary cap and trade markets for carbon credits in the United States, and options including payment for ecosystem services or avoided conversion, and carbon taxation. A preliminary analysis focusing on cap and trade and payment for avoided conversion or ecosystem services illustrates the misalignment between policies targeting vegetation management for enhanced carbon uptake and non-equilibrium carbon dynamics on arid United States rangelands. It is possible that current proposed carbon policy as exemplified by carbon credit exchange or offsets will result in a net increase in emissions, as well as investment in failed management. Rather than focusing on annual fluxes, policy and management initiatives should seek long-term protection of rangelands and rangeland soils to conserve carbon, and a broader range of environmental and social benefits. 相似文献
35.
Kristie?L.?EbiEmail author Jessica?Hartman Nathan?Chan John?Mcconnell Michael?Schlesinger John?Weyant 《Climatic change》2005,73(3):375-393
Climate is one factor that determines the potential range of malaria. As such, climate change may work with or against efforts
to bring malaria under control. We developed a model of future climate suitability for stable Plasmodium falciparum malaria transmission in Zimbabwe. Current climate suitability for stable malaria transmission was based on the MARA/ARMA
model of climatic constraints on the survival and development of the Anopheles vector and the Plasmodium falciparum malaria parasite. We explored potential future geographic distributions of malaria using 16 projections of climate in 2100.
The results suggest that, assuming no future human-imposed constraints on malaria transmission, changes in temperature and
precipitation could alter the geographic distribution of malaria in Zimbabwe, with previously unsuitable areas of dense human
population becoming suitable for transmission. Among all scenarios, the highlands become more suitable for transmission, while
the lowveld and areas with low precipitation show varying degrees of change, depending on climate sensitivity and greenhouse
gas emission stabilization scenarios, and depending on the general circulation model used. The methods employed can be used
within or across other African countries. 相似文献
36.
A Laser-induced Fluorescence Instrument for Detecting Tropospheric OH and HO2: Characteristics and Calibration 总被引:1,自引:0,他引:1
37.
Lara C. Whitely Binder Jennifer Krencicki Barcelos Derek B. Booth Meriel Darzen Marketa McGuire Elsner Richard Fenske Thomas F. Graham Alan F. Hamlet John Hodges-Howell J. Elizabeth Jackson Catherine Karr Patrick W. Keys Jeremy S. Littell Nathan Mantua Jennifer Marlow Don McKenzie Michael Robinson-Dorn Eric A. Rosenberg Claudio O. Stöckle Julie A. Vano 《Climatic change》2010,102(1-2):351-376
Climate change is expected to bring potentially significant changes to Washington State’s natural, institutional, cultural, and economic landscape. Addressing climate change impacts will require a sustained commitment to integrating climate information into the day-to-day governance and management of infrastructure, programs, and services that may be affected by climate change. This paper discusses fundamental concepts for planning for climate change and identifies options for adapting to the climate impacts evaluated in the Washington Climate Change Impacts Assessment. Additionally, the paper highlights potential avenues for increasing flexibility in the policies and regulations used to govern human and natural systems in Washington. 相似文献
38.
Unpacking governance: Building adaptive capacity to climate change of river basins in Brazil 总被引:1,自引:0,他引:1
Governance and institutions are critical determinants of adaptive capacity and resilience. Yet the make-up and relationships between governance components and mechanisms that may or may not contribute to adaptive capacity remain relatively unexplored empirically. This paper builds on previous research focusing on integrated water resources management in Brazil to ‘unpack’ water governance mechanisms that may shape the adaptive capacity of water systems to climatic change. We construct a river basin index to characterize governance approaches in 18 Brazilian river basins, apply a reliability test to assess the validity of these governance indicators, and use in-depth qualitative data collected in a subsample of the basins to explore the relationship between the governance indicators and adaptive capacity. The analysis suggests a positive relationship between integrated water governance mechanisms and adaptive capacity. In addition, we carry out a cluster analysis to group the basins into types of governance approaches and further unveil potential relationships between the governance variables and overall adaptive capacities. The cluster analysis indicates that tensions and tradeoffs may exist between some of the variables, especially with equality of decision making and knowledge availability; a finding that has implications for decision makers aiming to build adaptive capacity and resilience through governance and institutional means. 相似文献
39.
40.
Koen Kemel Axel Brandenburg Nathan Kleeorin Dhrubaditya Mitra Igor Rogachevskii 《Solar physics》2012,280(2):321-333
The negative effective magnetic pressure instability discovered recently in direct numerical simulations (DNSs) may play a crucial role in the formation of sunspots and active regions in the Sun and stars. This instability is caused by a negative contribution of turbulence to the effective mean Lorentz force (the sum of turbulent and non-turbulent contributions) and results in the formation of large-scale inhomogeneous magnetic structures from an initially uniform magnetic field. Earlier investigations of this instability in DNSs of stably stratified, externally forced, isothermal hydromagnetic turbulence in the regime of large plasma ?? are now extended into the regime of larger scale separation ratios where the number of turbulent eddies in the computational domain is about 30. Strong spontaneous formation of large-scale magnetic structures is seen even without performing any spatial averaging. These structures encompass many turbulent eddies. The characteristic time of the instability is comparable to the turbulent diffusion time, L 2/?? t, where ?? t is the turbulent diffusivity and L is the scale of the domain. DNSs are used to confirm that the effective magnetic pressure does indeed become negative for magnetic field strengths below the equipartition field. The dependence of the effective magnetic pressure on the field strength is characterized by fit parameters that seem to show convergence for larger values of the magnetic Reynolds number. 相似文献