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   114篇
  免费   8篇
  国内免费   1篇
安全科学   11篇
废物处理   2篇
环保管理   25篇
综合类   10篇
基础理论   45篇
污染及防治   19篇
评价与监测   4篇
社会与环境   6篇
灾害及防治   1篇
  2023年   6篇
  2021年   2篇
  2020年   6篇
  2019年   1篇
  2018年   6篇
  2017年   5篇
  2016年   2篇
  2015年   7篇
  2014年   4篇
  2013年   10篇
  2012年   4篇
  2011年   2篇
  2010年   5篇
  2009年   6篇
  2008年   4篇
  2007年   2篇
  2006年   3篇
  2005年   4篇
  2004年   4篇
  2002年   2篇
  2001年   1篇
  1999年   2篇
  1997年   2篇
  1996年   1篇
  1995年   2篇
  1994年   3篇
  1992年   1篇
  1991年   3篇
  1990年   1篇
  1988年   1篇
  1987年   2篇
  1986年   4篇
  1985年   2篇
  1984年   3篇
  1983年   1篇
  1981年   1篇
  1980年   1篇
  1977年   3篇
  1976年   2篇
  1974年   1篇
  1956年   1篇
排序方式: 共有123条查询结果,搜索用时 397 毫秒
31.
The vertical distribution and migration (seasonal, diel and ontogenetic) of Calanus helgolandicus are described from the shallow (100 m) shelf-seas to the south-west of the British Isles. In 1978 and 1979, the overwintering population of C. helgolandicus consisted primarily of Stage V copepodites and adults. By late winter/early spring the copepodites had moulted to adult females (>90%), which matured and bred the first cohorts of the year, prior to onset of the spring phytoplankton bloom in April/May. C. helgolandicus reached a peak of numerical abundance in August of 20x103 copepodites m-2 (over the depth range sampled -0 to 70 m), which was 200 times the population in winter. The seasonal peak of abundance occurred 4 mo after the peak of the bloom of phytoplankton in spring. The yearly development of the copepod was not always out of phase with the diatom bloom, as seen when the data from 1978 was placed in the context of a longer time-series collected at 10 m over 22 yr (1960–1981, inclusive). Large vertical migrations were observed in the younger copepodites (CI and II) in May from below to above the thermocline. In the remainder of the year, the CI and CII stages behaved differently and were located above the thermocline within the euphotic zone. The largest vertical displacements of biomass were seen in the summer months due to the migrations of the CV stages and adults, which had developed from the spring cohorts. It was contended that the seasonal and vertical migrations of C. helgolandicus are part of a more complex pattern of inherent behavior than has been reported previously and that, however difficult this is to discern in the natural populations, it always expresses itself.  相似文献   
32.
The kinetic response of ammonium- or silicate-limited and ammonium- or silicatestarved populations of Chaetoceros debilis, Skeletonema costatum, and Thalassiosira gravida was determined by a single addition of the limiting nutrient to a steady-state culture and subsequent monitoring of the nutrient disappearance of the limiting and non-limiting nutrients at frequent time intervals. The kinetic response of nonlimited (nutrient) populations of these three species was also determined. Three distinct modes of the uptake of the limiting nutrient were observed for ammonium-or silicate-limited populations of these three species, surge uptake (V s ), internally (cellular) controlled uptake (V i ), and externally (ambient limiting nutrient concentration) controlled uptake (V e ). Non-limited populations did not exhibit the three distinct segments of uptake, V s , V i and V e . Estimates of the maximal uptake rate (V max) and the Michaelis constant (K s ) were obtained from nutrient-limited populations during the V e segment of the uptake curve. Pooled values of V e for the three ammonium-limited populations yielded V max and K s estimates of 0.16 h-1 and 0.5 g-at NH4–N l-1. Kinetic data derived from the V e segment of the uptake curve for silicate-limited populations yielded different values of V max and K s for each of the three species. In a number of parameters that were measured, T. gravida was clearly different from C. debilis and S. costatum and its recovery from nutrient starvation was the slowest. Recovery of all species from silicate limitation or starvation was slower than from ammonium limitation or starvation. Ammonium-starved populations maintained a maximal uptake rate at a substrate concentration an order of magnitude lower (0.1 g-at NH4–N l-1) than that observed for NH4-limited populations (1.0 g-at NH4–N l-1). Adaptation to the severity of the nutrient limitation occurred as changes in the magnitude of cellular characteristics, such as short-term uptake potential (V s ) and affinity for the substrate (K s ). The consequence of these results are discussed in terms of another possible mechanism to explain changes in species composition and succession in nutrient-depleted environments.Contribution No. 944 from the Department of Oceanography, University of Washington, Seattle, Washington 98195, USA.  相似文献   
33.
Water is a salient issue in the Intermountain West of the United States (U.S.), with concerns ranging from water scarcity and drought to intermittent flooding and water quality risks. This paper investigates coverage of water issues across seven newspapers in the core of the U.S. Intermountain West region. Newspapers have the potential to set agendas and influence perceived salience of issues among consumers. The Intermountain West region shares common concerns about water supply and demand, climate change, and water quality. We investigate whether or not local daily newspaper coverage of water issues provides a more local or regional sensitivity. Findings from this exploratory study reveal differences in water coverage across local daily newspapers. The overall volume of water‐related articles differed across newspapers as did proportion of articles on specific water topics and connecting issues. Coverage of local issues was more dominant than might be expected given mass media trends, but water geography in articles extended across the U.S. and the world in every newspaper studied. Variations in newspaper coverage of water issues suggests more local nuance persists despite the experience of common water issues across the region.  相似文献   
34.
The process of deforestation in the Central Development Region (CDR) of Nepal is diverse in space and time, with rapid deforestation still occurring in areas outside the national parks and wildlife reserves. This paper identifies the spatial driving forces (SDFs) of deforestation in the CDR for 1975–2000 using satellite data of 1975 (MSS), 1990 (TM), and 2000 (ETM+) along with socio-demographic and socioeconomic variables. Radiometrically calibrated satellite images are individually classified into seven distinct classes and merged together to cover the entire CDR. Classification accuracies are also assessed. Areas of land use and cover within the areas of each Village Development Committee (VDC) and municipality represented by GIS polygons are calculated from the classified images by overlaying vector files of 1845 polygons representing sections of VDCs and municipalities in 30–1199 m, 1200–2399 m, 2400–4999 m and >5000 m elevation levels. These elevation levels were estimated from the DEM compiled from 24 ASTER scenes taken on different dates. Only the first three elevation levels are used in the analysis because area >5000 m is under permanent snow cover where human related forestry activities are almost negligible. A transition matrix is generated for 1975–1990 using classified images of 1975 and 1990 and then this product is used to further develop another transition matrix for 1990–2000 with the classified ETM+ 2000 images as the final stage. The GIS polygon layer is overlaid on the transition matrices to calculate deforestation areas for 1975–1990 and 1990–2000. Biophysical and socioeconomic information collected from various sources is then brought into a GIS platform for statistical analyses. Six linear regression models are estimated using SAS; in effect, two models for each elevation range representing the 1975–1990 and 1990–2000 periods of change to identify SDF influences on deforestation. These regression analyses reveal that deforestation in the CDR is related to multiple factors, such as farming population, genders of various ages, migration, elevation, road, distance from road to forest, meandering and erosion of river, and most importantly the conversion of forestland into farmland.  相似文献   
35.
36.
Cleft lip and/or palate (CL/CP) is the most common congenital craniofacial anomaly and parents often ask, “how did this happen?” Patients and families may benefit from access to a multidisciplinary team (MDT) from prenatal diagnosis into early adulthood. Multiple factors can contribute to the development of a cleft. We discuss the epidemiology and risk factors that increase the likelihood of having a newborn with a cleft. The purpose of this article is to review the prenatal investigations involved in the diagnosis and workup of these patients in addition to postpartum treatment, prognostic factors, and counseling families regarding future recurrence risk.  相似文献   
37.
38.
This paper contributes to the calling literature by using self‐determination theory—a theory that makes distinctions between different types of motivation—in order to gain a better understanding of how enacting a calling may relate both positively and negatively to well‐being. We use a daily diary method novel to the calling field and a sample with a distinctive calling, Church of England clergy. We expect daily calling enactment to relate positively to daily well‐being via more autonomous forms of motivation (intrinsic and identified motivation) and negatively via less autonomous forms (introjected motivation). Furthermore, we consider how the relationship between calling enactment and motivation may be moderated by perceived competence. The hypotheses were tested using multi‐level structural equation modeling. There was strong support for calling enactment relating positively to well‐being, and this relationship was fully mediated by intrinsic and identified motivation; the hypothesized negative pathway, from calling enactment, to introjected motivation, to well‐being, was not supported. However, perceived competence was found to moderate some of the relationships between calling and the motivation types, where calling enactment is linked to lower introjected motivation at high levels of competence. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   
39.
40.
This paper introduces the five papers that follow, all of which were originally presented at a workshop titled Monitoring the Environment: Scales, Methods, and Systems in Historical Perspective. The workshop, sponsored by the Society for the History of Technology and the American Society for Environmental History, examined past efforts to develop tools, methods, and systems for measuring or monitoring some aspect of the physical environment. Four of the papers included here focus on various aspects of air quality monitoring; the fifth has to do with monitoring the earth from space. Despite differences in time period and approach, each article examines how specific tools and methods – and the motivations for developing those tools and methods – evolved. Among other things, these papers make clear that systems for monitoring various aspects of the physical environment are shaped by a variety of stakeholders and suggest that efforts to construct such systems should not be viewed as a purely technical task.  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