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   291篇
  免费   34篇
林业   17篇
农学   5篇
  22篇
综合类   27篇
农作物   2篇
水产渔业   14篇
畜牧兽医   214篇
植物保护   24篇
  2022年   2篇
  2021年   5篇
  2020年   5篇
  2019年   5篇
  2018年   2篇
  2017年   8篇
  2016年   8篇
  2015年   6篇
  2014年   9篇
  2013年   12篇
  2012年   13篇
  2011年   17篇
  2010年   6篇
  2009年   7篇
  2008年   14篇
  2007年   14篇
  2006年   14篇
  2005年   10篇
  2004年   5篇
  2003年   13篇
  2002年   9篇
  2001年   11篇
  2000年   4篇
  1999年   11篇
  1998年   4篇
  1997年   2篇
  1994年   6篇
  1992年   7篇
  1991年   3篇
  1990年   5篇
  1989年   3篇
  1987年   3篇
  1986年   5篇
  1985年   6篇
  1984年   2篇
  1982年   2篇
  1979年   6篇
  1978年   3篇
  1976年   7篇
  1975年   2篇
  1974年   4篇
  1973年   7篇
  1972年   3篇
  1971年   4篇
  1970年   2篇
  1969年   3篇
  1968年   8篇
  1967年   6篇
  1966年   3篇
  1961年   2篇
排序方式: 共有325条查询结果,搜索用时 15 毫秒
311.
Genetic parameters for average daily gain between the age of 5 and 10 weeks (ADG), the average cross-sectional area of the m. Longissimus dorsi (L) (between the 2nd–3rd and 4th–5th lumbar vertebrae-based on in vivo computerized tomography (CT)) and dressing out percentage (DoP) were estimated in a group of 28,686 Pannon White rabbits reared in 5044 litters and born between 2000 and 2003. Using multivariate animal models with Bayesian procedures, estimated heritabilities were moderate and moderately high for ADG, L and DoP (0.21 to 0.29, 0.25 to 0.42 and 0.19 to 0.71, respectively). Litter effects were moderate for ADG, L and DoP estimates (0.20 to 0.22, 0.10 to 0.18 and 0.09 to 0.30, respectively). Genetic correlation coefficient estimates between ADG and L and ADG and DoP were moderate and negative (− 0.41 to − 0.01, − 0.70 to + 0.10). A moderately high positive genetic correlation was found between L and DoP (0.13 to 0.83).  相似文献   
312.
The effect of 10-day zearalenone administration starting 10 days after ovulation was studied in 6 cycling trotter mares in the summer period. After an entire oestrous cycle (Cycle 1), mares were given 7 mg purified zearalenone per os daily (1 mg/ml in ethyl alcohol) beginning on Day 10 of Cycle 2. Toxin exposure was continued until the subsequent ovulation. Luteal function and follicular activity were monitored daily by rectal palpation, ultrasonography and blood sampling for progesterone. During toxin exposure, all animals were in good physical condition. The toxin had no effect on the length of the interovulatory intervals, luteal and follicular phases. It did not influence significantly the plasma progesterone profiles (logistic curve parameters A1 to A6), the follicular activity (growth rate, maximum size of the ovulatory follicles, maximum number and the time of first increase in the number of large follicles) and the uterine oedema. It is concluded that in cyclic mares the methods used in this study could not detect any adverse effect of zearalenone (administered at a low dose similar to natural exposure) on reproduction.  相似文献   
313.
A simultaneous live/dead and acrosome staining, originally described for domestic mammals, was successfully applied on red deer (Cervus elaphus) and fallow deer (Dama dama) spermatozoa collected from the cauda epididymidis and vas deferens of shot stags. The staining is simple enough for routine application. Seven classes of spermatozoa were distinguished in the smears of frozen/thawed semen samples. Morphology, including cytoplasmic droplets, was evaluated as well. Percentage of live cells with intact acrosomes and with no other morphological aberrations might be a practical index of semen quality.  相似文献   
314.
REASON FOR PERFORMING STUDY: Increased radiopharmaceutical uptake (IRU) in the palmar processes of the distal phalanx is recognised but its clinical significance has not been established. OBJECTIVES: To investigate the relationship between radiographic, scintigraphic and MRI findings in the palmar processes of the distal phalanx. HYPOTHESES: Increased radiopharmaceutical uptake in the palmar processes of the distal phalanx is associated with MRI abnormalities; IRU and MRI abnormalities are over-represented in lame limbs. METHODS: Clinical data, radiographic, scintigraphic and MRI findings of 258 horses with unilateral or bilateral foot pain were recorded. Scintigraphic images were assessed subjectively and using region of interest and profile analysis, and intensity of IRU graded. Alteration in signal intensity in T1 and T2 weighted and short tau inversion recovery (STIR) MR images was documented, and MRI abnormalities graded. Relationships between scintigraphic, MRI, radiographic and clinical findings were assessed. RESULTS: Focal IRU was over-represented in palmar processes with most MRI abnormalities. There was a significant correlation between IRU and MRI grades and IRU was over-represented in palmar processes with MRI Grades 2 and 3. Both IRU and MRI abnormalities occurred most frequently in the medial palmar process. MRI abnormalities were generally over-represented in lame limbs. The most common MRI abnormality was mild diffuse decreased signal intensity in T1 and T2 weighted images, which was associated with mild generalised IRU. CONCLUSIONS: There was considerable variation in the radiographic, scintigraphic and MRI appearance of palmar processes of the distal phalanx. Focal IRU in a palmar process was seen in association with MRI abnormalities and lameness or as an incidental finding. Magnetic resonance imaging abnormalities occurred more frequently in lame limbs, either contributing to lameness or as a consequence of lameness. POTENTIAL RELEVANCE: Further investigation is needed to establish the clinical significance of MRI abnormalities in the palmar processes of the distal phalanx and their relationship with lesions in adjacent structures.  相似文献   
315.
Proximal hindlimb lameness remains a diagnostic challenge despite modern imaging techniques. In the case described here, a fracture of the ischium produced false negative results on initial ultrasound and scintigraphy examinations, despite a 14 day delay from onset of clinical signs to the time of the nuclear bone scan. However, the history and clinical examination were strongly suggestive of a pelvic injury and this was only confirmed by the use of a novel radiographic technique. False negative findings from diagnostic imaging can, and do, occur, even with high sensitivity techniques such as nuclear bone scans used after an appropriate delay period. Therefore, equal weighting should be given to all facets of a lameness investigation, including the history and clinical examination, while remembering the limitations of any imaging modalities used.  相似文献   
316.
OBJECTIVE: To determine the prevalence of detectable serum IgG concentrations in calves prior to ingestion of colostrum and to assess whether a detectable IgG concentration was related to dam parity, calf birth weight, calf sex, season of calving, or infectious agents that can be transmitted transplacentally. ANIMALS: 170 Holstein dairy calves. PROCEDURES: Serum samples were obtained from calves prior to ingestion of colostrum, and serologic testing for bovine viral diarrhea virus (BVDV) and Neospora caninum was performed. Relative risk, attributable risk, population attributable risk, and population attributable fraction for calves with a detectable serum IgG concentration attributable to positive results for N caninum and BVDV serologic testing were calculated. Logistic regression analysis was used to determine whether dam parity, calf sex, season of calving, and calf weight were associated with precolostral IgG concentration. RESULTS: 90 (52.9%) calves had a detectable total serum IgG concentration (IgG >or= 16 mg/dL). Relative risk, attributable risk, population attributable risk, and population attributable fraction for calves with a detectable serum IgG concentration attributable to positive results for N caninum serologic testing were 1.66, 0.34, 0.014, and 0.03, respectively. Calf sex, calf birth weight, and season of calving were not significant predictors for detection of serum IgG in precolostral samples. CONCLUSIONS AND CLINICAL RELEVANCE: Prevalence of IgG concentrations in precolostral serum samples was higher than reported elsewhere. There was no apparent link between serum antibodies against common infectious agents that can be transmitted transplacentally and detection of measurable serum IgG concentrations.  相似文献   
317.
Vascular complications are major causes of graft failure in liver transplantation. The use of different vascular grafts is common but the results are controversial. The aim of this study was to create an 'ideal' arterial interponate for vascular replacements in the clinical field. An autologous, tubular graft prepared from the posterior rectus fascia sheath was used for iliac artery replacement in dogs for 1, 3, 6 and 12 months. Forty-one grafts were implanted and immunosuppression was used in separate groups. The patency rate was followed by Doppler ultrasound. Thirty-seven grafts remained patent, 2 cases with thrombosis and 2 cases with stenosis occurred. There was no evidence of necrosis or aneurysmatic formation. The histological analysis included conventional light microscopic and immunohistochemical examinations for CD34 and factor VIII. The explanted grafts showed signs of arterialisation, appearance of elastin fibres, and smooth muscle cells after 6 months. Electron microscopy showed intact mitochondrial structures without signs of hypoxia. In conclusion, the autologous graft presents acceptable long-term patency rate. It is easy to handle and the concept of beneficial presence of the anti-clot mesothelium until endothelialisation seems to work. The first clinical use was already reported by our group with more than 2 years survival.  相似文献   
318.
The presence of the vanA gene was determined in enterococci from healthy poultry, originating from the Hungarian resistance monitoring system between 2001 and 2004. Enterococci (n = 562) were collected from intestinal samples of slaughtered broiler chickens. The presence of van genes was detected by polymerase chain reaction (PCR). The vancomycin-resistant enterococcus (VRE) strains carried only the vanA gene. Genus- and species-level identification of the vanA gene carrier strains was carried out by PCR using specific primers. In 2001, 25 out of the 289 isolated strains (8.6%) were vanA carriers (1 Enterococcus mundtii, 13 E. durans and 11 E.faecium). In 2002 (n = 87), 20 (23%) strains were vanA positive (11 E. durans and 9 E. faecium). In 2003 and 2004, none of the strains (n = 95 and 91, respectively) were positive for the most common van genes. In 2003, there was only one strain for which higher minimum inhibitory concentrations (MIC) of vancomycin (4 mg/L) and teicoplanin (8 mg/L) were found. In 2004 there were three strains for which the MIC of vancomycin was 8 mg/L, and 2 strains and 1 strain with teicoplanin MICs of 4 mg/L and 8 mg/L, respectively. The potential similarity of these strains was studied by pulsed-field gel electrophoresis (PFGE). The VRE strains were not closely related to one another. The annual data of vancomycin resistance indicate an association between the recovery of vancomycin-resistant enterococci and the use of avoparcin in animal feeds. This study indicates that with the reduced use of antibiotics in food animals, it is possible to decrease the rate of resistant bacteria. Although the use of avoparcin had been banned in 1998, the VRE strains disappeared only five years later.  相似文献   
319.
320.
Root, stem and leaf tissues, from cotton plants exposed to CO2 at ambient (370 μmol mol−1 (control)) or elevated (550 μmol mol−1 (FACE; free-air carbon dioxide enrichment)) levels in the field during the 1990 and 1991 growing seasons, were analyzed for nonstructural carbohydrates (glucose, fructose, sucrose and starch). Besides the FACE treatment, these plants were also exposed to two irrigation levels: 100% and 67% replacement of evapotranspiration. FACE had a greater effect upon cotton plant nonstructural carbohydrates than did irrigation treatments. Leaf carbohydrate content was increased by FACE, but this increase was much more pronounced in the stems and roots. Starch and soluble sugars in leaves in FACE plots tended to be consistently greater than in control leaves, without much change in carbohydrate content during the growing season. In contrast, root and stem, starch and soluble sugar pools were strongly increased by FACE and fluctuated strongly during the growing season. In both seasons, stem and taproot nonstructural carbohydrate content passed through a minimum during periods of heavy boll set. The fluctuations in stem and root carbohydrate content were therefore probably caused by the varying metabolic demands of the developing plant. These results suggest that a significant effect of CO2 enrichment on starch-accumulating plants is an increase of nonstructural carbohydrate, especially starch, in nonleaf storage pools. This buildup occurs somewhat independently of the water status of the plant, and these enlarged pools can be drawn upon by the growing plant to maintain growth during periods of high metabolic demand.  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