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   1234篇
  免费   119篇
林业   93篇
农学   50篇
基础科学   11篇
  232篇
综合类   38篇
农作物   51篇
水产渔业   208篇
畜牧兽医   526篇
园艺   14篇
植物保护   130篇
  2024年   3篇
  2023年   33篇
  2022年   27篇
  2021年   64篇
  2020年   91篇
  2019年   87篇
  2018年   84篇
  2017年   74篇
  2016年   68篇
  2015年   46篇
  2014年   63篇
  2013年   61篇
  2012年   82篇
  2011年   106篇
  2010年   60篇
  2009年   45篇
  2008年   65篇
  2007年   53篇
  2006年   41篇
  2005年   23篇
  2004年   22篇
  2003年   25篇
  2002年   26篇
  2001年   15篇
  2000年   11篇
  1999年   17篇
  1998年   7篇
  1997年   2篇
  1996年   4篇
  1995年   2篇
  1993年   2篇
  1992年   6篇
  1991年   5篇
  1990年   1篇
  1989年   4篇
  1988年   4篇
  1987年   3篇
  1986年   1篇
  1985年   2篇
  1983年   2篇
  1980年   2篇
  1979年   1篇
  1978年   3篇
  1973年   2篇
  1972年   1篇
  1971年   1篇
  1970年   2篇
  1967年   1篇
  1963年   1篇
  1954年   1篇
排序方式: 共有1353条查询结果,搜索用时 218 毫秒
31.
A 6-year old Salz ram was presented with a history of poor body condition, progressive gait abnormalities, pelvic limb lameness, and difficulty with copulation. Based on the history, clinical signs, hip palpation, and radiography, a diagnosis of hip dysplasia, previously unreported in sheep, was made.  相似文献   
32.
The effect was studied of an acute and non-persistent hyperglycaemia on the serum fructosamine and blood glycated haemoglobin concentrations in canine samples. Five dogs were given glucose solution intravenously and blood samples were taken from each dog before and at 5, 15, 30, 60 and 120 min and 24 h after the infusion. There was an intense hyperglycaemia 5 min after the injection was given, but no statistically significant differences in the serum fructosamine and glycated haemoglobin were observed. It was concluded that an acute and transient hyperglycaemia does not cause significant changes in the glycated haemoglobin and fructosamine concentrations in healthy dogs.  相似文献   
33.
Off flavours in pork sometimes produce tastes such as sourness, fishy, metallic or other non‐typical flavours and are often caused by low pH. Loss of function mutations in flavin containing mono‐oxygenase 3 (FMO3) are known to be associated with a fishy off flavour in both chicken eggs and cow's milk and a similar autosomal recessive disorder is present in humans resulting in a fishy odour. FMO3 is a member of a gene family that is clustered on human chromosome 1. Comparative mapping suggested that FMO3 and the remaining FMO genes (ex. FMO1 and FMO5) might map to the orthologous region on pig chromosome 9 (SSC9) where a quantitative trait locus (QTL) for off flavour was previously identified. Primers were designed to amplify FMO1, FMO3 and FMO5 gene fragments and several SNPs were discovered and genotyping tests developed. The genotypes from the Iowa State University Berkshire × Yorkshire resource population were used to linkage map FMO1 and FMO3 to SSC9 and FMO5 to pig chromosome 4 (SSC4). QTL and associations analyses were performed using the map containing FMO1 and FMO3. Results demonstrated that FMO3 and FMO1 mapped less than 1 cM away from the peak for the off flavour QTL previously detected on SSC9 and provide indications of an association between the FMO3 polymorphism and off flavour in pork.  相似文献   
34.
35.
A non-ambulatory dog with tetraparesis following a pain episode that had evolved over 2 months was submitted for medical treatment and diagnosed with intervertebral disk disease at C3-C4 and dorsal extradural compression at C1-C2 and C3-C4 using myelography and computed tomography. The dog experienced ambulation recovery after 15 days of treatment with only electroacupuncture and Chinese herbal medicine, with marked improvement occurring after only 10 treatments. Six months of follow-up demonstrated that the dog was stable and had no recurrence of symptoms. Therefore, it was concluded that the combination of electroacupuncture and Chinese herbal medicine was responsible for motor rehabilitation.  相似文献   
36.
  • 1. The coastline is very sensitive to both climatic and human influences but also provides essential goods and services upon which human welfare depends. Species inhabiting these coastal areas provide valuable resources and enhance ecosystem functioning: it is therefore essential to understand the main factors influencing species abundance patterns. The aim of this study is to estimate the amount of variation in nekton coastal assemblages explained by spatial, temporal and environmental variables.
  • 2. Nekton sampling was carried out over 17 months in the Terminos Lagoon, a reserve area situated in the Gulf of Mexico, using a shrimp trawl. At each station, 11 environmental variables were recorded. The influence of seasonal, spatial and environmental variables on nekton species abundance was analysed using Partial Canonical Correspondence Analysis (PCCA).
  • 3. The explanatory variables explained only 19.7% of the total observed variation in the nekton community for the Terminos Lagoon. The major part of the explained variation was due to the spatial effect (9.2%), while environmental variables and seasonality explained only 3.6% and 0.8%, respectively, suggesting the necessity to consider experimental fishing design in such artisanal fisheries.
  • 4. Results also suggest focusing on more integrative indicators of community structure such as measures of taxonomic diversity based on presence/absence or on measures related to functional attributes of communities rather than using species abundance patterns to predict changes in coastal ecosystems.
Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   
37.
In shrimp farms, food partitioning during the course of the day is contradictory, ethology studies may help in determining the proper frequency. Litopenaeus vannamei juveniles were placed in 30 L aquariums (41 m−2), exposed to a 12:12 h light–dark cycle. Feeding was provided at 10% of biomass three, four and seven times per day, with observations made in 15 min h−1 windows, initiated after the ration was offered. Latency to access the feeding tray and to start eating was recorded using instantaneous focal sampling and digestive tract filling (DTF) by the continuous focal method. Weight gain was recorded at the end of the experiment. We performed seven repetitions, with 28 individuals observed for 33 days for each treatment (490 h of observation). The three-times offering induced less latency for accessing the tray and for ingesting the feed as well as a higher DTF when compared with the other frequencies. Animals fed three and four times had similar weight gains, and were greater than those fed seven times. Our results indicate that a more spaced food offering stimulates the search for and ingestion of feed. As compared with other frequencies, the three-times-per-day option assumes lower labour costs and a more efficient use of the feed.  相似文献   
38.
We compared growth, photosynthetic performance and shade adaptation of rubber (Hevea brasiliensis Muell. Arg.) plants growing in natural shade (33, 55 and 77% reduction in incoming radiation) to control plants growing in full sunlight. Stem diameter and plant height, measured over a 15-month period, were greatest in plants grown in full sunlight, and both parameters decreased with increasing shade. At 7 and 14 months after planting (MAP), total plant dry mass was highest in control plants and lowest in plants in 77% shade. Expansion of the fourth leaf whorl, monitored at 5-6 MAP, was slowest in plants in 77% shade and fastest in unshaded plants, which had more leaves and higher leaf areas and inter-whorl shoot lengths. In response to increasing shade, specific leaf area increased, whereas leaf weight ratio and relative growth rate decreased. Chlorophyll a/b ratio decreased with increasing shade, indicating shade-induced partitioning of chlorophyll into light-harvesting complexes. Compared to the response in unshaded plants, CO2 assimilation saturated at lower photosynthetic photon flux densities in plants in 77% shade, with a lower upper-asymptote to the light response curve. Chlorophyll fluorescence revealed no evidence of sustained photoinhibitory damage in unshaded plants. Dynamic photoinhibition decreased with increasing shade, with the greatest depression in the ratio of variable to maximal fluorescence around midday. We conclude that shade adaptation and shade-induced reductions in dynamic photoinhibition account for the enhanced early growth of rubber in light shade.  相似文献   
39.
The recent decline of Mediterranean oak woodlands in SW Iberian Peninsula is related to insect pests which affect both cork oak (Quercus suber) and holm oak (Quercus rotundifolia). We identified twenty-six bird species as potential regular predators of twenty major pests by reviewing the diet of breeding, wintering and resident species in this ecosystem. Foraging guilds are strongly associated with predation at distinct stages of the pests’ life-cycle: ground-foragers prey on overwintering pupae and larvae of seed-borers, tree-foragers prey on eggs, larvae and pupae of defoliating and wood-boring pests, and aerial-sweepers prey on airborne imagines. Bird predation can cover the complete life-cycle of pest species because different species may be complementary due to a dissimilar exploitation of foraging niches and periods. Small generalist tree-foraging passerines are important pest predators given their high densities and widespread distribution in Mediterranean oak woodlands, but management practices can have a significant negative effect in their populations.  相似文献   
40.
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