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   26篇
  免费   1篇
林业   5篇
农学   3篇
  5篇
综合类   2篇
农作物   2篇
水产渔业   1篇
畜牧兽医   1篇
植物保护   8篇
  2022年   2篇
  2021年   1篇
  2020年   1篇
  2019年   1篇
  2018年   2篇
  2017年   3篇
  2016年   1篇
  2014年   1篇
  2013年   2篇
  2012年   1篇
  2011年   2篇
  2010年   2篇
  2009年   3篇
  2007年   1篇
  2005年   1篇
  1999年   1篇
  1996年   1篇
  1980年   1篇
排序方式: 共有27条查询结果,搜索用时 265 毫秒
1.
2.
3.
Artificial crystal lattices can be used to tune repulsive Coulomb interactions between electrons. We trapped electrons, confined as a two-dimensional gas in a gallium arsenide quantum well, in a nanofabricated lattice with honeycomb geometry. We probed the excitation spectrum in a magnetic field, identifying collective modes that emerged from the Coulomb interaction in the artificial lattice, as predicted by the Mott-Hubbard model. These observations allow us to determine the Hubbard gap and suggest the existence of a Coulomb-driven ground state.  相似文献   
4.
We report the effects of shifting cultivation on water quality in 16 creeks investigated once in 2007 and twice in 2008 in 16 apparently similar small neighboring watersheds,each of 3 to 5 ha,at four locations around Barkal sub-district under Rangamati District of Chittagong Hill Tracts in Bangladesh.Concentrations of SO 4 2and K +,and pH in creek water were lower,and NO 3-N and Na + concentrations were higher in shifting-cultivation land compared to land with either plantation or natural forest or a combination of these cover types.Shifting cultivation effects on some water quality parameters were not significant due to change in land cover of the watershed between two sampling periods either through introduction of planted tree species or naturally regenerated vegetation.Conductivity and concentrations of HCO 3,PO 4 3,Ca 2+ and Mg 2+ in creek water showed no definite trend between shifting cultivation and the other land cover types.At one area near the Forest Range Office of Barkal,creek water pH was 5.8 under land cover with a combination of shifting cultivation and plantation.At this area Na + concentration in shifting-cultivation land ranged from 32.33 to 33.00 mg L-1 and in vegetated area from 25.00 to 30.50 mg L-1 in 2007.At another area,Chaliatali Chara,SO 4 2concentration in a shifting-cultivation watershed ranged from 4.46 to 10.51 mg L-1,lower than in a vegetated watershed that ranged from 11.69 to 19.98 mg L-1 in 2007.SO 4 2concentration in this shifting-cultivation area ranged from 1.28 to 1.37 mg L-1 and in the vegetated area from 1.37 to 3.50 mg L-1 in 2008.  相似文献   
5.
6.
7.
Water quality of Kaptai reservoir in Chittagong Hill Tracts of Bangladesh   总被引:1,自引:0,他引:1  
A study was conducted in Kaptai reservoir, one of the largest man-made freshwater lakes of South-east Asia, to determine present status of water quality and its suitability for fishing and other uses. Water samplings were from middle part of the reservoir at 0.2 and 0.8 fractional depths at five different locations from upstream to downstream viz. Burburichara, Maichchari, Subolong, Basanthakum, and Rangamati. Water analyses show that concentrations of NO3-N, K+ and total P, and suspended solid at all the sampling stations were beyond the recommended values for fish culture. Concentrations of Na+, Ca2+, Mg2+, SO42-, Cl-, total dissolved solid (TDS), dissolved oxygen (DO) and chemical oxygen demand (COD) were within the standards for aquaculture. Concentrations of NO3-N, SO42-, K+ and total P showed no definite trend with depths, locations as well as rainy and dry seasons. Water pH, conductivity, Na+ and HCO3- contents were lower in rainy season, and DO and COD higher at almost all the locations in both the depths, compared with dry season. Total solids and concentrations of TDS, DO, COD, Ca2+, Mg2+ and Na+ were higher in upstream and decreased gradually towards downstream in the reservoir. Concentrations of DO and Ca2+ and pH were higher and Mg2+ less at 0.2-fractional depth than those at 0.8-fractional depth at almost all the locations. The reservoir is in mesotrophic condition containing high concentration of NO3-N and total P, in alarming status with the presence of excessive suspended solids from urban pollution around the town. It is necessary to adopt measures for protecting water quality in the reservoir due to such deteriorations.  相似文献   
8.
9.
Macrophomina phaseolina (Tassi) Goid. is the most important pathogen of jute and primarily causes seedling blight, leaf spot and stem rot. The pathogen was detected from field samples by a simple method of direct PCR (dPCR) which obviates the steps of DNA extraction. The leaf bits were treated with a lysis buffer at 65°C for 25 min, whereas the stem pieces were initially incubated at 65°C for 5 min followed by incubation at 60°C for 25 min and the lysate was used as PCR template. Based on the type of tissue, the composition and concentration of lysis buffer systems were optimized. For leaf samples the optimized buffer system composed of 20 mmol l -1 tris (hydroxymethyl aminomethane (Tris)-Cl (pH 8.0), 1.5 mmol l -1 ethylene diamine tetra acetate (EDTA) (pH 8.0), 1.4 mol l -1 sodium acetate and 200 μg/ml proteinase K. Further, 3% PVP (w/v) and β-mercaptoethanol (1% w/v) were added into the buffer. In case of stem samples, PVP was not applied and higher concentrations were used for other components. M. phaseolina could be detected from both leaf and stem samples generating amplicon of 350 bp. This is the first report of detecting M. phaseolina by a direct PCR method without DNA extraction.  相似文献   
10.
Shera  P. S.  Karmakar  Prasun  Sharma  Sudendhu  Kaur  Rabinder  Sangha  K. S. 《Phytoparasitica》2021,49(4):569-578
Phytoparasitica - Transgenic crops with genes from Bacillus thuringiensis (Bt) Berliner, a soil bacterium producing δ-endotoxin that is lethal to several phytophagous insects. Concerns related...  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