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   30620篇
  免费   337篇
  国内免费   239篇
安全科学   872篇
废物处理   1098篇
环保管理   4193篇
综合类   4894篇
基础理论   8758篇
环境理论   22篇
污染及防治   8028篇
评价与监测   1809篇
社会与环境   1320篇
灾害及防治   202篇
  2022年   188篇
  2021年   201篇
  2020年   173篇
  2019年   234篇
  2018年   427篇
  2017年   410篇
  2016年   593篇
  2015年   546篇
  2014年   731篇
  2013年   2199篇
  2012年   892篇
  2011年   1317篇
  2010年   1085篇
  2009年   1097篇
  2008年   1311篇
  2007年   1387篇
  2006年   1238篇
  2005年   1043篇
  2004年   1049篇
  2003年   962篇
  2002年   984篇
  2001年   1275篇
  2000年   876篇
  1999年   560篇
  1998年   438篇
  1997年   448篇
  1996年   455篇
  1995年   495篇
  1994年   449篇
  1993年   398篇
  1992年   420篇
  1991年   382篇
  1990年   382篇
  1989年   426篇
  1988年   350篇
  1987年   304篇
  1986年   277篇
  1985年   307篇
  1984年   289篇
  1983年   322篇
  1982年   326篇
  1981年   276篇
  1980年   245篇
  1979年   272篇
  1978年   232篇
  1977年   197篇
  1976年   202篇
  1975年   193篇
  1973年   172篇
  1972年   199篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
911.
Tripa is the last remaining peat-swamp forest that harbours a potentially viable Sumatran orangutan (Pongo abelii) sub-population in a formally but not effectively protected area. It appears to be a simple showcase where current efforts to financially support reducing emissions from deforestation and forest degradation (REDD+) converge with biodiversity and social co-benefits. In practice, however, situation is more complex. REDD+ efforts interact with global palm oil trade and regulatory approaches (the moratorium) to achieve national goals for emissions reduction under umbrella of nationally appropriate mitigation actions (NAMA). To contextualize this debate, we assessed (i) land-use history and formal basis of palm-oil companies’ rights; (ii) carbon (C) stocks, historical emission levels and potential emissions that can be avoided; (iii) economic benefits of land-use options and opportunity costs of avoiding emissions; (iv) biodiversity and environmental services; and (v) alternative options for “high C stock development” and employment generation. Natural forest cover declined (54 % in 1995, 18 % in 2009) while oil palm increased 4–39 %. Aboveground C stocks decreased from 148 Mg ha?1 in 1990 to 61 Mg ha?1 in 2009, leading to average annual emissions of 14.5 Mg (carbon dioxide) CO2e ha?1 year?1. While 41 % of these emissions yield less than American Dollar (USD) 5 of current economic benefits per Mg CO2e emitted and might be compensated by REDD+, nearly all new emissions derive from a breach of existing laws, regulations and voluntary palm-oil standards. Substantial investment in alternative employment is needed, rather than carbon payments per se, to support livelihoods in a low carbon emissions economy.  相似文献   
912.
In many insect species, sperm-depleted males (SDMs, i.e. males that have exhausted their sperm after a given number of matings) remain sexually active and continue to mate females. Here, we investigated the behavioural modifications that occur in both sexes of the parasitoid Asobara tabida Nees (Hymenoptera: Braconidae), after matings by fertile males and sperm-depleted males. We show that (i) virgin females, mated females and females mated to a SDM exhibited different behaviours and that (ii) males responded differently to females depending on whether the females had previously mated with an SDM or not. Our findings demonstrate that SDM influenced the reproductive behaviour of both males and females, especially with regard to male responsiveness and female attractiveness. These findings are discussed in the context of adaptive behaviour and fitness maximization in both males and females.  相似文献   
913.
Hypotheses of feeding behaviors and community structure are testable with rare direct evidence of trophic interactions in the fossil record (e.g., bite marks). We present evidence of four predation, scavenging, and/or interspecific fighting events involving two large paracrocodylomorphs (=‘rauisuchians’) from the Upper Triassic Chinle Formation (~220–210 Ma). The larger femur preserves a rare history of interactions with multiple actors prior to and after death of this ~8–9-m individual. A large embedded tooth crown and punctures, all of which display reaction tissue formed through healing, record evidence of a failed attack on this individual. The second paracrocodylomorph femur exhibits four unhealed bite marks, indicating the animal either did not survive the attack or was scavenged soon after death. The combination of character states observed (e.g., morphology of the embedded tooth, ‘D’-shaped punctures, evidence of bicarination of the marking teeth, spacing of potentially serial marks) indicates that large phytosaurs were actors in both cases. Our analysis of these specimens demonstrates phytosaurs targeted large paracrocodylomorphs in these Late Triassic ecosystems. Previous distinctions between ‘aquatic’ and ‘terrestrial’ Late Triassic trophic structures were overly simplistic and built upon mistaken paleoecological assumptions; we show they were intimately connected at the highest trophic levels. Our data also support that size cannot be the sole factor in determining trophic status. Furthermore, these marks provide an opportunity to start exploring the seemingly unbalanced terrestrial ecosystems from the Late Triassic of North America, in which large carnivores far outnumber herbivores in terms of both abundance and diversity.  相似文献   
914.
为探讨纳米Fe0粒子对产乙烯脱卤菌群脱氯性能和物种多样性的影响,采用纳米Fe0粒子与产乙烯脱卤菌群联合脱氯,并通过气相色谱、PCR-DGGE和TEM等技术手段进行相关表征.结果表明:当纳米Fe0粒子浓度为0~0.50 g·L-1时,体系的脱氯速率提高较小,低于40%,且菌种数量无明显变化;当其浓度为0.50~1.00 g·L-1时,体系的脱氯速率由0.31μmol·h-1提高到0.77μmol·h-1,体系的脱氯速率提高了60%,部分DGGE条带消失,多样性减少.TEM结果显示,产乙烯脱卤拟球菌在与纳米Fe0粒子接触部位有轻度破损,但细胞没有破裂.纳米Fe0粒子浓度较高时对产乙烯脱卤菌群的脱氯有明显的促进作用,但会使产乙烯脱卤菌群物种多样性减少.  相似文献   
915.
Enteric viruses transmitted via the faecal-oral route occur in high concentrations in wastewater and may contaminate drinking water sources and cause disease. In order to quantify enteric adenovirus and norovirus genotypes I and II (GI and GII) impacting a drinking source in Norway, samples of surface water (52), wastewater inlet (64) and outlet (59) were collected between January 2011 and April 2012. Samples were concentrated in two steps, using an electropositive disc filter and polyethylene glycol precipitation, followed by nucleic acid extraction and analysis by quantitative polymerase chain reaction. Virus was detected in 47/52 (90.4 %) of surface water, 59/64 (92 %) of wastewater inlet and 55/59 (93 %) of wastewater outlet samples. Norovirus GI occurred in the highest concentrations in surface water (2.51e + 04) and adenovirus in wastewater (2.15e + 07). While adenovirus was the most frequently detected in all matrices, norovirus GI was more frequently detected in surface water and norovirus GII in wastewater. This study is the first in Norway to monitor both sewage and a drinking water source in parallel, and confirms the year-round presence of norovirus and adenovirus in a Norwegian drinking water source.  相似文献   
916.
Noroviruses (NoVs) are responsible for numerous cases of waterborne and foodborne gastroenteritis every year. They are released in the sewage and their detection in this environment can reflect the epidemiology of the viral strains circulating in the community. A three-year (2007–2010) survey was conducted in order to evaluate the presence of human NoVs using RT-PCR in 518 sewage samples collected at the entrance and exit of two biological sewage treatment plants located in Monastir region, Tunisia. In this study, we aimed to genetically characterize the most prevalent GI and GII NoV strains, in order to obtain a rough estimate of the efficacy of disinfection treatments and to compare the results with clinical data documented in the same area during the same period. This work confirms the wide circulation and the genetic diversity of NoVs in Tunisia and the widespread distribution of NoV variants in both raw and treated wastewater. Indeed, NoV was detected in 192 (37.1 %) sewage samples, among them mixed infections with group A rotavirus were detected in 125 (65.1 %) cases. The genotypes of the GI NoVs were GI.1, GI.2, GI.4, GI.5, and GI of unassigned genotype (GI.UA), and the genotypes of the GII NoVs were all GII.12. This study enhances the currently poor environmental virological data gathered in Tunisia, demonstrates the benefit of environmental surveillance as a tool to determine the epidemiology of NoVs circulating in a given community, and underlines the need for the design and support of similar long-term studies in our country, in order to compensate for the absence of a national surveillance system for gastroenteric viruses.  相似文献   
917.
Differential migration has been extensively reported in spring, but less so in autumn, particularly in relation to sex in monomorphic bird species. Here, we analysed the autumn passage of a monomorphic, globally threatened passerine, the Aquatic Warbler Acrocephalus paludicola throughout Western Europe, with regard to age and sex. We showed that, overall, adults migrated earlier than first-year birds, and males migrated earlier than females during the autumn migration. This may be caused by an overall social dominance of adults over immatures, and differentiated migration strategy of males and females. In addition, we found male-skewed sex proportions, with a tendency to an equalised ratio in more southern stopover sites. This may indicate a male bias in the global population or different migration strategies of the sexes. Differential migration may cause the age and sex classes to be exposed differently to various threats affecting demographic structure of the species.  相似文献   
918.
Freshwater cyanobacterial blooms have drawn public attention because they threaten the safety of water resources and human health worldwide. Heavy cyanobacterial blooms outbreak in Lake Taihu in summer annually and vanish in other months. To find out the factors impacting the cyanobacterial blooms, the present study measured the physicochemical parameters of water and investigated the composition of microbial community using the 16S rRNA gene and internal transcribed spacer amplicon sequencing in the months with or without bloom. The most interesting finding is that two major cyanobacteria, Planktothrix and Microcystis, dramatically alternated during a cyanobacterial bloom in 2016, which is less mentioned in previous studies. When the temperature of the water began increasing in July, Planktothrix appeared first and showed as a superior competitor for M. aeruginosa in NO3?-rich conditions. Microcystis became the dominant genus when the water temperature increased further in August. Laboratory experiments confirmed the influence of temperature and the total dissolved nitrogen (TDN) form on the growth of Planktothrix and Microcystis in a co-culture system. Besides, species interactions between cyanobacteria and non-cyanobacterial microorganisms, especially the prokaryotes, also played a key role in the alteration of Planktothrix and Microcystis. The present study exhibited the alteration of two dominant cyanobacteria in the different bloom periods caused by the temperature, TDN forms as well as the species interactions. These results helped the better understanding of cyanobacterial blooms and the factors which contribute to them.  相似文献   
919.
Trichloroethylene (TCE) is a toxic organic compound, which can adversely affect human health. The chemical is one of the most frequently found contaminants in groundwater in the United States and around the world. A landfill in Maryland contaminated with high levels of TCE decades ago was added to the U.S. Environmental Protection Agency's National Priority List (NPL) in 1994. A biowall was installed on the site in 2013 to promote the bioremediation of TCE and subsequently of its degradation products. Six-year monitoring data indicated a steady removal of >99% groundwater TCE at the wall since installation. However, a concurrent buildup of intermediate byproducts was observed downgradient of the wall. An examination of the entire system was necessary to find the reason behind the inefficiency of the biowall. In this study, the background of the site, remediation plan, and installation were assessed. Monitoring data, including the concentration of TCE and its degradation byproducts, and geochemical and physical characteristics were evaluated to understand the conditions and challenges facing decision-makers of this project and possible options to improve biowall efficacy.  相似文献   
920.
Journal of Material Cycles and Waste Management - The use of lignocellulosic fibers as fillers in polymer matrices has aroused the interest of the scientific community and industrial sectors. In...  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