全文获取类型
收费全文 | 355篇 |
免费 | 15篇 |
专业分类
林业 | 38篇 |
农学 | 4篇 |
基础科学 | 1篇 |
83篇 | |
综合类 | 33篇 |
农作物 | 14篇 |
水产渔业 | 29篇 |
畜牧兽医 | 137篇 |
园艺 | 17篇 |
植物保护 | 14篇 |
出版年
2023年 | 2篇 |
2022年 | 1篇 |
2021年 | 5篇 |
2020年 | 3篇 |
2019年 | 6篇 |
2018年 | 9篇 |
2017年 | 8篇 |
2016年 | 14篇 |
2015年 | 7篇 |
2014年 | 20篇 |
2013年 | 24篇 |
2012年 | 32篇 |
2011年 | 30篇 |
2010年 | 16篇 |
2009年 | 9篇 |
2008年 | 25篇 |
2007年 | 23篇 |
2006年 | 23篇 |
2005年 | 22篇 |
2004年 | 24篇 |
2003年 | 15篇 |
2002年 | 22篇 |
2001年 | 5篇 |
2000年 | 5篇 |
1999年 | 4篇 |
1998年 | 4篇 |
1996年 | 3篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1991年 | 1篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1981年 | 1篇 |
1930年 | 2篇 |
1928年 | 1篇 |
排序方式: 共有370条查询结果,搜索用时 0 毫秒
361.
D'Hondt S Jørgensen BB Miller DJ Batzke A Blake R Cragg BA Cypionka H Dickens GR Ferdelman T Hinrichs KU Holm NG Mitterer R Spivack A Wang G Bekins B Engelen B Ford K Gettemy G Rutherford SD Sass H Skilbeck CG Aiello IW Guèrin G House CH Inagaki F Meister P Naehr T Niitsuma S Parkes RJ Schippers A Smith DC Teske A Wiegel J Padilla CN Acosta JL 《Science (New York, N.Y.)》2004,306(5705):2216-2221
Diverse microbial communities and numerous energy-yielding activities occur in deeply buried sediments of the eastern Pacific Ocean. Distributions of metabolic activities often deviate from the standard model. Rates of activities, cell concentrations, and populations of cultured bacteria vary consistently from one subseafloor environment to another. Net rates of major activities principally rely on electron acceptors and electron donors from the photosynthetic surface world. At open-ocean sites, nitrate and oxygen are supplied to the deepest sedimentary communities through the underlying basaltic aquifer. In turn, these sedimentary communities may supply dissolved electron donors and nutrients to the underlying crustal biosphere. 相似文献
362.
Bornhop DJ Latham JC Kussrow A Markov DA Jones RD Sørensen HS 《Science (New York, N.Y.)》2007,317(5845):1732-1736
Free-solution, label-free molecular interactions were investigated with back-scattering interferometry in a simple optical train composed of a helium-neon laser, a microfluidic channel, and a position sensor. Molecular binding interactions between proteins, ions and protein, and small molecules and protein, were determined with high dynamic range dissociation constants (Kd spanning six decades) and unmatched sensitivity (picomolar Kd's and detection limits of 10,000s of molecules). With this technique, equilibrium dissociation constants were quantified for protein A and immunoglobulin G, interleukin-2 with its monoclonal antibody, and calmodulin with calcium ion Ca2+, a small molecule inhibitor, the protein calcineurin, and the M13 peptide. The high sensitivity of back-scattering interferometry and small volumes of microfluidics allowed the entire calmodulin assay to be performed with 200 picomoles of solute. 相似文献
363.
Studies of evolved massive stars indicate that they form in a clustered mode. During the earliest evolutionary stages, these regions are embedded within their natal cores. Here we present high-spatial-resolution interferometric dust continuum observations disentangling the cluster-like structure of a young massive star-forming region. The derived protocluster mass distribution is consistent with the stellar initial mass function. Thus, fragmentation of the initial massive cores may determine the initial mass function and the masses of the final stars. This implies that stars of all masses can form via accretion processes, and coalescence of intermediate-mass protostars appears not to be necessary. 相似文献
364.
A survey of the production of polyunsaturated aldehydes (PUA) of manipulated plankton communities is presented here. PUA are phytoplankton-derived metabolites that are proposed to play an important role in chemically mediated plankton interactions. Blooms of different intensities of the diatom Skeletonema marinoi were generated in eight mesocosms filled with water from the surrounding fjord by adding different amounts of a starting culture and nutrients. This set-up allowed us to follow PUA production of the plankton community over the entire induced bloom development, and to compare it with the natural levels of PUA. We found that S. marinoi is a major source for the particulate PUA 2,4-heptadienal and 2,4-octadienal (defined as PUA released upon wounding of the diatom cells) during the entire bloom development. Just before, and during, the decline of the induced diatom blooms, these PUA were also detected in up to 1 nM concentrations dissolved in the water. In addition, we detected high levels of the PUA 2,4-decadienal that was not produced by the diatom S. marinoi. Particulate decadienal correlated well with the cell counts of the prymnesiophyte Phaeocystis sp. that also developed in the fertilized mesocosms. Particulate decadienal levels were often even higher than those of diatom-derived PUA, indicating that PUA sources other than diatoms should be considered when it comes to the evaluation of the impact of these metabolites. 相似文献
365.
Background
The presence of Anaplasma phagocytophilum, an Ixodes ricinus transmitted bacterium, was investigated in two flocks of Danish grazing lambs. Direct PCR detection was performed on DNA extracted from blood and serum with subsequent confirmation by DNA sequencing.Methods
31 samples obtained from clinically normal lambs in 2000 from Fussingø, Jutland and 12 samples from ten lambs and two ewes from a clinical outbreak at Feddet, Zealand in 2006 were included in the study. Some of the animals from Feddet had shown clinical signs of polyarthritis and general unthriftiness prior to sampling. DNA extraction was optimized from blood and serum and detection achieved by a 16S rRNA targeted PCR with verification of the product by DNA sequencing.Results
Five DNA extracts were found positive by PCR, including two samples from 2000 and three from 2006. For both series of samples the product was verified as A. phagocytophilum by DNA sequencing.Conclusions
A. phagocytophilum was detected by molecular methods for the first time in Danish grazing lambs during the two seasons investigated (2000 and 2006). 相似文献366.
Tarnow I Olsen LH Kvart C Hoglund K Moesgaard SG Kamstrup TS Pedersen HD Häggström J 《Veterinary journal (London, England : 1997)》2009,180(2):195-201
Natriuretic peptides are useful in diagnosing heart failure in dogs. However, their usefulness in detecting early stages of myxomatous mitral valve disease (MMVD) has been debated. This study evaluated N-terminal (NT) fragment pro-atrial natriuretic peptide (NT-proANP) and NT-pro-brain natriuretic peptide (NT-proBNP) in 39 Cavalier King Charles Spaniels (CKCS) with pre-clinical mitral valve regurgitation (MR), sixteen dogs with clinical signs of heart failure (HF) and thirteen healthy control dogs. Twenty seven CKCS and ten control dogs were re-examined 4 years after the initial examination and the status of the dogs 5 years after the initial examination was determined by telephone calls to the owner. All dogs were evaluated by clinical examination and echocardiography. CKCS with severe MR had higher NT-proANP and NT-proBNP compared to controls and CKCS with less severe MR. Dogs with clinical signs of HF had markedly elevated NT-proANP and NT-proBNP. Plasma concentrations of the natriuretic peptides measured at re-examination could predict progression in regurgitant jet size. 相似文献
367.
Bertram HC Kristensen M Østdal H Baron CP Young JF Andersen HJ 《Journal of agricultural and food chemistry》2007,55(6):2342-2348
Water-binding properties of myofibrils extracted from porcine muscle, and added hemoglobin with and without exposure to H2O2, were characterized using low-field proton NMR T2 relaxometry. The effects of pH and ionic strength in the samples were investigated as pH was adjusted to 5.4, 6.2, and 7.0 and ionic strength was adjusted to 0.29, 0.46, and 0.71 M, respectively. The formation of dityrosine as a measure of oxidative protein cross-linking revealed a significant increase in dityrosine concentrations upon H2O2 activation. The formation of dityrosine was strongly pH-dependent and increased with decreasing pH. In addition, increased levels of thiobarbituric acid reactive substances were observed upon addition of H2O2, implying that lipid oxidation was enhanced, however, with a different oxidation pattern as compared to the myofibrillar proteins. Low-field NMR relaxation measurements revealed reduced T2 relaxation times upon H2O2 activation, which corresponds to reduced water-holding capacity upon oxidation. However, a direct relationship between degree of oxidation and T2 relaxation time was not observed with various pH values and ionic strengths, and further studies are needed for a complete understanding of the effect of oxidation on myofibrillar functionality. 相似文献
368.
The plant hormone ethylene regulates fruit ripening, other developmental processes, and a subset of defense responses. Here, we show that 1-aminocyclopropane-1-carboxylic acid synthase (ACS)-silenced apple (Malus domestica) fruit that express a sense construct of ACS were more susceptible to Botrytis cinerea than untransformed apple, demonstrating that ethylene strengthens fruit resistance to B. cinerea infection. Because ethylene response factors (ERFs) are known to contribute to resistance against B. cinerea via the ethylene-signaling pathway, we cloned four ERF cDNAs from fruit of M. domestica: MdERF3, -4, -5, and -6. Expression of all four MdERF mRNAs was ethylene dependent and induced by wounding or by B. cinerea infection. B. cinerea infection suppressed rapid induction of wound-related MdERF expression. MdERF3 was the only mRNA induced by wounding and B. cinerea infection in ACS-suppressed apple fruit, although its induction was reduced compared with wild-type apple. Promoter regions of all four MdERF genes were cloned and putative cis-elements were identified in each promoter. Transient expression of MdERF3 in tobacco increased expression of the GCC-box containing gene chitinase 48. 相似文献
369.
Jörg Brunet Karin ValtinatMarian Lajos Mayr Adam FeltonMatts Lindbladh Hans Henrik Bruun 《Forest Ecology and Management》2011,262(9):1863-1871
The herbaceous understory forms the richest stratum in temperate broadleaved forests in terms of plant diversity. Understanding the process of understory succession is thus of critical importance for the development of management guidelines for biodiversity restoration in post-agricultural plantation forests.We studied effects of stand age, forest fragmentation, and soil and canopy conditions on species richness and abundance of four species groups in the understory of post-arable oak plantations in southern Sweden: herbaceous forest specialists, habitat generalists and open-land species, and woody species.The group of forest specialists may approach the richness of continuously forested sites after 60-80 years in non-fragmented plantations, but many forest species were sensitive to habitat fragmentation. Open-land species richness decreased during succession, while the richness of woody species and of generalists remained stable, and was not affected by fragmentation. Abundance of generalists gradually decreased in non-fragmented plantations, probably due to competition from colonizing forest specialists. Soil pH in post-arable stands remained consistently higher than in continuously forested stands, which maintained differences in species composition. The development of a shrub layer seemed to imply a competitive advantage for forest specialists compared to generalist species.For successful recovery of a rich understory, we suggest that post-arable plantations should be established on loamy soils of intermediate to high pH proximate to older forest with source populations, and that a continuous overstory canopy cover of 70-80% is maintained by regular light thinnings and promotion of a shrub layer. 相似文献
370.
Proesmans Willem Bonte Dries Smagghe Guy Meeus Ivan Decocq Guillaume Spicher Fabien Kolb Annette Lemke Isgard Diekmann Martin Bruun Hans Henrik Wulf Monika Van Den Berge Sanne Verheyen Kris 《Landscape Ecology》2019,34(3):487-501
Landscape Ecology - Small forest fragments are often the most abundant type of semi-natural habitat in intensive agricultural landscapes. Wild pollinators can use these forest patches as nesting or... 相似文献