全文获取类型
收费全文 | 130828篇 |
免费 | 2017篇 |
国内免费 | 1023篇 |
专业分类
测绘学 | 3048篇 |
大气科学 | 8856篇 |
地球物理 | 25866篇 |
地质学 | 46645篇 |
海洋学 | 11859篇 |
天文学 | 29494篇 |
综合类 | 411篇 |
自然地理 | 7689篇 |
出版年
2022年 | 796篇 |
2021年 | 1410篇 |
2020年 | 1558篇 |
2019年 | 1674篇 |
2018年 | 3529篇 |
2017年 | 3299篇 |
2016年 | 4030篇 |
2015年 | 2198篇 |
2014年 | 3899篇 |
2013年 | 6935篇 |
2012年 | 4172篇 |
2011年 | 5552篇 |
2010年 | 4883篇 |
2009年 | 6298篇 |
2008年 | 5668篇 |
2007年 | 5638篇 |
2006年 | 5202篇 |
2005年 | 3961篇 |
2004年 | 3840篇 |
2003年 | 3620篇 |
2002年 | 3453篇 |
2001年 | 3123篇 |
2000年 | 3023篇 |
1999年 | 2433篇 |
1998年 | 2553篇 |
1997年 | 2363篇 |
1996年 | 2027篇 |
1995年 | 2025篇 |
1994年 | 1726篇 |
1993年 | 1614篇 |
1992年 | 1539篇 |
1991年 | 1487篇 |
1990年 | 1566篇 |
1989年 | 1351篇 |
1988年 | 1229篇 |
1987年 | 1480篇 |
1986年 | 1277篇 |
1985年 | 1575篇 |
1984年 | 1761篇 |
1983年 | 1687篇 |
1982年 | 1579篇 |
1981年 | 1423篇 |
1980年 | 1308篇 |
1979年 | 1242篇 |
1978年 | 1204篇 |
1977年 | 1051篇 |
1976年 | 1034篇 |
1975年 | 986篇 |
1974年 | 989篇 |
1973年 | 1032篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Dubey Om Prakash Niwas Sri Awasthi A. K. 《Journal of the Indian Society of Remote Sensing》1986,14(1):39-44
Journal of the Indian Society of Remote Sensing - Development activities must be compatible for possibilities and limitation of natural environment and resources. Predevelopmental analysis must... 相似文献
102.
Discard mitigation - what we can learn from waste minimization practices in other natural resources?
Solutions to the problem of discarding in fisheries have been debated for decades. Despite this attention, measures to ameliorate discarding have had limited success. Regulators, researchers, and industry continue to struggle with fisheries management and foregone yield in the face of the continued wastage of valuable resources due to discarding.Waste minimization and by-product utilization are powerful imperatives in other sectors that are also reliant on the harvest of natural resources. This paper considers the performance of these sectors in waste minimization and by-product utilization, with the aim of identifying practices and processes that may be applied to ameliorate discarding in fisheries.This paper describes the handling, utilization, and mitigation of discards and waste in the livestock farming, agriculture, mining, and waste management industries, and in particular, in forestry. In terms of biological impact, economic objectives, and management approaches the harvesting of trees has substantial similarities to industrialized fishing. However, the forestry sector has found ways to utilize almost 100% of the natural product harvest by establishing markets and new products. Analogous developments within the fishing industry could substantially improve sustainability through reduced levels of discarding and wastage. Based on the experiences of these sectors it is suggested that evaluations of potential Management Strategies are developed to specifically examine discard mitigation approaches on a broader scale than previously conducted. 相似文献
103.
Ochre is an unwanted waste product that accumulates in wetlands and streams draining abandoned coal and metal mines. A potential commercial use for ochre is to remediate As contaminated soil. Arsenic contaminated soil (605 mg kg−1) was mixed with different ochres (A, B and C) in a mass ratio of 1:1 and shaken in 20 mL of deionised water. After 72 h As concentration in solution was ca. 500 μg kg−1 in the control and 1–2.5 μg kg−1 in the ochre treated experiments. In a second experiment soil:ochre mixtures of 0.05–1:1 were shaken in 20 mL of deionised water for 24 h. For Ochres A and C, as solution concentration was reduced to ca. 1 μg kg−1 by 0.2–1:1 ochre:soil mixtures. For Ochre B, as concentration only reached ca. 1 μg kg−1 in the 1:1 ochre:soil mix. Sorption of As was best modelled by a Freundlich isotherm using As sorption per mass of goethite in the ochre (log K = 1.64, n = 0.79, R2 = 0.76, p 0.001). Efficiency of ochre in removing As from solution increased with increasing total Fe, goethite, citrate dithionite extractable Fe and surface area. 相似文献
104.
Royce A. Francis Stefanie M. Falconi Roshanak Nateghi Seth D. Guikema 《Climatic change》2011,106(1):31-55
One effect of climate change may be increased hurricane frequency or intensity due to changes in atmospheric and geoclimatic
factors. It has been hypothesized that wetland restoration and infrastructure hardening measures may improve infrastructure
resilience to increased hurricane frequency and intensity. This paper describes a parametric decision model used to assess
the tradeoffs between wetland restoration and infrastructure hardening for electric power networks. We employ a hybrid economic
input–output life-cycle analysis (EIO-LCA) model to capture: construction costs and life-cycle emissions for transitioning
from the current electric power network configuration to a hardened network configuration; construction costs and life-cycle
emissions associated with wetland restoration; and the intrinsic value of wetland restoration. Uncertainty is accounted for
probabilistically through a Monte Carlo hurricane simulation model and parametric sensitivity analysis for the number of hurricanes
expected to impact the project area during the project cycle and the rate of wetland storm surge attenuation. Our analysis
robustly indicates that wetland restoration and undergrounding of electric power network infrastructure is not preferred to
the “do-nothing” option of keeping all power lines overhead without wetland protection. However, we suggest a few items for
future investigation. For example, our results suggest that, for the small case study developed, synergistic benefits of simultaneously
hardening infrastructure and restoring wetlands may be limited, although research using a larger test bed while integrating
additional costs may find an enhanced value of wetland restoration for disaster loss mitigation. 相似文献
105.
For agriculture, there are three major options for mitigating greenhouse gas (GHG) emissions: 1) productivity improvements, particularly in the livestock sector; 2) dedicated technical mitigation measures; and 3) human dietary changes. The aim of the paper is to estimate long-term agricultural GHG emissions, under different mitigation scenarios, and to relate them to the emissions space compatible with the 2 °C temperature target. Our estimates include emissions up to 2070 from agricultural soils, manure management, enteric fermentation and paddy rice fields, and are based on IPCC Tier 2 methodology. We find that baseline agricultural CO2-equivalent emissions (using Global Warming Potentials with a 100 year time horizon) will be approximately 13 Gton CO2eq/year in 2070, compared to 7.1 Gton CO2eq/year 2000. However, if faster growth in livestock productivity is combined with dedicated technical mitigation measures, emissions may be kept to 7.7 Gton CO2eq/year in 2070. If structural changes in human diets are included, emissions may be reduced further, to 3–5 Gton CO2eq/year in 2070. The total annual emissions for meeting the 2 °C target with a chance above 50 % is in the order of 13 Gton CO2eq/year or less in 2070, for all sectors combined. We conclude that reduced ruminant meat and dairy consumption will be indispensable for reaching the 2 °C target with a high probability, unless unprecedented advances in technology take place. 相似文献
106.
Seasonal hydrological forecasts, or outlooks, can potentially provide water managers with estimates of river flows and water resources for a lead time of several months ahead. An experimental modelling tool for national hydrological outlooks has been developed which combines a hydrological model estimate of sub‐surface water storage across Britain with a range of seasonal rainfall forecasts to provide estimates of area‐wide hydrological conditions up to a few months ahead. The link is made between a deficit in sub‐surface water storage and a requirement for additional rainfall over subsequent months to enable sub‐surface water storage and river flow to return to mean monthly values. The new scheme is assessed over a recent period which includes the termination of the drought that affected much of Britain in the first few months of 2012. An illustration is provided of its use to obtain return‐period estimates of the ‘rainfall required’ to ease drought conditions; these are well in excess of 200 years for several regions of the country, for termination within a month of 1 April 2012, and still exceed 40 years for termination within three months. National maps of sub‐surface water storage anomaly show for the first time the current spatial variability of drought severity. They can also be used to provide an indication of how a drought situation might develop in the next few months given a range of possible future rainfall scenarios. © 2013 CEH/Crown and John Wiley & Sons, Ltd. 相似文献
107.
108.
We present a comparison of the zonal mean meridional circulations derived from monthly in situ data (i.e. radiosondes and
ship reports) and from the NCEP/NCAR reanalysis product. To facilitate the interpretation of the results, a third estimate
of the mean meridional circulation is produced by subsampling the reanalysis at the locations where radiosonde and surface
ship data are available for the in situ calculation. This third estimate, known as the subsampled estimate, is compared to
the complete reanalysis estimate to assess biases in conventional, in situ estimates of the Hadley circulation associated
with the sparseness of the data sources (i.e., radiosonde network). The subsampled estimate is also compared to the in situ
estimate to assess the biases introduced into the reanalysis product by the numerical model, initialization process and/or
indirect data sources such as satellite retrievals. The comparisons suggest that a number of qualitative differences between
the in situ and reanalysis estimates are mainly associated with the sparse sampling and simplified interpolation schemes associated
with in situ estimates. These differences include: (1) a southern Hadley cell that consistently extends up to 200 hPa in the
reanalysis, whereas the bulk of the circulation for the in situ and subsampled estimates tends to be confined to the lower
half of the troposphere, (2) more well-defined and consistent poleward limits of the Hadley cells in the reanalysis compared
to the in-situ and subsampled estimates, and (3) considerably less variability in magnitude and latitudinal extent of the
Ferrel cells and southern polar cell exhibited in the reanalysis estimate compared to the in situ and subsampled estimates.
Quantitative comparison shows that the subsampled estimate, relative to the reanalysis estimate, produces a stronger northern
Hadley cell (∼20%), a weaker southern Hadley cell (∼20–60%), and weaker Ferrel cells in both hemispheres. These differences
stem from poorly measured oceanic regions which necessitate significant interpolation over broad regions. Moreover, they help
to pinpoint specific shortcomings in the present and previous in situ estimates of the Hadley circulation. Comparisons between
the subsampled and in situ estimates suggest that the subsampled estimate produces a slightly stronger Hadley circulation
in both hemispheres, with the relative differences in some seasons as large as 20–30%. 6These differences suggest that the
mean meridional circulation associated with the NCEP/NCAR reanalysis is more energetic than observations suggest. Examination
of ENSO-related changes to the Hadley circulation suggest that the in situ and subsampled estimates significantly overestimate
the effects of ENSO on the Hadley circulation due to the reliance on sparsely distributed data. While all three estimates
capture the large-scale region of low-level equatorial convergence near the dateline that occurs during El Nino, the in situ
and subsampled estimates fail to effectively reproduce the large-scale areas of equatorial mass divergence to the west and
east of this convergence area, leading to an overestimate of the effects of ENSO on the zonal mean circulation.
Received: 16 September 1998 / Accepted: 22 April 1999 相似文献
109.
The hypothesis that Se is secreted by birds via the preen gland or salt glands, thus contaminating the feathers, has been investigated. It is concluded that the feather vanes show indirectly in this way the birds' e?posure to Se. Therefore they can be used as an indicator tissue for this element. 相似文献
110.
A Central-European nowcasting system which has been developed for use in mountainous terrain is tested in the Whistler/Vancouver area as part of the SNOW-V10 experiment. The integrated nowcasting through comprehensive analysis system provides hourly updated gridded forecasts of temperature, humidity, and wind, as well as precipitation forecasts which are updated every 15 min. It is based on numerical weather prediction (NWP) output and real-time surface weather station and radar data. Verification of temperature, relative humidity, and wind against surface stations shows that forecast errors are significantly reduced in the nowcasting range compared to those of the driving NWP model. The main contribution to the improvement comes from the implicit bias correction due to use of the latest observations. Relative humidity shows the longest lasting effect, with >50 % reduction of mean absolute error up to +4 h. For temperature and wind speed this percentage is reached after +2 and +3 h, respectively. Two cases of precipitation nowcasting are discussed and verified qualitatively. 相似文献