全文获取类型
收费全文 | 217篇 |
免费 | 16篇 |
专业分类
林业 | 27篇 |
农学 | 4篇 |
基础科学 | 1篇 |
21篇 | |
综合类 | 15篇 |
农作物 | 15篇 |
水产渔业 | 5篇 |
畜牧兽医 | 112篇 |
园艺 | 13篇 |
植物保护 | 20篇 |
出版年
2023年 | 2篇 |
2022年 | 6篇 |
2021年 | 9篇 |
2020年 | 1篇 |
2019年 | 8篇 |
2018年 | 10篇 |
2017年 | 9篇 |
2016年 | 10篇 |
2015年 | 4篇 |
2014年 | 12篇 |
2013年 | 12篇 |
2012年 | 20篇 |
2011年 | 19篇 |
2010年 | 13篇 |
2009年 | 16篇 |
2008年 | 16篇 |
2007年 | 10篇 |
2006年 | 7篇 |
2005年 | 6篇 |
2004年 | 9篇 |
2003年 | 4篇 |
2002年 | 5篇 |
2001年 | 1篇 |
2000年 | 2篇 |
1999年 | 2篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1993年 | 1篇 |
1990年 | 3篇 |
1988年 | 1篇 |
1987年 | 3篇 |
1986年 | 1篇 |
1984年 | 2篇 |
1955年 | 2篇 |
1953年 | 1篇 |
1951年 | 1篇 |
1947年 | 1篇 |
1935年 | 1篇 |
1929年 | 1篇 |
排序方式: 共有233条查询结果,搜索用时 31 毫秒
101.
102.
Atrial Premature Depolarization‐Induced Changes in QRS and T Wave Morphology on Resting Electrocardiograms in Horses
下载免费PDF全文
![点击此处可从《Journal of veterinary internal medicine / American College of Veterinary Internal Medicine》网站下载免费的PDF全文](/ch/ext_images/free.gif)
103.
Epidemiology of Diabetes Mellitus among 193,435 Cats Attending Primary‐Care Veterinary Practices in England
下载免费PDF全文
![点击此处可从《Journal of veterinary internal medicine / American College of Veterinary Internal Medicine》网站下载免费的PDF全文](/ch/ext_images/free.gif)
104.
River regulation results in the disconnection and increased fragmentation of habitats in the river corridor. In this study, we investigated the within-population genetic variability and among-population genetic differentiation of 21 populations of Origanum vulgare along the River Meuse, using dominant AFLP markers, in order to asses the restoration potential of this species in the context of current river restoration efforts. The average observed within-population genetic diversity was high and suggests that river regulation and associated fragmentation of the populations have not strongly affected genetic diversity. The genetic differentiation between populations was high (ΦST = 0.24) and can be explained by founder effects, rather than by genetic drift in isolated populations. We also detected a pronounced hierarchic spatio-temporal structure in genetic variation. This structure can be related to the irregular patterns in the flow regime of the River Meuse. Large floods are the major vector of genetic structure, but geographic upstream proximity, probably mediated by small floods, also has an important effect on genetic structure. Three distinct groups of populations were observed, two of which could be related to the extreme flood events of the mid-nineties of last century. Assignment tests revealed occasional long-distance seed dispersal with extreme flood events and local colonisation with more regular floods. Our study species optimally took benefit of the opportunities offered by the river restoration programme, with a strong colonisation after floods, and illustrates the need for maintaining river dynamics to conserve and restore genetic diversity. 相似文献
105.
Hans Rediers Marijke Claes Luc Peeters Kris A. Willems 《Postharvest Biology and Technology》2009,51(2):257-262
In this study, the cold chain and its impact on food stuff microbiology was evaluated for fresh-cut endive. A survey was carried out to analyze endive temperature throughout the supply chain from producer, via processor and distributor to the restaurant. Data loggers accompanying the endive on its route provided a temperature profile of the endive. The effect of the outdoor temperature on initial cooling was evaluated and critical points regarding cold chain management in the supply chain were identified. Our experiments indicate that the cold chain is generally properly maintained. In parallel with temperature monitoring, indicator microorganisms were assessed at different points in the supply chain to examine the effects of endive temperature, temperature fluctuations, and the outdoor temperature on microbial food safety. Small temperature fluctuations in the supply chain had a small effect on the total level of aerobic mesophilic bacteria. However, at the best before-date, total coliforms and Enterobacteriaceae levels were significantly higher in endive samples subject to temperature fluctuations in the supply chain, compared to endive stored in optimal conditions. To our knowledge, this is the first study that combines microbiological analysis with the temperature profile of fresh-cut produce in a realistic food supply chain. 相似文献
106.
Dries Verheyen Jan Diels Endalkachew Kissi Jean Poesen 《Journal of Soils and Sediments》2014,14(11):1869-1885
Purpose
Visible and near-infrared (Vis-NIR) reflectance measurements may be an alternative technique to identify suspended sediment sources in streams of headwater catchments. In this study, we examined if Vis-NIR reflectance measurements are capable of estimating sediment source contributions to sediment yield and compared this technique with a more conventional (i.e. geochemical) technique.Materials and methods
Two headwater catchments in Ethiopia, Unta (2,052 ha) and Desera (1,657 ha), were analysed with the same techniques in order to find similarities and differences in the results obtained. The first technique used Vis-NIR spectral analysis as a fingerprint, using a partial least squares regression model. The second technique was a quantitative composite fingerprinting technique using geochemical analysis of source materials and suspended sediment samples. As a comparison, the partial least squares model was also used on the geochemical data. In August and September 2009, 30 soil samples of three different land uses (landslides, croplands, and grazing lands) and 21 suspended sediment samples at the catchment outlet were collected. Source samples were sieved to <63 μm. Geochemical analyses consisted of total element concentrations, percentage carbon, percentage nitrogen, and atom percentage 15N and δ13C. Reflectance measurements were taken on dried source samples with a spectrometer.Results and discussion
Neither technique was able to predict the contributions of the three land use types; they could only distinguish between landslide and topsoil material. The agreement between the results of both techniques was significant for the Unta catchment (R 2?=?0.80) but not for the Desera catchment (R 2?=?0.39). The uncertainty of the technique using Vis-NIR reflectance measurements was slightly higher than with the geochemical approach. Both techniques revealed that topsoil erosion played an important role during storm runoff discharges. Using the partial least squares model for the geochemical data revealed that uncertainty can differ greatly when using other statistical techniques.Conclusions
The quantitative composite fingerprinting technique using spectral signatures from both source and suspended sediment samples was able to quantify the contribution of two source materials (landslides and topsoil). It provided a faster and more cost effective alternative to the conventional geochemical procedure. 相似文献107.
108.
De Clercq D Baert K Croubels S van Loon G Maes A Tavernier R Deprez P De Backer P 《American journal of veterinary research》2006,67(3):448-454
OBJECTIVE: To determine the clinical effects and pharmacokinetics of amiodarone after single doses of 5 mg/kg administered orally or intravenously. ANIMALS: 6 healthy adult horses. PROCEDURE: In a cross over study, clinical signs and electrocardiographic variables were monitored and plasma and urine samples were collected. A liquid chromatography-mass spectrometry method was used to determine the percentage of protein binding and to measure plasma and urine concentrations of amiodarone and the active metabolite desethylamiodarone. RESULTS: No adverse clinical signs were observed. After IV administration, median terminal elimination half-lives of amiodarone and desethylamiodarone were 51.1 and 75.3 hours, respectively. Clearance was 0.35 L/kg x h, and the apparent volume of distribution for amiodarone was 31.1 L/kg. The peak plasma desethylamiodarone concentration of 0.08 microg/mL was attained 2.7 hours after IV administration. Neither parent drug nor metabolite was detected in urine, and protein binding of amiodarone was 96%. After oral administration of amiodarone, absorption of amiodarone was slow and variable; bioavailability ranged from 6.0% to 33.7%. The peak plasma amiodarone concentration of 0.14 microg/mL was attained 7.0 hours after oral administration and the peak plasma desethylamiodarone concentration of 0.03 microg/mL was attained 8.0 hours after administration. Median elimination half-lives of amiodarone and desethylamiodarone were 24.1 and 58.6 hours, respectively. CONCLUSION AND CLINICAL RELEVANCE: Results indicate that the pharmacokinetic distribution of amiodarone is multicompartmental. This information is useful for determining treatment regimens for horses with arrythmias. Amiodarone has low bioavailability after oral administration, does not undergo renal excretion, and is highly protein-bound in horses. 相似文献
109.
State-and-Transition Models for Heterogeneous Landscapes: A Strategy for Development and Application
Brandon T. Bestelmeyer Arlene J. Tugel George L. Peacock Daniel G. Robinett Pat L. Shaver Joel R. Brown Jeffrey E. Herrick Homer Sanchez Kris M. Havstad 《Strength and Conditioning Journal》2009,62(1):1-15
Interpretation of assessment and monitoring data requires information about how reference conditions and ecological resilience vary in space and time. Reference conditions used as benchmarks are often specified via potential-based land classifications (e.g., ecological sites) that describe the plant communities potentially observed in an area based on soil and climate. State-and-transition models (STMs) coupled to ecological sites specify indicators of ecological resilience and thresholds. Although general concepts surrounding STMs and ecological sites have received increasing attention, strategies to apply and quantify these concepts have not. In this paper, we outline concepts and a practical approach to potential-based land classification and STM development. Quantification emphasizes inventory techniques readily available to natural resource professionals that reveal processes interacting across spatial scales. We recommend a sequence of eight steps for the co-development of ecological sites and STMs, including 1) creation of initial concepts based on literature and workshops; 2) extensive, low-intensity traverses to refine initial concepts and to plan inventory; 3) development of a spatial hierarchy for sampling based on climate, geomorphology, and soils; 4) stratified medium-intensity inventory of plant communities and soils across a broad extent and with large sample sizes; 5) storage of plant and soil data in a single database; 6) model-building and analysis of inventory data to test initial concepts; 7) support and/or refinement of concepts; and 8) high-intensity characterization and monitoring of states. We offer a simple example of how data assembled via our sequence are used to refine ecological site classes and STMs. The linkage of inventory to expert knowledge and site-based mechanistic experiments and monitoring provides a powerful means for specifying management hypotheses and, ultimately, promoting resilience in grassland, shrubland, savanna, and forest ecosystems. 相似文献
110.
Yan Liang Guodong Han He Zhou Mengli Zhao Hennie A. Snyman Dan Shan Kris M. Havstad 《Strength and Conditioning Journal》2009,62(4):328-336
Vegetation features radiating from residential areas in response to livestock grazing were quantified for an arid steppe rangeland in the Keshiketeng Banner, Chifeng Prefecture, in northeastern Inner Mongolia in 2004 and 2006. The aim of this study was to estimate grazing impacts on the vegetation dynamics of these historical grazed ecosystems. Grazing intensities were classified as reference area (RA), light (LG), moderate (MG), and heavy (HG) according to the vegetation utilization across the study area. Rangelands were studied along a grazing gradient, where characteristics of plant communities, heights of dominant species, aboveground vertical structures, and belowground biomass were investigated. Along this grazing gradient, vegetation changed from the original dominant plant species Leymus chinensis (Trin.) Tzvel. to a semi-subshrub species Artemisia frigida Willd. when moving from the reference area (RA) to the region around the settlement. Canopy coverage, aboveground productivity, and the number of perennial species declined as one moved toward the residential area. Heights of five dominant species, except for Stipa grandis P. Smirn., declined with increased grazing intensity. Aboveground vertical structure in the RA treatment showed more resilience than the other treatments. There was no difference in root biomass in the top 1 m of soil (P > 0.05) between the RA treatment and the area immediately around settlement (HG treatment). Generally, we found that the intensity of grazing disturbance did not exceed the tolerance of the rangeland ecosystem within LG treatment. However, vegetative conditions in HG treatment became worse with increased grazing pressure. Rangelands in this arid steppe are under tremendous threat due to excessive forage utilization, which cannot be considered a sustainable practice. 相似文献