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   181篇
  免费   27篇
林业   12篇
农学   6篇
  36篇
综合类   13篇
农作物   9篇
水产渔业   57篇
畜牧兽医   58篇
园艺   4篇
植物保护   13篇
  2023年   2篇
  2022年   3篇
  2021年   9篇
  2020年   3篇
  2019年   19篇
  2018年   12篇
  2017年   7篇
  2016年   9篇
  2015年   11篇
  2014年   6篇
  2013年   12篇
  2012年   12篇
  2011年   9篇
  2010年   11篇
  2009年   11篇
  2008年   10篇
  2007年   7篇
  2006年   6篇
  2005年   4篇
  2004年   6篇
  2003年   6篇
  2002年   6篇
  2001年   6篇
  2000年   3篇
  1999年   3篇
  1998年   2篇
  1997年   3篇
  1996年   2篇
  1994年   1篇
  1990年   1篇
  1988年   1篇
  1985年   1篇
  1984年   1篇
  1975年   1篇
  1942年   1篇
  1899年   1篇
排序方式: 共有208条查询结果,搜索用时 15 毫秒
91.
Seven cases of idiopathic Horner's Syndrome in the Collie are described. Five males and two females presented with unilateral miosis, ptosis of the upper eyelid, enophthalmos and protrusion of the third eyelid. Thorough examination, pharmacological testing with phenylephrine, complete blood counts and radiography of the tympanic bullae and thorax were performed. The etiology was not identified in any of the cases. Clinical signs improved with pharmacologic testing within 20–40 min. In five dogs, total resolution of clinical signs was observed at 4 and 16 weeks after their initial appearance. Pharmacological testing suggested that the deficit could be at the preganglionic neuron.  相似文献   
92.
In order to better understand the enzootiology of trypanosomiasis caused by Trypanosoma evansi in the Brazilian Pantanal we examined domestic and wild mammals by microhematocrit centrifuge technique (MHCT), immunofluorescence antibody test (IFAT) and polymerase chain reaction (PCR). T. evansi infection was detected in all species sampled with exception of the sheep and the feral pig. High parasitemias were observed in capybaras (5/24), coatis (18/115), horses (31/321) and dogs (3/112). Among these species, only the capybaras did not develop anemia. Low parasitemias, only detected by PCR, were found in buffaloes (18/43), bovines (29/331), marsupials (1/4), small rodents (14/67), bats (7/18), and one armadillo (1/8). The highest prevalence of T. evansi infection was recorded in horses (73%), although no neurological signs in infected horses were observed. Diagnosis through standard parasitological tests and IFAT should be used with caution since they may overlook comprovedly infected horses. The relationship between ranch management and T. evansi infection in horse was investigated. The importance of other transmission mechanisms apart from the tabanids and reservoir hosts are discussed.  相似文献   
93.
In order to study the effect of undernutrition during gestation on the testicular development in rats and its impact on mitosis, apoptosis and the relative abundance of androgen receptor expression, twenty primiparous 3‐month‐old Sprague–Dawley (Rattus norvegicus) rats, weighing 246 ± 4.0 grams when the experiment began, were mated by the same male. Control group (CG), n = 10, fed ad libitum with water and rat chow and restricted group (RG, n = 10) fed throughout pregnancy and until birth with 40% of the ad libitum maternal daily feed intake. Litters from both groups suckled for 25 days, RG with 14 pups/litter and CG with 8 pups/litter. After weaning, all animals had access to ad libitum food and water. Testicular samples were taken from male pups at 2, 25 and 100 days of age. Immunohistochemistry was used to evidence androgen receptor (AR) expression in apoptotic (caspase 3‐positive) and proliferating (PCNA‐positive) cells. Three hundred nuclei of sustentacular (or Sertoli: SC), interstitial (or Leydig: LC), myoid (MC) cells as well as gonocytes (GC) were evaluated. Neither LC nor GC showed any differences between groups. However, SC androgen receptor (AR) positivity index in neonatal animals was lower in RG (1.27 ± 0.22 vs. 1.65 ± 0.17**). MC showed lower AR positivity index at 2 (2.69 ± 0.046 vs. 2.8 ± 0.055**) and 25 (1.34 ± 0.097 vs. 1.56 ± 0.1***) days of life; at 100 days of life, there was a greater number of apoptotic MC in the RG (8.5 ± 0.4 vs. 2.95 ± 1.1***). Thus, the present experiment demonstrates that the population dynamics of MC are affected by foetal programming due to undernutrition.  相似文献   
94.
Antioxidants have been widely used during in vitro production to decrease the negative effect of reactive oxygen species. It was reported that the complex resveratrol–methyl β‐cyclodextrin (RV ‐CD ) improves resveratrol's stability and bioavailability and increases its antioxidant activity. This study evaluates the effect of RV ‐CD during in vitro oocyte maturation (IVM ) or in vitro embryo culture (IVC ) on developmental competence and quantitative changes in gene expression of developmental important genes. In experiment 1, RV ‐CD was added to IVM media and maturation level, embryo development and oocytes, cumulus cells, and blastocysts gene expression by RT ‐qPCR were examined. In experiment 2, presumptive zygotes were cultured in SOF supplemented with RV ‐CD and embryo development and blastocysts gene expression by RT ‐qPCR were studied. A group without RV ‐CD (control?) and a group with cyclodextrin (control+) were included. No differences were found in cleavage rate or blastocyst yield between groups. However, the expression of LIPE was higher in blastocysts derived from oocytes treated with resveratrol compared with control groups (<  .05). Blastocysts produced by IVC with resveratrol showed that RV ‐CD could modify the expression of genes related to lipid metabolism (CYP 51A1 , PNPLA 2 and MTORC 1 ) compared with control groups (p  < .05). RV ‐CD in the IVM and IVC media could reduce accumulated fat by increasing lipolysis and suppressing lipogenesis of blastocysts.  相似文献   
95.
Food-borne salmonellosis continues to be a major public health concern, and contamination with Salmonella spp. in pre-harvest animal production is considered a primary contributor to this problem. Animal feeds can easily become contaminated during primary production, feed mixing and processing as well as during feeding. Consequently, monitoring and surveillance of feeds and feed ingredients for Salmonella spp. contamination may be useful or necessary in the prevention and control of this organism. Cultural and immunological detection methods for salmonellae have been used or suggested as possible approaches for use in animal feeds. Cultural methods remain advantageous owing to their ability to detect viable bacterial cells, while immunological methods have the capability of detecting nonculturable bacterial cells. Advancements and improvements in both methodologies offer opportunities for eventual routine use of these detection technologies in animal feed assays.  相似文献   
96.
Nature has evolved efficient strategies to synthesize complex mineralized structures that exhibit exceptional damage tolerance. One such example is found in the hypermineralized hammer-like dactyl clubs of the stomatopods, a group of highly aggressive marine crustaceans. The dactyl clubs from one species, Odontodactylus scyllarus, exhibit an impressive set of characteristics adapted for surviving high-velocity impacts on the heavily mineralized prey on which they feed. Consisting of a multiphase composite of oriented crystalline hydroxyapatite and amorphous calcium phosphate and carbonate, in conjunction with a highly expanded helicoidal organization of the fibrillar chitinous organic matrix, these structures display several effective lines of defense against catastrophic failure during repetitive high-energy loading events.  相似文献   
97.
An improved analytical method was developed which may be applied to quality control of stevioside and rebaudioside A contents in dried leaves of Stevia rebaudiana before processing; in a selective sampling program searching for plants of higher yield in diterpene glycosides content; or when a large number of samples are sent to the laboratory for analysis. The procedure developed involves two steps: solvent extraction followed by an isocratic HPLC analysis. The sample, 1 g of dried leaves of S. rebaudiana, is ground and solvent-extracted with EtOH 70% (w/w) in Erlenmeyer flasks by shaking for 30 min in a 70 degrees C water bath. After the extract was cooled, it was filtered and analyzed by HPLC using an NH(2) column (250 x 4.6 mm) and a mixture of acetonitrile/water (80:20, v/v) as mobile phase, pH 5 adjusted with acetic acid. The detection was in the UV range at 210 nm (0.04 AUFS). Quantitation was performed by means of an external standard calibration curve for each analyte which had been obtained from standard solutions of pure stevioside and rebaudioside A. Working under these conditions there were no observed interference effects. The method saves time in sample preparation, and reduces sample handling and chromatographic analysis time, while having little loss of precision [coefficient of variation (CV%) between 1.8% and 3.0%] and recovery [between 98.5% and 100.5%]. The method was applied to 30 samples of S. rebaudiana from Misiones (Northeastern Argentina), and the stevioside content found ranged between 3.78 and 9.75% (weight) whereas Rebaudioside A content ranged between 1.62 and 7.27% (weight).  相似文献   
98.
Artificial aging techniques were applied to samples of rum. These samples were then compared, by artificial neural nets, with traditionally aged rums. Analysis was based on the phenolic and furanic composition of each sample. There were found to be few statistical differences between samples, thus confirming the possibility of applying artificial aging techniques to obtain rum with phenolic and furanic characteristics that are similar to those of rum obtained by traditional methods.  相似文献   
99.
Aluminum in acidic conditions is toxic to plants. Aluminum tolerance in some plant species has been ascribed to arbuscular mycorrhizal fungal symbiosis. In this study, the application of aluminum was found to inhibit mycelia development of saprobe fungi Fusarium concolor and Trichoderma koningii and the hyphal length of the arbuscular mycorrhizal fungi Glomus mosseae and Glomus deserticola in vitro. Several levels of aluminum were applied to Eucalyptus globulus plants and inoculated with arbuscular mycorrhizal fungi alone or together with both saprobe fungi. The application of 1,500 mg kg?1 decreased the shoot and root dry weight, chlorophyll content and total P, Mg, and Ca concentrations in the shoot of E. globulus. However, both mycorrhizal fungi G. mosseae and G. deserticola inoculated alone increased the shoot dry weight of Eucalyptus, compared with a non- arbuscular mycorrhizal inoculated control treated with 1,500 mg kg?1 of aluminum. When 1,500 mg kg?1 of aluminum was applied, T. koningii increased the effect of G. deserticola on the shoot weight of eucalyptus, whereas with 3,000 mg kg?1, shoot weight and arbuscular mycorrhizal colonization decreased in all treatments. With 1,500 mg kg?1, the highest accumulation of aluminum in the shoot was obtained when G. deserticola was inoculated together with T. koningii. The possibility of manipulating an arbuscular mycorrhizal inoculation together with a saprobe fungus confers a high aluminum resistance in E. globulus. The effect of such combined inoculation is particularly important in some Chilean volcanic acid soils, mainly those which have been intensively cropped and are without lime addition, which facilitates the increase of phytotoxic aluminum species and limits their agricultural use. Therefore, such dual inoculation in field conditions deserves further investigation. Overall, the arbuscular mycorrhizal and saprobe fungi contribute to the increase in resistance of E. globulus to aluminium.  相似文献   
100.
Apiary trials on the use of three different treatments (Apilife Var, thymol solution in olive oil, and thymol solution in ethanol) for the control of Varroa destructor were conducted in Aragon (northeastern Spain). For the evaluation of the presence of residues of these treatments in honey an analytical method was developed. The method is applied to analyze honey samples before and after treatments with the acaricides mentioned. A solid-phase extraction on trifunctional silane SPE C18 cartridge and gas chromatography separation using a flame ionization detector allow reliable and precise determination of residues of thymol, menthol, eucalyptol, and camphor in honey. The results indicate that camphor is present in only low concentrations, residues of eucalyptol or menthol were not found at all, and only thymol left residues in high concentrations. Residues of thymol found in honey collected from the beehives ranged from 0.75 to 8.20 microg/g for Apilife Var, from 0.03 to 6.30 microg/g for thymol solution in olive oil, and from 0.05 to 6.20 microg/g for thymol solution in ethanol. Even so, natural treatments can be considered to be good alternatives for synthetic acaricides, especially because they do not represent a sanitary risk.  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