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   271篇
  免费   9篇
林业   1篇
农学   6篇
  29篇
综合类   73篇
农作物   7篇
水产渔业   12篇
畜牧兽医   130篇
园艺   9篇
植物保护   13篇
  2023年   3篇
  2022年   2篇
  2021年   3篇
  2019年   4篇
  2018年   2篇
  2017年   3篇
  2016年   2篇
  2015年   3篇
  2014年   4篇
  2013年   24篇
  2012年   9篇
  2011年   9篇
  2010年   7篇
  2009年   3篇
  2008年   9篇
  2007年   12篇
  2006年   6篇
  2005年   6篇
  2004年   8篇
  2003年   7篇
  2002年   4篇
  2001年   12篇
  2000年   9篇
  1999年   9篇
  1998年   2篇
  1997年   4篇
  1996年   3篇
  1995年   3篇
  1992年   6篇
  1991年   9篇
  1989年   4篇
  1988年   7篇
  1987年   2篇
  1986年   7篇
  1985年   5篇
  1982年   5篇
  1979年   4篇
  1978年   2篇
  1977年   2篇
  1975年   2篇
  1974年   2篇
  1971年   4篇
  1970年   3篇
  1969年   2篇
  1968年   3篇
  1927年   2篇
  1911年   2篇
  1908年   3篇
  1906年   2篇
  1902年   2篇
排序方式: 共有280条查询结果,搜索用时 0 毫秒
101.
102.
Countries that will ratify the new Protocol to abate acidification, eutrophication and ground-level ozone, also known as the Göteborg-protocol, are committed to meet national emission ceilings for SO2, NOx, VOCs and NH3 in 2010. AEA Technology calculated impacts and monetised benefits for four scenarios used during the preparation of the new Protocol, each scenario compared with the situation 1990. The calculated benefits were compared with the costs calculated by the International Institute for Applied Systems Analysis (IIASA) using the RAINS model. The overall conclusion is that the benefits are likely to exceed the costs of implementing the scenarios considered in the study, by a factor of between two and three. Based on the principal set of assumptions followed in the study, it appeared that impacts on haity and materials were negligible. Impacts on ecosystems remained unquantified.  相似文献   
103.
104.
105.
106.
Rates of degradation and adsorption of acetochlor [2‐chloro‐N‐ethoxymethyl‐6′‐ethylaceto‐o‐ toluidide] and terbuthylazine [N 2tert‐butyl‐6‐chloro‐N4‐ethyl‐1,3,5‐triazine‐2,4‐diamine] in a Horotiu sandy loam soil (Typic Orthic Allophanic) were determined under controlled temperature and soil moisture regimes. These were then combined with site‐specific soil properties and climatic conditions in the Pesticide Root Zone Model (PRZM‐3) to predict dissipation and leaching of the herbicides in the field. PRZM‐3 significantly under‐estimated dissipation of both herbicides in the field using parameters derived from the laboratory incubation studies. When these parameters were derived from the field trials, PRZM‐3 adequately predicted dissipation of both herbicides using a two‐rate dissipation sub‐model but under‐predicted the dissipation when a simpler single‐rate sub‐model was used. Earlier‐than‐expected appearance of both herbicides in sub‐soil layers were postulated to result from the non‐equilibrium adsorption/transport of the herbicides and preferential flow, which cannot be simulated by PRZM‐3. © 2000 Society of Chemical Industry  相似文献   
107.
A 42-day study was conducted to assess the impact of three West Nile virus vaccines given either as separate injections or incorporated with their counterpart equine encephalitis and tetanus vaccines on serological responses under field use conditions. Two hundred forty mature, West Nile virus seronegative (<4) horses were followed serologically pre- and postprimary and secondary vaccination with six different vaccination programs, all including West Nile virus antigens. Forty horses were unvaccinated sentinel horses. All vaccines stimulated both a primary and secondary (booster) response to vaccination that was significantly higher than that of seronegative controls. However, inclusion of West Nile virus with equine encephalitis viruses and tetanus toxoid in vaccines had a significant detrimental impact on West Nile virus serum neutralization antibody production to both the primary and secondary vaccinations.  相似文献   
108.
Cost-benefit analysis is one of the fundamental tools for the development of economic instruments for pollution control. The costs of various abatement measures are reasonably well characterised. However, assessment of the economic costs of pollutant impacts is less well developed. This paper reports on two studies carried out for DGXII of the European Commission, the ExternE-Project and the Green Accounting Research Project. Both studies have been performed by international, multi-disciplinary research teams.Analysis of the effects of emissions of PM10, SO2, NOx and VOCs (as ozone precursors) has included assessment of human health, materials, crops and other terrestrial ecosystems, and freshwater fisheries. The analysis follows the impact pathway approach, linking dose-response functions, valuation data and other models. It differs significantly to earlier top-down approaches that made only very limited use of the wealth of scientific data available. Most success has been achieved in analysis of impacts on human health, building materials and crops. Significant uncertainties exist for these receptors, though these have been identified and are now being addressed. Assessment of impacts on other receptors, perhaps most notably forests, is more limited. The methodology is particularly applicable for analysis of impacts on receptors for which the critical loads approach is not appropriate.  相似文献   
109.
A liquid chromatographic (LC) method is described for the determination of chlortetracycline hydrochloride (CTC) in poultry/swine and ruminant feeds in the 10-100 ppm range and in premix. CTC is extracted from ground feed/premix with acidified acetone, and the extract is filtered through a Millex-HV filter or disposable C18 column. The filtrate is partitioned with methylene chloride when additional cleanup is necessary. A Nova-Pak C18 column is used for LC separation with determination at 370 nm. The average recovery of CTC from premix was 95% with a standard deviation (SD) of 1.70 and a coefficient of variation (CV) of 1.79%. The overall average recovery from feeds was 77% with an SD of 3.18 and a CV of 4.10%.  相似文献   
110.
Spatio-temporal modeling of fine particulate matter   总被引:1,自引:0,他引:1  
Studies indicate that even short-term exposure to high concentrations of fine atmospheric particulate matter (PM2.5) can lead to long-term health effects. In this article, we propose a random effects model for PM2.5 concentrations. In particular, we anticipate urban/rural differences with regard to both mean levels and variability. Hence we introduce two random effects components, one for rural or background levels and the other as a supplement for urban areas. These are specified in the form of spatio-temporal processes. Weighting these processes through a population density surface results in nonstationarity in space. We analyze daily PM2.5 concentrations in three midwestern U.S. states for the year 2001. A fully Bayesian model is implemented, using MCMC techniques, which enables full inference with regard to process unknowns as well as predictions in time and space.  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