全文获取类型
收费全文 | 515篇 |
免费 | 14篇 |
专业分类
林业 | 66篇 |
农学 | 10篇 |
基础科学 | 4篇 |
204篇 | |
综合类 | 83篇 |
农作物 | 17篇 |
水产渔业 | 22篇 |
畜牧兽医 | 86篇 |
园艺 | 12篇 |
植物保护 | 25篇 |
出版年
2024年 | 1篇 |
2023年 | 5篇 |
2022年 | 3篇 |
2021年 | 14篇 |
2020年 | 7篇 |
2019年 | 12篇 |
2018年 | 25篇 |
2017年 | 12篇 |
2016年 | 14篇 |
2015年 | 16篇 |
2014年 | 14篇 |
2013年 | 26篇 |
2012年 | 40篇 |
2011年 | 35篇 |
2010年 | 26篇 |
2009年 | 20篇 |
2008年 | 44篇 |
2007年 | 24篇 |
2006年 | 28篇 |
2005年 | 30篇 |
2004年 | 25篇 |
2003年 | 23篇 |
2002年 | 30篇 |
2001年 | 11篇 |
2000年 | 3篇 |
1999年 | 4篇 |
1998年 | 6篇 |
1997年 | 2篇 |
1996年 | 3篇 |
1995年 | 1篇 |
1994年 | 3篇 |
1992年 | 2篇 |
1991年 | 5篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1987年 | 1篇 |
1984年 | 1篇 |
1981年 | 1篇 |
1978年 | 2篇 |
1974年 | 2篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1971年 | 1篇 |
1960年 | 1篇 |
排序方式: 共有529条查询结果,搜索用时 15 毫秒
481.
Markus Bestfleisch Jens Möhring Magda‐Viola Hanke Andreas Peil Henryk Flachowsky 《Plant Breeding》2014,133(1):115-120
The extension of the ripening season in open field production is of high economic interest for strawberry growers. Therefore, targeted breeding for extreme early or late ripening cultivars with high yield potential is of particular interest. Thirteen strawberry cultivars were crossed in a reciprocal way without selfing, and the 144 resulting F1 populations were evaluated in a field trial over a period of two consecutive years. The data were analysed using a mixed‐model approach adapted for diallel crossing designs using SAS 9.3. The variability in the crossing approach is mainly based on the general combining ability (GCA) of the cultivars (additive effects). Specific and reciprocal combining abilities (non‐additive effects) appear less important. The highest GCAs for the trait Marketable Yield were found for the cultivars ‘Polka’ and ‘Yamaska’. The trait Earliness is bilateral with significantly low GCAs for early ripening in ‘Clery’ and ‘Daroyal’ and significantly high GCAs for late ripening in ‘Yamaska’ and ‘Florence’. Crosses with these cultivars are likely to deliver populations with both high yield and an extended ripening period. 相似文献
482.
Markus Kankainen Jari Setälä Antti Kause Cheryl Quinton Susanna Airaksinen Juha Koskela 《Aquaculture Economics & Management (Blackwell Science)》2016,20(2):131-164
Economic values of different fish traits are needed to direct breeding programs to optimize economic benefits for aquaculture industry. The aim of this article is to highlight and calculate how different traits affect the value of farmed fish supply chain. Supply chain approach is needed to calculate economic impact of fish traits because several fish traits affect costs and returns not only in fish farming but also at the processing and retail level. In this article, economic values are calculated for 14 productivity and product quality traits in European whitefish (Coregonus lavaretus). Productivity affecting traits, such as growth, mortality and different yields, are included in the study. In addition, economic values are calculated for several quality traits like fillet gaping, appearance and fat content of flesh.Productivity traits had the highest economic importance if the traits could be improved. However, quality traits may cause even higher economic losses, if the quality decreases. Thus, the management of the breeding program should pay simultaneous attention to both quality and productivity traits. 相似文献
483.
Effects of dietary yeast inclusion and acute stress on postprandial plasma free amino acid profiles of dorsal aorta‐cannulated rainbow trout 下载免费PDF全文
D. Huyben A. Vidaković M. Langeland A. Nyman T. Lundh A. Kiessling 《Aquaculture Nutrition》2018,24(1):236-246
In a 4‐week experiment, 15 cannulated rainbow trout were fed three diets based on fish meal (FM), Saccharomyces cerevisiae yeast (SC) and Wickerhamomyces anomalus and S. cerevisiae yeast mix (WA). Fish were fed daily, and blood samples were collected on day 7 of each week at 0, 3, 6, 12 and 24 hr after feeding. In the final week, fish were exposed to a 1‐min netting stressor. All essential and non‐essential plasma amino acid levels except methionine were similar between fish fed diets FM, SC and WA. Plasma methionine and sarcosine were significantly higher in fish fed diets SC and WA, possibly due to the crystalline methionine level, form or feeding regime. Hydroxy‐proline and 3‐methyl‐histidine were higher in fish fed diet FM, which can be explained by the higher levels present in fish meal compared with yeast. In stressed fish, there were no dietary effects on plasma amino acid levels, but significant increases in taurine and cystathionine were found in stressed compared with unstressed fish. These results demonstrate that yeast‐based diets produce similar plasma amino acid profiles to fish meal and suggest that yeast may be a suitable fish meal replacement in diets for rainbow trout. 相似文献
484.
485.
486.
487.
Soil fertility depletion in smallholder agricultural systems in sub-Saharan Africa presents a formidable challenge both for food production and environmental sustainability. A critical constraint to managing soils in sub-Saharan Africa is poor targeting of soil management interventions. This is partly due to lack of diagnostic tools for screening soil condition that would lead to a robust and repeatable spatially explicit case definition of poor soil condition. The objectives of this study were to: (i) evaluate the ability of near infrared spectroscopy to detect changes in soil properties across a forest-cropland chronosequence; and (ii) develop a heuristic scheme for the application of infrared spectroscopy as a tool for case definition and diagnostic screening of soil condition for agricultural and environmental management. Soil reflectance was measured for 582 topsoil samples collected from forest-cropland chronosequence age classes namely; forest, recently converted, RC (17 years) and historically converted, HC (ca.70 years). 130 randomly selected samples were used to calibrate soil properties to soil reflectance using partial least-squares regression (PLSR). 64 randomly selected samples were withheld for validation. A proportional odds logistic model was applied to chronosequence age classes and 10 principal components of spectral reflectance to determine three soil condition classes namely; “good”, “average” and “poor” for 194 samples. Discriminant analysis was applied to classify the remaining 388 “unknown” samples into soil condition classes using the 194 samples as a training set. Validation r2 values were: total C, 0.91; total N, 0.90; effective cation exchange capacity (ECEC), 0.90; exchangeable Ca, 0.85; clay content, 0.77; silt content, 0.77 exchangeable Mg, 0.76; soil pH, 0.72; and K, 0.64. A spectral based definition of “good”, “average” and “poor” soil condition classes provided a basis for an explicitly quantitative case definition of poor or degraded soils. Estimates of probabilities of membership of a sample in a spectral soil condition class presents an approach for probabilistic risk-based assessments of soil condition over large spatial scales. The study concludes that reflectance spectroscopy is rapid and offers the possibility for major efficiency and cost saving, permitting spectral case definition to define poor or degraded soils, leading to better targeting of management interventions. 相似文献
488.
Ramos Silvio Junio Caldeira Cecílio Frois Gastauer Markus Costa Deborah Luciany Pires Furtini Neto Antonio Eduardo de Souza Filipe Bittencourt Machado Souza-Filho Pedro Walfir Martins Siqueira Jose Oswaldo 《New Forests》2019,50(5):859-872
New Forests - For the effective use of native plants for mineland revegetation, an understanding of seed dormancy break and germination requirements, and seed storage tolerance is indispensable. In... 相似文献
489.
490.
Patrick J Crowley Dr Clemens Lamberth Urs Müller Sebastian Wendeborn Kurt Nebel John Williams Olivia‐A Sageot Neil Carter Tanya Mathie Hans‐Joachim Kempf Jeremy Godwin Peter Schneiter Markus R Dobler 《Pest management science》2010,66(2):178-185
BACKGROUND: The excellent fungicidal activity of [1,2,4]triazolo[1,5‐a]pyrimidines suggested the search for further analogues with improved properties. RESULTS: A series of novel trisubstituted pyrido[2,3‐b]pyrazines has been designed and prepared as 6,6‐biheterocyclic analogues of related 5,6‐bicyclic [1,2,4]triazolo[1,5‐a]pyrimidines. Their fungicidal activity was evaluated against the plant pathogens Puccinia recondita Rob. ex Desm. f. sp. tritici (Eriks.) CO Johnston (wheat brown rust), Mycosphaerella graminicola (Fuckel) Schroter (Septoria tritici Rob., leaf spot of wheat) and Magnaporthe grisea (Hebert) Barr (Pyricularia oryzae Cav., rice blast). Structure–activity relationship studies revealed the advantage of a fluoro substituent in position 6 and of a secondary amine in position 8. CONCLUSION: 8‐Amino‐7‐aryl‐6‐halogen‐substituted pyrido[2,3‐b]pyrazines have been prepared as 6,6‐biheterocyclic analogues of similarly substituted triazolopyrimidine fungicides. A concise four‐step synthesis route has been worked out to prepare these novel compounds from commercially available starting materials. [(R)‐(1,2‐Dimethylpropyl)]‐[6‐fluoro‐7‐(2,4,6‐trifluorophenyl)pyrido[2,3‐b]pyrazin‐8‐yl]amine showed excellent activity against three economically important phytopathogens. Copyright © 2009 Society of Chemical Industry 相似文献