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   344篇
  免费   24篇
林业   12篇
农学   14篇
基础科学   7篇
  110篇
综合类   6篇
农作物   73篇
水产渔业   56篇
畜牧兽医   52篇
园艺   8篇
植物保护   30篇
  2023年   4篇
  2022年   8篇
  2021年   11篇
  2020年   14篇
  2019年   25篇
  2018年   28篇
  2017年   46篇
  2016年   36篇
  2015年   15篇
  2014年   22篇
  2013年   38篇
  2012年   22篇
  2011年   35篇
  2010年   22篇
  2009年   2篇
  2008年   16篇
  2007年   10篇
  2006年   9篇
  2005年   1篇
  2004年   3篇
  2002年   1篇
排序方式: 共有368条查询结果,搜索用时 250 毫秒
111.
Due to the variations in opacity and brightness of peroxide bleached pulp at Mazandaran Wood and Paper Industries Company (MWPI), empirical models were developed to predict chemimechanical pulp (CMP) brightness and opacity from peroxide bleaching conditions and to drive the optimum operating conditions. To overcome the inconsistency problem, a multi-variate regression analysis method was used for model building. The models were then validated using a new data set from the bleach plant at MWPI, assessing the models’ predictive ability and performance. The results show that there is a relationship between bleaching variables and such dependent variables as pulp brightness and opacity. In addition to the hydrogen peroxide charge and pulp initial brightness, the initial opacity had a significant reverse effect on the final CMP brightness. It was also found that the concentration of total Na+ in the CMP tower was the most important variable affecting the final pulp opacity. The validation results demonstrated that these models can be employed as useful tools for process optimization purposes.  相似文献   
112.
In the present study, 100 bacterial strains were isolated from the soil and tested for siderophore producing ability. Among siderophore producing bacteria, three superior isolates with the highest level of siderophore (F13, F58 and F66) selected for further study. Production of lecithinase, arginine dehydrolase, catalase, oxidase, hydrogen cyanide, indole acetic acid, solubilization of phosphate, gelatin hydrolysis, oxidative/fermentative, motility and gram staining by these strains was evaluated. In greenhouse experiment, the ability of selected isolates in solubilizing insoluble iron-containing compounds was examined at three moisture levels (0.45–0.6, 0.6–0.7 and 0.7–0.85 field capacity). Results showed that isolates F13 and F66 have greatest effects on chlorophyll amount and shoot dry weight compared to isolate F58. On average, iron concentration of sunflower in the presence of bacteria was 2.85-fold more than control, while it was 1.88-fold for roots. In addition, bacterial treatments enhanced resistance to water stress in sunflower. Based on biochemical tests and by comparison of 16S rRNA sequences, the F13, F58 and F66 isolates were closely related to Pseudomonas spp., Enterobacter spp. and Bacillus Sporothernodurans, respectively.  相似文献   
113.
This experiment was conducted to evaluate the effects of three nutrient recipes containing different concentrations of macronutrients in the vegetative stage [Vegetative Nutrient Solution: (VNS-I, VNS-II, and VNS-III)] and two nutrient recipes in reproductive stage [Reproductive Nutrient Solution: (RNS-I and RNS-II)], on physiological and biochemical parameters of strawberry ‘Paros’ in a soilless system. The results indicated the significant effects of nutrient solution on the photosynthetic capacity, yield, minerals uptake and titratable acidity of strawberry fruits. In the other hand fruit total soluble solids affected by vegetative nutrient solution. The highest yield was obtained under application of lowest level of minerals. Vegetative growth including leaf number and leaf area, as well as total chlorophyll were the highest as potassium (K+), calcium (Ca2+), and nitrogen (N) concentrations were increased. The highest content of N and Ca2+ uptake were in VNS-III × RNS-I formulation. Additionally, the highest vitamin C was in VNS-I formulation. Moreover, the most firmed fruits and the highest post-harvest shelf life of fruits were produced in VNS-III × RNS-I formulation.  相似文献   
114.
Blackleg disease, caused by the hemibiotrophic fungal pathogen Leptosphaeria maculans, is one of the most devastating disease of Brassica species worldwide. To date, a total of 20 race-specific blackleg resistance (R) genes have been reported and all of those loci are located in either the A or B genomes of various Brassica species. The B. oleracea genome (CC) shares a high ancestral synteny with the A genome of B. rapa, suggesting the presence of qualitative (race specific) resistance to blackleg disease is also possible in B. oleracea germplasm. In the present study the C genome of Korean B. oleracea germplasm was screened for the presence of blackleg R genes. Thirty-two inbred cabbage lines with unknown resistance profiles, along with five control B. napus lines with well-characterised race-specific R genes, were assessed for cotyledon resistance against two L. maculans isolates with known and highly-contrasting avirulence gene (Avr) profiles. Two cabbage accessions were identified which produced a strong resistance when challenged with either isolate, demonstrating the presence of effective blackleg R genes in the cabbage C genome. Additionally, 16 microsatellite markers linked to seven different R genes of the B. napus A genome were converted into markers for their homologous regions on the B. oleracea C genome. These markers were used to screen all B. oleracea lines to assess if the novel C genome R genes were syntenous to known R gene-homologous regions of the A genome. The resistant cabbage lines offer C genome R genes for the protection of B. oleracea varieties against incursion of blackleg disease, as well as novel additional resistance sources for introgression into B. napus and B. carinata breeding material.  相似文献   
115.
Nutrient deficiency may be a reason for citrus decline in many countries. In the current investigation, soil and leaf samples of 63 Washington Navel orange orchards in arid lands of southern Iran (Darab region) were analyzed to study the nutritional status of orange orchards and to find relationships between soil properties and nutrients content of soils and orange leaves. The soils differed widely in clay content (3–37%), pH value (7.04–7.95), calcium carbonate equivalent (18–86%), and organic matter content (0.3–12%). These soils represented a wide range of plant nutrients concentration. Majority of the studied soils had sufficient concentrations of all nutrients (except Fe). Results indicated that pH, organic matter, clay, and calcium carbonate contents are the most important characteristics that control the soil nutrients availability. The mean contents of N, K, P, Fe, Mn, Zn, and Cu in leaves were 2.59, 0.84, and 0.14% and 66, 44, 17, and 12?mg?kg?1, respectively. Most orchards showed K, Fe, and Zn deficiencies. We found no relationships between nutrients content in leaf and soil (except for K, Mn, and Zn); and this indicated that soil analysis may not be a reliable method for most nutrient deficiency diagnosis.  相似文献   
116.
The effects of adding surface modified graphene nanoplatelets (GNPs) in various weight percentages (0, 0.1, 0.2, 0.3, 0.4, 0.5 with respect to matrix) on the high velocity impact response of basalt fibers/epoxy composites were evaluated. High speed mechanical stirrer and ultrasonic waves were used for the dispersion of GNPs in the epoxy matrix, and hand layup method was utilized for the fabrication of the composite samples. High velocity impact testing was performed using a conical projectile. The results demonstrated that the maximum improvement in the impact limit velocity and energy absorption occurred in the 0.3 wt.% GNPs nanocomposite, i.e., 11 and 23 %, respectively. Also, the electron microscopy studies revealed that the addition of GNPs contributed in improving the impact properties by influencing the matrix and thus enhancing the interfacial characteristics between the basalt fibers and the matrix.  相似文献   
117.
The effect of cattle manure and sulfur fertilizer on seed yield and oil composition of pumpkin (Cucurbita pepo var. Styriaca) under inoculated with Thiobacillus thiooxidans was investigated in a factorial study based on a randomized complete block design. Experimental factors consisted of cattle manure (M) (M0: 0, M1: 10; and M2: 20 t ha?1), sulfur (S) (S0: 0, S1: 250; and S2: 500 kg ha?1) and T. thiooxidans (B): inoculated (B1) and non-inoculated (B0). Results demonstrated that the application of T. thiooxidans, cattle manure, and S fertilizer decreased the soil pH. The largest number of seed per fruit (367), highest fruit yield (70.57 t ha?1), seed iron (Fe) content (16.26 mg 100 g?1), and seed yield (111 kg ha?1) was obtained when 20 t ha?1 manure was applied in combination with 500 kg ha?1 S inoculated with T. thiooxidans. In this condition, the content of S, Fe, phosphorus (P), and nitrogen (N) in plant shoots was increased by 44.8%, 22.58%, 33.89%, and 10.38%, respectively, compared to the control. Moreover, the highest content of seed protein was observed in 10 t ha?1 manure and 500 kg ha?1 S fertilizer inoculated with T. thiooxidans. When 250 kg ha?1 S fertilizer was applied, 20 t ha?1 manure decreased seed P content sharply. At the rate of 500 kg ha?1 S fertilizer, the highest content of seed P was obtained from 20 t ha?1 manure. Totally, 20 t ha?1 cattle manure, along with 500 kg ha?1 S fertilizer as well as T. thiooxidans inoculation, improved oil and seed yield of medicinal pumpkin.  相似文献   
118.
Developing urbanization, water shortage, watercourse pollution, and demands for more food due to population growth require a more efficient water irrigation and fertilizer application. Retaining nutrients and water in agricultural soils brings about higher crop yields and prevents pollution of water courses. Among different solutions, zeolites, which are environmental friendly, ubiquitous, and inexpensive, have been extensively employed in agricultural activities. These minerals are considered as soil conditioners to improve soil physical and chemical properties including infiltration rate, saturated hydraulic conductivity (K s), water holding capacity (WHC), and cation exchange capacity (CEC). Natural and surface-modified zeolites can efficiently hold water and nutrients including ammonium (NH4 +), nitrate (NO3 ?) and phosphate (PO4 3?), potassium (K+), and sulfate (SO4 2?) in their unique porous structures. Their application as slow-release fertilizers (SRFs) are reported as well. Therefore, zeolite application can improve both water use efficiency (WUE) and nutrient use efficiency (NUE) in agricultural activities and consequently can reduce the potential of surface and groundwater pollution. This review paper summarizes findings in the literature about the impact of zeolite applications on water and nutrient retention in the agriculture. Furthermore, it explores benefits and drawbacks of zeolite applications in this regard.
Graphical Abstract ?
  相似文献   
119.
Effects of nanoclay (NC) on physical and mechanical properties of wood-plastic composite (WPC) were studied here. Virgin, recycled, and mixed (50/50% of virgin/recycled) polyvinyl chloride (PVC) were used as the matrix in the WPC. Specimens with three NC contents of 1.5%, 3%, and 5% were manufactured; they were then compared with control specimens. Totally, 12 treatments were manufactured. The physical and mechanical properties were measured in accordance with the ASTM standards. The highest properties were found in specimens made from virgin PVC. Addition of recycled PVC resulted in significant decrease in all properties. NC improved all physical and mechanical properties studied in the present research project; the highest properties were observed in specimens with 5% of NC content. The improvement in properties was as a result of formation of bonds between the hydroxyl groups of NC with the wood flour components. It was concluded that NC would significantly improve the properties in all the three PVC types of virgin, recycled, and mixed. From an industrial point of view, it was concluded that mixing virgin and recycled PVC can be recommended not only to decrease production costs, but also to partially solve the problem of PVC residue which are not bio-degradable.  相似文献   
120.
Field experiments were conducted to investigate the effects of irrigation regimes and N levels on assimilate remobilization of two barley cultivars (Yousefsix-rowed and Nimrouztwo-rowed) in 2011 and 2012. There were three levels of water regimes (full irrigation (I100), 75% and 50% of I100: I75 and I50, respectively) in 2011. Rain-fed treatment (I0) was included in 2012. Three N levels (0, 60, and 120 kg ha?1) were used. Grain yield and assimilate remobilization decreased by severe water stress (I0), however, the reduction of them were intensified by N fertilizer application. The N remobilization was negatively affected by N fertilization and water stress. The two-rowed showed higher N remobilization (10.7%) and contribution of N remobilized to N content of grain (5.8%) than the six-rowed. The two-rowed cultivar showed significantly higher assimilate remobilization and grain yield than the six-rowed under I50 (26.3% and 6.5%, respectively) and I0 (48.7% and 17.1%, respectively), while the six-rowed had similar or higher performances in terms of these traits under I100 and I75. This study showed that optimizing irrigation and N rates (decrease N level with increasing water stress) and selection of the suitable cultivars (Nimrouztwo-rowed) might increase assimilate remobilization and consequently grain yield under drought stress conditions.  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