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   141篇
  免费   6篇
安全科学   17篇
废物处理   4篇
环保管理   30篇
综合类   17篇
基础理论   49篇
环境理论   1篇
污染及防治   17篇
评价与监测   4篇
社会与环境   7篇
灾害及防治   1篇
  2023年   2篇
  2020年   1篇
  2019年   2篇
  2018年   8篇
  2017年   2篇
  2016年   7篇
  2015年   2篇
  2014年   2篇
  2013年   9篇
  2012年   6篇
  2011年   7篇
  2010年   4篇
  2009年   7篇
  2008年   5篇
  2007年   12篇
  2006年   9篇
  2005年   2篇
  2004年   4篇
  2003年   6篇
  2002年   6篇
  2000年   4篇
  1999年   2篇
  1997年   2篇
  1996年   5篇
  1994年   4篇
  1993年   2篇
  1992年   2篇
  1991年   1篇
  1990年   3篇
  1988年   1篇
  1987年   2篇
  1986年   1篇
  1985年   2篇
  1983年   3篇
  1982年   1篇
  1981年   2篇
  1979年   1篇
  1978年   2篇
  1977年   2篇
  1972年   1篇
  1964年   1篇
排序方式: 共有147条查询结果,搜索用时 31 毫秒
121.
Estrogens-sulphates such as 17beta-estradiol-3-sulphate and estrone-3-sulphate are excreted by livestock in the urine. These conjugates are precursors to the free counterparts 17beta-estradiol and estrone, which are endocrine disrupting chemicals. In this study microcosm laboratory experiments were conducted in three pasture soils from New Zealand to study the aerobic degradation and metabolite formation kinetics of 17beta-estradiol-3-sulphate at three different incubation temperatures. The degradation of 17beta-estradiol-3-sulphate followed a first-order kinetic and the temperature dependence of the rate constants was sufficiently described by the Arrhenius equation. Degradation was different between the three investigated soils and the rate constants across the soils were significantly correlated to the arylsulphatase activity at 7.5 and 15 degrees C. Estrone-3-sulphate and 17beta-estradiol were identified as primary metabolites and estrone as a secondary metabolite. Results suggest arylsulphatase activity originating from soil microbial biomass is the main driver for the degradation of 17beta-estradiol-3-sulphate.  相似文献   
122.
Radon-222 exhalation from the ground surface depends upon a number of variables such as the 226Ra activity concentration and its distribution in soil grains; soil grain size; soil porosity, temperature and moisture; atmospheric pressure, rainfall and temperature. In this study, 222Rn exhalation flux density measurements within and around the Ranger uranium mine in northern Australia were performed to investigate the effect of these variables within a tropical region. Measurements were taken at the waste rock dumps, ore stockpiles, mine pits, and at sites where effluent water with elevated 226Ra concentration has been spray irrigated over land, as well as at sites outside the mine. The sites selected represented a variety of geomorphic regions ranging from uranium-bearing rocks to ambient soils. Generally, wet season rains reduced 222Rn exhalation but at a few sites the onset of rains caused a step rise in exhalation flux densities. The results show that parameters such as 226Ra activity concentration, soil grain size and soil porosity have a marked effect on 222Rn flux densities. For similar geomorphic sites, 226Ra activity concentration is a dominant factor, but soil grain size and porosity also influence 222Rn exhalation. Surfaces with vegetation showed higher exhalation flux densities than their barren counterparts, perhaps because the associated root structure increases soil porosity and moisture retention. Repeated measurements over one year at eight sites enabled an analysis of precipitation and soil moisture effects on 222Rn exhalation. Soil moisture depth profiles varied both between seasons and at different times during the wet season, indicating that factors such as duration, intensity and time between precipitation events can influence 222Rn flux densities considerably.  相似文献   
123.
The global Sustainable Development Goals (SDGs) commenced in 2016 and provide an evidence-based framework for sustainable development planning and programming until 2030. There is emerging international practice and a growing catalogue of related reviews, assessments, guidelines and publications. While the expert community is clearly emphasising the need to adopt evidence- and science-based approaches to SDG implementation, policymakers now face the challenge of implementing the SDGs simultaneously in a coherent and integrated manner. Regular systematic reviews of national progress and approaches to implementing the SDGs are advisable to ensure that emerging science and knowledge is effectively informing national practice. This paper reviews the recent academic and expert literature as well as national experience in implementing the SDGs in 26 countries. It uses a systematic approach to analyse the degree to which key implementation stages and approaches recommended in the expert literature are being adopted and applied to support national SDG implementation on-the-ground. The review highlights that while progress has been made in some initial planning stages, key gaps remain in terms of the assessment of interlinkages, trade-offs and synergies between targets. Gaps are also clearly evident in the adoption of systems thinking and integrated analytical approaches and models. This is problematic as it may undermine effective implementation and the transformative potential of the SDGs. As more countries turn their attention to the SDGs, the review underscores the considerable risk that they will pursue the same ‘siloed’ or ‘linear’ approaches to sustainable development that have met with limited success in the past.  相似文献   
124.
The biochemical and energetic composition of body components of ten species of bathyal echinoids, and an asteroid, a holothuroid and a stalked crinoid were determined from individuals sampled from a variety of deep-water sites near the Bahamas (north Caribbean Sea) in October 1988. When compared with other studies of echinoderms, no geographic- or depth-related differences in biochemical or energetic composition were found. Body-wall tissues were composed primarily of skeletal material (mineral ash), but were comparatively high in organic material in the echinothuriid echinoids, and the asteroid and holothuroid. Gut tissues and pyloric cecae had high levels of lipid and protein, indicating their potential role in nutrient storage. Body-wall tissues were generally low in energy, but were highest in the echinoidsAraeosoma belli (7.7 kJ g–1 dry wt) andSperosoma antillense (8.0 kJ g–1 dry wt), the asteroidOphidiaster alexandri (8.9 kJ g–1 dry wt), and the holothuroidEostichopus regalis (13.1 kJ g–1 dry wt). Energy levels of gut and pyloric cecal tissues were two to three times higher than those of body-wall tissues. Total somatic tissue energy values varied greatly among species, ranging from 1.5 kJ in the echinoidAspidodiadema jacobyi to 142.1 kJ inE. regalis. As the bathyal echinoderms examined in this study occur in great abundance, they represent a significant reservoir of organic and inorganic materials and energy in deep-water benthic systems.  相似文献   
125.
‘Rapid ranking’ has been used for many years as a method of determining the priority which should be given to formal investigation of the wide range of hazards and risks present on major process industry sites. Such methods tend to evolve to meet the needs of specific applications. Some historical and recent applications are outlined, and the nature of the developments which they led to are discussed. Particular topics discussed include: development of the method such that it is usable by operating managers rather than specialists; use to raise risk consciousness; adaptation for use as an aid to hazard identification; use to define both which risks should be studied and which risks, even if low, should be incorporated in routine monitoring and periodic auditing programmes; use as a basis for comparison of the relative risks presented by a variety of different industrial installations; use for a range of different types of risk; and extension beyond ranking to include ‘shortlisting’ i.e. deciding which risks to include in a study programme and which to leave out. Philosophical difficulties with the approach are discussed, including the danger of omitting from detailed study a risk which is erroneously shown as low, and the uncertainty of the absolute level of the ranked risks. Approaches to minimizing these problems are discussed.  相似文献   
126.
127.
Males of some oscine passerines learn and share songs of neighboring males. This process can lead to the formation of song pattern neighborhoods or microhabitat song dialects. The degree to which song sharing occurs between populations and the spatial scale over which neighboring males share songs, however, can vary widely, and interpopulation comparisons have suggested that song sharing is more common in residents than in migrants. Here, we examine two populations of the orange-crowned warbler (Oreothlypis celata) to quantify patterns of song sharing at the northern (long-distance migrant) and southern (short-distance migrant) edges of the breeding distribution and to test if return rate, territory fidelity, and breeding dispersal explain the patterns found in the two populations. The southern population (O. celata sordida breeding on Santa Catalina Island, California; 33°N) had a higher annual return rate to their territories and exhibited higher song sharing in neighborhoods than their counterparts (O. celata celata breeding in Fairbanks, Alaska; 64°N). Year-to-year patterns of territory fidelity and breeding dispersal distances were similar between populations. Our results suggest that if migratory distance generally covaries with the proportion of returning males, this could explain different levels of song sharing between the short- and long-distance migrants.  相似文献   
128.
Grassland vegetation can provide visual cover for terrestrial vertebrates. The most commonly used method to assess visual cover is the Robel pole. We test the use of digital photography as a more accurate and repeatable method. We assessed the digital photography method on four forage grassland species (Pseudoroegneria spicata, Festuca campestris, Poa pratensis, Achnatherum richardsonii). Digital photos of 2-dimensional cutout silhouettes of three bird species sharp-tailed grouse, western meadowlark and savannah sparrow were used to model the impact of clipping (i.e., grazing) on visual cover. In addition, photos of artificial voles were used to model litter on cover available to small mammals. Nine sites were sampled and data were analyzed by the dominant grass species in each study plot. Regression analysis showed that digital photos (r2 = 0.62) were a better predictor than the Robel pole (r2 = 0.26) for assessment of cover. Clipping heights showed that clipping at less than 15 cm left the silhouettes 50% exposed. Digital photo analysis revealed that visual cover was affected by the type of grass species, with F. campestris > P. pratensis > A. richardsonii > P. spicata. Biomass and litter were both positively related to cover for small mammals.  相似文献   
129.
During the past ten years, a statistical program applicable to RCRA groundwater monitoring data has been developed with input from regulators, geologists, regulated individuals, and a small group of professional statisticians. At first driven by the RCRA regulations, the evolution of the statistical program now often influences changes in regulatory requirements, which in turn affect opinions on the best statistical approach for addressing the requirements. This article describes that evolution and the issues that have emerged over the years. In the following article, Dr. Robert Gibbons, another of the professional statisticians involved in the debate, responds to comments made in this article.  相似文献   
130.
Prediction of disease patterns for communicable diseases with low prevalence rates is difficult because of the random variations inherent in the data Smoothing of prevalence or incidence data prior to the analysis may facilitate these predictions. All of the analyses are based on census tract characterisiics. The disadvantages of this type of data are that the boundaries are arbitraty and lead to some heterogenous tracts. Also, the analyses depend totally on aggregate rather than individual data. The advantage of working with this type of data is its availability for all metropolitan areas. The San Antonio diphtheria epidemic has been previously referred to as an ethnic epidemic. This paper shows that it is even more an epidemic of lower socioeconomic groups. In this region of the country, socioeconomic characteristics are almost indistinguishable.  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