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   300篇
  免费   28篇
林业   22篇
农学   14篇
  79篇
综合类   11篇
农作物   23篇
水产渔业   18篇
畜牧兽医   101篇
园艺   8篇
植物保护   52篇
  2023年   4篇
  2022年   12篇
  2021年   18篇
  2020年   24篇
  2019年   21篇
  2018年   15篇
  2017年   16篇
  2016年   13篇
  2015年   16篇
  2014年   13篇
  2013年   14篇
  2012年   18篇
  2011年   20篇
  2010年   15篇
  2009年   10篇
  2008年   20篇
  2007年   14篇
  2006年   15篇
  2005年   9篇
  2004年   12篇
  2003年   8篇
  2002年   8篇
  2001年   1篇
  2000年   4篇
  1999年   1篇
  1996年   1篇
  1992年   1篇
  1983年   2篇
  1980年   1篇
  1978年   1篇
  1977年   1篇
排序方式: 共有328条查询结果,搜索用时 20 毫秒
51.
Considering the very high socio economic value of cork oak (Quercus suber L.) in Mediterranean areas, a better knowledge of local genetic resources is necessary in order to reach a good balance between the conservation issues and the need of an efficient cork production network. In such frame, local germplasm of Q. suber from the main cork production areas of Sardinia was analysed for DNA and isozyme polymorphisms and for cork quality in relation to some environmental parameters. A total number of 24 sample stands of cork oak were selected, representing typical vegetation, sylvicultural and cork quality features within the eight identified cork growing areas in Sardinia. Considerable variation was found between cork oak stands of the different areas. Results of the principal component analysis performed on the cork quality data and environmental characters of the eight areas, showed that the first three components explain 72.2% of the variation. The major characters involved in this differentiation were cork quality characters such as dimensional recover, moisture and Mg content of the cork and also elevation of stands m a.s.l. for the first component. The second component appears to be determined by some climatic parameters (average annual temperature and average of the minimum temperatures of coldest month) and by the Fe and Zn in the cork. For the third component, major characters involved in differentiation are average annual rainfall, bark thickness and Ca content in the cork.  相似文献   
52.
Tropical Animal Health and Production - A cross-sectional study was conducted to determine the seroprevalence and the risk factors associated with C. burnetii infection in cattle in the state of...  相似文献   
53.
Cockatiels are popular pets. Still, despite medical and surgical relevance, the radiographic anatomy of the cockatiel (Nymphicus hollandicus) skeleton, like that of different wild and exotic bird species, has seldom been described. This study set out to describe the radiographic anatomy of the cockatiel skeleton. Twelve adult male and nine adult female specimens were radiographed using a digital X-ray system and different views. The radiographic anatomy of these birds was similar to that of other Psittacidae. However, some particularities inherent to the target species were detected, such as the presence of four flexion zones in the skull (craniofacial, nasal, jugal arch and palatine), complete bony orbit comprising a suborbital arch, 34–38 vertebrae (10 or 11 cervical, 8 or 9 thoracic, 9 or 10 lumbosacral, 5 or 6 caudal vertebrae and a pygostyle comprising 2 fused vertebrae), eight or nine pairs of ribs and a notarium made up of fused T2–T6 vertebrae. Poor radiopacity of the notarium, ribs and respective uncinate processes, and synsacral vertebrae made demarcation of these structures difficult. The appendicular skeleton of the cockatiel was very similar to that of other Psittacidae, and there were no gender-related differences.  相似文献   
54.
Non-edible parts of crustaceans could be a rich source of valuable bioactive compounds such as the carotenoid astaxanthin and peptides, which have well-recognized beneficial effects. These compounds are widely used in nutraceuticals and pharmaceuticals, and their market is rapidly growing, suggesting the need to find alternative sources. The aim of this work was to set up a pilot-scale protocol for the reutilization of by-products of processed shrimp, in order to address the utilization of this valuable biomass for nutraceutical and pharmaceuticals application, through the extraction of astaxanthin-enriched oil and antioxidant-rich protein hydrolysates. Astaxanthin (AST) was obtained using “green extraction methods,” such as using fish oil and different fatty acid ethyl esters as solvents and through supercritical fluid extraction (SFE), whereas bioactive peptides were obtained by protease hydrolysis. Both astaxanthin and bioactive peptides exhibited bioactive properties in vitro in cellular model systems, such as antioxidant and angiotensin I converting enzyme (ACE) inhibitory activities (IA). The results show higher astaxanthin yields in ethyl esters fatty acids (TFA) extraction and significant enrichment by short-path distillation (SPD) up to 114.80 ± 1.23 µg/mL. Peptide fractions of <3 kDa and 3–5 kDa exhibited greater antioxidant activity while the fraction 5–10 kDa exhibited a better ACE-IA. Lower-molecular-weight bioactive peptides and astaxanthin extracted using supercritical fluids showed protective effects against oxidative damage in 142BR and in 3T3 cell lines. These results suggest that “green” extraction methods allow us to obtain high-quality bioactive compounds from large volumes of shrimp waste for nutraceutical and pharmaceutical applications.  相似文献   
55.
Abstract

Biofortification of soybean grains with lithium (Li) is a strategy to improve a food with high social acceptance, in order to promote health benefits. The aim of this work was to evaluate the development of plants and the production of biofortified soybeans with two Li sources. The experiment was conducted in a completely randomized design with five replicates. Ten treatments were obtained in a 2x5 factorial scheme, comprising two sources of Li (LiOH - Li hydroxide and Li2SO4 - Li sulfate) and five doses (0, 30, 60, 90 and 120?mg kg?1) in stages V4 and R1. The supply of Li promoted significant effects (p?≤?0.05) on the morphology, yield components and nutritional status of soybean plants. The highest grain yield was obtained with the use of Li2SO4 at the estimated dose of 45.7?mg kg?1. The plants accumulated Li between 8.00 and 11.20?mg kg ?1, respectively, with the use of Li2SO4 and LiOH. In the grains, the highest concentrations of Li were obtained with the application of 120?mg kg?1. Li2SO4 and LiOH are good sources for biofortification of soybean grains.  相似文献   
56.
Environmental stress as salinity can negatively affect the physiology of tomato plants. Conditions leading to a reduction of transpiration can contribute to greater tolerance to salinity. Use of kaolin-based particle film technology (PFT) may be an effective tool to control stomatal conductance and transpiration rate, thus mitigating the detrimental effect of salinity. The present three-year study has investigated the effects of kaolin application on leaf gas exchange, leaf water potential, leaf and canopy temperature of field-grown tomato, irrigated with brackish water by drip method, in southern Italy. Treatments were: (1) three salinity levels of irrigation water (electrical conductivity of water = 0.5, 5 and 10 dS m?1); (2) tomato plants treated or not with kaolin; and (3) two cultivars in each year. The increase in salinity caused the reduction of leaf water potential, stomatal conductance, net photosynthesis and transpiration rate, and the increase of leaf and canopy temperature. Kaolin has resulted in an improvement of leaf water potential, and the reduction in gas exchange variables in low-salinity conditions. Under high salinity, kaolin was effective in limiting the reductions in net photosynthesis and reducing leaf and canopy temperature. These latter variables were slightly affected by kaolin, in different ways in respect to the saline treatments; while in non-saline conditions were 0.2–0.5°C higher in the kaolin-treated plants, the situation was reversed in more saline treatment. The variation of leaf and canopy temperature shows that kaolin influences the thermal balance mainly for the dual effect of reflection of the incident radiation and partial occlusion of the stomata. Kaolin mitigated detrimental effects of salinity also on yield, contributing to the improvement of income for the farmers. The use of kaolin-based PFT may be an effective tool to alleviate salinity stress in tomato production under arid and semi-arid conditions.  相似文献   
57.
Tropical arthropod surveys generally use a combination of complementary sampling methods to increase the detection of species and individuals, and to decrease the number of singletons. However, given the high arthropod abundance and the taxonomic challenges of arthropod surveys, the combination of different sampling methods may be inefficient and may increase survey costs. Harvestmen were sampled using beating tray, nocturnal search, leaf-litter manual sorting and Winkler apparatus in 70 plots distributed in two areas in Central Amazonia. Every sampled method documented different assemblages, and only the nocturnal search method proved to be efficient in representing both harvestmen richness and composition. Given the data collected from leaf-litter manual sorting, Winkler apparatus and beating tray can be used in inventories to increase the number of species collected, but may be less useful for applied or monitoring studies. Although pooling data from three methods was effective to obtain an overview of species richness, it may not be the more efficient strategy for studies of assemblage associations with environmental variables. As each method may sample distinct assemblages that have different responses to the surrounding environment, pooling data from these different methods may obfuscate patterns of assemblage composition related to environmental factors instead of clarifying them.  相似文献   
58.
BACKGROUND: Rose‐ringed parakeets Psittacula krameri (Scop.) have recently become established in several European countries, with potential for significant negative economic and ecological impacts. However, in northern Europe the potential for reproductive output is largely unknown. In 2005 the authors established a captive outdoor colony in north‐east England and examined breeding success over 2 years. RESULTS: In 2006 (19 pairs, 15 clutches) the average first clutch size was 3.6 (±0.3) eggs. Six clutches were infertile, and overall the colony produced 1.4 (±0.5) fertile eggs per pair. Eleven pairs produced a second clutch following removal of the first; seven were infertile, and overall productivity was 0.7 (±0.4) fertile eggs per pair. Unsuccessful pairs were rearranged or replaced. In 2007, overall productivity was 2.5 (±0.4) and 1.8 (±0.4) fertile eggs per pair for the first and second attempts respectively. For pairs that remained unchanged through 2006–2007, productivity was consistent between years and breeding attempts. CONCLUSION: Where food and nest sites were not limiting, clutch sizes in north‐east England were similar to those in the native range, and consistent between first and second attempts. This has implications for the future expansion and management of the species. © Crown Copyright 2009. Reproduced with permission of Her Majesty's Stationery Office. Published by John Wiley & Sons, Ltd.  相似文献   
59.
For a conditioned taste aversion (CTA) agent to be successful in wildlife management applications, the compound must not be detectable by the animal. Levamisole is an effective CTA agent when administered by oral intubation, but it is readily detected by a number of species when mixed directly in food. This paper describes the development of an ion-exchange resin complex (resinate) to mask the taste of levamisole. Two different resins were evaluated, Amberlite IRP-64 and Amberlite IRP-69, and release studies indicated that the resinate formed using IRP-64 resin would be most suitable for use in wildlife management. Although it contained a relatively low loading of levamisole (77 g kg(-1)), the results indicated that the IRP-64 resinate should be stable in the mouth and release the levamisole quickly in the acid environment of the stomach (93% of levamisole was released into 0.1 M HCl in 5 min). In a bioassay using laboratory rats (Rattus norvegicus Berk), we showed that the taste of levamisole was successfully masked in a biscuit bait using the IRP-64 resinate and that a CTA was generated to untreated bait. The use of ion-exchange resins is a new approach in the taste-masking of CTA agents and could be applied to other wildlife management applications.  相似文献   
60.
Most of the Brazilian soils, especially in Cerrado biome, have high acidity and toxic aluminium, making the application of limestone an indispensable technique to obtain high yield in soybean crop. The hypothesis of this study was that contrasting base saturation provides changes in water-use efficiency (WUE) and agronomic traits of soybean populations. Thus, we evaluated the WUE and agronomic performance of F3 soybean populations under different base saturation levels. Each experiment was conducted in a randomized complete blocks design with three replicates and 10 F3 populations (P1, P2, P3, P4, P5, P6, P7, P8, P9 and P10) for two crop seasons. Segregating populations were obtained by bulk method. In the first experiment, F3 populations were evaluated without correction of base saturation (V = 30%), while in the second experiment, limestone was applied three months before sowing to increase base saturation to 60%. The traits evaluated were as follows: calcium, magnesium and potassium contents, water-use efficiency (WUE), plant height, first pod height, main stem diameter and grain yield. Our findings indicate that WUE and agronomic performance of F3 soybean populations depends on the saturation condition. We identified the P4 and P9 populations as the most promising for use in breeding programmes aiming at higher tolerance to abiotic stress caused by low base saturation in soil.  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