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   575篇
  免费   43篇
林业   50篇
农学   17篇
基础科学   6篇
  138篇
综合类   14篇
农作物   36篇
水产渔业   83篇
畜牧兽医   158篇
园艺   37篇
植物保护   79篇
  2024年   1篇
  2023年   13篇
  2022年   16篇
  2021年   14篇
  2020年   12篇
  2019年   21篇
  2018年   33篇
  2017年   33篇
  2016年   35篇
  2015年   23篇
  2014年   23篇
  2013年   77篇
  2012年   49篇
  2011年   46篇
  2010年   35篇
  2009年   28篇
  2008年   31篇
  2007年   17篇
  2006年   21篇
  2005年   19篇
  2004年   13篇
  2003年   8篇
  2002年   10篇
  2001年   4篇
  2000年   1篇
  1999年   3篇
  1998年   2篇
  1997年   1篇
  1996年   4篇
  1995年   2篇
  1993年   6篇
  1990年   1篇
  1989年   1篇
  1987年   1篇
  1985年   2篇
  1984年   4篇
  1983年   2篇
  1982年   1篇
  1979年   1篇
  1977年   2篇
  1968年   1篇
  1958年   1篇
排序方式: 共有618条查询结果,搜索用时 15 毫秒
611.
We aimed to investigate whether sodium chloride seed priming and irrigation at seedling stage enhance response of 5-leaf stage tomato plants (Lycopersium esculentum Mill.) to high salt stress. Three experimental groups were as; non-primed seeds, seeds primed with 0.05M sodium chloride (NaCl), and seeds primed and irrigated with 0.05M NaCl starting from sowing to salt stress application. Sodium chloride solutions (0.1M, 0.2M, 0.4M, and 0.6M) were added to cups under pots in every 2 days for 10 days to treatment groups. Control groups were irrigated with distilled water at the same time intervals. At least two experimental setups contained at least four plants, and two samplings of leaf and root tissues were performed for analysis of each plant to evaluate changes in pigment and proline contents, lipid peroxidation and electrolyte leakage levels, and ascorbate peroxidase and catalase activity. Priming reduced mean germination time, and increased final germination percentage together with energy of germination. Increased root and hypocotyl lengths as well as increases in fresh weights supported enhanced seedling vigor. Considering growth and stress parameters such as chlorophyll content, chlorophyll to carotenoid ratios, and lipid peroxidation and electrolyte leakage were less affected in primed plants. Moreover, improvement of the accumulation of osmoregulating defense molecules, such as proline and anthocyanin, and of the inductions of the antioxidative enzyme system points out to higher adaptive response of these plants against deleterious effects of salt.  相似文献   
612.
This study was carried out in order to determine the effect of various manganese fertilizers [manganese sulfate (MnSO4.3H2O) (MS), 27% manganese (Mn) and manganese ethylenediaminetetraacetic acid (Mn-EDTA) (ME), 12% Mn], their doses (0, 6, 9, 12 mg Mn kg?1 for the soil and 0, 0.2, 0.3, 0.4% for the leaf) on yield and net return of dwarf bean. Field experiments were conducted in the randomized blocks split plot design with four replications under Konya ecological conditions in Turkey. Soil applications were made on bands as a single application at sowing whereas foliar applications (FA) were made at two times. Results of the field experiments showed the highest bean yields were significantly obtained by the fertilizer of ME-FA sprayed (243.80 and 257.74 kg da?1). For both years, the lowest yields were obtained by the MS-SA applications (166.97 and 180.60 kg da?1). The maximum net income was US $104.16 da?1 and US $156.06 da?1 by years.  相似文献   
613.
This paper presents a study on the batch adsorption of a basic dye, methylene blue (MB), from aqueous solution onto ground hazelnut shell in order to explore its potential use as a low-cost adsorbent for wastewater dye removal. A contact time of 24 h was required to reach equilibrium. Batch adsorption studies were carried out by varying initial dye concentration, initial pH value (3–9), ionic strength (0.0–0.1 mol L?1), particle size (0–200 μm) and temperature (25–55°C). The extent of the MB removal increased with increasing in the solution pH, ionic strength and temperature but decreased with increase in the particle size. The equilibrium data were analysed using the Langmuir and Freundlich isotherms. The characteristic parameters for each isotherm were determined. By considering the experimental results and adsorption models applied in this study, it can be concluded that equilibrium data were represented well by Langmuir isotherm equation. The maximum adsorption capacities for MB were 2.14?×?10?4, 2.17?×?10?4, 2.20?×?10?4 and 2.31?×?10?4 mol g?1 at temperature of 25, 35, 45 and 55°C, respectively. Adsorption heat revealed that the adsorption of MB is endothermic in nature. The results indicated that the MB strongly interacts with the hazelnut shell powder.  相似文献   
614.
The chemical composition (fatty acids, tocopherols, and sterols) of the oil from 14 samples of turpentine (Pistacia terebinthus L.) fruits is presented in this study. The oil content of the samples varied in a relatively small range between 38.4 g/100 g and 45.1 g/100 g. The dominating fatty acid of the oil is oleic acid, which accounted for 43.0 to 51.3% of the total fatty acids. The total content of vitamin E active compounds in the oils ranged between 396.8 and 517.7 mg/kg. The predominant isomers were alpha- and gamma-tocopherol, with approximate equal amounts between about 110 and 150 mg/kg. The seed oil of P. terebinthus also contained different tocotrienols, with gamma-tocotrienol as the dominate compound of this group, which amounted to between 79 and 114 mg/kg. The total content of sterols of the oils was determined to be between 1341.3 and 1802.5 mg/kg, with beta-sitosterol as the predominent sterol that accounted for more than 80% of the total amount of sterols. Other sterols in noteworthy amounts were campesterol, Delta5-avenasterol, and stigmasterol, which came to about 3-5% of the total sterols.  相似文献   
615.
Conflict over marine fishery resources is a growing security concern. Experts expect that global changes in our climate, food systems and oceans may spark or exacerbate resource conflicts. An initial scan of 803 relevant papers and subsequent intensive review of 31 fisheries conflict studies, focused on subnational and international conflicts, suggests that four substantial scientific gaps need addressing to improve our understanding of the nature and drivers of fisheries conflict. First, fisheries conflict and levels of conflict intensity are not precisely defined. Second, complex adaptive systems thinking is underutilized but has the potential to produce more realistic causal models of fishery conflict. Third, comparative large‐scale data and suitably integrative methodologies are lacking, underscoring the need for a standardized and comparable database of fisheries conflict cases to aid extrapolation beyond single case‐studies. Fourth, there is room for a more widespread application of higher order concepts and associated terminology. Importantly, the four gaps highlight the homogenized nature of current methodological and theoretical approaches to understanding fishery conflict, which potentially presents us with an oversimplified understanding of these conflicts. A more nuanced understanding of the complex and dynamic nature of fishery conflict and its causes is not only scientifically critical, but increasingly relevant for policymakers and practitioners in this turbulent world.  相似文献   
616.
Atlantic salmon sport fisheries have declined remarkably in many countries and participation seems to correlate with salmon abundance. We investigated angling participation in the Atlantic salmon sport fishery in Norwegian rivers by incorporating facilitators for participation in a constraint–negotiation model. We conducted an Internet survey of Norwegian anglers yielding 3,635 responses (40% response rate). The structural model confirmed our hypotheses and supported the conceptual constraints-effects-mitigation model of leisure constraint negotiation. Of the constraints and facilitators investigated, the structural constraints and facilitators subcategory “quality of fishing” exerted the largest influence on angling participation. The influence of constraints and facilitators was mitigated by use of corresponding negotiation strategies where “skills, knowledge, and money,” and different substitution strategies were important. To increase participation, we suggest increasing salmon abundance, offering longer fishing stretches per angler, and providing better information about where to book salmon angling.  相似文献   
617.
618.
Nitrogen is an essential nutrient for greenhouse-grown lettuce (Lactuca sativa L.); however, excessive nutrient availability causes disease and detrimental effects on the leaf and root development. In this study, nitrogen content of the lettuce leaves was estimated by determining the chlorophyll concentrations of the leaves using image processing technique. The Hoagland solution was used as a fertilizer in five different doses (control, quarter of the solution, half of the solution, standard solution, and two times more of the solution). Multilayer perceptron neural network (MLPNN) model was developed based on the red, green, and blue components of the color image captured to estimate chlorophyll content and chlorophyll concentration index (SPAD values). According to the obtained results, the MLPNN model was capable of estimating the lettuce leaf chlorophyll content with a reasonable accuracy. The coefficient of determination was 0.98, and mean square error was 0.006 in validation process.  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