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   295篇
  免费   22篇
林业   19篇
农学   11篇
基础科学   4篇
  80篇
综合类   22篇
农作物   28篇
水产渔业   17篇
畜牧兽医   104篇
园艺   2篇
植物保护   30篇
  2023年   2篇
  2022年   3篇
  2021年   8篇
  2020年   9篇
  2019年   11篇
  2018年   13篇
  2017年   10篇
  2016年   15篇
  2015年   14篇
  2014年   14篇
  2013年   17篇
  2012年   23篇
  2011年   20篇
  2010年   16篇
  2009年   21篇
  2008年   14篇
  2007年   17篇
  2006年   12篇
  2005年   12篇
  2004年   14篇
  2003年   14篇
  2002年   7篇
  2001年   1篇
  2000年   8篇
  1999年   1篇
  1997年   3篇
  1996年   2篇
  1993年   1篇
  1992年   1篇
  1989年   1篇
  1988年   2篇
  1987年   1篇
  1985年   2篇
  1984年   3篇
  1983年   1篇
  1982年   1篇
  1978年   1篇
  1976年   1篇
  1968年   1篇
排序方式: 共有317条查询结果,搜索用时 109 毫秒
1.
Ductus venosus (DV) closure plays a key role in hepatic circulation adaptation to postnatal metabolic function, and DV patency might develop a congenital portosystemic shunt (CPSS). The noninvasive Color Flow Mapping (CFM) examination, a validated method to diagnose CPSS in adult dogs, is routinely performed to assess DV closure after birth in humans. This study aimed to describe the feasibility of the ultrasonographic evaluation of the DV after birth and to determine its closure time in healthy Great Dane neonates. Patency of DV in serial Color Flow Mapping (CFM) examinations and bodyweight (BW) were recorded on Days 0‐3‐6‐9 in 24 neonates that were classified as having patent (PDV) or closed ductusvenosus (CDV) basing on CFM signal presence/absence. Since the 3rd day, DV diameter was recorded. Data were analysed by ANOVA (p < 0.05). All dogs resulted healthy 1 year later. The number of PDV and CDV puppies at birth was not different on Day 3 (24 and 0 vs. 22 and 2, PDV and CDV, respectively), whereas it resulted different on Days 6 (24 and 0 vs. 14 and 10) and 9 (24 and 0 vs. 0 and 24); on Day 3, it was different compared to Days 6 and 9; on Day 6, it was different from Day 9. Reduction of DV diameter resulted positively related to neonatal BW growth. The CFM evaluation of DV closure after birth in Great Dane puppies represents a feasible technique. Present results suggest the time of functional closure in normal neonates within 9 days after birth. Thus, CFM examination, as an early screening test for DV patency evaluation, performed 10 days after birth, may identify suspicious dogs at risk that would require further investigations. Further studies are needed to deepen the role of a delayed closure in low bodyweight and preterm puppies.  相似文献   
2.
3.
Although conjugated linoleic acid (CLA) shows inhibitory effects on histamine release, eicosanoid production and pruritus in laboratory rodents, its use in canine atopic dermatitis (AD) has not been reported. The aims of this study were to assess the efficacy of CLA, black currant seed oil (BSO) or a combination of both, compared to placebo, in dogs with AD and to evaluate any changes in fatty acid metabolism with these treatments. Twenty-four dogs with AD were randomly allocated to four groups, and were treated orally each day for two months with either 1 mL/10 kg CLA (80% purity), 1 mL/10 kg pure BSO, 1 mL/10 kg CLA+1 mL/10 kg BSO, or 1 mL/10 kg sugar syrup (placebo). Serum was obtained on days 0, 30 and 60 for analysis of CLA metabolites, linoleic acid (LA), gamma-linolenic acid (GLA), dihomo-gamma-linolenic acid (DGLA) and arachidonic acid (AA). At the same time point, the owners were asked to assess pruritus and the veterinarians evaluated any skin lesions present. Although the best clinical results occurred with BSO treatment alone, improvement of clinical signs and pruritus was not significant with any of the treatments. Serum levels of GLA and DGLA significantly increased in BSO-treated dogs, but not in the CLA+BSO group. CLA at the dosage used in this study was not efficacious in treating canine AD, whereas BSO may help some dogs with AD, although further studies are necessary before this can be recommended as a treatment.  相似文献   
4.
The aim of this retrospective study was to describe clinical features, treatment and outcome of 21 dogs with metastatic cancer of unknown primary (MCUP), a biopsy‐proven malignancy being diagnosed at a metastatic stage, in which the anatomical origin of the primary tumour cannot be detected. All dogs underwent total‐body computed tomography. Signalment, type and duration of clinical signs, metastasis site, pathology results, treatment and outcome were recorded. Carcinoma was the most common diagnosis (57.1%), followed by sarcoma, melanoma and mast cell tumour. The median number of disease sites per dog was 2, with bones, lymph nodes, lungs and spleen being the most frequent metastatic locations. The median survival for all dogs was 30 days. Overall, a primary site was not identified in 20 (95.2%) dogs. MCUP encompasses a variety of different pathologic entities and harbours a poor prognosis.  相似文献   
5.
  1. Genetic information is crucial for the conservation of Dipturus oxyrinchus (Linnaeus, 1758), a threatened large skate with declining populations over most of its geographical range. The main aim of the present study was to investigate the genetic structure, connectivity and demographic history of the longnosed skate in Sardinia (western Mediterranean Sea).
  2. Patterns of population structure were assessed in 175 specimens from six sampling sites. Variation in two mitochondrial genes (cytochrome c oxidase subunit I (COI) and control region) highlighted high genetic diversity and low but significant genetic differentiation among sites, which clustered into three groups corresponding to the north‐west, north‐east and south Sardinian coasts.
  3. The observed genetic structuring could presumably depend on a combination of past geological events, contemporary restrictions to dispersal and biological characteristics of the species (e.g. site‐fidelity, no pelagic larval stage, limited dispersal of juveniles and/or adults).
  4. Demographic analyses showed signs of past population expansion, but substantial current stability of Sardinian populations. From a conservation perspective, these results are encouraging, and indicate that Sardinian populations are still large and stable, and seem not to have suffered negative side‐effects from the ever‐growing fishing pressure in the region.
  5. The occurrence of genetic structuring strongly supported the close monitoring of populations to identify any erosion of their gene pool, and high genetic variability of the Sardinian D. oxyrinchus populations could thus represent priority populations for conservation purposes, providing potential sources for recolonization in cases of local extinctions in other areas of the distribution range of the species.
  6. When the sequences from Sardinia were compared with those available from other areas, the data seem to exclude the possibility that the Atlantic and Mediterranean host totally isolated populations or even different species, as recently suggested. However, additional markers and a larger sampling sites are needed to confirm these findings.
  相似文献   
6.
Growth and carcass quality of European rainbow trout populations were compared in a full sib family test over five experimental periods. In total, 131 full-sib families of 17 different populations, (i.e. 19 500 fish), were included. A special system for family testing in trout was developed. This consisted of separate hatching of single pair matings, separate rearing of families up to marketable size and common fattening under two stocking densities. Thus, growth was studied separately for the rearing and the fattening period. The observed differences in rearing and fattening weight between and within populations were quite distinct and of significance for production and breeding efficiency. Similar ranking of populations after fattening in different years and under different stocking densities indicated that the final weight was highly genetically controlled. Carcass characteristics determined at marketable size showed somewhat smaller differences between populations. Populations with the highest fattening weight did not generally produce the most valuable carcasses. The results are discussed with respect to their impact on breeding strategies.  相似文献   
7.
Improving cereal grain carbohydrates for diet and health   总被引:1,自引:0,他引:1  
Starch and cell wall polysaccharides (dietary fibre) of cereal grains contribute to the health benefits associated with the consumption of whole grain cereal products, including reduced risk of obesity, type 2 diabetes, cardiovascular disease and colorectal cancer. The physiological bases for these effects are reviewed in relation to the structures and physical properties of the polysaccharides and their behaviour (including digestion and fermentation) in the gastro-intestinal tract. Strategies for modifying the content and composition of grain polysaccharides to increase their health benefits are discussed, including exploiting natural variation and using mutagenesis and transgenesis to generate further variation. These studies will facilitate the development of new types of cereals and cereal products to face the major health challenges of the 21st century.  相似文献   
8.
Soil microbial processes and Testacea (Protozoa) as indicators of heavy metal pollution The influence of the emissions from a copper smelter on soil microbial processes was investigated at 4 meadow sites along a concentration gradient in Brixlegg (Austria). The first site is within 300 m of the source, further sites are situated 1125 m, 2425 m and 5900 m from the smelter. Heavy metal pollution close to the smelter induced a decrease of microbial biomass, respiration, dehydrogenase activity and the related enzyme activities in soil samples (5–10 cm soil depth): Protease, alkaline phosphatase, arylsulfatase, actual and potential nitrification. Thus, soil microbial processes in the 5–10 cm layer appear to be directly affected by heavy metals. Regarding the testate amoebae, their low individual and species numbers at 5–10 cm soil depth obstruct clear trends of this animal group. However, comparing the heavy polluted site with the control area, abundances, species numbers and biomass of testate amoebae slightly decreased at the polluted site (5–10 cm). Contrary to the results in the 5–10 cm layer, most soil microbial processes as well as abundances, species numbers and biomass of testaceans in the upper soil (0–5 cm) seem to be more strongly influenced by the supply of organic substrate than by the content of heavy metals in the soil.  相似文献   
9.
10.
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