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   284篇
  免费   6篇
林业   44篇
农学   4篇
基础科学   2篇
  108篇
综合类   35篇
农作物   7篇
水产渔业   29篇
畜牧兽医   35篇
园艺   12篇
植物保护   14篇
  2023年   3篇
  2021年   3篇
  2020年   4篇
  2019年   7篇
  2018年   5篇
  2017年   11篇
  2016年   2篇
  2015年   9篇
  2014年   5篇
  2013年   13篇
  2012年   17篇
  2011年   15篇
  2010年   3篇
  2009年   8篇
  2008年   13篇
  2007年   17篇
  2006年   19篇
  2005年   13篇
  2004年   9篇
  2003年   14篇
  2002年   10篇
  2001年   10篇
  2000年   4篇
  1999年   3篇
  1998年   7篇
  1996年   2篇
  1995年   14篇
  1994年   3篇
  1993年   2篇
  1992年   2篇
  1991年   1篇
  1990年   5篇
  1989年   3篇
  1988年   2篇
  1987年   2篇
  1986年   3篇
  1985年   2篇
  1984年   4篇
  1983年   2篇
  1982年   2篇
  1981年   2篇
  1980年   1篇
  1979年   2篇
  1978年   2篇
  1977年   2篇
  1976年   2篇
  1975年   2篇
  1973年   1篇
  1972年   1篇
  1968年   1篇
排序方式: 共有290条查询结果,搜索用时 203 毫秒
51.
Winfried Schröder  Stefan Nickel  Simon Schönrock  Roman Schmalfuß  Werner Wosniok  Michaela Meyer  Harry Harmens  Marina V. Frontasyeva  Renate Alber  Julia Aleksiayenak  Lambe Barandovski  Oleg Blum  Alejo Carballeira  Maria Dam  Helena Danielsson  Ludwig De Temmermann  Anatoly M. Dunaev  Barbara Godzik  Katrin Hoydal  Zvonka Jeran  Gunilla Pihl Karlsson  Pranvera Lazo  Sebastien Leblond  Jussi Lindroos  Siiri Liiv  Sigurður H. Magnússon  Blanka Mankovska  Encarnación Núñez-Olivera  Juha Piispanen  Jarmo Poikolainen  Ion V. Popescu  Flora Qarri  Jesus Miguel Santamaria  Mitja Skudnik  Zdravko Špirić  Trajce Stafilov  Eiliv Steinnes  Claudia Stihi  Ivan Suchara  Lotti Thöni  Hilde Thelle Uggerud  Harald G. Zechmeister 《Annals of Forest Science》2017,74(2):31

Key message

Moss surveys provide spatially dense data on environmental concentrations of heavy metals and nitrogen which, together with other biomonitoring and modelling data, can be used for indicating deposition to terrestrial ecosystems and related effects across time and areas of different spatial extension.

Context

For enhancing the spatial resolution of measuring and mapping atmospheric deposition by technical devices and by modelling, moss is used complementarily as bio-monitor.

Aims

This paper investigated whether nitrogen and heavy metal concentrations derived by biomonitoring of atmospheric deposition are statistically meaningful in terms of compliance with minimum sample size across several spatial levels (objective 1), whether this is also true in terms of geostatistical criteria such as spatial auto-correlation and, by this, estimated values for unsampled locations (objective 2) and whether moss indicates atmospheric deposition in a similar way as modelled deposition, tree foliage and natural surface soil at the European and country level, and whether they indicate site-specific variance due to canopy drip (objective 3).

Methods

Data from modelling and biomonitoring atmospheric deposition were statistically analysed by means of minimum sample size calculation, by geostatistics as well as by bivariate correlation analyses and by multivariate correlation analyses using the Classification and Regression Tree approach and the Random Forests method.

Results

It was found that the compliance of measurements with the minimum sample size varies by spatial scale and element measured. For unsampled locations, estimation could be derived. Statistically significant correlations between concentrations of heavy metals and nitrogen in moss and modelled atmospheric deposition, and concentrations in leaves, needles and soil were found. Significant influence of canopy drip on nitrogen concentration in moss was proven.

Conclusion

Moss surveys should complement modelled atmospheric deposition data as well as other biomonitoring approaches and offer a great potential for various terrestrial monitoring programmes dealing with exposure and effects.
  相似文献   
52.
Biochar amendment can alter soil properties, for instance, the ability to adsorb and degrade different chemicals. However, ageing of the biochar, due to processes occurring in the soil over time, can influence such biochar-mediated effects. This study examined how biochar affected adsorption and degradation of two herbicides, glyphosate (N-(phosphonomethyl)-glycine) and diuron (3-(3,4-dichlorophenyl)-1,1-dimethylurea) in soil and how these effects were modulated by ageing of the biochar. One sandy and one clayey soil that had been freshly amended with a wood-based biochar (0, 1, 10, 20 and 30% w/w) were studied. An ageing experiment, in which the soil-biochar mixtures were aged for 3.5 months in the laboratory, was also performed. Adsorption and degradation were studied in these soil and soil-biochar mixtures, and compared to results from a soil historically enriched with charcoal. Biochar amendment increased the pH in both soils and increased the water-holding capacity of the sandy soil. Adsorption of diuron was enhanced by biochar amendment in both soils, while glyphosate adsorption was decreased in the sandy soil. Ageing of soil-biochar mixtures decreased adsorption of both herbicides in comparison with freshly biochar-amended soil. Herbicide degradation rates were not consistently affected by biochar amendment or ageing in any of the soils. However, glyphosate half-lives correlated with the Freundlich Kf values in the clayey soil, indicating that degradation was limited by availability there.  相似文献   
53.
Lake Hallstättersee is a holomictic alpine lake, which is influenced by salt mining since the middle Bronze Age. Beside the constant saline waste water load, two massive brine spills loaded the lake with additional 16,900 tons sodium chloride (??10,250 tons Cl?) from 1977 to 1979 and 3,000 tons salt (??1,820 tons Cl?) in 2005. The effect of waste water intrusions from salt mining on stratification of Lake Hallstättersee was analysed over a period of 40 years. Water density, dissolved oxygen and total phosphorus (TP) concentrations were measured and an exponential model was fitted to describe the wash-out of chloride from Lake Hallstättersee after the brine spills. Furthermore, the time required returning to holomixis and steady chloride content after the second brine spill was estimated. During the whole sampling period the minimum and maximum volume-weighted annual mean chloride concentrations were 23.58 mg/L in 1979 and 3.19 mg/L in 1998. However, the mixing regime of Lake Hallstättersee, as well as the chloride concentrations, varied considerably and exhibited three holomictic and three meromictic periods between 1970 and 2009. Holomictic periods were observed when the yearly density gradient was below 0.06 kg/m3, deepwater oxygen in spring above 4 mg/L and consequently declining TP concentration in the deepest water layer below 60 mg/m3, otherwise meromictic periods were observed. Our study showed that Hallstättersee was 13 years ectogenic meromictic and 27 years holomictic during the study period.  相似文献   
54.
In 1998, the Organic Arable Farming Experiment Gladbacherhof (OAFEG) was started in order to explore the impact of different organic arable production systems (mixed farming, stockless farming with rotational ley, stockless cash crop farming) and of different tillage intensities (conventional plough as a full inversion tillage, two-layer plough, inversion tillage at reduced depth, non-inversion tillage) on sustainability parameters. In this article, we present results on the development of soil organic matter (SOM) levels. Starting with organic mixed farming with approximately 0.7 livestock units (LU) per ha cattle before set-up of the experiment, only the mixed farming system in the experiment was able to maintain SOM levels. The stockless system with ley maintained soil organic carbon (SOC), but lost soil total nitrogen (STN), and the stockless cash crop system had a significant SOM loss in the magnitude of 7.7 t SOM ha?1, or roughly 8.4% of the initial SOM mass. Reducing tillage intensity had no impact on SOM masses, but only on organic matter stratification in soils. We conclude that specialization of organic farms towards stockless arable crop production requires special attention on SOM reproduction to avoid detrimental effects. Further, reduced tillage intensity does not necessarily have a positive effect on SOM.  相似文献   
55.
The scientific interest in the fate of antibiotic substances in the environment has increased during the past decades. Especially in animal husbandry, the assumed quantity of antibiotics excreted has caused major concerns as the environment can be contaminated by these compounds via different paths. In this study in Northern Germany, manure and leachate samples from dairy farms were analysed in order to verify if this kind of animal husbandry can be a source of antibiotic residues found in the environment. Neither in liquid manure nor in leachate were the analysed antibiotics detected. These results clearly show the minor importance of dairy cows as sources of antibiotic residues in the aquatic environment. To explain this fact, we propose the three following reasons: (i) the amount of antibiotics administered in dairy farming is low compared to pig or poultry production; (ii) manure storage is a useful process to minimize the antibiotic residues as the substances applied to dairy cows are sensitive to degradation processes during that period; (iii) excreted directly on grasslands, the substances degrade very quickly or adsorb to soil and are therefore not present in the leachate.  相似文献   
56.
Population viability risk management (PVRM) provides a framework for explicitly including qualitative information about the possible outcomes of a management decision with regard to the viability of an endangered population in conservation management. Multi-criteria decision-making (MCDM) techniques enables managers to select the most preferred choice of action in a context where several criteria apply simultaneously. In that context a combined approach of the PVRM concept and a MCDM technique is presented for the development, evaluation and finally ranking of the in situ conservation strategies. We discuss the concept based on a case study for the maintenance of a gene conservation forest of an English yew population (Taxus baccata L.) in Styria, Austria. As part of the PVRM the analytic hierarchy process (AHP) is used to evaluate six conservation strategies with regard to the viability of the yew population. The viability of the population is evaluated based on the results of an analysis of the current environmental, social and economical state and a characterization of the ecological parameters of its population. The most significant risk factors (illegal cutting, browsing by game, tree competition, light availability and genetic sustainability) are structured and prioritised according to their impact on the viability of the yew population applying the AHP. Effects of the six conservation strategies on the viability of the yew population are determined through a qualitative assessment of the probability of a decrease of the population along with four different environmental scenarios. In this context strategy IV combining selective thinning, protection measures, game control with public relation activities seems to be the most effective alternative. The benefits of the combined approach of the PVRM concept with the AHP for the rational analysis of conservation strategies for this endangered tree species are discussed.  相似文献   
57.
A new approach in soil remediation washing techniques is the use of l-cysteine based on the formation of organic complexes. In this study, the applicability of l-cysteine for the mobilisation of different mercury species from contaminated soils was evaluated. Soils were treated with l-cysteine solutions with S?CHg molar ratios of 1, 2, 10, 20, 100 and 200. In 24?h batch experiments, leachates with water could mobilise 1% of Hg. The addition of l-cysteine led to an increase of Hg mobilisation of 42% for soils with inorganically bound Hg. In column experiments, the maximum Hg removal rate was 75%. For soils with organically bound Hg or HgS, only 1?C5% of Hg was mobilised. Thus, the extraction of Hg from soils with l-cysteine is highly dependent on the Hg-binding form. Hg speciation analyses of leachates indicate that Hg?Cl-cysteine complexes are labile complexes which can be easily transformed. Soil samples speciation analysis revealed that reduction to elemental mercury takes place at low S?CHg ratios (1 to 10), assumingly by microbial activity. At higher S?CHg ratios of 10 and 100, precipitation of stable Hg?CS complexes could be observed. These species transformation processes are limitations for considering l-cysteine leaching as a remediation strategy.  相似文献   
58.
Predicting the temperature of the Barents Sea   总被引:4,自引:0,他引:4  
Knowledge of the influence of the physical environment on commercially important fish stocks in the North Atlantic has increased during the last decade. To allow this information to be used in fisheries management, some forecast of the environment is important. Predictions of temperature in the Arcto-boreal Barents Sea have been given for many years, both as subjective opinions of scientists and implicitly in stock assessment assumptions of, e.g., mortality rates. To evaluate an objective statistical forecasting system, we have analysed time series representing mechanisms previously proposed as influencing the temperature of the Barents Sea. These include components of suggested periodic nature, large-scale advective effects, regional processes, and atmospheric teleconnections. The predictability of Barents Sea temperature based on the above mechanisms was evaluated through calculations of auto- and cross-correlations, linear regression, spectral analysis and autoregressive modelling. Forecasts based on periodic fluctuations in temperature performed poorly. Advection alone did not explain a major part of the variability. The precision of predictions six months ahead varied with season; forecasts from spring to autumn had least uncertainty. A first-order autoregressive model, including modelled atmospherically driven volume flux to the western Barents Sea during the preceding year and the position of the Gulf Stream off the eastern coast of the USA two years earlier, explained 50% of the total historical temperature variability.  相似文献   
59.
在奥地利及其他多数欧洲国家英国紫杉濒临灭绝,被列为濒危树种.基于不同地理位置的自然群落的比较,调查了奥地利两块基因资源保育林内英国紫杉的空间结构、更新状况及可采取的保育方法等.每块样地圆杆材分布变化较大.林地Stiwollgraben内紫杉单位面积植株总数,平均胸径和平均株高分别为492 n·hm-2, 8.8 cm and 6.3 m;Leininger Riese仅为45 n·hm-2, 16.3 cm and 7.6 m.Stiwollgraben群落紫杉长势较好,健康植株79%以上,而Leininger Riese群落的健康植株低于49%.两块样地内紫杉更新模式差异较大,与其各自的树龄动态分布相一致.1年龄幼树相比较,Stiwollgraben林地内紫杉密度为13019株/公顷,而Leininger Riese仅为1368株/公顷.Leininger Riese林地内未发现树高51-150cm的幼树,而Stiwollgraben林地内树高30-150cm的幼树鲜能见到.这种情况下,英国紫杉林的保育需要管理完善的保护区、采伐期间采取长期轮伐,同时还要防止牲畜啃食和减轻种间竞争,以此来增强红豆杉的生存能力.图4表4参41.  相似文献   
60.
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