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   2204篇
  免费   327篇
  国内免费   694篇
安全科学   372篇
废物处理   45篇
环保管理   269篇
综合类   1475篇
基础理论   522篇
污染及防治   216篇
评价与监测   85篇
社会与环境   155篇
灾害及防治   86篇
  2024年   13篇
  2023年   63篇
  2022年   115篇
  2021年   128篇
  2020年   126篇
  2019年   117篇
  2018年   92篇
  2017年   129篇
  2016年   149篇
  2015年   138篇
  2014年   136篇
  2013年   165篇
  2012年   200篇
  2011年   176篇
  2010年   149篇
  2009年   148篇
  2008年   113篇
  2007年   144篇
  2006年   137篇
  2005年   113篇
  2004年   87篇
  2003年   95篇
  2002年   72篇
  2001年   48篇
  2000年   61篇
  1999年   43篇
  1998年   45篇
  1997年   50篇
  1996年   29篇
  1995年   43篇
  1994年   28篇
  1993年   25篇
  1992年   14篇
  1991年   12篇
  1990年   8篇
  1989年   2篇
  1988年   3篇
  1987年   3篇
  1985年   1篇
  1984年   1篇
  1979年   1篇
  1978年   1篇
  1977年   1篇
  1972年   1篇
排序方式: 共有3225条查询结果,搜索用时 93 毫秒
741.
Natural disasters such as large earthquakes may rapidly result in cascading events such as post-earthquake fires (PEFs) to trigger. This is particularly the case in industrial facilities which is well known as natural-hazard triggered technological accidents (NaTechs). This study provides a response framework for NaTechs caused by earthquake in fuel storage facilities. To do this, seismic vulnerability of fuel storage tanks and possible damage fashions are studied. Considering fuel leakages can result in PEFs, possible scenarios are simulated numerically using Process Hazard Analysis Software Tool (PHAST). A case study including 20 fuel tanks adjacent one to another is investigated to simulate a domino effect when different arbitrary tanks start to ignite; hence, the worst case scenario can be determined. Based on the results of the case studied, inability to extinguish the possible PEFs over less than 9 min can lead to spreading them to the adjacent tanks. The results indicate that it takes about 40 min the adjacent tanks involve in the fires. Therefore, it is of paramount importance to provide an emergency response plan in advance to properly respond to the fires. The study here also highlights the role of preventive strategies in reducing the associated risks of PEFs in industrial facilities.  相似文献   
742.
In recent years, genetic engineering technology has been playing a great role in improving crops. As far as property is concerned, transgenic crops are mainly classified into three types. One is anti-herbicide crops; next is anti-disease and anti-insect pest transgenic crops. The third is high added-value transgenic crops, such as insulin tomatoes China has cultivated. We have successfully expressed hepatitis B virus surface antigen genes in tomatoes and potatoes. Besides, scientists have al…  相似文献   
743.
Some species may have a larger role than others in the transfer of complex effects of multiple human stressors, such as changes in biomass, through marine food webs. We devised a novel approach to identify such species. We constructed annual interaction-effect networks (IENs) of the simulated changes in biomass between species of the southeastern Australian marine system. Each annual IEN was composed of the species linked by either an additive (sum of the individual stressor response), synergistic (lower biomass compared with additive effects), or antagonistic (greater biomass compared with additive effects) response to the interaction effect of ocean warming, ocean acidification, and fisheries. Structurally, over the simulation period, the number of species and links in the synergistic IENs increased and the network structure became more stable. The stability of the antagonistic IENs decreased and became more vulnerable to the loss of species. In contrast, there was no change in the structural attributes of species linked by an additive response. Using indices common in food-web and network theory, we identified the species in each IEN for which a change in biomass from stressor effects would disproportionately affect the biomass of other species via direct and indirect local, intermediate, and global predator–prey feeding interactions. Knowing the species that transfer the most synergistic or antagonistic responses in a food-web may inform conservation under increasing multiple-stressor impacts.  相似文献   
744.
孙昭安  朱彪 《环境科学》2023,44(12):6857-6868
已有研究表明除了作物碳(根际沉积碳和秸秆碳)对农田土壤有机碳(SOC)的输入外,土壤碳还来源于土壤自养微生物固定SOC的贡献以及土壤无机碳(SIC)的固定(无机化学途径和微生物的生物矿化途径).农田SOC的高低主要受到外源作物碳输入和原有SOC分解的平衡作用.作物碳输入在短期内通常促进SOC的分解,呈现正(根际)激发效应.通过整合分析主要作物的根际激发效应和秸秆还田的激发效应的研究,发现作物根系生长和秸秆还田引起的(根际)激发效应大小平均值分别为75%和67%.尽管秸秆还田通过激发效应引起SOC分解的额外释放,但是土壤残留秸秆碳通常大于激发效应导致SOC的额外损失,因此秸秆还田可能增加SOC的储量.在农田系统中,秸秆碳和根际沉积碳往往共存,这导致土壤碳输入和输出至少有3个碳源(根际沉积碳、秸秆碳和土壤碳),由于多碳源体系的区分方法存在挑战,目前这两种作物碳(根际沉积碳和秸秆碳)对SOC分解的激发效应影响是不清晰的.最后,提出了新量化方法,可以多源区分根际CO2排放以及SOC中作物碳输入的碳源,以及区分碱性土壤中无机化学和微生物途径对SIC的贡献.研究有助于提高对农田土壤SOC和SIC输入和输出途径的理解,以及农田土壤碳平衡评估的精确度.  相似文献   
745.
我国钾资源贫乏,目前使用的钾肥主要靠国外进口.通过物理、化学和生物的方法,对云母类矿石进行活化而制成云母类矿物钾肥,不失为解决我国南方土壤钾素缺乏问题的一条有效途径.本文对中科院地化所提供的通过活化处理制取的云母类矿物钾肥进行了肥效试验.结果表明,施用云母类矿物钾肥与施用等钾量的氯化钾相比,无论是作物的吸钾能力,还是土壤的供钾能力.前者都比后者显著提高.因此,开发云母类矿物钾肥资源具有广阔的前景.  相似文献   
746.
The paper presents an inventory, perhaps the most comprehensive till date, of the major process-industry accidents involving ‘domino effect’. The inventory includes, among other relevant information, the sequence of accidents that had occurred in each domino episode. The information has been analyzed to identify several patterns which may be useful in further work on understanding domino effect and reducing the probability of its occurrence in future. A concept of ‘local domino effect’ has been introduced.  相似文献   
747.
Energy efficiency policies have a special importance within carbon emission reduction policies to mitigate the climate change effects. However, potential reductions of energy consumption and, consequently, its resulting emissions, can be offset through the so called “rebound effect”. The concept of “rebound effect” refers to a set of mechanisms whereby the improvement of efficiency reduces the cost of the energy service and this results in the household energy consumption rising and totally or partially negating the reduction achieved by the energy efficiency improvement. This paper provides a methodology to estimate the static direct plus indirect rebound effect of energy efficiency improvements in the use of energy in households. It is based on the combination of econometric estimations of energy demand functions, re-spending modelling and generalised intput-output of energy modelling. It also provides estimations for Catalonia.  相似文献   
748.
加勒比松1a生幼林氮磷钾不同配比的追肥试验表明,追肥后6a,肥效都极显著;其中以第2a的效果最显著,最大树高、胸径、材积分别比不追肥增加39.1%~52.6%、45.4%~109.3%和34.1%~405.6%;6a后肥效下降,但追肥仍比不追肥的树高、胸径、材积增长8.7%~20%、10.9%~17.9%、31.5%~54.7%。氮磷钾配合施用的效果最佳,施氮磷而缺钾有负效应。当氮磷钾相同配比(N30P30K30)时有特殊的低效应。  相似文献   
749.
Natura 2000, the nature network based on the European Bird and Habitat Directives, is explicitly grounded on ecological science. To acquire a permit under the Dutch Nature Conservation Act, an appropriate assessment of significant effects must be conducted based on the best available scientific knowledge. In this way the scientific and policy world are directly linked. This article focuses on ‘significant effect’ as a boundary object to analyse how science–policy interactions shape the meaning and assessment of significant effect and how these interpretations influence the decision-making process. To this end, two conflicts over significant effect are investigated: the conflict over the 2006-spring permit for the mussel seed fishery, and the 2011 permit for the planned World Championship powerboat races. In both cases nature organisations started a court process against the government-granted permits in protest to the “no significant effect” claim, stating that there was insufficient certainty for this conclusion. These conflicts are approached as controversies between discourse coalitions with different interpretations of the ecological knowledge. We show how significant effect became a focal point in the controversies, limiting the debate to ecological arguments and science-based expertise, but also creating options for parties to advance their protest by articulating uncertainties. Only uncertainty of incomplete knowledge was explicitly addressed, excluding ambiguity of values and unpredictability of the actual ecosystem. We suggest that acknowledging the value aspect in disputes on significant effect would leave more space for effective solutions of the problems under debate.  相似文献   
750.
An Allee effect arising from density-dependent mating success can have significant impacts at the ecosystem level when considered in the context of predator-prey interactions. These are captured by a mathematical model for the exchange of biomass between a structured predator population (continuous weight distribution) and a resource. Because the predator’s mating success affects the amount of resources required for the production of offsprings and their future growth into mature organisms, it influences the flux of biomass between trophic levels. Under simple assumptions, the equations can be reduced to an equivalent unstructured predator-prey model in which the Allee effect modulates the predation rate: the mating probability multiplies the rate of predator growth as well as the rate of resource depletion. Implications of the Allee effect for the bifurcation structure and equilibrium densities are examined. The model is compared to a modified version in which the Allee effect instead modulates the assimilation efficiency, hence the mating probability does not appear in the dynamical equation for the resource density. Both models exhibit qualitatively similar dynamics. However, compared to the model in which the Allee effect modulates predation, the model in which the Allee effect modulates assimilation efficiency predicts (i) unrealistically inefficient resource assimilation when predator density is low, (ii) a higher risk of catastrophic extinction resulting from a change in the parameter controlling the strength of the Allee effect, and (iii) no possibility of an increase in population size when the density dependence is enhanced.  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