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   758篇
  免费   79篇
  国内免费   1篇
林业   23篇
农学   10篇
  103篇
综合类   82篇
农作物   20篇
水产渔业   38篇
畜牧兽医   506篇
园艺   17篇
植物保护   39篇
  2024年   2篇
  2023年   9篇
  2022年   15篇
  2021年   25篇
  2020年   27篇
  2019年   42篇
  2018年   18篇
  2017年   18篇
  2016年   18篇
  2015年   27篇
  2014年   29篇
  2013年   33篇
  2012年   54篇
  2011年   57篇
  2010年   40篇
  2009年   26篇
  2008年   61篇
  2007年   69篇
  2006年   52篇
  2005年   36篇
  2004年   49篇
  2003年   49篇
  2002年   45篇
  2001年   4篇
  2000年   3篇
  1999年   12篇
  1998年   2篇
  1997年   2篇
  1995年   4篇
  1994年   1篇
  1993年   1篇
  1992年   1篇
  1990年   2篇
  1988年   1篇
  1987年   1篇
  1985年   1篇
  1984年   1篇
  1955年   1篇
排序方式: 共有838条查询结果,搜索用时 15 毫秒
11.
Sarcocystidae is a family of coccidian protozoa from the phylum Apicomplexa that includes Toxoplasma, Neospora, Sarcocystis, Hammondia, and Besnoitia spp. All species undergo a 2‐host sexual and asexual cycle. In the definitive host, replication is enteroepithelial, and infection is typically asymptomatic or less commonly causes mild diarrhea. Clinical disease is most frequently observed in the intermediate host, often as an aberrant infection, and is mostly associated with neurologic, muscular, or hepatic inflammation. Here, we review the literature regarding intestinal Sarcocystidae infections in dogs and cats, with emphasis on the life cycle stages and the available diagnostic assays and their limitations. We also report the diagnostic findings for an 11‐year‐old dog with acute neutrophilic hepatitis, biliary protozoa, and negative biliary culture. Although Toxoplasma and Neospora IgG titers were both high, PCR for these 2 organisms was negative for bile. The organisms were identified by 18S rDNA PCR as most consistent with Hammondia, either H heydorni or H triffittae. This is the first report of presumed Hammondia organisms being found in canine bile.  相似文献   
12.
The objective was to optimize rebreeding of nonpregnant, previously inseminated beef cattle. In Experiment 1, 43 cows received a used intravaginal progesterone-releasing insert (IVPRI; Days 0-7) 12.3 d after ovulation and received concurrently no treatment, 100 microg gonadotropin releasing hormone (GnRH), 1 mg estradiol cypionate (ECP), or 150 mg progesterone. Emergence of a new ovarian follicular wave was most synchronous (P < 0.0001) in the GnRH group. In Experiment 2, 675 heifers were given GnRH or no treatment on Day 0, fed melengestrol acetate (MGA; 0.5 mg/head/d) from Days 0-5 (Day 0 = 13-14 d after timed insemination; TAI), given 0.5 mg ECP or nothing on Day 7, and reinseminated 6-12 h after onset of estrus. Estrus was more synchronous (P < 0.05) in heifers given GnRH versus no treatment on Day 0. In Experiment 3, 317 TAI heifers were resynchronized with either MGA or a used IVPRI with or without ECP on Day 7; estrus was more synchronous (P < 0.05) and pregnancy rates were higher (54.1% versus 39.2%, P < 0.05) in heifers given a used IVPRI than those fed MGA. For resynchronization of heifers, pregnancy rates were not significantly improved with GnRH treatment, but were higher with a used IVPRI than with MGA.  相似文献   
13.
OBJECTIVE: To determine the prevalence of appendicular osteosarcoma (OSA) in Greyhounds compared with other breeds and identify potential intrinsic risk factors associated with development of OSA. DESIGN: Retrospective case series. ANIMALS: 179 dogs with primary appendicular OSA. PROCEDURES: Medical records of dogs in which primary appendicular OSA had been diagnosed between 1996 and 2005 were reviewed. Prevalence and crude odds ratios for OSA were calculated for various breeds by comparison with a reference population of mixed-breed dogs. Age and sex were examined as potential risk factors for the 3 breeds with highest prevalence. RESULTS: Breed period prevalence of OSA was highest for Greyhounds (21/339 [6.2%]), followed by Rottweilers (51/969 [5.3%]) and Great Danes (13/297 [4.4%]); all 21 Greyhounds with OSA were identified as having retired from racing. Sex was not identified as a risk factor for OSA in these breeds, but in all 3 breeds, risk of OSA increased with age. Greyhounds were significantly older at the time of OSA diagnosis (mean, 9.9 years) than were Rottweilers (8.3 years) and Great Danes (7.8 years). Rottweilers and Great Danes were more likely to have OSA involving the forelimbs than the hind limbs. The most frequent lesion sites for all 3 breeds were the proximal end of the humerus and distal end of the radius. The proximal end of the femur was also a common site for the Greyhounds. CONCLUSIONS AND CLINICAL RELEVANCE: Results of the present study suggested that Greyhounds, Rottweilers, and Great Danes had an increased risk of developing OSA, compared with mixed-breed dogs.  相似文献   
14.
Disseminated Aspergillus flavus infection in broiler breeder pullets   总被引:1,自引:0,他引:1  
Increased morbidity and mortality occurred in a 5-wk-old broiler breeder replacement pullet flock. The affected broiler pullet flock was housed on the first floor of a two-story confinement building. Mortality increased to 0.1%/day compared to the flock on the second floor, which had mortality levels of less than 0.01%/day. Clinical signs in the affected chickens included inactivity, decreased response to stimuli, and anorexia. No respiratory or neurologic signs were observed. On necropsy, affected pullets were dehydrated and emaciated and had disseminated variably sized single or multiple heterophilic granulomas that contained intralesional septate and branching fungal hyphae. Lesions were extensive around the base of the heart in the thoracic inlet and in the kidneys. Other affected organs included eyelid, muscle, proventriculus, ventriculus, intestine, liver, spleen, lung, and heart. Aspergillus flavus was cultured from the visceral granulomas. The source of flock exposure to the organism was not determined.  相似文献   
15.
The objective of this research was to determine the effect of stocking density and inclusion of subtherapeutic chlortetracycline in the diet on Salmonella fecal prevalence and antimicrobial resistance in growing swine. A 2 x 2 factorial design was employed on a privately owned commercial swine farm. Four finisher rooms were included in the study. Two of the rooms received 50 g/tonnes of chlortetracycline in the ration, two rooms received no antimicrobials in the feed. In each room, alternate pens were assigned to either high stocking density (0.60 m2/pig) or low stocking density (0.74 m2/pig). Pigs were placed in the finisher rooms at 10 weeks of age and followed for 6 weeks. Individual fecal samples were collected from the floors of each pen and cultured once weekly. Antimicrobial resistance phenotypes were determined. Data were analyzed using multilevel, multivariable logistic regression. Pigs fed chlortetracycline were at increased odds (OR 6.88, 95% CI 2.77-17.12) to shed Salmonellae. No other associations between treatments (CTC and stocking density) and Salmonella prevalence or reduced susceptibility to antimicrobials were identified. Variance in the odds of a fecal sample to be positive was distributed mostly at the lowest level, the individual fecal sample. The increased risk of shedding associated with inclusion of subtherapeutic chlortetracycline in swine diets is discordant with previous results by our group, suggesting farm or strain specific factors may impact this association. Understanding this risk may provide a potential intervention for controlling Salmonella pre-harvest.  相似文献   
16.
The purpose of this study was to determine the serological and molecular prevalence of Bartonella spp. infection in a sick dog population from Brazil. At the S?o Paulo State University Veterinary Teaching Hospital in Botucatu, 198 consecutive dogs with clinicopathological abnormalities consistent with tick-borne infections were sampled. Antibodies to Bartonella henselae and Bartonella vinsonii subsp. berkhoffii were detected in 2.0% (4/197) and 1.5% (3/197) of the dogs, respectively. Using 16S-23S rRNA intergenic transcribed spacer (ITS) primers, Bartonella DNA was amplified from only 1/198 blood samples. Bartonella seroreactive and/or PCR positive blood samples (n=8) were inoculated into a liquid pre-enrichment growth medium (BAPGM) and subsequently sub-inoculated onto BAPGM/blood-agar plates. PCR targeting the ITS region, pap31 and rpoB genes amplified B. henselae from the blood and/or isolates of the PCR positive dog (ITS: DQ346666; pap31 gene: DQ351240; rpoB: EF196806). B. henselae and B. vinsonii subsp. berkhoffii (pap31: DQ906160; rpoB: EF196805) co-infection was found in one of the B. vinsonii subsp. berkhoffii seroreactive dogs. We conclude that dogs in this study population were infrequently exposed to or infected with a Bartonella species. The B. henselae and B. vinsonii subsp. berkhoffii strains identified in this study are genetically similar to strains isolated from septicemic cats, dogs, coyotes and human beings from other parts of the world. To our knowledge, these isolates provide the first Brazilian DNA sequences from these Bartonella species and the first evidence of Bartonella co-infection in dogs.  相似文献   
17.
Adrenalectomies for canine adrenal tumours are associated with peri-operative morbidity and mortality. Objectives of this study included assessing the prognostic value of tumour- or surgery-related variables in predicting peri-operative mortality and overall survival in dogs undergoing adrenalectomies for primary adrenal tumours as well as pre-treatment with phenoxybenzamine on survival to discharge with pheochromocytomas specifically. A multi-institutional retrospective cohort study was performed across nine institutions. Electronic medical record searches identified 302 dogs which met the inclusion criteria. Data collected included dog-related, tumour-related, treatment-related, surgery-related, and outcome variables. Univariate and multivariable logistic regression and cox proportional hazards models were used to identify variables associated with death prior to discharge and tumour-related survival. Overall, 87% of dogs survived to discharge with a tumour-related survival time of 3.96 years. Post-operative complications were reported in 25%. Increased surgical time (p = 0.002) and pre-surgical medical treatment other than phenoxybenzamine (p = 0.024) were significantly associated with increased peri-operative mortality while ureteronephrectomy (p = 0.021), post-operative pancreatitis (p = 0.025), and post-operative aspiration pneumonia (p < 0.001) were significantly associated with decreased overall survival. Phenoxybenzamine pretreatment had no effect on peri-operative mortality. Thirty-seven of 45 (82%) dogs with pheochromocytomas not pretreated survived to discharge, and 50 of 59 (85%) dogs with pheochromocytomas pretreated with phenoxybenzamine survived to discharge (p = 0.730). This study provides information on risk factors for death prior to discharge and tumour-related survival that may help guide clinical management and owner expectations. In addition, the study findings challenge the previously reported benefit of phenoxybenzamine for pretreatment of dogs undergoing adrenalectomies for pheochromocytomas.  相似文献   
18.
This study is a bibliometric analysis of journal articles generated from an intramural grant program in the agbiosciences. Using citation analysis and bibliometric mapping, the study analyzes 515 journal articles published from 1999 to 2017. Results show the growth of journal article output, identify the major research fields and topics, describe national and international authorial and institutional collaborations, and quantify the performance and impact of the article output. The grant program’s journal article output presents a multi-disciplinary range of scholarly publications that reflect the disciplines of The Ohio State University’s College of Food, Agricultural, and Environmental Sciences, which houses the grant program.  相似文献   
19.
‘Bailer’ (Endless Summer™) is a new, pink- or blue-flowered hydrangea that flowers on new wood continuously throughout the growing season. It is also winter-hardy in northern, temperate climates (USDA Z4). Use of Endless Summer as a florist's potted hydrangea would provide consumers with a dual-use product (flowering potted plant, landscape shrub). The objectives were to determine if Endless Summer could be forced as a florist's hydrangea using two forcing regimes (immediate, standard), two soil pH regimes, and two pinching treatments. ‘Merritt Supreme Pink’ (pink), ‘Blue Danube’ (blue), and Endless Summer (blue, pink) were forced under immediate (no cold treatment, short- and long-day photoperiods) and standard (6 weeks cold, 4 °C to overcome dormancy) conditions. Since commercial liners were not yet available, cuttings of Endless Summer were used in the immediate forcing experiment. Days to visible flower bud, first color, full flower were recorded, as well as height, no. of branches, no. of flowers, and flower size. In the immediate forcing experiment, only Endless Summer produced flowers. Cultivars differed significantly (P < 0.001) for days to visible flower bud, days to first color, days to full flower, and height. The number of flowers and flower size were not significantly different among pink cultivars. In the standard forcing experiment, Endless Summer reached days to visible flower bud, days to first color, and days to full flower significantly earlier than either comparison, although it exhibited weaker stems and less intense flower pigmentation. Pinching (blue pH) had a significant effect on all traits except the days to full flower and flower size, although no pinching treatment was significant for pink pH. Photoperiod was significant only for the days to visible flower bud (pink pH), days to full flower (blue pH), and final height (blue pH). Further research is needed before Endless Summer can be grown as a dual-use florist's potted hydrangea with acceptable quality.  相似文献   
20.
This study aimed at capturing the spatial variability of landscape patterns and their trajectories of change from 1950 to 2000 within a watershed, which is representative of areas of intensive agricultural use. After an analysis of landscape features changes for the entire watershed based on aerial photographs, hierarchical clustering analysis provided a typology of landscape patterns for the cadastral lots. Following that, the trajectory of change of each lot was characterized (nature, importance, direction, rate of change). Seven types of landscape patterns are distinguished by the relative importance of different classes of landscape features and 51 trajectories of change were identified for the lots. The analysis shows that although the majority of lots were subjected to a homogenization of their landscape patterns since 1950, this trend is not entirely uniform and that since 2000 it occurs alongside trends towards diversification of certain landscape features on some lots. Furthermore, nearly a third of the lots are not following the main trajectories of change detected. Thus, the results suggest that extrinsic forces (policies, technologies) that are directing main changes in areas of intensive agricultural use toward uniformity could be modulated by internal forces (uses and values of the population). A better understanding of theses internal forces seems crucial to manage landscapes. From a methodology standpoint, although the hierarchical clustering analyses appear useful for understanding the spatial and temporal variability of landscape patterns, particular attention must be given to validating the typology chosen to characterize them.  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