全文获取类型
收费全文 | 300篇 |
免费 | 9篇 |
国内免费 | 4篇 |
专业分类
安全科学 | 7篇 |
废物处理 | 5篇 |
环保管理 | 73篇 |
综合类 | 32篇 |
基础理论 | 95篇 |
环境理论 | 1篇 |
污染及防治 | 60篇 |
评价与监测 | 21篇 |
社会与环境 | 16篇 |
灾害及防治 | 3篇 |
出版年
2023年 | 2篇 |
2022年 | 5篇 |
2021年 | 4篇 |
2020年 | 4篇 |
2019年 | 1篇 |
2018年 | 5篇 |
2017年 | 9篇 |
2016年 | 14篇 |
2015年 | 6篇 |
2014年 | 5篇 |
2013年 | 14篇 |
2012年 | 12篇 |
2011年 | 19篇 |
2010年 | 18篇 |
2009年 | 16篇 |
2008年 | 17篇 |
2007年 | 22篇 |
2006年 | 16篇 |
2005年 | 24篇 |
2004年 | 9篇 |
2003年 | 11篇 |
2002年 | 13篇 |
2001年 | 8篇 |
2000年 | 7篇 |
1999年 | 5篇 |
1998年 | 2篇 |
1997年 | 4篇 |
1996年 | 3篇 |
1995年 | 1篇 |
1994年 | 6篇 |
1993年 | 2篇 |
1992年 | 1篇 |
1991年 | 3篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1986年 | 3篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1971年 | 1篇 |
1966年 | 1篇 |
1963年 | 1篇 |
1934年 | 1篇 |
排序方式: 共有313条查询结果,搜索用时 15 毫秒
81.
82.
Plants offer metabolically rich floral nectar to attract visiting pollinators. The composition of nectar includes not only
sugars, but also amino acids. We have examined the amino acid content of the nectar of ornamental tobacco and found that it
is extremely rich (2 mM) in proline. Because insect pollinators preferentially utilize proline during the initial phases of
insect flight and can reportedly taste proline, we determined whether honeybees showed a preference for synthetic nectars
rich in proline. We therefore established an insect preference test and found that honeybees indeed prefer nectars rich in
the amino acid proline. To determine whether this was a general phenomenon, we also examined the nectars of two insect-pollinated
wild perennial species of soybean. These species also showed high levels of proline in their nectars demonstrating that plants
often produce proline-rich floral nectar. Because insects such as honeybees prefer proline-rich nectars, we hypothesize that
some plants offer proline-rich nectars as a mechanism to attract visiting pollinators. 相似文献
83.
In Part I, the concepts of inherent, local and distant residence times (DRTs) were reviewed as metrics of the extent to which chemical discharges or emissions in one region or box are transported to distant regions. In this second part, the concepts are applied to geographically relevant systems to illustrate their applicability to the assessment of chemicals for long-range transport potential (LRTP). It is shown that the relative ranking of chemicals as characterized by the DRT method is similar to that of the characteristic travel distance concept. A DRT source-receptor matrix is developed that can express the chemical-specific potential of source regions to contaminate a specific receptor region of concern such as the Arctic. The matrix can be modified to identify for a specific source region the likely destinations of emissions as well as to assess the relative vulnerability of regions in the global environment to contaminants of concern. 相似文献
84.
85.
Water level management in Mississippi River Pool 25 differentially influences off-channel habitats in the mid-pool and lower
pool. Hydrologic models indicate lower pool off-channel habitats dry with greater frequency and duration compared to similar
habitats at mid-pool. We examined the influence of this contrasting hydrology on substrate characteristics, organic matter,
macroinvertebrate, and fish communities in off-channel habitats during 2001–2003. Benthic organic matter standing stocks were
stable in mid-pool habitats but lower pool values were variable because of annual differences in moist-soil vegetation production.
Generally, small-bodied and multivoltine invertebrate taxa had high community biomass and dominated lower pool habitats, whereas
longer-lived and large-bodied taxa were more abundant and had higher community biomass in mid-pool habitats having longer
hydroperiods. Fish communities were dominated by cyprinids in both habitats, and mid-pool habitats tended to be higher in
overall species richness. Unique fish taxa were collected in each pool, with primarily rheophilic forms in mid-pool habitats
and limnophilic forms in lower pool habitats. Results indicate that contrasting hydrology associated with a mid-pool control
point directly and indirectly influences biological communities in off-channel habitats. Further, management regimes that
promote hydrologic diversity in off-channel habitats may enhance biological diversity at larger spatial and temporal scales. 相似文献
86.
Reid VanBenthysen Ethan Thibaudeau Brad L. Kinsey 《Journal of Manufacturing Processes》2013,15(2):194-200
The specimen parameter that is often mentioned with respect to the ability to achieve electromagnetic forming (EMF) is the specimen thickness. If the skin depth is small compared to this parameter, efficient forming will be achieved. However, another parameter that may affect the ability to achieve efficient forming is the specimen's planar area, i.e., the length and width of the specimen. This would particularly become an important factor if EMF is used to fabricate meso/microscale components. In this research, a flat spiral coil was used to flange 0.508 mm thickness, CuZn30 specimens of varying widths (i.e., 10, 14, 18, 22, 35, and 47 mm). These widths were varied in order to modify the projected area of the coil over the specimen. Results showed that a decrease in the specimen width was generally associated with a decrease in forming (i.e., lower flanging angle) due to edge effects in induced eddy currents. Since the magnetic field distribution from the flat spiral coil is asymmetric, material was overhung on both sides of the die. This yielded an extra half turn on the left side of the specimen, and increased forming. The die was also translated to assess differences in flanging generated. In order to achieve meso/microforming with EMF, attention to the interaction between coil design and specimen dimensions is required. 相似文献
87.
Australian approaches to coastal vulnerability assessment 总被引:2,自引:1,他引:1
The Australian coastline is one of the longest and most diverse of any in the world, and Australian researchers have developed
preliminary models of the behaviour of major coastal systems such as beaches and reefs. The Australian population is particularly
focused along the coastline, especially in metropolitan centres; however, the population of regional centres along the coast
is increasing steadily in response to a phenomenon termed seachange. Coastal systems are increasingly threatened by potential
impacts as a result of climate change, as indicated by the successive assessments by the Intergovernmental Panel on Climate
Change (IPCC). Although Australia played a central role in applying a common methodology (CM), developed from IPCC guidelines
in the 1990s, and in devising alternative approaches, which were initially trialled at nine sites on the Australian coast,
there has not been a nationally co-ordinated approach to assessing the coastal vulnerability of Australia, and such an approach
is only emerging now. Instead, there have been a series of different approaches adopted to look at the different parts of
the Australian coast, including wetland mapping in northern Australia; geomorphic unit mapping in South Australia; storm surge
vulnerability modelling in Queensland; probabilistic approaches to beach erosion in New South Wales; indicative mapping of
potential coastal retreat in Tasmania. Additionally, there have been methods proposed by insurers and coastal engineers to
meet their requirements. Since 2005, the Australian government has once again seen the need for a national coastal vulnerability
assessment, and a series of studies are planned or under way to achieve the aims of a National Climate Change Adaptation Framework. 相似文献
88.
In this, Part I of a two-part series, a review is presented of some generally appreciated residence time properties of multimedia models. The novel concept of “distant residence time” (DRT) is developed to provide additional insights into the characterization of environmental transport. DRT is the proportionality constant between the rate of emission of a contaminant into one compartment or region and the mass that results at steady-state in a distant compartment. The concept, which can be viewed as an expression of environmental mobility, is illustrated for various configurations of compartments and is shown to be consistent with the concepts of global fractionation and cold condensation. The dynamic responses of chemical quantities at distant locations to changing emission rates are also discussed. It is shown that approximate solutions for DRTs and their time dependence are useful for characterizing the long-range transport of chemicals and for interpreting monitoring data. 相似文献
89.
90.