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1.
This session presented a wide range of papers on cooperativeresearch, design of alternative gears and fishing strategies,and new analyses to support management. The contributed papersreflected a real desire to explore different approaches andstrategies to fishery management. It is apparent that fishery policy has had a mixed record ofsuccess and failure at best. In most regions of the world, manystocks are still being overfished or have been severely overfishedin the past. Although rebuilding programmes for overfished stockshave been developed, nationally as well as internationally,only a few have been successful, many others are works in progressand, in too many cases, rebuilding 相似文献
2.
Chironomid remains from the sediment of Lake Vuolep Njakajaure reflect limnological conditions resulting from changing climate and vegetation throughout the Holocene, but do not strictly follow accepted climate trends or the vegetation history based on regional pollen and macrofossil analyses. Chironomid community changes appear to be influenced by organic nutrient input from the surrounding catchment vegetation and lake hydrology, both of which are indirectly responding to some combination of climate change, hypolimnetic oxygen concentration, and changes in basin morphology. The chironomid-based quantitative mean July air-temperature reconstruction differs from other regional quantitative records; this discrepancy is likely related to limnological conditions particular to Lake Vuolep Njakajaure. Comparison of a northern Swedish temperature transfer function and one from western Canada reveals differences in the mean July air-temperature optima of several common taxa, suggesting that the existing conservative estimates of Holocene climate change in northern Sweden may be underestimated due to the limited temperature gradient captured by the Swedish training set. 相似文献
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Rutger Rosenberg 《Marine pollution bulletin》1985,16(6):227-231
Increased inputs of nutrients to marine coastal areas over the last decades have created a basis for eutrophication of the waters surrounding Sweden. In combination with relatively low water exchange in these vertically stratified and almost non-tidal waters, local and regional effects of increased macro-algal biomass, and decreased oxygen concentrations in bottom water leading to mortalities of benthic animals and decreased fish catches have at times been observed. The effects were first noted in the Baltic, but are now obvious also in Swedish and Danish coastal areas in the Kattegat and the Belt Sea. Similar symptoms have recently also been recorded off the Danish North Sea coast. Other shallow coastal and shelf areas, where stratification occurs, can be regarded as potentially eutrophic risk areas. 相似文献
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Norman J. Rosenberg 《Climatic change》1982,4(3):239-254
In a prior paper (Part I), the point was made that, assuming an unchanged climate, water use efficiency in agricultural crop
production will likely be favored by the increase in CO2 concentration projected to occur within the next half century. Since climatic changeis likely to result from the CO2 concentration increase, its possible impacts on agricultural productivity must also be considered. An attempt to do so, using
the Great Plains region of North America as a case study, is reported in this paper (Part II).
A number of climatic models predict significant increases in surface temperature. Manabe and Wetherald's (1980) model provides
the most specific projections for a hypothetical Northern hemisphere continent. That model also predicts an intensification
of the hydrologic cycle with rainfall distribution altered so that some zones will receive more and some less as a result
of a doubling in the atmospheric CO2 concentration. The zone between 37 and 47° N latitude will suffer a reduction in availability of soil moisture.
A number of regression models of grain yield as a function of temperature and precipitation have been used to anticipate the
impacts of the projected climatic changes. The value of this approach is questioned. An alternative approach - the study of
the migration of major agricultural crops across strong climatic gradients - is proposed. Changes in the geographical distribution
of the hard red winter wheat zone in North America provide an example. The point is also made that factorscurrently limiting food production must be considered in order to predict the possible impacts of any given climatic change. In the
central Great Plains today, the energy consumed by evapotranspiration often exceeds that supplied by net radiation since sensible
heat advection from dryer regions to the south and west provides a major additional input of energy. If, as models project,
the excess of precipitation over evaporation increases south of 37° N, the advection of sensible heat and, hence, the rates
of evapotranspiration and degree of water stress on growing plants could be reduced in the adjacent regions to the north.
Published as Paper No. 6123, Journal Series, Nebraska Agricultural Experiment Station. The work reported was conducted under
Regional Research Project 11-033 and Nebraska Agricultural Station Project 11-049.
George Holmes Professor of Agricultural Meteorology, Center for Agricultural Meteorology and Climatology, Institute of Agriculture
and Natural Resources, University of Nebraska, Lincoln, Nebraska, 68583-0728. 相似文献
7.
Dennis D. Baldocchi Shashi B. Verma Norman J. Rosenberg 《Boundary-Layer Meteorology》1983,25(1):43-54
Air flow was observed above and within canopies of a number of kinds of soybeans. The Clark cultivar and two isolines of the Harosoy cultivar were studied in 1979 and 1980, respectively. Wind speed above the canopy was measured with cup anemometers. Heated thermistor anemometers were used to measure air flow within the canopy. Above-canopy air flow was characterized in terms of the zero-plane displacement (d), roughness parameter (z o) and drag coefficient (C d). d and z o were dependent on canopy height but were independent of friction velocity in the range 0.55 to 0.75 m s?1 · C d for the various canopies ranged from 0.027 to 0.035. Greater C d values were measured over an erectophile canopy than over a planophile canopy. C d was not measurably affected by differences in leaf pubescence. Within-canopy wind profiles were measured at two locations: within and between rows. The wind profile was characterized by a region of great wind shear in the upper canopy and by a region of relatively weak wind shear in the middle canopy. Considerable spatial variability in wind speed was evident, however. This result has significant implications for canopy flow modeling efforts aimed at evaluating transport in the canopy. In the lower canopy, wind speed within a row increased with depth whereas wind speed between two rows decreased with depth. The wind speeds at the two locations tended to converge to a common value at a height near 0.10 m. The attenuation of within-canopy air flow was stronger in canopies with greater foliage density. Canopy flow attenuation seemed to decrease with increasing wind speed, suggesting that high winds distorted the shape of the canopy in such a manner that the penetration of wind into the canopy increased. 相似文献
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While it is intuitively attractive to link health status and the quality of housing, it is methodologically complex to identify the relative importance of housing because individual characteristics and environmental variables act as confounders. A secondary issue is that the data sets which contain detailed data on health status and environmental variables often contain only limited data on housing. Similarly, housing surveys rarely contain detailed data on health and environmental variables. Respondents from Montreal, Toronto and Vancouver in the public use micro-data files of the 1996/97 cycle of the National Population Health Survey make up the data sets for a series of logistic regression models where health status, allergies, asthma, arthritis, migraines and bronchitis/emphysema act as the dependent variables. Sets of variables which measure housing, the environment (smoking and alcohol consumption) and the socio-economic status of individuals are used as independent variables. The issues of confounders and the limitations of the data are illustrated by the results of the analysis. If we are to go beyond local area surveys and carry out broader analyses of the links between health status and the quality of housing, researchers and data collection agencies will need to re-think the artificial divisions between these two critical aspects of peoples' lives. 相似文献