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   993篇
  免费   10篇
  国内免费   4篇
林业   38篇
农学   2篇
基础科学   8篇
  90篇
综合类   333篇
农作物   64篇
水产渔业   10篇
畜牧兽医   429篇
园艺   8篇
植物保护   25篇
  2023年   3篇
  2021年   4篇
  2020年   3篇
  2018年   5篇
  2014年   3篇
  2012年   75篇
  2011年   92篇
  2010年   9篇
  2009年   12篇
  2008年   55篇
  2007年   76篇
  2006年   80篇
  2005年   85篇
  2004年   59篇
  2003年   46篇
  2002年   47篇
  2001年   40篇
  2000年   45篇
  1999年   14篇
  1998年   5篇
  1997年   9篇
  1996年   6篇
  1995年   7篇
  1994年   10篇
  1993年   8篇
  1992年   9篇
  1991年   10篇
  1990年   16篇
  1989年   28篇
  1986年   8篇
  1984年   3篇
  1982年   3篇
  1981年   3篇
  1979年   4篇
  1970年   3篇
  1969年   3篇
  1966年   3篇
  1963年   4篇
  1957年   3篇
  1953年   3篇
  1930年   3篇
  1927年   3篇
  1923年   4篇
  1915年   6篇
  1913年   5篇
  1912年   5篇
  1910年   2篇
  1905年   2篇
  1903年   2篇
  1902年   2篇
排序方式: 共有1007条查询结果,搜索用时 46 毫秒
101.
Vc等生长调节剂对橡胶树种子活力的影响   总被引:2,自引:0,他引:2  
用0.1%浓度的Vc处理橡胶树种子,提高了种子的活力指数,并促进脂质降解和核酸合成等代谢活性,但对种子的水分吸收没有效应。  相似文献   
102.
向日葵产量构成和成熟期性状的配合力分析   总被引:1,自引:0,他引:1  
  相似文献   
103.
104.
105.
106.
Samples of serum taken from 42 dogs with clinical signs and histories indicating pruritic skin disease and/or diseases of the ear were tested in a commercial allergen-specific assay for immunoglobulin E. Dogs which had been treated with glucocorticoids and/or antihistamines were not excluded. The samples were separated into two equal aliquots, given different randomised numbers, and analysed in two batches on two separate days. The laboratory was blinded to the identification numbers and the history of each dog, but knew the purpose of the study. The results for 48 allergens were expressed in modified absorbance units (MAU). The overall median MAU was 29. For each allergen the mean difference between the MAU values of the paired duplicates was determined and the difference was compared to zero by a paired t test. The number of means that were not 0 (P<0.05) in each allergen group were: seven of 10 grasses, seven of nine weeds, two of 13 trees, six of 10 fungi, and three of six environmental allergens. A single 2 x 2 table for the 48 allergens was created with MAU > or = 60 defined as 'positive' and < 60 as 'negative'. There were 116 of 188 (62 per cent) pairs that were reproducibly 'positive' and 1756 of 1828 (96 per cent) pairs that were reproducibly 'negative'.  相似文献   
107.
A three-year-old Border collie was presented with a two-week history of lethargy, stiff gait, polydipsia and polyuria. Biochemical analysis revealed hypercalcaemia. Serum concentrations of 25-hydroxyvitamin D (25[OH]D) and 1,25-dihydroxyvitamin D (1,25[OH]2D) were markedly elevated and parathyroid hormone was undetectable. Subsequent analysis of the dog's diet revealed that the food contained excessive amounts of vitamin D. The hypercalcaemia resolved following treatment with bisphosphonates and dietary change. Hypervitaminosis D was diagnosed in a second unrelated dog, which had been fed the same brand of dog food as case 1. The dog was also hypercalcaemic and had markedly elevated serum concentrations of 25(OH)D and 1,25(OH)2D. Hypervitaminosis D in dogs has been reported to occur secondarily to ingestion of either rodenticides containing cholecalciferol or antipsoriatic ointments that contain vitamin D analogues. Hypervitaminosis D has also been reported following the treatment of hypoparathyroidism. To the authors' knowledge, this is the first report of hypervitaminosis D in dogs following the accidental over supplementation of a commercial diet with vitamin D. While the benefits of adequate dietary vitamin D are well established in dogs, the potential deleterious effects of over supplementation of vitamin D should also be acknowledged.  相似文献   
108.
109.
OBJECTIVE: To describe and analyze the left ventricular free wall (LVFW) radial and longitudinal motions in a population of healthy Maine Coon cats by use of quantitative 2-dimensional color tissue Doppler imaging (TDI). ANIMALS: 23 healthy young Maine Coon cats (mean +/- SD: age, 2.1 +/- 0.9 years; weight, 5.0 +/- 1.0 kg). PROCEDURE: TDI was performed by the same trained observer (VC) on all cats. Radial LVFW velocities were recorded in endocardial and epicardial LVFW segments, and longitudinal velocities were recorded in the mitral annulus and in basal and apical LVFW segments. Isovolumic contraction and relaxation times were calculated in each myocardial segment, and the coefficients of variation (CVs; %) were determined for each TDI parameter. RESULTS: LVFW velocities were significantly higher in the endocardial layers than in the epicardial layers and also significantly higher in the basal than in the apical segments. Annular velocities were significantly higher than basal myocardial velocities in systole and early diastole. Coefficient of variation values were lower for radial velocities, particularly in systole, and were also lower for time intervals (16% to 22%) than for myocardial velocities (19% to 62%). CONCLUSIONS AND CLINICAL RELEVANCE: Because Maine Coon cats are predisposed to an inherited hypertrophic cardiomyopathy, which is a common cause of death in this breed, TDI could provide a useful tool for early detection of the disease. Tissue Doppler imaging indices may complete the conventional analysis of the left ventricular function in Maine Coon cats. However, the usefulness of TDI indices in the early detection of myocardial dysfunction needs to be clarified.  相似文献   
110.
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