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   554篇
  免费   59篇
  国内免费   5篇
安全科学   43篇
废物处理   22篇
环保管理   147篇
综合类   131篇
基础理论   118篇
污染及防治   93篇
评价与监测   34篇
社会与环境   19篇
灾害及防治   11篇
  2025年   3篇
  2024年   7篇
  2023年   15篇
  2022年   14篇
  2021年   17篇
  2020年   19篇
  2019年   11篇
  2018年   14篇
  2017年   19篇
  2016年   20篇
  2015年   16篇
  2014年   21篇
  2013年   37篇
  2012年   21篇
  2011年   28篇
  2010年   21篇
  2009年   21篇
  2008年   34篇
  2007年   30篇
  2006年   33篇
  2005年   18篇
  2004年   19篇
  2003年   22篇
  2002年   20篇
  2001年   18篇
  2000年   15篇
  1999年   8篇
  1998年   7篇
  1997年   8篇
  1996年   7篇
  1995年   10篇
  1994年   6篇
  1993年   2篇
  1992年   6篇
  1991年   3篇
  1990年   2篇
  1989年   4篇
  1988年   2篇
  1986年   2篇
  1985年   3篇
  1983年   4篇
  1981年   6篇
  1980年   4篇
  1979年   3篇
  1977年   2篇
  1976年   4篇
  1970年   1篇
  1969年   1篇
  1966年   1篇
  1935年   1篇
排序方式: 共有618条查询结果,搜索用时 15 毫秒
191.
This paper presents a general framework for constructing a predictive distribution of the exposure to an environmental hazard sustained by a randomly selected member of a designated population. The individual’s exposure is assumed to arise from random movement through the environment, resulting in a distribution of exposure that can be used for environmental risk analysis. A specialization of the general framework is that of predicting human exposure to air pollution that can be used to develop models for such things as exposure to particulate matter; practical aspects of their construction are considered. These models can help answer questions such as what fraction of the population sustained ‘high’ levels of exposure for say 5 days in a row. The immediate implementation of the above framework takes the form of a computing platform referred to as pCNEM. This provides a facility for simulating exposures to airborne pollutants and is described in detail elsewhere. This paper considers some theoretical aspects underpinning probabilistic exposure models of this type, with the ideas illustrated in developing a model for predicting human exposure to PM 10.  相似文献   
192.
季节性干旱现象在我国中亚热带地区时有发生,为了研究该区域大气-生态系统之间的相互作用关系及其碳水收支状况,2002年起在江西省千烟洲(26.7°N,115.1°E)人工林生态系统建立了通量观测塔。2003年7月该人工林生态系统遭遇了历史上少有的高温少雨天气,本研究应用基于生理生态学过程的EALCO(Ecological Assimilation of Land and Climate Observation)模型及2003和2004年通量观测数据对该生态系统的水热通量进行了模拟,同时分析了干旱胁迫对它们产生的影响。结果显示,模型能够很好的模拟该生态系统的能量通量的日变化,净辐射、显热和潜热通量模拟值与实测值相关系数的平方(R2)及标准差分别为0.99和8.05 W.m-2;0.81和41.02 W.m-2;0.90和31.49 W.m-2,模型可以解释87%的日蒸散量的变化。从模拟结果看,2003年7月下旬(发生较严重干旱胁迫)较2004年同期(干旱程度轻)相比,冠层及土壤水势下降约2倍,植物蒸腾的日变化形式改变,根系吸水滞后冠层蒸腾的时间缩短约半小时,冠层导度下降40%~60%。模拟与观测结果均表明,2003年7月下旬每天正午的波文比大都介于1~2.2,而2004年同期正午的波文比则介于0.2~0.6。EALCO模型通过Ball模型将植物碳水过程耦合在一起,从而可以很好的模拟植物的气孔行为,进而准确的模拟植物水热过程对干旱的响应。土壤水分匮乏对冠层导度的限制是2003年干旱期间冠层潜热通量模拟值下降的根本原因。  相似文献   
193.
Average radial growth rates of the hemispherical aragonite colonies deposited by the Indo-Pacific scleractinian reef coral Platygyra spp. were determined by measuring the thickness of density variations in the skeleton that are revealed by X-radiography. Ninety-one specimens from 21 localities were examined, but only 54 of these exhibited well-defined growth-banding. The apparent temperature dependence of growth rate is linear over the range 23.9° to 29.3°C, averaging 5.4±0.94 mm/year at 24°C, 8.0±0.42 mm/year at 27°C, and 9.7 ±0.58 mm/year at 29°C (90% confidence limits). Expression of the influence of temperature on growth rate in terms of the Arrhenius equation yields an activation energy of 20,680 cal/mole, which is comparable to values for typical biological reactions, but is only half that reported for skeletogenesis in another reef coral, Pocillopora damicornis, on the basis of controlled incubation studies involving 45Ca uptake.  相似文献   
194.
    
W. White  N. Hall  I. Potter 《Marine Biology》2002,141(6):1153-1164
The lengths-at-age of individuals of the nervous shark Carcharhinus cautus in Shark Bay, Western Australia, have been determined and used to explore the types of situation when it might be advisable to shift from employing a von Bertalanffy equation to a more complex equation for describing the growth of this species and of elasmobranchs in general. The reproductive biology of C. cautus was also examined in order to construct curves for describing growth throughout life from conception as well as from parturition. The presence, in November and early December, of fresh bite marks on the sides of mature females and of a very high proportion of spent individuals among mature males indicate that C. cautus copulates in late October/early November. Ovulation and conception occur in late November/early December and parturition takes place approximately 11 months later. Since mature non-pregnant females contain vitellogenic ova for 12-13 months, i.e. from November or December to the following December, and mature pregnant females contain embryos for 11 months, i.e. from December to October, C. cautus has a biennial reproductive cycle. By parturition, the females and males of C. cautus had reached ~28% and 32% of their lengths at their maximum observed ages, respectively. The maximum recorded total lengths and ages of females and males of C. cautus were 133 cm and 16 years and 111 cm and 12 years, respectively. Females and males reached maturity at ~101 and ~91 cm, respectively, and at least 50% of females and males had become mature by the end of their sixth and fourth years of life after parturition, respectively. The three-parameter, von Bertalanffy growth curves provided reasonably good fits to the lengths-at-age of females and males of C. cautus during just postnatal life and throughout the whole of pre- and postnatal life. While the four-parameter, Schnute growth curve significantly improved the fit to these data for both females and males from conception and for females from parturition, it was recognised that the likelihood ratio test is very sensitive when, as in these cases, there are a large number of data points. A number of interrelated factors were thus taken into account when discussing circumstances when it might be appropriate to switch from using a von Bertalanffy growth curve to the more complex Schnute growth curve.  相似文献   
195.
196.
Samples have been collected from major horizons of 34 podzol profiles distributed throughout Scotland, all developed from granite or granitic tills and under Calluna moorland. the pH in water and calcium chloride pastes, exchangeable cations and cation exchange capacity, and extractable aluminium of the soils collected have been measured, and the results studied in relation to reported atmospheric deposition of H+, non-marine sulphur and nitrate. for all horizons, significant positive correlations were found between soil pH and rainfall mean pH, as might be expected when the critical load of H+ deposition is exceeded. Acidifying pollutant deposition also apparently increased soil extractable aluminium concentrations in the B and C horizons. However, exchangeable base cation concentrations tended to increase, rather than decrease, with increasing precipitation acidity. This effect was attributed to increases in biogeochemical cycling of base cations, increases in leaching inputs of base cations from overlying A/E horizon soils, and increases in the inputs of base cations leached from upslope. the results suggest that the simple steady state mass approach to the quantification of critical loads, as often applied, may be an oversimplification.  相似文献   
197.
Rich PM  Breshears DD  White AB 《Ecology》2008,89(2):342-352
Ecosystem responses to key climate drivers are reflected in phenological dynamics such as the timing and degree of "green-up" that integrate responses over spatial scales from individual plants to ecosystems. This integration is clearest in ecosystems dominated by a single species or life form, such as seasonally dynamic grasslands or more temporally constant evergreen forests. Yet many ecosystems have substantial contribution of cover from both herbaceous and woody evergreen plants. Responses of mixed woody-herbaceous ecosystems to climate are of increasing concern due to their extensive nature, the potential for such systems to yield more complex responses than those dominated by a single life form, and projections that extreme climate and weather events will increase in frequency and intensity with global warming. We present responses of a mixed woody-herbaceous ecosystem type to an extreme event: regional-scale pi?on pine mortality following an extended drought and the subsequent herbaceous green-up following the first wet period after the drought. This example highlights how reductions in greenness of the slower, more stable evergreen woody component can rapidly be offset by increases associated with resources made available to the relatively more responsive herbaceous component. We hypothesize that such two-phase phenological responses to extreme events are characteristic of many mixed woody-herbaceous ecosystems.  相似文献   
198.
199.
Global increases in ultraviolet‐B radiation (UVBR) associated with stratospheric ozone depletion are potentially contributing to the decline of numerous amphibian species around the world. Exposure to UVBR alone reduces survival and induces a range of sublethal effects in embryonic and larval amphibians. When additional environmental stressors are present, UVBR can have compounding negative effects. Thus, examination of the effects of UVBR in the absence of other stressors may substantially underestimate its potential to affect amphibians in natural habitats. We examined the independent and interactive effects of increased UVBR and high conspecific density would have embryonic and larval striped marsh frogs (Limnodynastes peronii). We exposed individuals to a factorial combination of low and high UVBR levels and low, medium, and high densities of striped marsh frog tadpoles. The response variables were time to hatching, hatching success, posthatch survival, burst‐swimming performance of tadpoles (maximum instantaneous swim speed following an escape response), and size and morphology of tadpoles. Consistent with results of previous studies, we found that exposure to UVBR alone increased the time to hatching of embryos and reduced the burst‐swimming performance and size of tadpoles. Similarly, increasing conspecific density increased the time to hatching of embryos and reduced the size of tadpoles, but had no effect on burst‐swimming performance. The negative effect of UVBR on tadpole size was not apparent at high densities of tadpoles. This result suggests that tadpoles living at higher densities may invest relatively less energy in growth and thus have more energy to repair UVBR‐induced damage. Lower densities of conspecifics increased the negative effects of UVBR on developing amphibians. Thus, low‐density populations, which may include declining populations, may be particularly susceptible to the detrimental effects of increased UVBR and thus may be driven toward extinction faster than might be expected on the basis of results from single‐factor studies. Relaciones entre la Densidad Conespecífica y los Efectos de la Radiación Ultravioleta‐B sobre el Tamaño de Renacuajos de Limnodynastes peronei  相似文献   
200.
纳米零价铁(nanoscale zero-valent iron, nZVI)具有污染物去除效率高、易制备、成本低、环境友好等优点,在环境修复领域得到广泛应用。目前针对nZVI的研究热点是通过改性,改善其易团聚、易被氧化等缺点并提升修复性能。本研究将负载法和聚合物包覆改性法相结合,使用活性炭和绿色无毒聚天冬氨酸(polyaspartic acid, PASP)对nZVI起到了良好的稳定和缓释效果,减少了nZVI的团聚并增大了比表面积、延长了反应平衡时间,显著提升了对水中Cr(Ⅵ)的去除效果。铁碳比为2∶1时,复合材料的修复性能是nZVI与活性炭单独处理加和的1.75倍,最高可去除99.91%的Cr(Ⅵ)。本研究还通过正交实验筛选了复合材料的最佳制备条件,分析了C-PASP-nZVI投加量、污染物浓度和pH对含Cr(Ⅵ)废水修复效果的影响。C-PASP-nZVI对Cr(Ⅵ)的吸附动力学过程符合Lagergren准二级模型,说明复合材料对Cr(Ⅵ)的去除过程由化学吸附主导。以上研究结果表明,C-PASP-nZVI是一种可用于重金属污染水体修复的潜在理想材料。  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