全文获取类型
收费全文 | 365篇 |
免费 | 13篇 |
专业分类
林业 | 25篇 |
农学 | 11篇 |
基础科学 | 5篇 |
95篇 | |
综合类 | 21篇 |
农作物 | 15篇 |
水产渔业 | 33篇 |
畜牧兽医 | 137篇 |
园艺 | 12篇 |
植物保护 | 24篇 |
出版年
2023年 | 3篇 |
2022年 | 8篇 |
2021年 | 15篇 |
2020年 | 18篇 |
2019年 | 20篇 |
2018年 | 11篇 |
2017年 | 8篇 |
2016年 | 8篇 |
2015年 | 11篇 |
2014年 | 8篇 |
2013年 | 14篇 |
2012年 | 21篇 |
2011年 | 37篇 |
2010年 | 21篇 |
2009年 | 11篇 |
2008年 | 19篇 |
2007年 | 23篇 |
2006年 | 21篇 |
2005年 | 12篇 |
2004年 | 22篇 |
2003年 | 17篇 |
2002年 | 7篇 |
2001年 | 5篇 |
2000年 | 3篇 |
1999年 | 5篇 |
1998年 | 1篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1995年 | 3篇 |
1994年 | 2篇 |
1993年 | 1篇 |
1992年 | 3篇 |
1989年 | 5篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1973年 | 1篇 |
1970年 | 1篇 |
1964年 | 2篇 |
排序方式: 共有378条查询结果,搜索用时 0 毫秒
371.
Nebai Mesanza Rosa Raposo Margarita Elvira‐Recuenco Irene Barnes Ariska van der Nest Mnica Hernndez Maria Teresa Pascual Iskander Barrena Unai San Martín Alejandro Cantero Laura Hernandez‐Escribano Eugenia Iturritxa 《Forest Pathology》2021,51(1):e12650
A historical outbreak of needle blight disease was recorded during 2018 to 2019 in plantations of Pinus radiata and Pinus nigra in the North of Spain. The main pathogens involved in this historical outbreak were identified as Lecanosticta acicola and Dothistroma septosporum. Recently, a variety of tree species in three arboreta planted between 2011 and 2013 in the Basque Country as part of the European project REINFFORCE were showing symptoms of needle blight and defoliation. The aim of this study was to determine which pine species were affected with these pathogens. Tree species sampled included several provenances of P. brutia, P. elliottii, P. nigra, P. pinaster, P. pinea, P. ponderosa, P. sylvestris and P. taeda. Using molecular identification methods, Lecanosticta acicola was confirmed infecting Pinus brutia (Provenance: Alexandropolis, Greece and var. eldarica, Crimea) and represents a new host species for this pathogen. Pinus elliottii (Provenance: Georgia, USA) and P. ponderosa (Provenance: Central California, USA) are new host reports of L. acicola for Spain. Dothistroma septosporum was found for the first time on P. brutia (Provenance: Marmaris, Turkey) and P. ponderosa (Provenance: Oregon, USA) in Spain and was also detected infecting P. nigra (Provenance: Sologne Vayrières, France). 相似文献
372.
Holtgrieve GW Schindler DE Hobbs WO Leavitt PR Ward EJ Bunting L Chen G Finney BP Gregory-Eaves I Holmgren S Lisac MJ Lisi PJ Nydick K Rogers LA Saros JE Selbie DT Shapley MD Walsh PB Wolfe AP 《Science (New York, N.Y.)》2011,334(6062):1545-1548
Humans have more than doubled the amount of reactive nitrogen (Nr) added to the biosphere, yet most of what is known about its accumulation and ecological effects is derived from studies of heavily populated regions. Nitrogen (N) stable isotope ratios ((15)N:(14)N) in dated sediments from 25 remote Northern Hemisphere lakes show a coherent signal of an isotopically distinct source of N to ecosystems beginning in 1895 ± 10 years (±1 standard deviation). Initial shifts in N isotope composition recorded in lake sediments coincide with anthropogenic CO(2) emissions but accelerate with widespread industrial Nr production during the past half century. Although current atmospheric Nr deposition rates in remote regions are relatively low, anthropogenic N has probably influenced watershed N budgets across the Northern Hemisphere for over a century. 相似文献
373.
374.
Mattia Brambilla Fabio Casale Valentina Bergero G. Matteo Crovetto Riccardo Falco Irene Negri Paolo Siccardi Giuseppe Bogliani 《Biological conservation》2009,142(10):2033-2042
Species conservation largely depends on knowledge of habitat needs of target species. GIS-models are increasingly used to assess habitat preferences and distribution of target species, but their accuracy is constrained by availability of digital data layers. We developed a two-steps approach aiming at showing pros and cons of landscape (GIS)- and site-level habitat models, identifying key habitat factors for conservation of a threatened bird species, the red-backed shrike Lanius collurio. A spatially explicit GIS-model was generated using landscape variables, and a second model at site level was developed using fine-scale variables measured on the ground. The GIS-based model was then extrapolated to the entire region to obtain a map of distribution of suitable habitats. Positive associations between shrike occurrence and both hedgerow length and partial shrub cover were detected at both scales. Shrikes were also positively associated with grassland cover at landscape level and with partial cover of untilled herbaceous vegetation at the finer scale, and negatively affected by lucerne cover. The GIS-model led to an affordable map of predicted habitat suitability which should help conservationists to focus on different local priorities, but was unable to identify effects of untilled and lucerne cover. Site-level model gave fine details for habitat management, but its application elsewhere requires ground-measurements of factors. Combining the multiscale models could indicate more urgent actions at large scales (e.g. maintaining suitable habitats, or improving connectivity among isolated patches) and draw a detailed figure of the most suitable habitat for the species. Shrike occurrence was associated with a higher number of shrub and tree species: the indicator value of the species should ensure general benefits for biodiversity from dedicated management. 相似文献
375.
Karina Ribeiro Irene Bastos Franceschini‐Vicentini Luciene Patrici Papa Michael B. New Wagner C. Valenti 《Aquaculture Research》2012,43(12):1756-1763
Effects of the ratio of dietary fatty acids, namely n‐3 (mainly long chain polyunsaturated – LC‐PUFA) to n‐6 PUFA on the fecundity of Macrobrachium amazonicum were evaluated. In T1, the diet had equal and low levels of dietary n‐3 and n‐6 fatty acids (6 mg g?1). In T2, the concentration of n‐3 (6 mg g?1) was a half of the concentration of the n‐6 (12 mg g?1), and in T3, the diet had equal and high concentrations of n‐3 and n‐6 (12 mg g?1). Females with ovaries in stages I, III and V were collected. Higher gonadosomatic index (GSI) (6.89%) was observed in females in ovarian stage V than at other ovarian stages; however, the hepatosomatic index (HIS) showed high values in all females with ovaries in the stage III. A ratio of 1:2 n‐3:n‐6 fatty acids increased the GSI of mature females and the number of eggs spawned. Raising the level of both n‐3 and n‐6 fatty acids from ~0.6% to ~1.2% of the diet did not produce any effect on the GSI or on fecundity, suggesting that the ratio is more important than the absolute value of these two families of fatty acids. 相似文献
376.
The Authors observed, in Italy, over a number of years, isolated and grouped trees of the genus Quercus that declined over one or more vegetative seasons. The spread was very fast; in fact the trees declined in the course of 2–3 vegetative seasons. A series of symptoms was observed: production of epicormic shoots, yellowing of leaves, laceration of the bark, bleeding from the trunk. Many fungi were isolated: Armillaria spp., Cephalosporium spp., Cladosporium spp., Cylindrocarpon spp., Diplodia mutila, Hypoxylon mediterraneum, Phoma cavae, Pbomopsis quercina, Sporotrix spp. Future research will attempt to ascertain the possible causes of the decline. 相似文献
377.
Straight AF Cheung A Limouze J Chen I Westwood NJ Sellers JR Mitchison TJ 《Science (New York, N.Y.)》2003,299(5613):1743-1747
Completion of cell division during cytokinesis requires temporally and spatially regulated communication from the microtubule cytoskeleton to the actin cytoskeleton and the cell membrane. We identified a specific inhibitor of nonmuscle myosin II, blebbistatin, that inhibited contraction of the cleavage furrow without disrupting mitosis or contractile ring assembly. Using blebbistatin and other drugs, we showed that exit from the cytokinetic phase of the cell cycle depends on ubiquitin-mediated proteolysis. Continuous signals from microtubules are required to maintain the position of the cleavage furrow, and these signals control the localization of myosin II independently of other furrow components. 相似文献
378.
Wong JW Hennessy MK Hayward DG Krynitsky AJ Cassias I Schenck FJ 《Journal of agricultural and food chemistry》2007,55(4):1117-1128
A method was developed to determine organophosphorus pesticides (OPs) in dried ground ginseng root. Pesticides were extracted from the sample using acetonitrile/water saturated with salts, followed by solid-phase dispersive cleanup, and analyzed by capillary gas chromatography with electron ionization mass spectrometry in selective ion monitoring mode (GC-MS/SIM) and flame photometric detection (GC-FPD) in phosphorus mode. The detection limits for most of the pesticides were 0.025-0.05 microg/g using GC-FPD but were analyte-dependent for GC-MS/SIM, ranging from 0.005 to 0.50 microg/g. Quantitation was determined from 0.050 to 5.0 microg/g with r 2 > 0.99 for a majority of the pesticides using both detectors. Recovery studies were performed by fortifying the dried ground ginseng root samples to concentrations of 0.025, 0.1, and 1.0 microg/g, resulting in recoveries of >90% for most pesticides by GC-FPD. Lower (<70%) and higher (>120%) recoveries were most likely from complications of pesticide lability or volatility, matrix interference, or inefficient desorption from the solid-phase sorbents. There was difficulty in analyzing the ginseng samples for the OPs using GC-MS at the lower fortification levels for some of the OPs due to lack of confirmation. GC-FPD and GC-MS/SIM complement each other in detecting the OPs in dried ground ginseng root samples. This procedure was shown to be effective and was applied to the analysis of OPs in ginseng root samples. One particular sample, a ground and dried American ginseng (Panax quinquefolius) root sample, was found to contain diazinon quantified at approximately 25 microg/kg by external calibration using matrix-matched standards or standard addition using both detectors. The advantage of using both detectors is that confirmation can be achieved using GC-MS, whereas the use of a megabore column in GC-FPD can be used to quantitate some of the nonpolar OPs without the use of matrix-matched standards or standard addition. 相似文献