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   280篇
  免费   23篇
林业   64篇
农学   36篇
基础科学   2篇
  45篇
综合类   5篇
农作物   20篇
水产渔业   72篇
畜牧兽医   34篇
园艺   5篇
植物保护   20篇
  2024年   1篇
  2023年   1篇
  2022年   6篇
  2021年   5篇
  2020年   8篇
  2019年   15篇
  2018年   11篇
  2017年   15篇
  2016年   16篇
  2015年   11篇
  2014年   11篇
  2013年   23篇
  2012年   11篇
  2011年   16篇
  2010年   15篇
  2009年   9篇
  2008年   25篇
  2007年   19篇
  2006年   13篇
  2005年   19篇
  2004年   3篇
  2003年   11篇
  2002年   6篇
  2001年   7篇
  2000年   6篇
  1999年   2篇
  1998年   6篇
  1997年   1篇
  1996年   1篇
  1995年   1篇
  1994年   1篇
  1989年   1篇
  1988年   2篇
  1984年   2篇
  1983年   1篇
  1978年   1篇
  1972年   1篇
排序方式: 共有303条查询结果,搜索用时 15 毫秒
91.
The effects of carbon (C) levels on growth, photosynthesis, chlorophyll content, and nutrient partitioning on five kenaf varieties were investigated. Kenaf plants were grown in pots containing sandy beach ridges interspersed with swales (BRIS) soil. Organic carbon at levels of 0, 10, 20, 30, and 40 t ha?1, were applied to the pots. The results showed that plant height, stem diameter, leaf number, leaf area, chlorophyll content and photosynthesis rate increased with an increase in carbon levels up to 20 t ha?1but decreased with additional increase in carbon levels. The proportion of nitrogen in leaves was minimum at 0 and maximum at 20 t ha?1carbon levels. In stem and roots, proportion of nitrogen (N) decreased after 10 t ha?1carbon, while in leaves phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mg) increased after 20 t ha?1. Variety HC2 showed maximum N, P, and K in leaves and total nutrient content.  相似文献   
92.
Twenty nine cross populations developed according to line x tester mating design along with their twelve parents raised from true potato seeds, were used to study variability and correlation for seven characters. The range of variation for all the characters were found to be wide and pronounced which indicated that characters were quantitative in nature and were under polygenic control. For all the characters, greater portion of the total δ^2p was mostly contributed by the δ^2g. Among the seven characters, tuber weight per plant showed the highest δ^2g, PCV, GCV, H2b, GA and expected GA%.On the other hand, dry matter contents (%) showed the lowest H^2b. Phenotypic and genotypic correlation coefficients of plant height with no. of tubers per plant and tuber weight per plant; no. of branches per plant with no. of tubers per plant and tuber weight per plant were found to be significant and positive.  相似文献   
93.
94.
Potatoes(Solanum tuberosum L)are the thirdlargest food crop in Bangladesh following rice andwheat and make a major contribution to the total foodsupply of the country.Although in many westerncountries potato is the number one staple food,it is al-most entirely used as a vegetable in Bangladesh.Thepotato is a short duration crop that produces a largeamount of calories in a short period of time[1].Thepotato produces more protein and calories per unitarea per unit time than any other major food…  相似文献   
95.
An experiment was conducted to observe the phosphate sorption potential of some soils of Bangladesh. Three soil series of calcareous origin, namely Sara (Aquic Eutrochrept), Gopalpur (Aquic Eutrochrept) and Ishurdi (Aeric Haplaquept), and two soil series of non-calcareous origin, namely Tejgaon (Rhodic Paleustult) and Ghatail (Aeric Haplaquept), were selected. The soils were equilibrated with dilute solution of calcium chloride containing graded concentrations of phosphate (0, 1, 2, 5, 10, 25 and 50?μg?P?mL?1), and the amount of phosphate sorbed or desorbed was determined. Although all the soils showed potential for sorbing phosphate from applied phosphorus, their ability to sorb phosphorus differed. Increasing rates of phosphate application increased the amount of P sorption but reduced phosphate sorption percentage in all soils except Tejgaon. Phosphate was sorbed by the soils in the order: Tejgaon > Ghatail > Ishurdi > Gopalpur > Sara at 50?μg?P?mL?1 application. Soils possessing higher amounts of free iron oxide and clay sorbed more phosphate from applied phosphorus.  相似文献   
96.
The soil physicochemical characteristics and amounts of microbial biomass C, N, and S in 19 soils (10 grassland, 2 forest, and 7 arable soils) were investigated to clarify the S status in granitic regosols in Japan, in order to determine the relationships between biomass S and other soil characteristics and to estimate approximately the annual Sand N flux through the microbial biomass. Across the sites, the amount of biomass C ranged from 46 to 1,054, biomass N from 6 to 158, and biomass S from 0.81 to 13.44 mg kg-1 soil with mean values of 438.8, 85.8, and 6.15 mg kg-1 soil, respectively. Microbial biomass Nand S accounted for 3.4–7.7% and 1.1–4.0% of soil total Nand S, respectively. The biomass C: N, C : S, and N : S ratios varied considerably across the sites and ranged from 3.0–10.4, 32.5–87.7, and 5.0–18.8, respectively. Microbial biomass S was linearly related to biomass C and biomass N. The regression accounted for 96.6% for biomass C and 92.9% for biomass N of the variance in the data. The amounts of biomass C, N, and S were positively correlated with a number of soil properties, particularly with the contents of organic C, total N, SO4-S, and electrical conductivity and among themselves. The soil properties, in various linear combinations showed a variability of 84–97% in the biomass nutrients. Stepwise multiple regression indicated that biomass C, N, and S were also dependent on SO4-S as a second factor of significance which could limit microbial growth under the conditions prevailing at the study sites. Annual flux of Nand S was estimated through the biomass using the turnover rates of 0.67 for Nand 0.70 for S to be approximately 129 kg Nand 9.7 kg S ha-1 y-l, respectively, and was almost two times higher in grassland than arable soils.  相似文献   
97.
Vivek Maize Hybrid 9‐ a popular single‐cross hybrid developed by crossing CM 212 and CM 145 was released for commercial cultivation in India. The parental lines, being deficient in lysine and tryptophan, were selected for introgression of opaque‐2 allele using CML 180 and CML 170 as donor lines through marker‐assisted backcross breeding. The opaque‐2 homozygous recessive genotypes with >90% recovery of the recurrent parent genome were selected in BC2F2, and the seeds with <25% opaqueness in BC2F3 were forwarded for seed multiplication. Vivek Quality Protein Maize (QPM) 9, the improved QPM hybrid, showed 41% increase in tryptophan and 30% increase in lysine over the original hybrid. The grain yield of the improved hybrid was on par with the original hybrid. The newly improved QPM maize hybrid released in 2008 will help in reducing the protein malnutrition because its biological value is superior over the normal maize hybrids. This short duration QPM maize hybrid has been adopted in several hill states of North Western and North Eastern Himalayan regions.  相似文献   
98.
A simple spectrophotometric method was developed to quantify chlorophenol (CP) concentrations after reaction with potassium permanganate and quenching with sodium sulfite. Other quenching agents (peroxide, sodium thiosulfate and hydroxylamine hydrochloride) were found to create absorbance in the spectral range required for CP quantification. Analysis at pH 12 gave greater absorption and sensitivity for the method compared with pH 5.6. The calibration curves of the proposed methods were linear in the concentration ranges 0.0061–0.61 and 0.0078–0.78 mM with detection limit of 0.0006 and 0.0008 mM for dichlorophenols and monochlorophenols, respectively. The oxidation kinetics of five chlorophenols in aqueous solution with excess potassium permanganate were evaluated using the analytical method. The pseudo-first-order reaction rates were found to be relatively rapid 1.42 × 10−3 to 0.024 s−1 and followed the sequence 2-chlorophenol (2-CP) > 2,6-dichlorophenol (2,6-DCP) > 4-chlorophenol (4-CP) > 2,4-dichlorophenol (2, 4-DCP) > 3-chlorophenol (3-CP). The apparent second-order rate constant was calculated from the measured pseudo-first-order rate constant with respect to CP with initial KMnO4 concentration (1.5 mM) and follows the same sequence of pseudo-first-order rate constant. This shows that chlorine atoms in the structure of chlorophenol had a significant influence on the oxidation of chlorophenols by potassium permanganate. Permanganate can be used for the treatment of chlorophenol-contaminated soil and groundwater.  相似文献   
99.
We develop a new Bayesian two-stage space-time mixture model to investigate the effects of air pollution on asthma. The two-stage mixture model proposed allows for the identification of temporal latent structure as well as the estimation of the effects of covariates on health outcomes. In the paper, we also consider spatial misalignment of exposure and health data. A simulation study is conducted to assess the performance of the 2-stage mixture model. We apply our statistical framework to a county-level ambulatory care asthma data set in the US state of Georgia for the years 1999?C2008.  相似文献   
100.
Vibrio cholerae and V. vulnificus are of major concern due to their effect on public health throughout the world. It is therefore imperative to identify a gene and method that are suitable for the accurate species-specific detection of these two species. A duplex polymerase chain reaction (PCR) assay was developed using two sets of primers targeting the groEL gene for the accurate simultaneous detection of V. cholerae and V. vulnificus. The nucleotide sequence of the groEL gene was compared with the sequences of other Vibrio and non-Vibrio species. The specificity of two primer sets for duplex PCR was checked using 24 Vibrio and 8 non-Vibrio species. The primer sets were found to be specific for these two species and could detect both of the target bacterial species without any ambiguity, even when comparing closely related species. For both species, the detection limit was 100 pg of purified genomic DNA. The duplex PCR showed high specificity and sensitivity for each species and was sufficient for the detection of V. cholerae and V. vulnificus from artificially infected shellfish tissue, flounder, and even inoculated seawater. This method is simple and cost-effective, and can be utilized for the simultaneous detection of both species, thus representing an effective tool for both epidemiologist and ecologist.  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