全文获取类型
收费全文 | 20964篇 |
免费 | 102篇 |
国内免费 | 103篇 |
专业分类
安全科学 | 396篇 |
废物处理 | 1007篇 |
环保管理 | 2519篇 |
综合类 | 3635篇 |
基础理论 | 5544篇 |
环境理论 | 6篇 |
污染及防治 | 4664篇 |
评价与监测 | 1399篇 |
社会与环境 | 1922篇 |
灾害及防治 | 77篇 |
出版年
2022年 | 159篇 |
2021年 | 145篇 |
2019年 | 108篇 |
2018年 | 724篇 |
2017年 | 686篇 |
2016年 | 718篇 |
2015年 | 279篇 |
2014年 | 379篇 |
2013年 | 1195篇 |
2012年 | 648篇 |
2011年 | 1318篇 |
2010年 | 903篇 |
2009年 | 1013篇 |
2008年 | 1219篇 |
2007年 | 1458篇 |
2006年 | 633篇 |
2005年 | 594篇 |
2004年 | 564篇 |
2003年 | 645篇 |
2002年 | 613篇 |
2001年 | 672篇 |
2000年 | 468篇 |
1999年 | 296篇 |
1998年 | 175篇 |
1997年 | 170篇 |
1996年 | 160篇 |
1995年 | 212篇 |
1994年 | 205篇 |
1993年 | 177篇 |
1992年 | 177篇 |
1991年 | 200篇 |
1990年 | 181篇 |
1989年 | 173篇 |
1988年 | 176篇 |
1987年 | 162篇 |
1986年 | 137篇 |
1985年 | 135篇 |
1984年 | 176篇 |
1983年 | 170篇 |
1982年 | 167篇 |
1981年 | 119篇 |
1980年 | 120篇 |
1979年 | 133篇 |
1978年 | 113篇 |
1977年 | 107篇 |
1976年 | 98篇 |
1975年 | 107篇 |
1974年 | 126篇 |
1973年 | 95篇 |
1972年 | 94篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
We determined the nuclear 18S rRNA sequences for 41 species of octocorals and used these to address the validity of the historical
ordinal divisions and the current subordinal divisions within the subclass Octocorallia. We also explored the phylogenetic
affinities of the species Dendrobrachia paucispina, which was originally classified in the order Antipatharia (subclass Ceriantipatharia) although polyp structure indicates
it belongs in the subclass Octocorallia. Trees constructed using maximum likelihood techniques are incongruent with the current
and historical taxonomy of the Octocorallia. There appeared to be three major clades of octocorals. The first clade included
most, but not all, pennatulaceans as a monophyletic group. The second clade contained 21 species, representing all major octocoral
groups other than pennatulaceans. The third clade contained members from three suborders of the Alcyonacea and one member
of the Pennatulacea. These data could not be used to distinguish the branching order of the three major clades. The species
D. paucispina had a close affinity with the genera Corallium and Paragorgia (Alcyonacea: Scleraxonia), although its morphology suggests it is more similar to the genus Chrysogorgia (Alcyonacea: Calcaxonia). The morphological character of dimorphism (the presence of both autozooids and siphonozooids within
a single colony) corresponded loosely with the topology of the most likely trees, and a single origin of dimorphism could
not be rejected. Despite sampling from the majority of families within the Octocorallia, many of the relationships within
this group remain ambiguous.
Received: 16 June 2000 / Accepted: 14 September 2000 相似文献
992.
One-day-old anarchistic (selected for successful worker reproduction) and wild-type honey-bee workers were introduced into queenright colonies of honey-bees of two treatments. In treatment 1, all eggs and larvae were offspring of queens from an anarchistic line. In treatment 2, all eggs and larvae were offspring of wild-type queens. In both treatments, adult workers were wild type. This experimental arrangement was used to test the importance of larval genotype on ovary activation in young adult workers. After 12 days, the introduced bees were dissected to determine the frequency of ovary activation. In those colonies provided with wild-type brood, 0% of introduced wild-type bees and 16% of anarchistic bees had activated ovaries. In those colonies provided with anarchistic brood, 13% of introduced wild-type bees and 41% of anarchistic bees had activated ovaries. These results strongly support the hypothesis that selection for high levels of worker reproduction in anarchistic stocks has reduced the amount or composition of brood pheromones produced by larvae that normally signal workers to refrain from reproduction. They also suggest that anarchistic workers have a higher threshold for these signals than wild-type bees. 相似文献
993.
994.
Uptake of Chromium by Trees: Prospects for Phytoremediation 总被引:3,自引:0,他引:3
995.
996.
L. Schultz P. Shah E. Giandomenico B. Chiera 《Environmental Modeling and Assessment》2016,21(2):169-179
Link Emissions Models estimate traffic-related air pollution emissions at the individual road link level and inform governmental policies for air quality management. The current South Australian Link Emissions Model (CLEM) assumes constant spatiotemporal traffic flow at a single fixed mean speed, a potential limitation as the variability of exhaust emissions with vehicle speed has been established in the literature.We extend CLEM to eliminate the assumption of constant traffic flow, through the derivation of mean Australian vehicle speed distributions for different road types. Specifically, we successfully model the vehicle speed profile data from the second National In-Service Emissions study using Nearest Neighbour Kernel Density Estimation. We propose a mean speed Distribution Link Emissions Model (DLEM) for exhaust emission estimation based on the derived mean speed distributions. DLEM is an augmented, enhanced version of CLEM, accommodating a range of vehicle speeds and road types. The performance of the extended model, DLEM, is analysed in comparison to the current model, CLEM, through a case study analysis of vehicle exhaust emissions on a typical arterial road in Adelaide, South Australia. Results indicate use of DLEM and, by extension, mean vehicle speed distributions, has a strong impact on emission estimation. In particular, the fixed speed model, CLEM, may be substantially underestimating exhaust emissions of carbon monoxide, non-methane volatile organic compounds and particulate matter less than 2.5 μm in diameter. These are common exhaust pollutants that have been extensively linked with adverse health effects including respiratory morbidity and premature mortality. 相似文献
997.
Gopal R. Patil 《Environmental Modeling and Assessment》2016,21(5):629-642
Tailpipe emissions in the road transportation system are a major source of air pollution and greenhouse gases. One of the possible approaches is to influence drivers’ routing decisions such that the emissions and fuel consumption is minimized. In order to evaluate such condition, we develop environmental traffic assignment (E-TA) models based on user equilibrium (UE) and system optimal (SO) behavioral principles. Extending the traditional travel time-based UE and SO principles to E-TA is not straightforward because, unlike travel time, the rate of emissions increases with the increase in vehicle speed beyond a certain point. The results of various TA models show a network-wide traffic control strategy in which vehicles are routed according to SO-based E-TA, can reduce system-wide emissions. However, a system in which drivers make routing decisions to minimize their own emissions (E-UE system) results in a paradoxical situation of increased individual as well as system-wide emissions. 相似文献
998.
Industrially utilized river basins are frequently exposed to contaminants originating from polluting activities. However, the physical instability and probability of mass movement mobilization of contaminated soil into rivers have only received little attention. In this study, we present a GIS-based method to produce a regional overview of where and how contaminated areas are potentially exposed to slope instability. A landslide susceptibility-index was used to study the degree and distribution of overlap between contaminated sites and unstable ground. A contaminated area instability hazard classification was produced integrating slope instability and contamination risk classification. Our results indicate that mass movement can be tied mainly to a slope gradient ≥16°, a proximity to the river that is <500 m, a distance of <500 m from roads, concave surface curvature, and sand- and silt soils. Forty-six (22%) of all considered contaminated sites are located within areas with a non-negligible slope instability, of which a majority, 30 sites (14%) are situated on ground with a low or moderate instability. Three sites with a class 2 contamination risk (the 2nd highest class) are located on ground with a very high slope instability. 相似文献
999.
J. F. Jasonsmith B. C. T. Macdonald I. White 《Environmental monitoring and assessment》2017,189(4):188
Wybong Creek discharges salts into the agriculturally and industrially important Hunter River in New South Wales, Australia. Abrupt increases in salinity occur periodically in the mid-Wybong Creek catchment. In order to understand the processes which cause these abrupt increases, changes in surface and groundwater were investigated. It is shown that salinity increases can be attributed to highly discrete groundwater discharge directly into the river from below. Hourly electrical conductivity data measured in the river showed regular, diurnal electrical conductivity fluctuations of up to 350 μS cm?1. These fluctuations could not be attributed to barometric pressure, temperature, or evapotranspiration. Instead, a similar periodicity in surface water electrical conductivity and groundwater height in nearby groundwater wells was found. Fluctuations were of similar periodicity to the orthotides which cause fluctuations in surface water height and are induced by Earth tides. The geology in the mid-catchment area indicates conditions are optimal for Earth tides to impact groundwater. The reporting of orthotidal changes in water chemistry in this article is believed to be the first of its kind in the scientific literature, with the large fluctuations noted having important implications for water monitoring and management in the catchment. Further research investigating Earth-tide-induced phases of groundwater heights will better constrain the relationships between surface water chemistry and groundwater height. 相似文献
1000.
This study investigates land cover change near the abandoned Pine Point Mine in Canada’s Northwest Territories. Industrial mineral development transforms local environments, and the effects of such disturbances are often long-lasting, particularly in subarctic, boreal environments where vegetation conversion can take decades. Located in the Boreal Plains Ecozone, the Pine Point Mine was an extensive open pit operation that underwent little reclamation when it shut down in 1988. We apply remote sensing and landscape ecology methods to quantify land cover change in the 20 years following the mine’s closure. Using a time series of near-anniversary Landsat images, we performed a supervised classification to differentiate seven land cover classes. We used raster algebra and landscape metrics to track changes in land cover composition and configuration in the 20 years since the mine shut down. We compared our results with a site in Wood Buffalo National Park that was never subjected to extensive anthropogenic disturbance. This space-for-time substitution provided an analog for how the ecosystem in the Pine Point region might have developed in the absence of industrial mineral development. We found that the dense conifer class was dominant in the park and exhibited larger and more contiguous patches than at the mine site. Bare land at the mine site showed little conversion through time. While the combination of raster algebra and landscape metrics allowed us to track broad changes in land cover composition and configuration, improved access to affordable, high-resolution imagery is necessary to effectively monitor land cover dynamics at abandoned mines. 相似文献