首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   106篇
  免费   1篇
  国内免费   1篇
安全科学   3篇
废物处理   11篇
环保管理   18篇
综合类   9篇
基础理论   41篇
污染及防治   18篇
评价与监测   6篇
社会与环境   1篇
灾害及防治   1篇
  2022年   1篇
  2021年   1篇
  2020年   1篇
  2018年   3篇
  2017年   2篇
  2016年   4篇
  2015年   1篇
  2014年   2篇
  2013年   4篇
  2012年   7篇
  2011年   6篇
  2010年   5篇
  2009年   2篇
  2008年   6篇
  2007年   4篇
  2006年   9篇
  2005年   2篇
  2004年   2篇
  2003年   1篇
  2002年   1篇
  2001年   3篇
  2000年   2篇
  1999年   2篇
  1998年   1篇
  1997年   2篇
  1996年   1篇
  1995年   2篇
  1993年   1篇
  1992年   3篇
  1991年   3篇
  1990年   2篇
  1989年   1篇
  1987年   1篇
  1986年   1篇
  1984年   1篇
  1983年   2篇
  1981年   5篇
  1980年   4篇
  1977年   1篇
  1976年   1篇
  1969年   1篇
  1967年   2篇
  1955年   1篇
  1940年   1篇
排序方式: 共有108条查询结果,搜索用时 93 毫秒
1.
2.
Summary Genetic parentage of 135 nestlings from 27 broods of polygynous and monogamous pied flycatchers Ficedula hypoleuca was analyzed by means of multilocus DNA fingerprinting. The minisatellite probe alpha-globin 3HVR detected approximately 12 scorable bands per fingerprint, and the proportion of bands shared between presumably unrelated adults averaged 0.22+0.08 SD. The fingerprints of 125 of the 135 nestlings made a complete match to those of their putative parents. In 4 nestlings a single mismatched band occurred, but since band sharing with both putative parents was high, the single mismatches were assumed to be caused by mutation. The 6 remaining nestlings had 5 or more mismatched bands each, low band-sharing proportions with their putative father and high band-sharing proportions with their putative mother. We thus conclude that they were all sired through extra-pair copulations (EPCs). Hence, only 4% of nestlings were sired through EPCs, and none resulted from intraspecific brood parasitism. One of the cuckolding males was identified, explaining all 5 mismatched bands in the nestling's fingerprint. Three of the illegitimate nestlings were from primary nests of polygynous males; 3 were from nests of monogamous males. The fact that many males in this study started to advertise for a second female in a distant territory several days before their first mate began egglaying, and still managed to secure almost exclusive paternity in their first brood, suggests that male polyterritoriality is not costly in terms of lost paternity. Common anti-cuckoddry tactics performed by male birds, like high rate of within-pair copulation and continuous mate-guarding thoughout the female's fertilizable period, do not seem to be important in pied flycatchers.Offprint requests to: J.T. Lifjeld  相似文献   
3.
4.
Some of the largest concentrations of dugongs (Dugong dugon) occur in the coastal waters of eastern Cape York Peninsula, Queensland, Designation of the Great Barrier Reef Marine Park has prompted the development of a program for management of dugong hunting by the aboriginal communities of the region. Assessment of the population by aerial surveys combined with monitoring of the aboriginal hunters' harvest suggest that the take is well below the sustainable yield. However, the reproductive rate of dugongs is so low that it will be a decade before the status of the population can be established. Therefore, a conservative management policy for dugongs is recommended while acknowledging the rights of traditional hunters. Greater participation of the aboriginal communities in the management program is sought to overcome initial misunderstandings and hostility.  相似文献   
5.
The aim of this paper was to investigate the effects of nitrogen (N) deposition on tree N cycling and identify potential biomarkers forNdeposition. Between April and October 2002 extensive fieldwork was undertaken at Mardley Heath in Hertfordshire. This woodland, located adjacent to the A1(M) motorway, is exposed to high levels of atmospheric nitrogen oxides from the traffic. Measurements of 15N, in vivo nitrate reductase (NR) activity, tissue, xylem and surface nitrate concentrations as well as N concentration and growth were made along a 700-m transect at 90° to the motorway. The 15N data show that oxidised N from the road traffic is taken up by nearby trees and is incorporated into plant tissues. Our measurements of NR activities suggest elevated rates close to the motorway. However, xylem sap, leaf tissue and leaf surface nitrate concentrations showed no differences between the roadside location and the most distant sampling point from the motorway. Taken together the 15N and nitrate reductase data suggest uptake and assimilation of N through the foliage.We conclude that for this lowland deciduouswoodland, tissue, xylem and surface measurements of nitrate are unreliable biomarkers for N deposition whereas 15N, growth measurements and integrated seasonal NR might be useful. The results also point to the benefit of roadside tree planting to screen pollution from motor vehicles.  相似文献   
6.
The aim of this paper is to assess how policy goals in relation to the promotion of green growth, energy security, pollution control and greenhouse gas (GHG) emissions reductions have been aligned in policies that have been implemented in selected countries during the last decades as a basis for discussing how a multi objective policy paradigm can contribute to future climate change mitigation. The paper includes country case studies from Brazil, Canada, China, the European Union (EU), India, Japan, Mexico, Nigeria, South Africa, South Korea and the United States covering renewable energy options, industry, transportation, the residential sector and cross-sectoral policies. These countries and regions together contribute more than two thirds of global GHG emissions. The paper finds that policies that are nationally driven and that have multiple objectives, including climate-change mitigation, have been widely applied for decades in both developing countries and industrialised countries. Many of these policies have a long history, and adjustments have taken place based on experience and cost effectiveness concerns. Various energy and climate-change policy goals have worked together in these countries, and in practice a mix of policies reflecting specific priorities and contexts have been pursued. In this way, climate-change mitigation has been aligned with other policy objectives and integrated into broader policy packages, though in many cases specific attention has not been given to the achievement of large GHG emission reductions. Based on these experiences with policy implementation, the paper highlights a number of key coordination and design issues that are pertinent to the successful joint implementation of several energy and climate-change policy goals.  相似文献   
7.
 Early development of the Antarctic sea urchin Sterechinus neumayeri was examined under two differ-ent culture regimes: one to simulate development near-bottom (“demersal development”) and the other to simulate the development of embryos in the water column (“pelagic development”). When embryos of both treatments reached the hatching blastula stage at 5 d post-fertilization (−1.5 °C), the blastulae that had undergone demersal development evidenced significant differences (by ANOVA or suitable non-parametric comparison) in the following: a thicker blastoderm layer (12%, P < 0.001), higher ash-free dry weights (19%, P < 0.01), lower mass-specific respiration rates (50%, P < 0.001), higher incorporation rates of 35S-methionine into protein (23%, P < 0.003), and a differential pattern of protein synthesis. When embryos developed demersally, they remained in the jelly-coat material released with the eggs at spawning. Quantitative isolation of this jelly-coat material in S. neumayeri demonstrated that it contained a significant amount of organic matter, 115 ng ash-free dry mass per egg, equivalent to 17% of the egg's initial organic mass. Uptake of external nutrients during embryogenesis may be a significant component of the physiological energetics of this polar invertebrate by allowing the utilization of jelly-coat material released by a female during spawning. Received: 21 April 1999 / Accepted: 5 June 2000  相似文献   
8.
The razorback sucker ( Xyrauchen texanus ) is a large, long-lived catostomid fish endemic to the Colorado River drainage of western North America, endangered because of recruitment failure. Efforts to preserve the species have emphasized artificial propagation and reintroduction. Given the importance of maintaining genetic diversity in such a program, we examined mitochondrial DNA diversity in a source population (Lake Mohave, Arizona-Nevada) and three hatchery-produced year classes (1987, 1989, 1990). The source contained considerable variation, indicated by high haplotype diversity ( ĥ = 0.97) and a large number of unique haplotypes (17 in 25 individuals). Diversity also was high in the 1987 ( ĥ = 0.89, 6 haplotypes in 10 individuals) and 1989 hatchery-produced year classes ( ĥ = 0.91, 7 in 11), but significantly lower in the 1990 year class ( ĥ = 0.71, 4 in 10). Low diversity in the last class was likely because of differences among females in fecundity, viability of progeny, or both. Because natural populations have collapsed throughout the species' range, we must identify methods that preserve the most diversity. We examined three potential alternatives: standard hatchery propagation, natural spawning in predator-free environments, and protective custody of larvae collected from the lake with reintroduction after growth to a size likely to survive. The last is the preferred alternative and should be pursued as the most cost-effective option for preserving genetic diversity in the razorback sucker.  相似文献   
9.
Non-mosaic trisomy 20 is rare in fetuses surviving beyond the first trimester. We report a case of a fetus with non-mosaic trisomy 20 in amniotic fluid cultures obtained during the prenatal evaluation of an unusual thoraco-abdominal mass which was found at autopsy to be pulmonary sequestration. Gross inspection and autopsy of the fetus revealed multiple anomalies. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   
10.
Landfill gases produced during biological degradation of buried organic wastes include methane, which when released to the atmosphere, can contribute to global climate change. Increasing use of gas collection systems has reduced the risk of escaping methane emissions entering the atmosphere, but gas capture is not 100% efficient, and further, there are still many instances when gas collection systems are not used. Biotic methane mitigation systems exploit the propensity of some naturally occurring bacteria to oxidize methane. By providing optimum conditions for microbial habitation and efficiently routing landfill gases to where they are cultivated, a number of bio-based systems, such as interim or long-term biocovers, passively or actively vented biofilters, biowindows and daily-used biotarps, have been developed that can alone, or with gas collection, mitigate landfill methane emissions. This paper reviews the science that guides bio-based designs; summarizes experiences with the diverse natural or engineered substrates used in such systems; describes some of the studies and field trials being used to evaluate them; and discusses how they can be used for better landfill operation, capping, and aftercare.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号