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   416篇
  免费   43篇
林业   14篇
农学   6篇
基础科学   1篇
  47篇
综合类   77篇
农作物   14篇
水产渔业   34篇
畜牧兽医   246篇
园艺   5篇
植物保护   15篇
  2022年   3篇
  2021年   4篇
  2020年   7篇
  2019年   10篇
  2018年   7篇
  2017年   15篇
  2016年   13篇
  2015年   15篇
  2014年   8篇
  2013年   21篇
  2012年   15篇
  2011年   22篇
  2010年   14篇
  2009年   11篇
  2008年   13篇
  2007年   21篇
  2006年   30篇
  2005年   22篇
  2004年   11篇
  2003年   26篇
  2002年   21篇
  2000年   7篇
  1999年   3篇
  1998年   12篇
  1997年   12篇
  1996年   5篇
  1995年   3篇
  1994年   4篇
  1993年   12篇
  1992年   4篇
  1991年   7篇
  1990年   3篇
  1989年   5篇
  1988年   4篇
  1987年   5篇
  1986年   5篇
  1985年   7篇
  1984年   3篇
  1982年   3篇
  1979年   3篇
  1977年   4篇
  1973年   3篇
  1972年   4篇
  1971年   2篇
  1970年   2篇
  1969年   2篇
  1945年   3篇
  1944年   2篇
  1941年   2篇
  1910年   2篇
排序方式: 共有459条查询结果,搜索用时 796 毫秒
101.
102.
103.
104.
Benign and malignant splenic masses can appear similar on B-mode imaging, making ultrasound sensitive but not specific in their diagnosis. Our goal was to characterize color and/or power Doppler characteristics of vasculature within and adjacent to a splenic mass, which would distinguish benign vs. malignant lesions. The hypothesis was that malignant splenic masses will have altered vascular patterns compared with benign masses. Color and power Doppler cineloops evaluating the vasculature within the mass and normal splenic parenchyma were obtained in sagittal and transverse planes using a standardized protocol. Categories of evaluation included presence of peritoneal effusion, a large aberrant or tortuous vessel within the mass, relative blood flow within the mass compared with normal parenchyma, and path of vessels in the adjacent parenchyma entering into the mass. All patients had histopathologic or definitive cytologic diagnosis. Thirty-one dogs were included. There were 13 malignant masses and 18 were benign. Peritoneal effusion was significantly associated with malignancy (P = 0.0007). Presence of an aberrant or tortuous vessel within the mass was nearly significant (P = 0.059). There was no significant difference in any of the color or power Doppler blood flow evaluations. Ultrasonographic findings of a splenic mass and peritoneal effusion may indicate malignancy. The presence of an aberrant vessel within a splenic mass could suggest malignancy; however more data are needed.  相似文献   
105.
Between 65% and 91% of human‐patient sonographers report musculoskeletal symptoms related to their work activities. Ergonomic risk factors associated with musculoskeletal symptoms and musculoskeletal disorders (MSDs) include force, repetition, and awkward postures of the upper extremities. We hypothesized that veterinary sonographers experience similar risk factor exposures as their colleagues in human‐patient sonography, and that work‐related exposures may lead to similar prevalence of musculoskeletal symptoms and disorders. The Occupational Safety and Health Administration and Society of Diagnostic Medical Sonography published MSD prevention guidelines in 2003. Similar guidance for sonographers examining animal patients does not exist. This cross‐sectional study was designed to evaluate the prevalence of musculoskeletal symptoms among veterinary sonographers and identify reported risk factors. A 59‐item survey questionnaire was administered via email to veterinary specialists likely to perform ultrasound. Musculoskeletal pain related to performing ultrasound exams was reported by 62% of the respondents. Musculoskeletal symptoms were significantly associated with female gender (odds ratio [OR], 4.55; 95% confidence interval [CI], 2.04–10.19), age (OR, 1.06; 95% CI, 1.01, 1.10), previous work‐related trauma (OR, 6.86; 95% CI, 1.71, 27.40), not consistently using a normal height chair (OR, 2.63; 95% CI, 1.19, 5.80), and 15°–45° abduction of shoulder (OR, 2.34; 95% CI, 1.11, 4.92) . It was concluded that the prevalence of musculoskeletal symptoms among veterinary sonographers was similar to that occurring in human‐patient sonographers. © 2012 Veterinary Radiology & Ultrasound.  相似文献   
106.
Objective   To determine if juvenile pearl oysters ( Pinctada maxima ) infected with Haplosporidium hinei are also infected with another haplosporidian parasite, Minchinia occulta .
Design   Archived samples of pearl oysters infected with H. hinei were examined using polymerase chain reaction (PCR) assays and in situ hybridisation (ISH) to analyse and identify haplosporidians. A 144-bp and 220-bp region of Minchinia DNA were targeted by PCR and amplified DNA from formalin-fixed H. hinei -infected pearl oyster samples was sequenced. A 25-bp oligonucleotide probe targeting a variable section of the parasite's small subunit rRNA gene was used in ISH.
Results   The results of DNA-based diagnostic assays supported each other. The sequences obtained by PCR were found to be almost identical to M. occulta from rock oysters and the ISH assay demonstrated infection with M. occulta in affected pearl oysters. ISH indicated a prevalence of infection of 26.7% in one of the previous outbreaks.
Conclusion   Pearl oyster spat are susceptible to infection by a Minchinia parasite, most likely M. occulta , which was recently identified in rock oysters within the pearl-producing zones of Western Australia and is associated with mortalities of up to 80% in this species. The occurrence of haplosporidian co-infections in pearl oysters suggests the immunocompetence of juvenile oysters may be an important factor in preventing infection and therefore preventing mortalities such as those occurring in the recent outbreaks of pearl oyster oedema disease.  相似文献   
107.
Our aim was to evaluate the inspection of arriving passengers for the illegal transport of animal products through the international airport into Taiwan. Passenger-violation data were retrieved from the Bureau of Animal and Plant Health Inspection and Quarantine (BAPHIQ) in Taiwan. Monte Carlo simulations with 5000 iterations were applied to estimate the predicted violation numbers considering factors such as passenger's nationality/ethnicity, sex, and monthly statistics of violations. The results showed that Chinese-related passengers and passengers from South East Asian countries have a relatively higher potential risk for incurring violations during the period from Christmas to Chinese Lunar New Year. Most monthly estimated violation risks are significantly higher than observed violation risks in 2001 and 2002, except April, July, and August. Due to the low sensitivity of the current detection system (reflected by the higher estimated violation risks and a two-fold detection increase after the implementation of an inspection service using detector dogs), we recommend additional preventive measures be taken.  相似文献   
108.
A total of 1,950 serum samples from dairy cattle in California, USA were tested for the presence of antibodies to Mycobacterium avium subspecies paratuberculosis (MAP) using a commercial enzyme-linked immunosorbent assay (ELISA) kit. The sampled animals came from 65 herds and were sampled to reflect the relative numbers and distribution of dairy herds within three geographic regions in the state. Using the manufacturers suggested cut-off for a positive test, 89 animals (4.6%) were positive. The seroprevalence was 6.9% in the northern region of the state, 3.7% in the central region and 5.2% in the southern region. Using the sensitivity and specificity claimed by the manufacturer of the ELISA kit, the true prevalence in California dairy cattle overall was calculated as 9.4% (99% CI, 7.7%, 11.1%) and the true prevalences for the northern, central and southern regions were 14.1% (99% CI, 9.6%, 18.65%), 7.5% (99% CI, 5.6%, 9.4%), and 10.6% (99% CI, 5.9%, 15.6%), respectively.  相似文献   
109.
OBJECTIVE: To quantitate the density of Dermatophagoides farinae and D pteronyssinus and concentrations of house dust mite (HDM) allergens (Der f 1, Der p 1, and Group 2 allergens) in the indoor microenvironment of dogs. Sample Population-50 homes in Columbus, Ohio. PROCEDURES: n each home, samples of dust were collected from 3 locations in which dogs spent most time. Whenever possible, the species of mites collected was identified. Mite density (mites/g of dust) was assessed, and allergen concentrations were assayed by standardized ELISAs. Relative humidity and temperature in each home were monitored during a 5-day period. Characteristics of homes and sample sources were evaluated. RESULTS: Dust samples from all 50 homes contained > or = 1 HDM allergen; Der f 1 and Der p 1 were detected in 100 and 74% of homes, respectively. Fifteen homes had HDMs; compared with D pteronyssinus, D farinae was found more commonly (14/15 homes) and at a higher density. Basements, homes without central air-conditioning, and dog beds that were > or = 1 year old had high HDM allergen concentrations. Homes with > or = 2 microg of Der f 1 or Group 2 allergens/g of dust or > or = 100 mites/g of dust were significantly more likely to have a maximum relative humidity > or = 75%. CONCLUSIONS AND CLINICAL RELEVANCE: Results indicate the presence of HDMs and HDM allergens in the specific microenvironment of dogs in homes. Factors associated with high levels of exposure were identified, which may be associated with increased risk for sensitization and development of atopic diseases.  相似文献   
110.
This is a final report of an experimental transmission of sheep scrapie agent by intracerebral inoculation to Rocky Mountain elk (Cervus elaphus nelsoni). It documents results obtained in experimental (n = 6) and control (n = 2) elk. During the first 2 years postinoculation (PI), 3 animals died or were euthanized because of infection or injuries other than spongiform encephalopathy (SE). In years 3 and 4 PI, 3 other inoculated elk died after brief terminal neurological episodes. Necropsy of these animals revealed moderate weight loss but no other gross lesions. Microscopically, characteristic lesions of SE were seen throughout the brain and spinal cord, and the tissue was positive for proteinase K-resistant prion protein (PrPres) by immunohistochemistry (IHC) and by Western blot. Scrapie-associated fibrils (SAF) were observed by negative-stain electron microscopy in the brain of elk with neurologic signs. PrPres and SAF were not detected in the 3 inoculated elk necropsied during the first 2 years or in the 2 control animals. Retrospective analysis of the gene-encoding cervid PrP revealed a polymorphism at codon 132. The elk with SE were either homozygous (MM) or heterozygous (LM). These findings confirm that intracerebral inoculation of sheep scrapie agent results in SE with accumulations of PrPres in the central nervous system of elk. Based on morphologic and IHC findings, the experimentally induced SE cannot be distinguished from chronic wasting disease of elk with currently available diagnostic techniques.  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