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   502篇
  免费   20篇
林业   38篇
农学   21篇
基础科学   2篇
  120篇
综合类   27篇
农作物   22篇
水产渔业   26篇
畜牧兽医   223篇
园艺   4篇
植物保护   39篇
  2023年   11篇
  2022年   10篇
  2021年   14篇
  2020年   23篇
  2019年   17篇
  2018年   24篇
  2017年   15篇
  2016年   19篇
  2015年   17篇
  2014年   18篇
  2013年   27篇
  2012年   44篇
  2011年   47篇
  2010年   25篇
  2009年   19篇
  2008年   32篇
  2007年   32篇
  2006年   24篇
  2005年   29篇
  2004年   25篇
  2003年   16篇
  2002年   10篇
  2001年   5篇
  2000年   1篇
  1999年   4篇
  1998年   1篇
  1997年   3篇
  1995年   2篇
  1994年   1篇
  1993年   2篇
  1992年   1篇
  1990年   1篇
  1986年   1篇
  1985年   1篇
  1984年   1篇
排序方式: 共有522条查询结果,搜索用时 875 毫秒
61.
62.
Essential fatty acids should be included in the diet to ensure adequate fish growth. Despite the great number of studies on fatty acid nutrition of fish, there are still several unknowns. The aim of the present study was to investigate fatty acid nutrition of jundiá, a Latin American freshwater catfish. Four diets were formulated containing (i) coconut oil (?C, negative control), (ii) coconut oil + high‐docosahexaenoic‐acid‐fish oil (+C, positive control) and coconut + sunflower + linseed oils at different ratios, producing either (iii) a diet rich in linoleic acid (LA) (HighLA) or 4) a diet low in LA (LowLA). All diets contained significant amounts of saturated fatty acids (at least 57.5% total fatty acids in HighLA) and monounsaturated fatty acids (at least 19.1% total fatty acids in ?C). Diets were fed to jundiá fingerlings (1.5 g) for 70 days; growth, body composition and liver histology were evaluated. The ?C diet, without essential fatty acids, promoted significantly lower fish growth, body fat accumulation and hepatic lipidosis. Fish fed HighLA and LowLA diets presented similar growth as fish fed +C diet. These findings suggest that diet formulations for jundiá catfish fingerlings can include only plant oils without negative effect on growth, survival, body composition, fish health or parameters of feed utilization (ingestion rate and protein utilization).  相似文献   
63.
Twig cankers and diebacks were observed on cherry laurel (Prunus laurocerasus L.) hedges located in a private garden of Perugia (Central Italy). Four fungal isolates, forming gray colonies and aerial mycelium, were obtained from cankers. For each isolate, Koch’s postulates were fulfilled by inoculating cherry laurel plants. Based on cultural characteristics, rep-PCR and phylogenetic analyses on ITS and EF1-α nucleotides sequences, the isolates were identified as Diplodia seriata De Not. To the best of our knowledge, this is the first report of D. seriata as a new pathogen of P. laurocerasus. The severe symptoms and the wide distribution of the host plant make the pathogen potentially dangerous for this ornamental species.  相似文献   
64.
The aim of this study was to compare blood copy, haematological and glucose values between cats experimentally infected with either Mycoplasma haemofelis (Group HF: 10 cats), ‘Candidatus M. haemominutum’ (Group HM: 3 cats) or ‘Candidatus M. turicensis’ (Group TU: 3 cats). Blood samples were collected regularly up to 85 days post-infection (DPI) for haemoplasma real-time quantitative PCR, haematology, Coombs’ testing and blood glucose measurement. Statistical analysis was performed using a general linear model (ANOVA) appropriate for a repeated measures experiment with significance set as P < 0.05. Cats in Group TU had significantly lower blood copy numbers than cats in Group HF (P < 0.001) and HM (P < 0.001). All Group HF cats developed anaemia (often severe), macrocytosis and evidence of erythrocyte-bound antibodies whereas Groups HM and TU cats did not. Group HF had significantly lower PCVs, haemoglobin concentrations and red blood cell counts, and significantly higher mean cell volumes, than Groups HM and TU. In Group HF, erythrocyte-bound antibodies reactive at 4 °C (both IgM and IgG) appeared between 8 and 22 DPI and persisted for two to four weeks, whereas those reactive at 37 °C (primarily IgG) appeared between 22 and 29 DPI and persisted for one to five weeks. In most cats antibodies appeared after the fall in haemoglobin started. Although Group TU had significantly lower glucose concentrations than Groups HF (P = 0.006) and HM (P = 0.027), mean blood glucose concentrations remained within the reference range in all groups. This study demonstrates that M. haemofelis infection, in contrast to ‘Candidatus M. haemominutum’ and ‘Candidatus M. turicensis’ infection, can result in a severe macrocytic anaemia and the development of cold and warm reactive erythrocyte-bound antibodies.  相似文献   
65.
Turnera ulmifolia is a plant popularly known in Brazil and South America as chanana. Some species of Turnera are widely used in folk medicine for different types of inflammatory diseases. In this study, the preventive intestinal antiinflammatory activity of a lyophilized infusion obtained from the aerial parts of T. ulmifolia was tested in the trinitrobenzenesulphonic acid (TNBS) model of rat colitis. The results obtained revealed that pretreatment to colitic rats with the extract, at 250 and 500 mg/kg, significantly attenuated the colonic damage induced by TNBS. This beneficial effect was associated with an improvement in the colonic oxidative status, since the infusion prevented the glutathione depletion that occurred as a consequence of the colonic inflammation. On the other hand, this antioxidant activity was confirmed in in vitro studies. In conclusion, the preventive effect exerted by the lyophilized infusion of T. ulmifolia in the TNBS model of rat colitis is probably related to its antioxidant properties, due to its flavonoids content.  相似文献   
66.

Background  

A key challenge for conservation biologists is to determine the most appropriate demographic and genetic management strategies for wildlife populations threatened by disease. We explored this topic by examining whether genetic background and previous pathogen exposure influenced survival of translocated animals when captive-bred and free-ranging bighorn sheep (Ovis canadensis) were used to re-establish a population that had been extirpated in the San Andres Mountains in New Mexico, USA.  相似文献   
67.
A series of carbon-honeycomb monoliths from kenaf natural fibers (KNF) have been prepared and characterized. Firstly, KNF were physically mixed with polyvinyl acetate (PVA) as a binder and next the mixture was extruded through a die to form disc type monoliths. After the extrusion, the monoliths were dried, carbonized and, finally, physically activated with synthetic air at different temperatures (350-550 °C). The carbon-honeycomb monoliths were characterized by N2 adsorption at −196 °C, mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM). The experimental results indicate that the method proposed in this work was suitable for the synthesis of solid carbon monoliths with the presence of large meso- and macropores like long parallel and straight canals extended through their structure. MIP data and SEM images illustrate an evident and progressive aperture of the blocked parallel channels with an increase of the activation temperature.  相似文献   
68.
69.
The textile industries are characterized as one of the biggest consumers of potable water and chemical products throughout its process, being responsible for the elevated wastewater generation with intense coloration and wide polluting potential. In this context, the present study proposes the development and application of a new coagulant material for textile wastewater treatment. The proposed coagulant (α-Fe2O3-MO) was composed by hematite nanoparticles (α-Fe2O3) obtained by a simple non-pollutant methodology, associated with Moringa oleifera (MO) seeds saline extract compounds. Coagulation/flocculation (CF) efficiency was evaluated by removal of physicochemical parameters such as apparent color, turbidity, and compounds with absorption at UV254nm (UV254nm) through CF tests carried out on Jar test equipment and sedimentation carried out in the presence and absence of external magnetic field (600 k Am?1). Kinetics sedimentation was from 0 to 90 min. The use of this new coagulant allowed the removal of 92.37% for apparent color, 91.43% for turbidity, and 46.09% for UV254nm, indicating that the proposed coagulant association was efficient in the treatment of this type of wastewater under external magnetic field with only 10 min of sedimentation. In addition, the resulting sludge from CF process was tested as base material for a new coagulant synthesis, demonstrating great reuse potential. Therefore, the new proposed coagulant, composed of α-Fe2O3 and the compounds present in the seed extract of MO, has applicability for textile wastewater treatment demonstrating high removal rate for all evaluated parameters with cost reduction in the proposed treatment for this wastewater.  相似文献   
70.
The safe recycling of organic wastes such as the nutrients obtained from agriculture activities is a relevant aspect of the “One Health” strategy, a worldwide initiative including all aspects of health care for humans and animals, as well as aspects related to the conservation and development of the environment. It represents an important opportunity to mitigate the potential impact of microbial pathogens likely present in nutrient natural sources, as digestate, when applied to land as fertilizers. The objectives of the current study were to determine the inactivation of enteric microorganisms in swine digestate (effluent and sludge) during storage in anaerobic conditions and at different ambient temperatures of tropical zones (16, 22, and 37 °C). Human adenovirus 2 (HAdV-2), bacteriophage PhiX-174, and Salmonella enterica serovar typhimurium (S. typhimurium) were used as enteric microbial models to determine the minimum storage time required to reduce at least 3log of enteric microorganisms load in both matrices at the mentioned temperatures. The minimum storage time required for S. typhimurium was shorter than those observed for viruses at 37 °C, while reduction of at least 3log for S. typhimurium was observed after just 1 day; 20 and 90 days were needed for similar reductions for HAdV-2 and PhiX-174, respectively. Similar results were also observed at lower temperatures: 30 and 45 days were needed for S. typhimurium at 22 and 16 °C, respectively, but 30 and 90 days were needed at 22 °C for HAdV-2 PhiX-174, respectively, or 90 and 120 days at 16 °C for HAdV-2 PhiX-174, respectively. This is a pioneering study on the evaluation of inactivation of enteric viruses in swine digestate in usual tropical ambient temperatures; it demonstrates that the time for a considerable inactivation is longer than that observed for a enteric microorganisms (S. typhimurium), and shows that the storage of swine digestate at the referred temperatures can be used as a low-cost post-treatment to inactivate enteric microorganisms, allowing a further use as safer fertilizer.  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