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   349篇
  免费   10篇
  国内免费   3篇
安全科学   28篇
废物处理   17篇
环保管理   41篇
综合类   98篇
基础理论   63篇
环境理论   1篇
污染及防治   75篇
评价与监测   21篇
社会与环境   14篇
灾害及防治   4篇
  2023年   2篇
  2022年   2篇
  2021年   2篇
  2020年   6篇
  2019年   4篇
  2018年   14篇
  2017年   12篇
  2016年   28篇
  2015年   13篇
  2014年   14篇
  2013年   38篇
  2012年   19篇
  2011年   32篇
  2010年   15篇
  2009年   17篇
  2008年   22篇
  2007年   15篇
  2006年   22篇
  2005年   15篇
  2004年   12篇
  2003年   8篇
  2002年   6篇
  2001年   7篇
  2000年   1篇
  1999年   6篇
  1998年   1篇
  1997年   1篇
  1996年   2篇
  1995年   1篇
  1994年   1篇
  1992年   4篇
  1991年   4篇
  1990年   2篇
  1987年   1篇
  1983年   6篇
  1982年   2篇
  1970年   1篇
  1966年   2篇
  1963年   1篇
  1959年   1篇
排序方式: 共有362条查询结果,搜索用时 15 毫秒
61.
Women have the right to support that enables them to breastfeed. Supporting breastfeeding in emergencies is important because artificial feeding places mothers and children at risk. In emergencies, artificial feeding is dangerous to the infant, difficult and requires substantial resources. In contrast, breastfeeding guards infant health. It is also protective against postpartum haemorrhage, maternal depletion, maternal anaemia and closely spaced births and should therefore concern not only nutritionists, but also those involved in reproductive health. However, it is common for women's ability to breastfeed to be undermined in emergencies by the indiscriminate distribution of breast-milk substitutes and the absence of breastfeeding support. Controlling the distribution of breast-milk substitutes, providing supportive environments, and appropriate medical and practical assistance to breastfeeding women safeguards the health and well-being of mothers and babies. Greater collaboration between the nutrition and reproductive health sectors is required to promote best practice in protecting breastfeeding women and their children in emergencies.  相似文献   
62.
Genetic variability and structuring of rabbitfish populations with contrasting life histories, Siganus argenteus and Siganus fuscescens were determined using allozyme analysis. A total of 13–14 polymorphic loci were examined from samples collected in 2002 and 2003 from eight reefs representing 25 populations north (Kuroshio Current) and south (Mindanao Current) of the bifurcation of the North Equatorial Current along the eastern Philippine coast. S. fuscescens populations (H OBS = 0.085) showed higher heterozygosity than S. argenteus (H OBS = 0.053), consistent with predictions of the neutral theory for demersal egg spawners compared to pelagic egg spawners. The generally lower genetic variability of Kuroshio populations may be due to greater environmental disturbance affecting larval mortality and recruitment success. There was no significant overall population genetic structuring for S. argenteus (F ST = 0.01485, P > 0.05) compared to S. fuscescens (F ST = 0.03275, P < 0.05). The latter species showed highly significant genetic structuring among Kuroshio and Mindanao Current populations in both 2002 and 2003 (F CT = 0.08120, P < 0.05; F CT = 0.07500, P < 0.05, respectively), as well as among populations within regions. This conforms to expectations of correlations between observed population genetic structure and life history features related to dispersal potential and gene flow. However, there were significant temporal (i.e., 2002 vs. 2003 samples) genetic variations for both S. fuscescens (F CT = 0.08542, P < 0.05) and S. argenteus (F CT = 0.06330, P < 0.05), which may reflect interannual variability in recruitment success. Differences in population spatial genetic patterns between the two reef fish species suggest that broad scale physical factors (e.g. NEC bifurcation) and regional environmental perturbations (e.g. incidence of typhoons) affect population genetic structure of sympatric congeneric species with different life histories differently. Finer scale ecological processes, which affect larval dispersal and recruitment (e.g., local hydrographic features, distribution of habitats), particularly in the Mindanao Current region, exert more influence on structuring populations of S. fuscescens.  相似文献   
63.
The development of decentralized sources of power out of renewable sources of energies has been triggering far-reaching consequences for Distribution System Operators over the past decade in Europe. Our paper benchmarks across 23 European countries the impact of the development of renewables on the physical characteristics of power distribution networks and on their investments. It builds on a large spectrum of databases of quantitative indicators about the dynamics of installed capacity of renewable energy resources and the power generation out of them, electricity independence, quality of electricity distribution, smart grids investments, Network System Operators capital expenditures, length of the distribution networks, overall costs of power networks paid by private agents, and electricity losses, all in relation with the development of decentralized generation. The heterogeneity of these indicators across Europe appears to be wide notably because of physical constraints, historic legacies, or policy and regulatory choices. A cluster analysis allows for deriving six groups of countries that display statistically homogenous characteristics. Our results may provide decision makers and regulators with a tool helping them to concentrate on the main issues specific to their countries as compared to the European median, and to look for possible solutions in the experience of other clusters which are shown to perform better for some indicators.  相似文献   
64.
Phosphorus (P) is an essential macronutrient in agriculture; however, lack of reporting makes its supply chain a black box. By using literature synthesis on the P challenge, we identify four areas where the reporting process is problematic: P reserves and resources; P losses along the supply chain; P externalities; and access to data. We find that in these areas, the reporting system is inconsistent, inaccurate, incomplete, fragmented and non-transparent. We use systems analysis to discuss implications of reporting on the sustainability of the P supply chain. We find that reporting is essential for the achievement of global P governance and the human right to adequate food. It can also inform decision makers and other impacted stakeholders on policies on agriculture, food security, pollution and international conflict. An improved P reporting process also allows a better evaluation of global sustainability commitments such as the United Nations Sustainable Development Goals.  相似文献   
65.
Determining the influences of anthropogenic perturbations on side channel dynamics in large rivers is important from both assessment and monitoring perspectives because side channels provide critical habitat to numerous aquatic species. Side channel extents are decreasing in large rivers worldwide. Although riprap and other linear structures have been shown to reduce side channel extents in large rivers, we hypothesized that small “anthropogenic plugs” (flow obstructions such as dikes or berms) across side channels modify whole-river geomorphology via accelerating side channel senescence. To test this hypothesis, we conducted a geospatial assessment, comparing digitized side channel areas from aerial photographs taken during the 1950s and 2001 along 512 km of the Yellowstone River floodplain. We identified longitudinal patterns of side channel recruitment (created/enlarged side channels) and side channel attrition (destroyed/senesced side channels) across n?=?17 river sections within which channels were actively migrating. We related areal measures of recruitment and attrition to the density of anthropogenic side channel plugs across river sections. Consistent with our hypothesis, a positive spatial relationship existed between the density of anthropogenic plugs and side channel attrition, but no relationship existed between plug density and side channel recruitment. Our work highlights important linkages among side channel plugs and the persistence and restoration of side channels across floodplain landscapes. Specifically, management of small plugs represents a low-cost, high-benefit restoration opportunity to facilitate scouring flows in side channels to enable the persistence of these habitats over time.  相似文献   
66.
In the vulnerable Arctic environment, the impact of especially hazardous wastes can have severe consequences and the reduction and safe handling of these waste types are therefore an important issue. In this study, two groups of heavy metal containing particulate waste materials, municipal solid waste incineration (MSWI) fly and bottom ashes and mine tailings (i.e., residues from the mineral resource industry) from Greenland were screened in order to determine their suitability as secondary resources in clay-based brick production. Small clay discs, containing 20 or 40% of the different particulate waste materials, were fired and material properties and heavy metal leaching tests were conducted before and after firing. Remediation techniques (washing in distilled water and electrodialytical treatment) applied to the fly ash reduced leaching before firing. The mine tailings and bottom ash brick discs obtained satisfactory densities (1669–2007 kg/m3) and open porosities (27.9–39.9%). In contrast, the fly ash brick discs had low densities (1313–1578 kg/m3) and high open porosities (42.1–51. %). However, leaching tests on crushed brick discs revealed that heavy metals generally became more available after firing for all the investigated materials and that further optimisation is therefore necessary prior to incorporation in bricks.  相似文献   
67.
Plasma PBDE and thyroxine levels in rats exposed to Bromkal or BDE-47   总被引:2,自引:0,他引:2  
In experimental models, polybrominated diphenyl ethers (PBDEs), a group of brominated flame retardants, have caused effects in a number of biological end-points, including neurobehavioural effects, disturbances in thyroid and steroid hormone homeostasis, and other steroid-related effects. Almost exclusively, only external dose metrics (dose per body weight basis) have been studied in connection to the observed effects. In this study we report on new analyses of plasma PBDE levels in surplus samples from earlier studies on thyroid hormones (TH) in exposed rodents. Female, 7-week old Sprague-Dawley rats were given either Bromkal 70-5 DE (Study I; 18 or 36 mg/kg bw/day) or BDE-47 (Study II; 1, 6 or 18 mg/kg bw/day) daily by gavage for two weeks. At an external dose of 18 mg/kg bw/day significant TH effects (decreased plasma free thyroxin levels) were observed in both studies, corresponding to an internal (plasma) dose of 463 microg sumPBDE/g lipid (Study I) or 421 microg BDE-47/g lipid (Study II). If we compare the contribution of different BDE congeners to the total BDE level in rat plasma after Bromkal exposure (Study II), and in the Bromkal mixture itself, the most important congener in the Bromkal mixture were also found in plasma. However, the relative concentration of BDE-99 was lower, and that of BDE-153 was higher, than that of the mixture, indicating selectivity in uptake, metabolism and/or excretion of the individual BDE congeners. Explicitly, the possible in vivo conversion of BDE-99 to BDE-47, and of BDE-154 to BDE-153 could not be excluded. The internal dose in the present rat study could be compared to reported human serum doses of PBDE. Human serum/blood levels have a wide range, from 3 to 6 ng sumPBDE/g lipid in background samples from Europe, about 10 times higher in US sample, and up to 100 times higher (300-600 ng/g lipid) in upper-end levels in collected samples from USA. As a consequence, the margin between effects levels in the rat and exposure levels in man varies widely, with a quotient roughly from 1000 to 100,000. Generally, it could be expected that this margin is lower than if external dose metrics would be used. An even lower margin could be expected as recent studies have shown effects in offspring at lower doses than those giving effects in our studies. Lastly, it should be noted that humans are already exposed to a mixture of chemicals in daily life, a fact that complicates this kind of comparison.  相似文献   
68.
69.
This study focuses on the relationship between job stressors and mental strain in hospital work, adjusting for differences in personality traits. Questionnaires were obtained from 760 full-time employees. Fourteen scales of job stressors were clustered into four factors: professional latitude, clinical demands, workload problems and role difficulties. A mental strain index was derived from the addition of three sub-scales: depression, anxiety and irritation. Two personality traits were measured: Locus of Control (Rotter) and Striver-Achiever (Sales). The four job demand factors were dichotomized into high-low grouping variables. A 24 factorial analysis of covariance was conducted, using the two personality traits as covariates, in order to test and adjust for trait-related strain. Results show that Locus of Control adjusted differences in mental strain appear significantly related to work stressors. A direct relationship was found with role difficulties, professional latitude and workload problems. Moreover, high levels of role difficulties and low levels of professional latitude interact significantly with adjusted levels of mental strain. The Striver-Achiever trait, however, appears most strongly correlated with workload problems but not with mental strain. We believe that this exploratory analysis suggests that the stressor-strain relationship might be best conceived as a combination of direct and complex pathways, relating facets of both job demands and of personality with outcomes, under a cognitive and conditional paradigm.  相似文献   
70.
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