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   449篇
  免费   3篇
  国内免费   29篇
安全科学   13篇
废物处理   11篇
环保管理   153篇
综合类   151篇
基础理论   100篇
污染及防治   17篇
评价与监测   9篇
社会与环境   25篇
灾害及防治   2篇
  2023年   2篇
  2022年   1篇
  2021年   2篇
  2020年   7篇
  2019年   3篇
  2018年   5篇
  2017年   9篇
  2016年   7篇
  2015年   12篇
  2014年   24篇
  2013年   27篇
  2012年   18篇
  2011年   28篇
  2010年   13篇
  2009年   32篇
  2008年   34篇
  2007年   25篇
  2006年   20篇
  2005年   25篇
  2004年   16篇
  2003年   17篇
  2002年   18篇
  2001年   14篇
  2000年   15篇
  1999年   12篇
  1998年   8篇
  1997年   10篇
  1996年   7篇
  1995年   9篇
  1994年   7篇
  1993年   4篇
  1992年   2篇
  1991年   4篇
  1990年   1篇
  1989年   3篇
  1988年   3篇
  1987年   4篇
  1986年   3篇
  1985年   3篇
  1984年   8篇
  1983年   4篇
  1982年   5篇
  1981年   1篇
  1980年   2篇
  1979年   4篇
  1978年   2篇
  1977年   1篇
排序方式: 共有481条查询结果,搜索用时 15 毫秒
41.
树脂吸附法处理邻甲苯胺生产废水的研究   总被引:6,自引:0,他引:6  
在最佳工艺条件下,采用NDA-804树脂对邻甲苯胺生产废水进行吸附-脱附实验。原废水经吸附处理后,邻甲苯胺去除率和CODcr去除率均大于99%.树脂脱附率接近100%。高浓度脱附液可以回收邻甲苯胺,达到了废水治理与资源化的效果。  相似文献   
42.
溪源宫水源保护区浮游植物群落结构分析研究   总被引:1,自引:0,他引:1  
文章主要对2011年8月至12月溪源宫水源保护区浮游植物群落结构进行调查分析。溪源宫水体共鉴定出浮游植物6门51属137种,主要都是以绿藻门、硅藻门、蓝藻门为主。通过采用浮游植物生物量以及多样性指数对研究区域水体进行了评价,结果表明溪源宫水源保护区水质状况较好。同时还将溪源宫水源保护区、闽江、山仔水库等不同水源地的浮游植物群落结构进行对比分析,发现不同营养状态下,水体中浮游植物群落结构有显著的不同。  相似文献   
43.
A long-standing hypothesis in behavioural ecology posits that males with greater resource-holding potential (RHP) control resource sites deemed more valuable by sexually-receptive females and, thereby, males controlling such sites accrue greater reproductive success (RS). This hypothesis has historically been investigated using three separate but non-mutually exclusive relationships (male RHP vs. resource value, resource value vs. male RS and male RHP vs. RS). The relationships between these three variables are predicted to be strongly positive, however, due to measurement error and biological noise, perfect correlations (r = 1.0) are rare in biology even for well-established relationships. Moreover, the inaccurate identification of either the male trait(s) important to RHP or the resource characteristic sought by females will weaken the observed strength of the relationships. Here, I use meta-analysis to quantitatively describe the general pattern of these relationships in animals. I predict that the relationships between male RHP, resource-value and RS should be significantly positive (male RHP and resource-value should explain a large amount of the variation in male RS). My meta-analysis supports this hypothesis; however, in the best case scenario only ca. 20% of the variation in the response variable was explained. I conclude by identifying areas in which we need to improve our investigations of resource-defence animals and recommending approaches to meet these needs. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.  相似文献   
44.
The synergies and trade-offs between the water, energy, and food sectors are represented by the Water-Energy-Food Nexus. The Nexus Approach is an integrated decision making practice that can be used by policy makers to optimize these synergies and manage trade-offs. In this paper, the direction of the Nexus Approach regarding the development of modelling tools is explored. The objective of this paper is to review the existing Nexus modelling tools used for integrated policy making to determine and to help policy makers, practitioners, and agencies trying to implement the Nexus Approach to identify a tool that is most suited to their modelling needs. The predominant capabilities of the current tools lie in the understanding of Nexus complexity, consideration of financial elements in the tools, recognition of the importance of multiple Nexus Approach directions, incorporation of different time scales, and enhanced tool accessibility. The main limitations are the extensive data requirements of current tools, and the poor synergy between tools assessing individual Nexus areas. This enhanced overview of the existing tools allows policy makers to maximize the synergies between the Nexus areas, to avoid consumption dilemmas, and to facilitate sustainable development.  相似文献   
45.
Environmental Management - Are societal wastes all bad? Some of them, including heat from power plants and certain organic wastes, have been demonstrated to be potentially valuable for growing...  相似文献   
46.
Naturally-occurring infanticide was observed in a population of California ground squirrels (Spermophilus beecheyi). In four seasons, 40 infanticides were observed. All victims were post-emergent pups. Of 37 killings in which the killer was sexed 36 were by females. All infanticidal females were mothers at the time they killed, but in no case was a mother seen to kill or harm her own young. The victim was cannibalized in 22 cases and taken immediately into the killer’s burrow in 16 others. In no case did killers gain access to the victimized mother’s burrow or territory and female pups were not killed preferentially over males. In light of evolutionary explanations, infanticide in this population may best fit the resource exploitation hypothesis, in which killers commit infanticide to gain a nutritional benefit. Resource competition is a possible auxiliary explanation, since any time a female kills unrelated young she is eliminating possible competitors to her own offspring. This behavior could confer a fitness advantage on killers or it could be an adaptively neutral, alternative feeding strategy. More data are necessary to distinguish between these hypotheses. Received: 26 January 1995/Accepted after revision: 9 September 1995  相似文献   
47.
Once the ‘risk’ of the industry is recognized, there are at least two sources of higher-than-normal returns to investment in mineral extraction: Ricardian rents to resources with different economic qualities and monopoly rents. An estimate of the relative importance of these sources in the Canadian nickel industry over the period 1961-74 is made and it is found that Ricardian rents and, for one firm, monopoly rents, were important.  相似文献   
48.
人工接种堆肥和自然堆肥微生物区系与分子多态性的变化   总被引:5,自引:1,他引:5  
采用传统培养方法和PCR-DGGE技术研究了人工接种堆肥和自然堆肥微生物群落的演变过程。结果表明:(1)传统培养方法显示,两种堆肥堆制过程中微生物数量均呈“升高—降低—升高—降低”变化趋势,整个堆肥过程中细菌数量占优势。(2)DGGE图谱显示,两种堆肥不同时期存在不同的细菌种群,其条带数量亦呈“升高—降低—升高—降低”变化趋势。堆肥升温期条带丰富但优势条带不明显;堆肥高温期条带数量减少但出现优势条带,表明高温阶段以嗜热菌或耐高温菌为主;堆肥降温期条带数量再次增多;堆肥腐熟期条带数量少且无优势条带,表明腐熟阶段微生物种群数量少且代谢强度趋于平缓。(3)DGGE图谱表明,人工接种菌株成为堆肥高温期优势菌株。人工接种增加了堆肥中微生物总量,提高了堆肥微生物种群多样性,并且促进了堆肥菌群演替,从而缩短堆肥腐熟时间。  相似文献   
49.
湖南木兰科植物资源的调查研究   总被引:2,自引:0,他引:2  
本文分析了湖南木兰科分布的自然条件,结合其形态性状讨论了它们的分类学问题、地理分布特点、资源状况以及自然生长状况。文末提出了湖南省木兰科的保护植物名单。  相似文献   
50.
Colony level sex allocation in a polygynous and polydomous ant   总被引:2,自引:0,他引:2  
The colony-level sex allocation pattern of eusocial Hymenoptera has attracted much attention in recent studies of evolutionary biology. We conducted a theoretical and empirical study on this subject using the dolichoderine ant Technomyrmex albipes. This ant is unusual in having a dispersal polymorphism in both males and females. New colonies are founded by an alate female after mating with one or more alate males in the nuptial flight. In mature colonies, the reproductive role of the foundress queen is taken over by wingless offspring (supplementary reproductives). Mature colonies are extremely polygynous, with many wingless queens reproducing through intea-colonial mating with wingless males (inbreeding), and producing both alate and wingless sexuals. The population sex ratio of wingless sexuals was found to be extremely female-biased, while the population allocation ratio of alates was almost 1:1. This result suggests that there is local mate competition among wingless sexuals. A specific model for this extraordinary life cycle predicted that the asymmetry of regression relatedness (b f/b m) will disappear during the first few generations of wingless reproductives after the foundress dies. If colonies begin to produce alates after several wingless generations, this undermines the hypotheses for intercolonial sex ratio variation based on the relatedness asymmetry. We compared the magnitude of variation in sex ratios and other characteristics between two levels (within-colony-inter-nest and between-colony). Although there was considerable within-colony variation in all the examined characteristics, between-colony variances were always larger. This means that allocation is important at the whole-colony level, not that of the nest. There was no apparent correlation between the sex ratio of alates and colony size. Furthermore, partial correlation analysis indicated that neither the number of workers nor investment in alates explained the variation in the sex ratio of alates. The only factor which was significantly correlated with the sex ratio of alates was the sex ratio of wingless sexuals (a positive correlation). We conclude that both the alate and wingless sex ratios may be influenced by a common primary sex ratio at the egg stage, the variance of which may have genetic components. In the wingless sexuals, partial correlation analysis indicated that colony size and the number of workers explained the sex allocation ratio. The number of wingless females was strongly (positively) correlated with the total investment in wingless sexuals, while the number of males showed no such correlation. There is, however, no convincing explanation for the variation in sex allocation ratio of wingless sexuals, because the estimates of investment in wingless males may have a large sampling error. Correspondence to: K. Tsuji  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