全文获取类型
收费全文 | 523篇 |
免费 | 45篇 |
国内免费 | 3篇 |
专业分类
林业 | 56篇 |
农学 | 17篇 |
基础科学 | 2篇 |
98篇 | |
综合类 | 67篇 |
农作物 | 27篇 |
水产渔业 | 36篇 |
畜牧兽医 | 194篇 |
园艺 | 15篇 |
植物保护 | 59篇 |
出版年
2024年 | 1篇 |
2023年 | 2篇 |
2022年 | 12篇 |
2021年 | 24篇 |
2020年 | 21篇 |
2019年 | 18篇 |
2018年 | 20篇 |
2017年 | 24篇 |
2016年 | 21篇 |
2015年 | 23篇 |
2014年 | 15篇 |
2013年 | 20篇 |
2012年 | 42篇 |
2011年 | 42篇 |
2010年 | 29篇 |
2009年 | 20篇 |
2008年 | 36篇 |
2007年 | 26篇 |
2006年 | 30篇 |
2005年 | 31篇 |
2004年 | 16篇 |
2003年 | 19篇 |
2002年 | 17篇 |
2001年 | 8篇 |
2000年 | 7篇 |
1999年 | 8篇 |
1998年 | 6篇 |
1997年 | 4篇 |
1995年 | 2篇 |
1994年 | 3篇 |
1993年 | 3篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1989年 | 3篇 |
1988年 | 1篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1981年 | 1篇 |
1967年 | 1篇 |
1965年 | 1篇 |
1960年 | 1篇 |
1929年 | 1篇 |
排序方式: 共有571条查询结果,搜索用时 15 毫秒
471.
Emmanuelle Sebert-Cuvillier Valérie Simon-Goyheneche Frédéric Paccaut Olivier Chabrerie Olivier Goubet Guillaume Decocq 《Landscape Ecology》2008,23(7):787-801
The effect of environmental heterogeneity on spatial spread of invasive species has received little attention in the literature.
Altering landscape heterogeneity may be a suitable strategy to control invaders in man-made landscapes. We use a population-based,
spatially realistic matrix model to explore mechanisms underlying the observed invasion patterns of an alien tree species,
Prunus serotina Ehrh., in a heterogeneous managed forest. By altering several parameters in the simulation, we test for various hypotheses regarding
the role of several mechanisms on invasion dynamics, including spatial heterogeneity, seed dispersers, site of first introduction,
large-scale natural disturbances, and forest management. We observe that landscape heterogeneity makes the invasion highly
directional resulting from two mechanisms: (1) irregular jumps, which occur rarely via long-distance dispersers and create
new founder populations in distant suitable areas, and (2) regular, continuous diffusion toward adjacent cells via short-
and mid-distance vectors. At the landscape scale, spatial heterogeneity increases the invasion speed but decreases the final
invasion extent. Hence, natural disturbances (such as severe storms) appear to facilitate invasion spread, while forest management
can have contrasting effects such as decreasing invasibility at the stand scale by increasing the proportion of light interception
at the canopy level. The site of initial introduction influences the invasion process but without altering the final outcome.
Our model represents the real landscape and incorporates the range of dispersal modes, making it a powerful tool to explore
the interactions between environmental heterogeneity and invasion dynamics, as well as for managing plant invaders.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
472.
473.
A blinded,randomized, placebo‐controlled trial of the safety of lokivetmab (ZTS‐00103289), a caninized anti‐canine IL‐31 monoclonal antibody in client‐owned dogs with atopic dermatitis 下载免费PDF全文
474.
LOW‐FIELD MAGNETIC RESONANCE IMAGING APPEARANCE OF POSTARTHROSCOPIC MAGNETIC SUSCEPTIBILITY ARTIFACTS IN HORSES 下载免费PDF全文
Aurelie L. Thomas Michael C. Schramme Olivier M. Lepage Emilie M. Segard 《Veterinary radiology & ultrasound》2016,57(6):587-593
An awareness of magnetic susceptibility artifacts is important for interpreting prepurchase and postoperative magnetic resonance imaging (MRI) studies in horses. These artifacts occur when a metallic or a paramagnetic substance creates a local magnetic field deformity. Aims of the current experimental study were to determine prevalence of these artifacts after arthroscopy in a sample of nonlame horses, and to describe effects of time and type of pulse sequence on low‐field MRI signal intensity and detection of the artifacts. Ten, nonlame Standardbred horses were prospectively recruited. All horses underwent arthroscopy of both metacarpophalangeal joints for purposes unrelated to the study. Serial low‐Field MRI examinations were performed on each horse and each joint (before, and 6 and 12 weeks postsurgery). In two horses, more detailed longitudinal evaluations were performed with additional MRI examinations. Magnetic susceptibility artifacts were detected postoperatively at the surgical access sites in eight metacarpophalangeal joints at both 6 and 12 weeks after surgery (40% prevalence). Neither of the two longitudinally followed horses had artifacts at any time. Artifacts were only detected on gradient echo (GRE) sequences. Findings indicated that magnetic susceptibility artifacts can be present in postarthroscopy MRI studies in horses and can persist up to 12 weeks after arthroscopy. For this sample of horses, the artifacts did not interfere with evaluation of the joint. Further longitudinal studies are needed to determine the full duration of magnetic susceptibility artifact persistence in affected tissues. 相似文献
475.
476.
Dufour C Da Silva E Potier P Queneau Y Dangles O 《Journal of agricultural and food chemistry》2002,50(12):3425-3430
Three tests of increasing complexity were used to assess the antioxidant activity of five synthetic gallic esters of sucrose bearing 3, 6, 7, or 8 galloyl units. In addition, two of these compounds had 1 or 2 hydrocarbon (C10-C12) acyl chains. Reaction with the DPPH radical led to the evaluation of the number of radicals trapped per galloyl unit n (3-4), as well as the apparent second-order rate constant for H atom donation k (1200-1500/M/s). These results indicated similar contribution and reactivity of all the galloyl units. Inhibition of the AAPH-initiated peroxidation of linoleic acid in a micellar medium confirmed the additive contribution of the galloyl units, whereas the presence of the hydrocarbon acyl chains had no influence. These results suggest an inhibition of initiation at high antioxidant levels and an underlying prooxidant effect of the galloyl radicals at low concentrations. Finally, LDL peroxidation was inhibited in proportion to the number of galloyl units, in agreement with the preceding tests. 相似文献
477.
Yann Nouvellon Jean-Paul Laclau Daniel Epron Antoine Kinana André Mabiala Olivier Roupsard Jean-Marc Bonnefond Guerric le Maire Claire Marsden Jean-Daniel Bontemps Laurent Saint-André 《Forest Ecology and Management》2010,259(9):1796-1807
Specific leaf area (SLA; m2leaf kg?1leaf) is a key ecophysiological parameter influencing leaf physiology, photosynthesis, and whole plant carbon gain. Both individual tree-based models and other forest process-based models are generally highly sensitive to this parameter, but information on its temporal or within-stand variability is still scarce. In a 2–4-year-old Eucalyptus plantation in Congo, prone to seasonal drought, the within-stand and seasonal variability in SLA were investigated by means of destructive sampling carried out at 2-month intervals, over a 2-year period. Within-crown vertical gradients of SLA were small. Highly significant relationships were found between tree-average SLA (SLAt) and tree size (tree height, Ht, or diameter at breast height, DBH): SLAt ranged from about 9 m2 kg?1 for dominant trees to about 14–15 m2 kg?1 for the smallest trees. The decrease in SLAt with increasing tree size was accurately predicted from DBH using power functions. Stand-average SLA varied by about 20% during the year, with lowest values at the end of the 5-month dry season, and highest values about 2–3 months after the onset of the wet season. Variability in leaf water status according to tree size and season is discussed as a possible determinant of both the within-stand and seasonal variations in SLA. 相似文献
478.
Galland S Mora N Abert-Vian M Rakotomanomana N Dangles O 《Journal of agricultural and food chemistry》2007,55(18):7573-7579
This work describes the chemical synthesis of O-aryl-beta-D-glucosides and 1-O-beta-D-glucosyl esters of hydroxycinnamic acids. In particular, O-aryl-beta-D-glucosides were efficiently prepared via a simple diastereoselective glycosylation procedure using phase transfer conditions. Despite the lability of its ester linkage, 1-O-beta-D-caffeoylglucose could also be obtained using a Lewis acid catalyzed glycosylation step and a set of protective groups that can be removed under neutral conditions. Hydroxycinnamic acid O-aryl-beta-D-glucosides were then quantitatively investigated for their affinity for the naturally occurring anthocyanin malvin (pigment). Formation of the pi-stacking molecular complexes (copigmentation) was characterized in terms of binding constants and enthalpy and entropy changes. The glucosyl moiety did not significantly alter these thermodynamic parameters, in line with a binding process solely involving the polyphenolic nuclei. 相似文献
479.
A cellular microRNA mediates antiviral defense in human cells 总被引:4,自引:0,他引:4
Lecellier CH Dunoyer P Arar K Lehmann-Che J Eyquem S Himber C Saïb A Voinnet O 《Science (New York, N.Y.)》2005,308(5721):557-560
In eukaryotes, 21- to 24-nucleotide-long RNAs engage in sequence-specific interactions that inhibit gene expression by RNA silencing. This process has regulatory roles involving microRNAs and, in plants and insects, it also forms the basis of a defense mechanism directed by small interfering RNAs that derive from replicative or integrated viral genomes. We show that a cellular microRNA effectively restricts the accumulation of the retrovirus primate foamy virus type 1 (PFV-1) in human cells. PFV-1 also encodes a protein, Tas, that suppresses microRNA-directed functions in mammalian cells and displays cross-kingdom antisilencing activities. Therefore, through fortuitous recognition of foreign nucleic acids, cellular microRNAs have direct antiviral effects in addition to their regulatory functions. 相似文献
480.
Vanai Paino Jean Paul Peillex Olivier Montlahuc Aimé Cambon Jean Pierre Bianchini 《Compost science & utilization》2013,21(2):62-69
Three kinds of tropical soils (inceptisol, mollisol and oxisol: USDA) were amended with increasing quantities of municipal refuse compost. Prepared mixtures: 0, 1.2, 2.5, 5, 10 and 25.6 percent (by volume) of compost were utilized as growing substract (without mineral fertilizer) in pot vegetation trials including three successive plantations taking corn as the test plant. Plant yields and heavy metal concentrations were determined. Urban compost effects on soil chemical parameters were evaluated. Corn growth had been significantly enhanced by the presence of urban compost showing no toxic effects. However, this fertilizing effect decreases after successive harvestings. Cadmium and lead concentrations in the plants were found to be under detection concentration limits (0.5 and 5.2 ppm respectively). Concentrations of copper and zinc in the plants increased relative to the amounts of urban compost but never reached toxic concentrations. 相似文献