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   192篇
  免费   19篇
林业   17篇
农学   6篇
  49篇
综合类   5篇
农作物   20篇
水产渔业   7篇
畜牧兽医   62篇
园艺   5篇
植物保护   40篇
  2023年   2篇
  2022年   3篇
  2021年   8篇
  2020年   11篇
  2019年   13篇
  2018年   11篇
  2017年   8篇
  2016年   10篇
  2015年   15篇
  2014年   6篇
  2013年   8篇
  2012年   15篇
  2011年   13篇
  2010年   11篇
  2009年   7篇
  2008年   14篇
  2007年   12篇
  2006年   11篇
  2005年   6篇
  2004年   6篇
  2003年   6篇
  2002年   5篇
  2001年   1篇
  2000年   2篇
  1996年   1篇
  1992年   1篇
  1983年   2篇
  1980年   1篇
  1978年   1篇
  1977年   1篇
排序方式: 共有211条查询结果,搜索用时 15 毫秒
101.
Apuleia leiocarpa is an environmentally and economically significant Atlantic Forest species threat-ened by ongoing exploitation. The vegetative propagation of ...  相似文献   
102.
103.
During 2003-2005, 399 abortion samples (315 fetuses and 84 placentae) were collected from 107 ovine and caprine farms in northern Sardinia. Tissues from aborted fetuses and placentae were examined by PCR assay to detect DNA from Coxiella burnetii, Chlamydophila abortus, Salmonella enterica Serovar abortusovis, Toxoplasma gondii, and Neospora caninum. The DNA from at least 1 of these 5 infectious agents was amplified in 41% of ovine fetuses, while only 17% of the caprine fetuses yielded a positive amplification result for at least 1 of the 5 agents. Out of a total of 366 ovine aborted samples, T. gondii DNA was detected most frequently (18.1% of fetuses and 13.1% of placentae), followed by S. abortusovis (13% of fetuses and 14.4% of placentae), C. burnetii (10.9% of fetuses, of 9.2% placentae), C. abortus (2.4% of fetuses, 6.5% of placentae), and N. caninum (2% of placentae). In 33 fetuses and 9 placentae, the simultaneous presence of pathogens with different associations was detected. Out of a total of 31 caprine aborted samples, T. gondii was detected most frequently (13% of fetuses and 25% of placentae), followed by C. abortus (12.5% of placentae), C. burnetii (12.5% of placentae), and N. caninum (8.6%).  相似文献   
104.
Right auricle aneurysm (RAA) has been reported to be a rare congenital or acquired condition in dogs, however published CT characteristics are limited to a small number of cases. The aim of this 13-year, single-center, retrospective, cross-sectional study was to describe the prevalence and appearance of RAA in a larger group of dogs. Reports of 10,886 dogs that underwent thoracic CT examination for various reasons were reviewed. Computed tomographic data of dogs with presumed RAA (based on published imaging characteristics) were retrieved from the archive. Oblique multiplanar reformatted images were used to record RAA site, shape, and dimensions (neck, maximum height and width). Patients’ sex, age, and body weight were evaluated for any association with the presence of RAA. Presumed RAA was detected in 23/10,886 dogs having thoracic CT in the selected period of time (prevalence 0.21%). Three RAA phenotypes were described: diffuse saccular dilation in 19 of 23 dogs, focal saccular dilation in three of 23 dogs, and fusiform in one of 23 dogs. The bodyweights of dogs with presumed RAA were significantly lower than those of the remaining 10836 dogs without RAA (median 8 kg [IQR 5; range 37.6] and median 16 kg [IQR 23; range 116.9] respectively; P < 0.003. Female sex was also significantly associated with RAA (P = 0.03). Findings indicated that RAA has a low prevalence in dogs, can be detected with CT, can be present in asymptomatic dogs, and can have varying appearances. In this sample of dogs, female sex and low body weight were significantly associated with RAA.  相似文献   
105.
Commercial seeds are widely used for re‐vegetation interventions in Mediterranean areas. These seeds mostly consist of species and varieties of non‐local provenance. The current practice relies mainly on forage or turf and fast growing species, even if it is often inefficient. Twenty‐two local populations or commercial varieties of annual and perennial species belonging to the botanical families Leguminosae, Graminaceae and Compositae were evaluated in a 4‐year field experiment in order to investigate their potential in terms of establishment and persistence in the re‐vegetation of an inactive sand quarry. Native species showed better performances than commercial varieties and encouraged further actions for the valorisation of local plant biodiversity. Among legumes, the best adapted species was the perennial Lotus cytisoides that showed high persistence in combination with other positive traits. A few annual species, that is, Melilotus indica, Trifolium subterraneum and Ornithopus sativus performed well and persisted until the end of the experiment. Among perennial grasses, Cynodon dactylon survived to drought and low soil nutrients. Both native annual grasses Lolium rigidum and Aegilops geniculata performed very well during the first 2 years of experiments. Both forbs, the perennial Cichorium intybus and the annual Chrysanthemum coronarium did not guarantee a satisfactory persistence. Some native species were evidenced, which may play an important role in the re‐vegetation of sand quarries and have good potential to be further characterized before introduction in the seed market. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   
106.
Preureteral vena cava (circumcaval ureter, retrocaval ureter) occurs in a third of the feline population and has been associated with ureteral strictures in humans. The aim of this retrospective cross‐sectional study was to describe the contrast‐enhanced multidetector row computed tomographic (MDCT) characteristics of presumed preureteral vena cava in a group of cats. Medical records from two institutions located in different continents were searched from 2010–2013 for cases with complete contrast‐enhanced MDCT examinations of the abdomen (i.e. included the entire course of the ureters and prerenal and renal segments of the caudal vena cava) and a diagnosis of preureteral caudal vena cava. For cases meeting inclusion criteria, CT scan data were retrieved and characteristics of the preureteral caudal vena cava were recorded. Presence of concomitant renal or ureteral diseases was also recorded. A total of 272 cats had contrast‐enhanced abdominal CT scans during the study period and of these, 68 cats (22.43 ± 4.96%) had a diagnosis of presumed preureteral vena cava. In all affected cats, a “reverse‐J ureter” was observed, i.e. a ureter running medially at the level of L4–5, passing dorsally to the caudal vena cava and then exiting ventrally between the caudal vena cava and aorta returning to its normal position. Having a preureteral vena cava resulted in an increased risk for concurrent urinary signs (OR = 3.00; CI: 95%; 1.28–6.99; P = 0.01). Findings supported the use of contrast‐enhanced MDCT for characterizing morphology of preureteral vena cava and its relation with ureters in cats.  相似文献   
107.
108.
The present work aims to investigate if the variation of each parameter in Longissimus lumborum muscle could correspond to the same or to a similar variation of the parameter in the other muscles. The work presents results of Pearson's correlations between Longissimus lumborum samples and other muscle samples, such as Biceps femoris, Rectus femoris, Semimembranosus, Supraspinatus and Semitendinosus in horse meat. A total of 27 male IHDH (Italian Heavy Draught Horse) breed foals were employed. They were slaughtered at 11 months of age and the above‐mentioned muscles were sampled. The Longissimus lumborum muscle showed to be representative of other muscles and of the whole carcass for some chemical parameters (moisture, protein and ash) and for some fatty acids profile patterns such as C12:0, C14:0, total monounsaturated fatty acid and polyunsaturated fatty acid, but poor correlations were recorded for intramuscular fat concentration, rheological and colorimetric parameters. Although almost all the qualitative parameters in meat are affected by the anatomical site and by the muscle, the Longissimus lumborum is often not representative in horse meat with regard to modifications of this parameters.  相似文献   
109.
Due to the importance of presurgical, noninvasive, and accurate diagnostic tools in mammary carcinoma characterization, this prospective secondary observational cohort study was designed to evaluate and compare the diagnostic accuracy of B‐mode, Doppler, contrast enhancement ultrasonography, or acoustic radiation force impulse–elastography in identifying mammary carcinomas types with high degree of malignancy. A total of 246 mammary carcinomas from 141 female dogs were analyzed using B‐mode, Doppler, contrast enhancement ultrasonography, and acoustic radiation force impulse ultrasonography prior to their histopathological classification according to types (simple, complex, or special) and grade (I, II, or III). Qualitative and quantitative variables were compared between carcinoma types and grades by Fisher's or analysis of variance. Diagnostic performance was estimated by receiver‐operating characteristic analysis, using histopathological classification as a reference. Deformability (acoustic radiation force impulse) had a diagnostic specificity of 100% and sensitivity of 12% in identifying special carcinomas. A width:length ratio greater than 0.53 can be suggestive of special carcinoma, with 80% sensitivity and 76% specificity. Contrast wash‐in and peak enhancement times lower than 7.5 and 13.5 s, respectively, were indicative of complex carcinoma at 62% sensitivity and 60% specificity. Contrast wash‐in, peak enhancement, and wash‐out times greater than 6.5, 12.5, and 64.5 s, respectively; were indicative of grade II and III carcinoma at 68% sensitivity and 62% specificity. In conclusion, B‐mode ultrasonography, contrast enhancement ultrasonography, and acoustic radiation force impulse–elastography enabled the identification of some of the characteristics of high‐grade mammary carcinoma types and grades in female dogs with limited accuracy. The findings from this study may contribute to oncology research and clinical management canine patients.  相似文献   
110.
Anitschkow cells (AC) are a peculiar type of stromal cells observed in myocardium, cardiac valves and coronary vessels wall whose origin, characterization and role remain controversial. In human heart, they represent a histological hallmark of Aschoff nodules in rheumatic fever, but they have also been observed in other myocardial pathologies. Firstly, they have been considered a myocyte‐derived cells, but light microscopy, immunohistochemical and ultrastructural studies pointed out that a macrophagic/histiocytic origin cannot be excluded. Many authors also reported extracardiac AC or an Anitschkow nuclear pattern, thus suggesting that these cells may represent a chromatin pattern rather than a specific cell type. In veterinary medicine, AC were described in myocarditis, myocardial necrosis, degenerative and inflammatory endocardial diseases of several species. Recently, AC have been observed in intramural coronary arteries of different animals (including cattle and fish) affected by arteriosclerotic processes. Stress related to the intensive livestock farming could represent a mechanotransduction promoting factor of arteriosclerotic changes allowing the development of Anitschkow chromatin pattern. Further studies both in human and veterinary medicine are needed to confirm the origin and role of these peculiar cells.  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