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   3111篇
  免费   34篇
  国内免费   14篇
安全科学   163篇
废物处理   154篇
环保管理   644篇
综合类   355篇
基础理论   746篇
环境理论   5篇
污染及防治   756篇
评价与监测   212篇
社会与环境   106篇
灾害及防治   18篇
  2024年   12篇
  2023年   32篇
  2022年   40篇
  2021年   32篇
  2020年   28篇
  2019年   41篇
  2018年   66篇
  2017年   67篇
  2016年   93篇
  2015年   58篇
  2014年   86篇
  2013年   283篇
  2012年   145篇
  2011年   178篇
  2010年   122篇
  2009年   123篇
  2008年   156篇
  2007年   189篇
  2006年   152篇
  2005年   105篇
  2004年   106篇
  2003年   116篇
  2002年   90篇
  2001年   68篇
  2000年   46篇
  1999年   52篇
  1998年   38篇
  1997年   44篇
  1996年   45篇
  1995年   42篇
  1994年   42篇
  1993年   34篇
  1992年   37篇
  1991年   26篇
  1990年   29篇
  1989年   19篇
  1988年   13篇
  1987年   20篇
  1986年   25篇
  1985年   17篇
  1984年   18篇
  1983年   28篇
  1982年   28篇
  1981年   25篇
  1980年   19篇
  1979年   16篇
  1977年   11篇
  1975年   9篇
  1974年   10篇
  1971年   11篇
排序方式: 共有3159条查询结果,搜索用时 15 毫秒
161.
162.
Insecticides in health,agriculture and the environment   总被引:2,自引:0,他引:2  
  相似文献   
163.
    
Fog harvesting is useful for passively collecting fresh water in arid regions, but the efficiency of current mesh‐based harvesters is compromised by their poor drainage. Inspired by the linear needles of redwood trees, “fog harps” are developed whose array of vertical wires enables an unobstructed drainage pathway. A full‐scale (1 m2 frame) fog harp is fabricated by winding a stainless steel wire around a spinning aluminum frame featuring threaded rods. The fog harp is field tested for a full year at a local farm (Blacksburg, VA, USA), alongside the control case of a mesh harvester. Under moderate fog conditions, the fog harp collects anywhere from 2 to 78 times more water compared to the mesh harvesters. Under light fog conditions, the fog harp collects up to several hundred milliliters of water per day while the mesh is unable to collect any water at all. The water harvesting performance of fog harps is therefore unprecedented in two ways: they substantively elevate the performance ceiling when exposed to healthy fog while also enabling, for the first time, appreciable water harvesting under light fog.  相似文献   
164.
Applications of in situ agrobiodiversity conservation practices within agricultural production systems have the potential to reduce the risks of agricultural modernisation and enhance sustainable development. The aims and approaches for in situ conservation differ according to the requirements of communities and nations. Approaches to in situ conservation in the decade after the Convention of Biological Diversity are reviewed within the contexts of marginal agricultural systems in Nepal, Turkey and Switzerland. Numerous approaches are currently utilised, including: the informal de facto retention of agrobiodiversity; the provision of state assistance; the marketing of agrobiodiversity products; the use of technological innovations to develop local diversity; the establishment of conservation reserves; community assistance programmes and the raising of awareness of the issue amongst all sectors of societies. Emerging complementary in situ approaches applicable in the rural margins suggest a framework for effectively conserving agrobiodiversity by working with local people.  相似文献   
165.
Ant colonies are factories within fortresses (Oster and Wilson 1978). They run on resources foraged from an outside world fraught with danger. On what basis do individual ants decide to leave the safety of the nest? We investigated the relative roles of social information (returning nestmates), individual experience and physiology (lipid stores/corpulence) in predicting which ants leave the nest and when. We monitored Temnothorax albipennis workers individually using passive radio-frequency identification technology, a novel procedure as applied to ants. This method allowed the matching of individual corpulence measurements to activity patterns of large numbers of individuals over several days. Social information and physiology are both good predictors of when an ant leaves the nest. Positive feedback from social information causes bouts of activity at the colony level. When certain social information is removed from the system by preventing ants returning, physiology best predicts which ants leave the nest and when. Individual experience is strongly related to physiology. A small number of lean individuals are responsible for most external trips. An individual’s nutrient status could be a useful cue in division of labour, especially when public information from other ants is unavailable.  相似文献   
166.
    
Building of dams and subsequent abstraction upstream of rivers significantly affects major wetland systems. Knowledge of anthropogenic impacts of river regulation, relative to stochastic variation, is essential if managers are able to adequately manage flows to wetlands. We built annual flow and inundated area models for the Macquarie Marshes supplied by the Macquarie River, based on available annual rainfall data (1879–2006). We used LOESS, the flexible local polynomial regression method, ideal for modelling complex processes where no theoretical models exist. To compare effects of river regulation and abstraction, we developed two models, before river regulation (‘natural’ or ‘unregulated’) and after river regulation (‘regulated’). The division was when Burrendong dam, the most significant regulatory structure affecting flows, was built in 1963 and completed in 1967. After this point, water was diverted upstream, predominantly for irrigation. We developed ‘natural’ and ‘regulated’ flow models for three flow gauges Dubbo, Warren and Oxley based on annual rainfall at rainfall stations in the upper catchment and flow, and then inundated area models based on flow and local rainfall to fit annual inundated area data (1979–2006) in the Macquarie Marshes, using LOESS and leave‐one‐out samples without overfitting. We evaluated the performance of the proposed models and used these models to predict annual flows and inundated areas from 1879 to 2006. Comparison was done in terms of ‘natural’ and ‘regulated’ data using Kolmogorov–Smirnov test, identifying significant reductions in flow and wetland area. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   
167.
Fetal triploidy is commonly found in early pregnancy. The majority of these pregnancies spontaneously abort in the first trimester. Occasionally, the pregnancy progresses to the second and third trimesters. We reviewed the maternal serum alpha-fetoprotein (MSAFP), amniotic fluid alpha-fetoprotein (AFP), amniotic fluid acetylcholinesterase (ACHE), fetal pathology, and placental pathology in sex second-trimester pregnancies complicated by fetal triploidy. Four of these patients had MSAFP values greater than 7.5 multiples of the median (MoM). Five of six pregnancies had MSAFP values greater than 2.25 MoM. All five of these patients had a partial mole. Four patients had amniotic fluid AFP values greater than 2.0 MoM. Two fetuses had associated neural tube defects. These were the only patients with positive amniotic fluid ACHE. None of the other patients had fetuses with anomalies that are known to be associated with an elevated MSAFP. The elevated MSAFP appeared to be related to the presence of a partial mole. Two of the five cases with an MSAFP greater than 2.25 MoM did not have sonographic evidence of a significant anomaly. Therefore, karyotyping can be of benefit in evaluating patients with elevated MSAFP.  相似文献   
168.
    
This paper discusses the findings of the first car MAX-DOAS (multi-axis differential optical absorption spectroscopy) field campaign (300 km long) along the National Highway-05 (N5-Highway) of Pakistan conducted on 13 and 14 November, 2012. The main objective of the field campaign was to assess the spatial distribution of tropospheric nitrogen dioxide (NO2) columns and corresponding concentrations along the N5-Highway from Islamabad to Lahore. Source identification of NO2 revealed that the concentrations were higher within major cities along the highway. The highest NO2 vertical column densities (NO2 VCDs) were found around two major cities of Rawalpindi and Lahore. This study also presents a comparison of NO2 VCDs measured by the ozone monitoring instrument (OMI) and car MAX-DOAS observations. The comparison revealed similar spatial distribution of the NO2 columns with both car MAX-DOAS and satellite observations, but the car MAX-DOAS observations show much more spatial details. Maximum NO2 VCD retrieved from car MAX-DOAS observations was up to an order of magnitude larger than the OMI observations in urban areas.  相似文献   
169.
170.
Human gene therapy is currently seeing an increase in the use of plasmid (pDNA)-based vectors as a preferred choice of vehicle for delivery of the therapeutic gene into the body. In this regard, the environmental impacts of the waste streams from the possible industrial scale manufacture of pDNA require more detailed assessment. In this study, an initial assessment was made of the nutrient phosphorus (P) inputs to four fermentation processes recommended for the industrial scale production of pDNA for the purposes of gene therapy. Phosphorus inputs to each of the four selected fermentation processes ranged from approximately 60 mg l?1 up to 3000 mg l?1 in the fresh media. However, the spent media waste from each of the processes exhibited only a minor reduction in the phosphorus concentrations indicating minimal uptake of P by the microorganisms. This unutilised excess level of phosphorus nutrient within the waste streams poses a strong potential for environmental impact. Waste minimisation studies were undertaken on one model fermentation process with the aim of reducing unnecessary phosphorus input. An optimised media containing a 98% reduction in added P to the media was developed. This phosphorus-minimised media had little quantitative effect upon cell biomass produced and no effect upon the quantity or quality of pDNA produced, relative to the control media. The reduction in P requirement results in an overall cost savings of 12% per fermentation batch, would simplify subsequent wastewater treatment and would contribute to slowing the depletion rate of a valuable, finite natural resource.  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