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   256篇
  免费   26篇
林业   10篇
农学   14篇
  63篇
综合类   10篇
农作物   28篇
水产渔业   11篇
畜牧兽医   119篇
园艺   4篇
植物保护   23篇
  2024年   1篇
  2023年   5篇
  2022年   9篇
  2021年   12篇
  2020年   9篇
  2019年   13篇
  2018年   20篇
  2017年   10篇
  2016年   15篇
  2015年   8篇
  2014年   25篇
  2013年   20篇
  2012年   19篇
  2011年   18篇
  2010年   7篇
  2009年   6篇
  2008年   11篇
  2007年   14篇
  2006年   11篇
  2005年   11篇
  2004年   11篇
  2003年   7篇
  2002年   6篇
  2001年   4篇
  2000年   3篇
  1999年   2篇
  1997年   3篇
  1996年   1篇
  1994年   1篇
排序方式: 共有282条查询结果,搜索用时 62 毫秒
231.
In the present study, fish meal (FM) was replaced by pea (Pisum sativum) protein (PP) in diet for Rainbow trout (Oncorhynchus mykiss) at levels of 0% (PP0), 25% (PP25), 50% (PP50), 75% (PP75) and 100% (PP100), and the effect of dietary PP level on the digestive system tracts and liver was investigated by micromorphological and histopathological evaluations. Morphometric measurements (mm 100g fish−1) of the liver width and stomach length in rainbow trout were found to be significantly larger (p <0.05) in fish with high-level pea protein as the main protein source (PP75, PP100) compared to the low-level PP replacement group (PP25). No significant differences were found in morphometric measurements for pyloric caecum and intestines among treatment groups, whereas the number of the caecum of fish fed the PP25 diets significantly increased over the control (PP0) (p<0.05). In the histological examination of the liver, mild hydropic and vacuolar degeneration was observed in all experimental groups except PP0 and PP25. The measurements of pyloric caecum fold height, enterocyte length and width of tunica muscularis of the high-level pea protein groups of PP75 and PP100 were significantly higher (p <0.05) compared to the control group. In conclusion, 25% substitution of PP can be suggested for FM in trout diets, because the findings of the present study provided evidence that the digestive system improved by increasing the number of pyloric caecum at this replacement level.  相似文献   
232.
Two 5-month-old golden retriever dogs were referred for the evaluation of a mass arising from the left ventrolateral conjunctiva of the lower eyelid. The masses were externally located, deemed to be cystic in nature, and were surgically removed, and in one case, 0.15 mL of clear fluid was collected. Cytological examination of the aspirated fluid revealed proteinaceous, basophilic amorphous material, and few epithelial cells with foamy cytoplasm and small nuclei. No micro-organisms were detected. Histological examination of the cysts showed a wall composed of single to double cell layers. The cells were cuboidal to flattened, nonciliated, lined with mild submucosal connective tissues and slight inflammation composed of lymphocytes, plasma cells, and rare macrophages. In some areas, lobules of acinar glandular tissue were observed. To the authors' knowledge, this is the first case report of conjunctival dacryops in dogs. The complete surgical removal of the cysts was curative in both cases.  相似文献   
233.
In most developing countries where local community ownership is common, successful forest conservation initiatives must be adapted to engage and train rural communities. Decentralization of decision-making and stewardship by the State is required to maintain forests as a common good with extended benefits to society. Despite a tendency to operate in isolation, three Oaxacan community forest enterprises (CFEs), Textitlán, Ixtlán and Pueblos Mancomunados, have vertically integrated from forest management to retailing furniture through a company: TIP Muebles. This exploratory study aims to provide insight and outline the factors impacting the ability of CFEs to succeed in the marketplace given the fact that each deals with the same regulation structure of public forest policy. The results of this research suggest that the main challenges are related to human capital, regulatory challenges and centralized forest policy for forest product production, the taxation system for timber production, and endogenous factors such as the forest quality and the decisions based on tradition rather than efficiency. In this context, the integration of chains of production is a fact in only a few cases and financial success continues to be slow. The studied CFEs are resilient and slightly surpassing the profitability threshold despite the challenges identified. Adaptation of their decision-making structure allows them to face the changing dynamics of the market. More democratic approaches to decentralization of Mexican forest policy, trust development between social and private enterprises, and an improvement in internal CFEs systems could offer opportunities for improved competitiveness for CFEs. CFE strategies need to be understood as part of a complex rural livelihood where diversification of income generating activities often conflicts with competitive and specialized production.  相似文献   
234.
Water, Air, & Soil Pollution - Mobilization of arsenic (As) in the subsurface environment can result in elevated concentrations of As in groundwater and potential human exposure and adverse...  相似文献   
235.
The high specific richness of the vascular flora of the National Park of ‘Alta Murgia’ (Apulia, Italy) has been originated by a long co-evolutionary process of biophysical and anthropic systems. Natural disturbances on the one hand and the anthropic on the other, as years go by, in their mutual interaction, have created suitable conditions for the coexistence of a high number of taxa. Following an ecological and floristic survey of grasslands of Alta Murgia, many species of great phyto-geographical value or, however, threatened by genetic erosion and/or extinction together with other plants traditionally employed by man as officinal and for food and non-food purposes, were recorded. The ecological conditions that allow the persistence of these plant communities must be searched in the delicate equilibrium established among the natural dynamics and the set of disturbance regime, for great part due to the traditional land use. The actual social and economic transformations of the area, without safeguarding programmes to be carried out according to sustainability criteria, can produce a serious biodiversity decline. Starting from the ‘sustainable use’ definition of the CBD, the present paper deals with some focal points to realize the sustainable management of the biodiversity of the Park of Alta Murgia.  相似文献   
236.
During their rehydration in aqueous media, active dry yeasts (ADY) may be supplemented with inactive yeasts, yeast derivatives, or other optional complementary nutrients to improve their fermentation capacity. We found that yeast sterols solubilized in situ during ADY rehydration were particularly efficient for stimulating the fermenting capacity of ADY. Spontaneous solubilization of sterols during rehydration occurred by the formation of micelles by membrane phospholipids and specific cell wall polysaccharides and sterols, both compounds being provided by inactive dry yeasts (IDY). These micelles contained a specific distribution of the initial sterols from the inactive yeasts. Above a concentration of 100 mg L(-1) in the rehydration medium, these micelles acted as emulsifiers. Their critical micellar concentration (cmc) was found to be about 4 g L(-1). During rehydration, purified micelles, at a concentration near the cmc, were able to interact quickly with yeast cell membranes by modifying the yeast plasma membrane order [monitored by steady-state fluorescence anisotropy of 1-(4-trimethylammoniumphenyl)-6-phenyl-1,3,5-hexatriene-p-toluenesulfonate (TMA-DPH) probe] and by increasing the sterol contents of ADY. Such an enrichment of ADY by very low concentrations of solubilized sterols was very efficient for the completion of fermentations. This is useful when musts are limited in available phytosterols or when micro-oxygenation is not desirable during fermentation.  相似文献   
237.
Some of the practical aspects of long-term calibration-set building are presented in this study. A calibration model able to predict the Kolbach index for brewing malt is defined, and four different validations and resampling schemes were applied to determine its real predictive power. The results obtained demonstrated that one single performance criterion might be not sufficient and can lead to over- or underestimation of the model quality. Comparing a simple leave-one-sample-out cross-validation (CV) with two more challenging CVs with leave-N-samples-out, where the resamplings were repeated 200 times, it is demonstrated that the error of prediction value has an uncertainty, and these values change according to the type and the number of validation samples. Then, two kinds of test-set validations were applied, using data blocks based on the sample collection's year, demonstrating that it is necessary to consider long-term effects on NIR calibrations and to be conservative in the number of factors selected. The conclusion is that one should be modest in reporting the prediction error because it changes according to the type of validation used to estimate it and it is necessary to consider the long-term effects.  相似文献   
238.
Water, Air, &; Soil Pollution - In the last 20&;nbsp;years, a new generation of materials was developed: the biodegradable plastics. They reduce the accumulation of plastic in the environment...  相似文献   
239.
A 9-year-old, spayed, female Maremmano shepherd had a bilateral mastectomy for multiple mammary adenocarcinomas 2 years previous and was referred to the Cardiology Service of the School of Veterinary Medicine of Milan after an acute episode of cardiogenic collapse. Because of severe cardiovascular symptoms and poor prognosis, the dog was euthanized. Necropsy examination revealed the presence of multiple firm grayish neoplastic nodules in the myocardium of the left ventricle and scattered in the pulmonary parenchyma. Neoplastic nodules were also detected in the spleen, pancreas, liver, kidneys, and omentum. Histological examination revealed the coexistence of tubular adenocarcinoma and an undifferentiated sarcoma in the myocardium. Immunohistochemical staining of the sarcoma cells was negative for cytokeratin, desmin, and smooth muscle myosin, thus excluding their epithelial or myoepithelial origin, as well as an origin from smooth muscles cells. These findings, together with the coexpression of vimentin and alpha-smooth muscle actin, suggested that the sarcoma was derived from myofibroblasts. To the authors' knowledge, this is the first report describing cardiac sarcoma of presumptive myofibroblastic origin in a dog with simultaneous occurrence of cardiac metastasis of mammary gland adenocarcinoma.  相似文献   
240.

Background

Streptococcus spp. and other Gram-positive, catalase-negative cocci (PNC) form a large group of microorganisms which can be found in the milk of cows with intramammary infection. The most frequently observed PNC mastitis pathogens (major pathogens) are Streptococcus uberis, Strep. dysgalactiae, and Strep. agalactiae. The remaining PNC include a few minor pathogens and a large nonpathogenic group. Improved methods are needed for the accurate identification and differentiation of PNC.A total of 151 PNC were collected from cows with intramammary infection and conclusively identified by 16S rRNA sequencing as reference method. Nine phenotypic microbiological tests (alpha-hemolysis, CAMP reaction, esculin hydrolysis, growth on kanamycin esculin azide agar and on sodium chloride agar, inulin fermentation, hippurate hydrolysis, leucine aminopeptidase and pyrrolidonyl peptidase activity), multiplex PCR for the three major pathogens (target genes for Strep. uberis, Strep. dysgalactiae and Strep. agalactiae: pauA, 16S rRNA, and sklA3, respectively), and mass spectroscopy using the matrix-assisted laser desorption ionization-time of flight (MALDI-TOF MS) were evaluated for the diagnosis and discrimination of the three clinically most relevant PNC.

Results

The probability that a strain of Strep. uberis, Strep. dysgalactiae and Strep. agalactiae was correctly identified by combining the results of the 9 phenotypic tests was 92%, 90%, and 100%, respectively. Applying the multiplex PCR, all strains of the three major pathogens were correctly identified and no false positive results occurred. Correct identification was observed for all strains of Strep. uberis and Strep. agalactiae using MALDI-TOF MS. In the case of Strep. dysgalactiae, some variability was observed at the subspecies level, but all strains were allocated to one single cluster.

Conclusions

The results of the present study show that reliable identification of the clinically most relevant PNC (Strep. uberis, Strep. agalactiae and Strep. dysgalactiae) can be obtained by use of a combination of colony morphology, hemolysis type and catalase reaction, and a multiplex PCR with specific primers restricted to these 3 pathogens. The MALDI-TOF MS is a fast method that shows promising results, although identification of Strep. dysgalactiae at the subspecies level is not yet satisfactory.  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