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   324篇
  免费   38篇
林业   20篇
农学   12篇
  55篇
综合类   14篇
农作物   15篇
水产渔业   41篇
畜牧兽医   166篇
园艺   2篇
植物保护   37篇
  2023年   5篇
  2022年   12篇
  2021年   17篇
  2020年   20篇
  2019年   29篇
  2018年   15篇
  2017年   16篇
  2016年   19篇
  2015年   14篇
  2014年   15篇
  2013年   22篇
  2012年   13篇
  2011年   25篇
  2010年   12篇
  2009年   14篇
  2008年   14篇
  2007年   20篇
  2006年   11篇
  2005年   15篇
  2004年   7篇
  2003年   4篇
  2002年   6篇
  2001年   6篇
  2000年   3篇
  1999年   5篇
  1998年   2篇
  1997年   5篇
  1996年   2篇
  1995年   1篇
  1994年   1篇
  1993年   3篇
  1992年   1篇
  1989年   1篇
  1988年   1篇
  1986年   1篇
  1976年   2篇
  1973年   1篇
  1971年   1篇
  1970年   1篇
排序方式: 共有362条查询结果,搜索用时 15 毫秒
51.
Tropical Animal Health and Production - The objective of this study was to analyze the correlation between condemnations in slaughterhouses situated in Minas Gerais State and notifications to the...  相似文献   
52.
Criollo horse breeding is an important economic activity in South America. Because of their athletic performance, these animals tend to show great incidence of musculoskeletal disorders, many of them diagnosed by means of perineural blocks. However, incorrect interpretation of these blocks may be due to anatomical differences in nerve distribution. The objective of this study was to describe the innervation of the digit region of thoracic limbs in Criollo horses, in order to improve the interpretation of tests for claudication diagnosis based on nerve block. Thirty thoracic limbs from Criollo horses were dissected. It could be observed that in 90% of the limbs, dorsal branches of the palmar nerve originated proximally to the proximal sesamoid bone. In 93% of the cases, the palmar digital nerve and the dorsal branches communicated; in 87% of the cases, communication between branches of the dorsal branch was observed; and in 27% (8/30) of the limbs, the palmar metacarpal nerve and the dorsal branch presented communications. None of the specimens showed complete symmetry in the distribution of nerves in contralateral limbs. The high frequency of communication between the nerves may be a particularity of the Criollo breed that may interfere with the interpretation of perineural blocks. Based on the anatomical position, it may be inferred that divergent results in Criollo horses may occur when abaxial sesamoid nerve block is used. Palmar digital nerve block may be less influenced by these variations, provided it is performed as distal as possible from the ungular cartilage.  相似文献   
53.
Triticale (X Triticosecale, Wittmack) is generally accepted as a very rustic crop which can grow in difficult soils such as those with low pH, where aluminum (Al) and/or manganese (Mn) are frequently in excess. The first aim of the present work was to establish the parameters for the future evaluation of Mn excess tolerance. Plants were grown in pots with sand fed with a nutrient solution (pH 4.5) to which MnSO4 .4H2O was added. The biomass of plants (cv. Arabian) grown during one monm in a range of Mn concentrations (2,2.75,11, 16.5,22, 33, and 44 ppm) was determined in Experiment I. Subsequently a shorter range (10, 50, 100, and 200 ppm) was chosen and used with four cvs. (Arabian, Beagle, Borba, and TTE 9201) during the complete growth period (Experiment II). During this experiment the effects of Mn concentrations on the net photosynthetic rates, stomatal conductance, photosynthetic capacity, photochemical efficiency of PSII, quantum yield of photosynthetic non cyclic electron transport and leaf content of chlorophylls, and carotenoids in the several cvs. were studied. The final biomass and yield were taken as the ultimate criteria for ranking the cvs. It was concluded that 10 ppm Mn concentration was optimal for the growth and 50 ppm the lowest limit to produce toxicity which indicates that triticale was rather tolerant. All the physiological parameters determined after one month of growth and the performance of the photosystems were negatively affected by the Mn concentrations, but the changes were not sufficient to be used for an early (one month old plants) ranking of the cvs. consistent with the biomass and final grain yield. However, all the results agree that the cv. Arabian was the most sensitive because it suffered the strongest decreases and was affected by 50 ppm Mn concentration. The plants of the cv. TTE 9201 were the least affected as far as photosynthetic parameters are concerned.  相似文献   
54.
Genotoxic and antigenotoxic effects of acerola fruit at two stages of ripeness were investigated using mice blood cells. The results show that no ripeness stage of acerola extracts presented any genotoxic potential to damage DNA (Comet assay) or cytotoxicity (MTT assay). When antigenotoxic activity was analyzed, unripe fruit presented higher DNA protection than ripe fruit (red color) extract. The antioxidant capacity of substances also showed that unripe samples inhibit the free radical DPPH more significantly than the ripe ones. The results about determination of compounds made using HPLC showed that unripe acerola presents higher levels of vitamin C as compared to ripe acerola. Thus, vitamin C and the complex mixture of nutrients of Malpighia glabra L., and especially its ripeness stages, influenced the interaction of the fruit extract with the DNA. Acerola is usually consumed when ripe (red fruit), although it is the green fruit (unripe) that has higher potential as beneficial to DNA, protecting it against oxidative stress.  相似文献   
55.
Foliar spots caused by Pseudomonas coronafaciens pv. garcae (Pcg), Pseudomonas amygdali pv. tabaci (Pat) and Pseudomonas cichorii (Pch) are major bacterial diseases that can reduce coffee production. However, little is known about the genetic diversity and molecular mechanisms underlying the pathogenicity to coffee plants of these bacteria. In this study, genome sequences of Pcg, Pat and Pch strains isolated from coffee plants in Minas Gerais state, Brazil, were used to assess their variability and plasticity, and compare their type III secretion system (T3SS) and apoplastic effector repertoires as well as tabtoxin biosynthetic/detoxification genes. Genomic diversity was found for all three phytopathogens, among which Pch possesses the highest number of exclusive proteins. The Pcg genome is the most stable whereas that of Pch is the most plastic, which is related to their host ranges. When compared with those of Pseudomonas syringae pv. tomato DC3000, hrp/hrc gene sequences are more conserved in Pcg and Pat than in Pch, which also possesses the smallest T3SS and the largest apoplastic effector repertoires. The only T3SS effector family common to all three pathogens is AvrE, suggesting that, as for other plant–Pseudomonas interactions, it may play a crucial role for pathogenicity towards coffee plants. Apoplastic proteins associated with maintaining the redox balance and degrading proteins/peptides not previously described as important in plant–bacteria interactions were found. Gain/loss of the tabtoxin biosynthetic cluster with retention of the antitoxin gene was observed, indicating that tabtoxin production is not a limiting factor for the occurrence of mixed infections.  相似文献   
56.
Genetic Resources and Crop Evolution - Macauba [Acrocomia aculeata (Jacq.) Lodd. ex Mart.], a palm tree native to Brazil, has a high potential as an alternative source for vegetal oil production....  相似文献   
57.
Genetic Resources and Crop Evolution - Hancornia speciosa Gomes is native tree to South America, and its fruits are a source of income for communities and the food industry. The reduction of...  相似文献   
58.
59.
An annual individual tree survival and growth model was developed for pure even-aged stands of maritime pine in Portugal, using a large data set containing irregularly time-spaced measurements and considering thinning effects. The model is distance-independent and is based on a function for diameter growth, a function for height growth and a survival function. Two approaches are compared for modeling annual tree growth. The first approach directly estimates a future diameter or height using well-known growth functions formulated in difference form. The second approach estimates diameter or height using a function in differential form estimating the increment over a year period. In both approaches, the function parameters were related to tree and stand variables reflecting the competition status of the tree as well as of a thinning response factor. Variable growth and survival rates were assumed in the modeling approaches. An iterative method was used to continuously update tree and stand attributes using a cut-off to convert the survival probability for a living or a dead tree. The individual tree diameter growth model and the survival probability model were fitted simultaneously using seemingly unrelated regression (SUR). Parameters of the height function were obtained separately as the number of observations for height was much lower than the number of observations for diameter, which may affect the statistical inference and the estimation of contemporaneous cross-equation error correlation inherent to the system of equations. PRESS residuals were used to evaluate the predictive performance of the diameter and the height growth functions. Additional statistics based in the log likelihood function and also in the survival probability were computed to evaluate the survival function. The second modeling approach, which integrates components of growth expansion and decline, performed slightly better than the first approach. A variable accounting for the thinning response that was tested proved to be significant for predicting diameter growth, even if the model already included competition-related explanatory variables, namely the basal area of trees larger than the subject tree. However, this thinning response factor was not significant for predicting height growth.  相似文献   
60.
Potential antagonists were isolated from the epiphytic flora associated with oranges and pome fruit. A total of 1465 microorganisms were tested in a preliminary screening against blue and green moulds on pome and citrus fruit, respectively. Among them, approximately 3% reduced incidence and severity by more than 50% and 4 microorganisms fulfilled the selection criteria of reduction in severity and incidence by 75%. The most effective was a yeast identified as Metschnikowia andauensis, strain NCYC 3728 (PBC-2), isolated from the surface of ‘Bravo de Esmolfe’ apple fruit cultivated in North Portugal. The biocontrol activity of M. andauensis PBC-2 was dependent on its applied concentration. At 5 × 106 cfu/mL incidence (% of infected wounds) and severity (lesion diameter) were reduced by 62 and 70%, respectively and at 1 × 107 cfu/mL, the greatest reduction was achieved, 90% of incidence and 95% of severity. The broad spectrum of action of M. andauensis PBC-2 was evaluated with effective control being achieved against Rhizopus stolonifer, Penicillium expansum and Botritys cinerea, on ‘Rocha’ pears and on different apple cultivars and against Penicillium digitatum and Penicillium italicum on mandarins and oranges. In semi-commercial trials in cold storage, the reduction of blue mould was 90%. Rapid colonization of fresh apple fruit wounds was observed during the first 24 h of cold storage, followed by a significant population increase during the first 15 days of storage and then the population remained stable until the end of storage.  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