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   210篇
  免费   15篇
林业   46篇
农学   15篇
  41篇
综合类   6篇
农作物   16篇
水产渔业   29篇
畜牧兽医   42篇
园艺   8篇
植物保护   22篇
  2023年   1篇
  2022年   5篇
  2021年   2篇
  2020年   6篇
  2019年   2篇
  2018年   13篇
  2017年   7篇
  2016年   9篇
  2015年   7篇
  2014年   6篇
  2013年   23篇
  2012年   17篇
  2011年   15篇
  2010年   10篇
  2009年   8篇
  2008年   16篇
  2007年   10篇
  2006年   7篇
  2005年   6篇
  2004年   6篇
  2003年   3篇
  2002年   4篇
  2001年   3篇
  2000年   4篇
  1999年   5篇
  1998年   1篇
  1997年   4篇
  1995年   6篇
  1994年   1篇
  1993年   1篇
  1992年   2篇
  1989年   1篇
  1988年   3篇
  1987年   1篇
  1986年   1篇
  1982年   1篇
  1979年   1篇
  1977年   1篇
  1976年   1篇
  1974年   1篇
  1973年   3篇
  1971年   1篇
排序方式: 共有225条查询结果,搜索用时 109 毫秒
41.
Conservation biology often relies on the protection of (semi)natural habitat remnants. However, the ever increasing human population is taking over natural resources and habitats. Here, contrary to most other studies, we ask how human-associated severe changes in the environment can be used to enrich local biodiversity. We tested if industrial activity (gravel excavation) leads to the creation of habitats that support grassland butterflies and how these areas add to the richness of local species when compared to typical semi-natural habitats (grasslands). We also identified key factors affecting the richness, abundance, diversity and commonness of butterfly species to provide practical recommendations. Species richness, diversity index and the occurrence of rare species were higher in gravel-pit shores than in grasslands. The richness of butterfly species and their abundance were positively affected by the richness of plant species, shrub density and age of the gravel-pit but negatively by the cover of water reservoirs in the surrounding area and the isolation of gravel-pits from grasslands. Butterfly diversity was positively influenced by the richness of plant species and proximity of human settlement but negatively by area of the shore and isolation. Our study is the first one to show the high value of gravel-pits for the conservation of butterflies. We recommend the inclusion of gravel-pits in a system of ecological networks and management of their surroundings to improve the colonization rate of rare species. We suggests that directing interest to the possible positive effects of industrial development on biodiversity may support conservation efforts.  相似文献   
42.
A study was conducted to compare the nutrient utilization, growth, and rumen enzyme profile of mithun (Bos frontalis) and Tho-tho cattle (Bos indicus) reared in the same feeding and managemental conditions. For the purpose, male mithun (n = 8) and male Tho-tho cattle (n = 8) of 1.5 years age, selected from the farm of National Research Centre on Mithun, Nagaland, India, were fed on mixed-tree-leaves-based ration as per the requirement of NRC (2001) for cattle for 12 months. Average daily gain (ADG), average dry matter intake (DMI), and feed conversion ratio (FCR) for all animals were recorded. A metabolic trial was conducted at 6 months of the experiment to assess the digestibility coefficient of different nutrients and nutritive value of ration. At 12 months of the experiment, rumen liquor was collected from all animals and analyzed for rumen enzyme profiles, viz., carboxymethylcellulase, xylanase, α-amylase, β-glucosidase, α-glucosidase, urease, and protease. It was found that ADG (507.8 g vs 392.8 g), DM intake (6.59 vs 5.85 kg/day) and DMI/W0.75 (98.75 g vs 91.00 g/day), crude protein intake (780 vs 700 g/day), and total digestible nutrient intake (3.65 vs 3.32 kg/day) were higher (p < 0.05) in mithun than cattle. The nitrogen balance was higher and FCR was better (p < 0.05) in mithun compared with cattle. The digestibility coefficient of different nutrients was similar (p > 0.05) between the species. The microbial enzyme profiles of mithun and cattle were not different (p > 0.05). The better growth performance of mithun than cattle as found in the present study clearly indicates that the mithun has higher genetic potential for growth than Tho-tho cattle of north-eastern hilly region of India.  相似文献   
43.
44.
Soil fertility is declining in most agro‐ecosystems in sub‐Saharan Africa, and incorporation of forage legumes into production systems to utilize the nitrogen fixed by the legumes could alleviate the problem, if efficient nitrogen‐fixing legumes are used. The amounts of nitrogen fixed by Lablab, Medicago, Trifolium, and Vicia species and their contribution to the following wheat crop were estimated in field experiments on an Alfisol at Debre Zeit in the Ethiopian highlands. The amounts of nitrogen (N) fixed ranged from 40 kg N ha‐1 for T. steudneri to 215 kg N ha‐1 for L. purpureus. The increase in grain yields of wheat following the legumes ranged from 16% for T. steudneri to 71% for M. tranculata where no N fertilizer was applied to the wheat. Additional N fertilizer applied to wheat at 60 kg N ha‐1 had no significant effects on wheat grain or straw DM andN yields. In another experiment, eight lablab treatments consisting of factorial combinations of two cultivars (Rongai and Highworth), two Rhizobium inoculation treatments (inoculated and uninoculated) and two times of harvest (for hay at 50% flowering and for seed at seed maturity), were compared on lablab forage production and N yield, and residual effects on two succeeding wheat crops. Inoculation had no significant effects on nodulation, shoot DM or N yields. Rongai had significantly higher shoot DM and N yields than Highworth. Lablab harvested at flowering had significantly higher shoot DM and N yields than lablab harvested at seed maturity. Grain yields of the first wheat crop following the various lablab crops were 93–125% higher than grain yields of the wheat following wheat (continuous wheat) where no N fertilizer was applied. Therefore, lablab is a potential forage crop for incorporation into cereal production systems to improve feed quality and to reduce dependence on N fertilizers for cereal production.  相似文献   
45.
Fissuring associated with kernel elongation was evident in a moisture-adsorbing environment at 15 °C of relative humidity 88.72±0.28% with moisture content from 6% (d.b.) to 16.3% (d.b.). The average length and width of 800 kernels was measured during the sorption test using a Cervitec Grain Inspector equipped with two digital cameras. Samples were exposed to both a moisture-adsorbing and desorbing environments at 15 °C with relative humidities of 23.4±0.53%, 55.9±0.27%, 70.98±0.28% and 88.72±0.28%. On image analysis, the kernels changed in size from 5.13 to 4.84 mm in length and 2.9 to 2.73 mm in width. Both length and width changed as expected during moisture-adsorbing and moisture-desorbing tests. Fissured kernel percent was related to changes in the average length of the kernels during the moisture-adsorbing tests. The average length and fissured kernel percent of rice kernels measured by image analysis may be considered as a reliable indicator of changes in their dimensions during quasi-static moisture sorption processes.  相似文献   
46.
采用多级采样的方法研究了孟加拉国农村耕作区内棕榈树的传统利用模式和当地的管理经验。农民管理棕榈主要为获取树液产品,生产以糖为主的次生品。树液可直接用作饮料,也可加工成糖蜜或酒精饮料。7块不同地块为棕榈提供生长环境,20.40%的棕榈种植在果园内。尽管中等级的农民拥有多数棕榈(33%),但是主要管理棕榈的是没有土地的农民,他们靠棕榈维持生计。这些农民将自己的智慧应用到棕榈管理当中,从种植到开孔取树液再到产品加工。如果能更科学地管理棕榈,加上农民的智慧,棕榈业将会对当地经济发展起到重要作用,也会丰富当地生物多样性。  相似文献   
47.
ABSTRACT Sequence-tagged microsatellite profiling was used to develop 110 microsatellites for Puccinia graminis f. sp. tritici (causal agent of wheat stem rust). Low microsatellite polymorphism was exhibited among 10 pathogenically diverse P. graminis f. sp. tritici isolates collected from Australian cereal growing regions over a period of at least 70 years, with two polymorphic loci detected, each revealing two alleles. Limited cross-species amplification was observed for the wheat rust pathogens, P. triticina (leaf rust) and P. striiformis f. sp. tritici (stripe rust). However, very high transferability was revealed with P. graminis f. sp. avenae (causal agent of oat stem rust) isolates. A genetic diversity study of 47 P. graminis f. sp. avenae isolates collected from an Australia-wide survey in 1999, and a historical group of 16 isolates collected from Australian cereal growing regions from 1971 to 1996, revealed six polymorphic microsatellite loci with a total of 15 alleles. Genetic analysis revealed the presence of several clonal lineages and subpopulations in the pathogen population, and wide dispersal of identical races and genotypes throughout Australian cereal-growing regions. These findings demonstrated the dynamic population structure of this pathogen in Australia and concur with the patterns of diversity observed in pathogenicity studies.  相似文献   
48.
Paddy and Water Environment - Most of the lands of the southern coastal zone of Bangladesh are protected from tidal flooding and storm surges by embankments constructed during the 1960s and 1970s,...  相似文献   
49.
Increased knowledge on the spatial distribution of marine resources is crucial for the implementation of a true ecosystem approach to management and the conservation of marine organisms. For exploited fish species characterized by aggregation behaviour during spawning time, the identification and tracking of spawning areas is essential for a correct assessment of their productivity and population abundance. To elucidate this concept, we reconstructed the spatio‐temporal distribution of adult plaice (Pleuronectes platessa, Pleuronectidae) during spawning time along the 20th century. Historical data reveal that not only the abundance but also the former population richness was much higher than previously estimated and has declined because of protracted over‐exploitation during the last 30 years. We conclude that forecast of stock recovery to former levels of abundance neglecting spatial reorganizations might be over‐optimistic and shaded by a lost memory of the past population richness. These results reinforce the importance of managing exploited marine resources at a greater spatial resolution than has been carried out in the history of fishery management.  相似文献   
50.
Sweet cherry (Prunus avium L.) is a self-incompatible species. Determination of the S-genotypes of cherry cultivars is crucial for breeding and to select appropriate cultivars for cross-fertilisation and fruit set. In this study, we characterised the S-genotypes of 25 sweet cherry cultivars, some of which had being bred at the Research and Breeding Institute of Pomology (RBIP), Holovousy, Czech Republic, and others were European cultivars in the RBIP collection. S-genotyping was carried out by polymerase chain reaction using consensus primers for the S-RNase and SFB genes, and capillary electrophoresis. Nine different known S-haplotypes (S1, S2, S3, S4, S5, S6, S9, S13, and S16) were identified and the cultivars were assigned to 12 incompatibility groups. One local cultivar, ‘Pta?ka z Plzně’, originated from a wild forest seedling and used as a pollinator, was assigned to Group 0 of universal donors. The pedigree of some cultivars was confirmed by their S-genotype. This study represents the ?rst comprehensive S-genotype screening of sweet cherry genetic resources in the Czech Republic and will be useful for the design of crossing programmes and orchard management of these sweet cherry cultivars.  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