全文获取类型
收费全文 | 219篇 |
免费 | 14篇 |
国内免费 | 1篇 |
专业分类
测绘学 | 1篇 |
大气科学 | 14篇 |
地球物理 | 43篇 |
地质学 | 95篇 |
海洋学 | 10篇 |
天文学 | 62篇 |
自然地理 | 9篇 |
出版年
2021年 | 1篇 |
2020年 | 6篇 |
2019年 | 5篇 |
2018年 | 13篇 |
2017年 | 7篇 |
2016年 | 6篇 |
2015年 | 8篇 |
2014年 | 7篇 |
2013年 | 6篇 |
2012年 | 6篇 |
2011年 | 4篇 |
2010年 | 7篇 |
2009年 | 6篇 |
2008年 | 10篇 |
2007年 | 8篇 |
2006年 | 6篇 |
2005年 | 7篇 |
2004年 | 8篇 |
2003年 | 8篇 |
2002年 | 4篇 |
2001年 | 4篇 |
2000年 | 8篇 |
1999年 | 3篇 |
1998年 | 7篇 |
1997年 | 9篇 |
1996年 | 6篇 |
1995年 | 7篇 |
1994年 | 3篇 |
1993年 | 4篇 |
1992年 | 2篇 |
1991年 | 4篇 |
1989年 | 2篇 |
1988年 | 7篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1984年 | 7篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1980年 | 1篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1974年 | 3篇 |
1973年 | 3篇 |
1971年 | 1篇 |
1963年 | 1篇 |
1962年 | 1篇 |
1960年 | 2篇 |
1957年 | 1篇 |
1955年 | 1篇 |
1949年 | 1篇 |
排序方式: 共有234条查询结果,搜索用时 328 毫秒
41.
42.
Till Kuhlbrodt Stefan Rahmstorf Kirsten Zickfeld Frode Bendiksen Vikebø Svein Sundby Matthias Hofmann Peter Michael Link Alberte Bondeau Wolfgang Cramer Carlo Jaeger 《Climatic change》2009,96(4):489-537
This paper discusses the risks of a shutdown of the thermohaline circulation (THC) for the climate system, for ecosystems
in and around the North Atlantic as well as for fisheries and agriculture by way of an Integrated Assessment. The climate
model simulations are based on greenhouse gas scenarios for the 21st century and beyond. A shutdown of the THC, complete by
2150, is triggered if increased freshwater input from inland ice melt or enhanced runoff is assumed. The shutdown retards
the greenhouse gas-induced atmospheric warming trend in the Northern Hemisphere, but does not lead to a persistent net cooling.
Due to the simulated THC shutdown the sea level at the North Atlantic shores rises by up to 80 cm by 2150, in addition to
the global sea level rise. This could potentially be a serious impact that requires expensive coastal protection measures.
A reduction of marine net primary productivity is associated with the impacts of warming rather than a THC shutdown. Regional
shifts in the currents in the Nordic Seas could strongly deteriorate survival chances for cod larvae and juveniles. This could
lead to cod fisheries becoming unprofitable by the end of the 21st century. While regional socioeconomic impacts might be
large, damages would be probably small in relation to the respective gross national products. Terrestrial ecosystem productivity
is affected much more by the fertilization from the increasing CO2 concentration than by a THC shutdown. In addition, the level of warming in the 22nd to 24th century favours crop production
in northern Europe a lot, no matter whether the THC shuts down or not. CO2 emissions corridors aimed at limiting the risk of a THC breakdown to 10% or less are narrow, requiring departure from business-as-usual
in the next few decades. The uncertainty about THC risks is still high. This is seen in model analyses as well as in the experts’
views that were elicited. The overview of results presented here is the outcome of the Integrated Assessment project INTEGRATION. 相似文献
43.
Sub-micron scale distributions of trace elements in zircon 总被引:2,自引:1,他引:1
Amy E. Hofmann John W. Valley E. Bruce Watson Aaron J. Cavosie John M. Eiler 《Contributions to Mineralogy and Petrology》2009,158(3):317-335
Sub-micron scale zoning of Ti concentrations and correlations between concentrations of Ti and other trace elements (P, Ce,
and Y) and cathodoluminescent (CL) banding is observed in natural zircons. Ion images were made using the Caltech Microanalysis
Center’s CAMECA NanoSIMS 50L with an O− primary beam focused to ~300 nm on the sample surface. The high spatial resolution of this technique allows for interrogation
of chemical variations at or below the scale of CL banding in natural zircons. Images produced in this manner display two
types of correlations among Ti, P, Ce, and Y (which appears to be a proxy for CL intensity): strong (correlation coefficients
>0.8) and subtle (correlation coefficients ~0.15–0.4). Strongly correlated images, which display Ti variations of ca. a factor
of 3 between adjacent CL bands and overall elevated trace element concentrations in CL-dark bands, were found within an oscillatory-zoned,
trace element enriched sector of a CL sector-zoned zircon. Three possible causes for such correlations include: temperature-dependent
equilibrium partitioning, trace element partitioning limited by diffusion in the host melt and surface-controlled, non-equilibrium
growth. Comparison of our data with the expected results of these processes suggests that: (1) Ti partitioning in zircon is
dependent upon non-equilibrium effects in addition to temperature and/or (2) the incorporation of elements that co-vary with
Ti in zircon (e.g., Y, P and Ce) is also temperature-dependent. Sub-micron scale, high-Ti regions are also found within Proterozoic
Adirondack and >4 Ga Jack Hills zircons as well as trace element enrichments (including Ti) along cracks within Jack Hills
zircons. 相似文献
44.
A. Hofmann K. Arlt H. Balthasar S.M. Bauer W. Bittner J. Paschke E. Popow J. Rendtel D. Soltau T. Waldmann 《Astronomische Nachrichten》2012,333(9):854-862
The new Solar telescope GREGOR is designed to observe small‐scale dynamic magnetic structures below a size of 70 km on the Sun with high spectral resolution and polarimetric accuracy. For this purpose, the polarimetric concept of GREGOR is based on a combination of post‐focus polarimeters with pre‐focus equipment for high precision calibration. The Leibniz‐Institute for Astrophysics Potsdam developed the GREGOR calibration unit which is an integral part of the telescope. We give an overview of the function and design of the calibration unit and present the results of extensive testing series done in the Solar Observatory “Einsteinturm” and at GREGOR (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
45.
Ian Cartwright Uwe Morgenstern William Howcroft Harald Hofmann Robin Armit Michael Stewart Chad Burton Dylan Irvine 《水文研究》2020,34(21):4034-4048
Determining mean transit times in headwater catchments is critical for understanding catchment functioning and understanding their responses to changes in landuse or climate. Determining whether mean transit times (MTTs) correlate with drainage density, slope angle, area, or land cover permits a better understanding of the controls on water flow through catchments and allows first-order predictions of MTTs in other catchments to be made. This study assesses whether there are identifiable controls on MTTs determined using 3H in headwater catchments of southeast Australia. Despite MTTs at baseflow varying from a few years to >100 years, it was difficult to predict MTTs using single or groups of readily-measured catchment attributes. The lack of readily-identifiable correlations hampers the prediction of MTTs in adjacent catchments even where these have similar geology, land use, and topography. The long MTTs of the Australian headwater catchments are probably in part due to the catchments having high storage volumes in deeply-weathered regolith, combined with low recharge rates due to high evapotranspiration. However, the difficulty in estimating storage volumes at the catchment scale hampers the use of this parameter to estimate MTTs. The runoff coefficient (the fraction of rainfall exported via the stream) is probably also controlled by evapotranspiration and recharge rates. Correlations between the runoff coefficient and MTTs in individual catchments allow predictions of MTTs in nearby catchments to be made. MTTs are shorter in high rainfall periods as the catchments wet up and shallow water stores are mobilized. Despite the contribution of younger water, the major ion geochemistry in individual catchments commonly does not correlate with MTTs, probably reflecting heterogeneous reactions and varying degrees of evapotranspiration. Documenting MTTs in catchments with high storage volumes and/or low recharge rates elsewhere is important for understanding MTTs in diverse environments. 相似文献
46.
We analyze radio observations, magnetograms and extrapolated field line maps, Hα filtergrams, and X-ray observations of two
flare events (6 February 1992 in AR 7042 and 25 October 1994 in AR 7792) and study properties, evolution and energy release
signatures of sigmoidal loop systems. During both events, the loop configuration seen in soft X-ray (SXR) images changes from
a preflare sigmoidal shape to a relaxed post-flare loop system. The underlying magnetic field system consists of a quadrupolar
configuration formed by a sheared arcade core and a remote field concentration. We demonstrate two possibilities: a sigmoidal
SXR pattern can be due to a single continuous flux tube (the 1992 event). Alternatively, it can be due to a set of independent
loops appearing like a sigmoid (the 1994 event). In both cases, the preflare and post-flare loops can be well reproduced by
a linear force-free field and potential field, respectively, computed using preflare magnetograms. We find that thermal and
non-thermal flare energy release indicators of both events become remarkably similar after applying spatial and temporal scale
transformations. Using the spatial scaling between both events we estimated that the non-thermal energy release in the second
event liberated about 1.7 times more energy per unit volume. A two-and-a-half times faster evolution indicates that the rate
of the energy release per unit volume is more than four times higher in this event. A coronal type II burst reveals ignition
and propagation of a coronal shock wave. In contrast, the first event, which was larger and released about a 10 times more
energy during the non-thermal phase, was associated with a CME, but no type II burst was recorded. During both events, in
addition to the two-ribbon flare process an interaction was observed between the flaring arcade and an emerging magnetic flux
region of opposite polarity next to the dominant leading sunspot. The arcade flare seems to stimulate the reconnection process
in an `emerging flux-type' configuration, which significantly contributes to the energy release. This regime is characterized
by the quasiperiodic injection of electron beams into the surrounding extended field line systems. The repeated beam injections
excite pulsating broadband radio emission in the decimetric-metric wavelength range. Each radio pulse is due to a new electron
beam injection. The pulsation period (seconds) reflects the spatial scale of the emerging flux-type field configuration. Since
broadband decimetric-metric radio pulsations are a frequent radio flare phenomenon, we speculate that opposite-polarity small-scale
flux intrusions located in the vicinity of strong field regions may be an essential component of the energy release process
in dynamic flares. 相似文献
47.
For the interpretation of many boundary-layer field experiments the geostrophic wind is needed as an external parameter. However, quite often and especially in remote areas this wind is not known at all or difficult to determine because there are not enough measurements of the surface pressure.Here it is shown how measurements carried out with the HELIPOD system, a helicopter-borne meteorological turbulence measuring system, may be used to evaluate the geostrophic wind. This is done by the analysis of the pressure field at different heights. An additional analysis of the temperature field in the same heights allows for the discussion of the quality of the derived geostrophic wind. An intercomparison with the vertical wind profile enables us to discuss the influence of the curvature of the isobars. From this, finally, also the gradient wind can be estimated. 相似文献
48.
49.
Ocean Dynamics - The existence of cross-sectionally averaged morphodynamic equilibria of tidal inlets is investigated, using a cross-sectionally averaged model, and their sensitivity to variations... 相似文献
50.
Thomas M. Soniat Eileen E. Hofmann John M. Klinck Eric N. Powell 《International Journal of Earth Sciences》2009,98(1):99-114
The eastern oyster (Crassostrea virginica) is affected by two protozoan parasites, Perkinsus marinus which causes Dermo disease and Haplosporidium nelsoni which causes MSX (Multinucleated Sphere Unknown) disease. Both diseases are largely controlled by water temperature and salinity and thus are potentially sensitive to climate variations resulting from the El Niño-Southern Oscillation (ENSO), which influences climate along the Gulf of Mexico coast, and the North Atlantic Oscillation (NAO), which influences climate along the Atlantic coast of the United States. In this study, a 10-year time series of temperature and salinity and P. marinus infection intensity for a site in Louisiana on the Gulf of Mexico coast and a 52-year time series of air temperature and freshwater inflow and oyster mortality from Delaware Bay on the Atlantic coast of the United States were analyzed to determine patterns in disease and disease-induced mortality in C. virginica populations that resulted from ENSO and NAO climate variations. Wavelet analysis was used to decompose the environmental, disease infection intensity and oyster mortality time series into a time–frequency space to determine the dominant modes of variability and the time variability of the modes. For the Louisiana site, salinity and Dermo disease infection intensity are correlated at a periodicity of 4 years, which corresponds to ENSO. The influence of ENSO on Dermo disease along the Gulf of Mexico is through its effect on salinity, with high salinity, which occurs during the La Niña phase of ENSO at this location, favoring parasite proliferation. For the Delaware Bay site, the primary correlation was between temperature and oyster mortality, with a periodicity of 8 years, which corresponds to the NAO. Warmer temperatures, which occur during the positive phase of the NAO, favor the parasites causing increased oyster mortality. Thus, disease prevalence and intensity in C. virginica populations along the Gulf of Mexico coast is primarily regulated by salinity, whereas temperature regulates the disease process along the United States east coast. These results show that the response of an organism to climate variability in a region is not indicative of the response that will occur over the entire range of a particular species. This has important implications for management of marine resources, especially those that are commercially harvested. 相似文献