全文获取类型
收费全文 | 1126篇 |
免费 | 112篇 |
国内免费 | 4篇 |
专业分类
林业 | 33篇 |
农学 | 29篇 |
基础科学 | 13篇 |
132篇 | |
综合类 | 174篇 |
农作物 | 39篇 |
水产渔业 | 112篇 |
畜牧兽医 | 538篇 |
园艺 | 25篇 |
植物保护 | 147篇 |
出版年
2023年 | 7篇 |
2021年 | 13篇 |
2020年 | 28篇 |
2019年 | 16篇 |
2018年 | 23篇 |
2017年 | 24篇 |
2016年 | 23篇 |
2015年 | 29篇 |
2014年 | 29篇 |
2013年 | 62篇 |
2012年 | 55篇 |
2011年 | 61篇 |
2010年 | 43篇 |
2009年 | 29篇 |
2008年 | 61篇 |
2007年 | 56篇 |
2006年 | 52篇 |
2005年 | 54篇 |
2004年 | 41篇 |
2003年 | 55篇 |
2002年 | 46篇 |
2001年 | 30篇 |
2000年 | 22篇 |
1999年 | 32篇 |
1998年 | 18篇 |
1997年 | 14篇 |
1996年 | 11篇 |
1994年 | 8篇 |
1993年 | 15篇 |
1992年 | 8篇 |
1991年 | 12篇 |
1990年 | 7篇 |
1989年 | 15篇 |
1988年 | 11篇 |
1987年 | 11篇 |
1985年 | 16篇 |
1984年 | 10篇 |
1983年 | 9篇 |
1982年 | 8篇 |
1981年 | 7篇 |
1979年 | 8篇 |
1978年 | 8篇 |
1977年 | 9篇 |
1976年 | 8篇 |
1974年 | 8篇 |
1973年 | 9篇 |
1972年 | 9篇 |
1966年 | 11篇 |
1963年 | 6篇 |
1961年 | 6篇 |
排序方式: 共有1242条查询结果,搜索用时 15 毫秒
191.
The prevalence of verotoxins, Escherichia coli O157:H7, and Salmonella in the feces and rumen of cattle at processing.
下载免费PDF全文
![点击此处可从《The Canadian veterinary journal. La revue veterinaire canadienne》网站下载免费的PDF全文](/ch/ext_images/free.gif)
J Van Donkersgoed T Graham V Gannon 《The Canadian veterinary journal. La revue veterinaire canadienne》1999,40(5):332-338
Fecal samples collected from cattle at processing during a 1-year period were tested for verotoxins (VT1, VT2), Escherichia coli O157:H7, and Salmonella. Verotoxins were detected in 42.6% (95% CI, 39.8% to 45.4%), E. coli O157:H7 in 7.5% (95% CI, 6.1% to 9.1%), and Salmonella in 0.08% (95% CI, 0.004% to 0.5%) of the fecal samples. In yearling cattle, the median within-lot prevalence (percentage of positive samples within a lot) was 40% (range, 0% to 100%) for verotoxins and 0% for E. coli O157:H7 (range, 0% to 100%) and Salmonella (range, 0% to 17%). One or more fecal samples were positive for verotoxins in 80.4% (95% CI, 72.8% to 86.4%) of the lots of yearling cattle, whereas E. coli O157:H7 were detected in 33.6% (95% CI, 26.0% to 42.0%) of the lots. In cull cows, the median within-lot prevalence was 50% (range, 0% to 100%) for verotoxins and 0% (range, 0% to 100%) for E. coli O157:H7 and Salmonella (range, 0% to 0%). Verotoxins were detected in one or more fecal samples from 78.0% (95% CI, 70.4% to 84.2%) of the lots of cull cows, whereas E. coli O157:H7 were detected in only 6.0% (95% CI, 3.0% to 11.4%) of the lots of cull cows. The prevalence of verotoxins in fecal samples was lower in yearling cattle than in cull cows, whereas the prevalence of E. coli O157:H7 in fecal samples was higher in yearling cattle than in cull cows. The prevalence of E. coli O157:H7 in fecal samples was highest in the summer months. Rumen fill, body condition score, sex, type of cattle (dairy, beef), and distance travelled to the plant were not associated with the fecal prevalence of verotoxins or E. coli O157:H7. The prevalence of verotoxins in fecal samples of cull cows was associated with the source of the cattle. It was highest in cows from the auction market (52%) and farm/ranch (47%) and lowest in cows from the feedlot (31%). In rumen samples, the prevalence of verotoxins was 6.4% (95% CI, 4.2% to 9.4%), and it was 0.8% (95% CI, 0.2% to 2.3%) for E. coli O157:H7, and 0.3% (95% CI, 0.007% to 1.5%) for Salmonella. 相似文献
192.
193.
194.
Crop growth modelling techniques were used to investigate the performance of a wheat crop over a range of weather conditions, nitrogen application rates and soil types. The data were used to predict long term benefits of using spatially variable fertilizer application strategies where fertilizer application rate was matched to the soil type, against a strategy of uniform fertilizer application. The model was also run with modified soil properties to determine the importance of soil moisture holding capacity in the variability of crop yield. It was found that the benefits of spatially variable nitrogen management when fertilizer was applied at the beginning of the season were modest on average. The range of results for different weather conditions was much greater than the average benefit. A large proportion of the variability of crop performance between soil types could be explained by differing soil moisture holding capacity. Devising techniques for managing this variability was concluded to be important for precision farming of cereals.Agricultural Engineering 相似文献
195.
Mostafa A.R. Hossain Graham S. Haylor Malcolm C.M. Beveridge 《Aquaculture International》1998,6(5):379-385
Groups of 3–4 g African catfish (Clarias gariepinus Burchell, 1822; Family: Clariidae) were offered feeds of two types in three combinations: feed with a radio-opaque marker (Ballotini, 0.16–0.25 mm), feed without marker and a 50:50 mixture of marked and unmarked feeds. Stomach contents were estimated by X-radiography and gastrectomy just after meal termination and at different time intervals (4, 8, 12, 16, 20, 24, 32, 40 and 48 h). There were no significant differences among treatment groups confirming that there was no effect of the marker on feed preference and evacuation rate. Estimations of gastric evacuation rate calculated from gastrectomy and by X-ray sampling were not significantly different. Therefore, gastric evacuation rate of African catfish can be accurately estimated by feeding marked feed and then using X-radiography to monitor feed passage through the gut. © Rapid Science Ltd. 1998 相似文献
196.
197.
Influence of likelihood function choice for estimating crop model parameters using the generalized likelihood uncertainty estimation method 总被引:3,自引:0,他引:3
Proper estimation of model parameters is required for ensuring accurate model predictions and good model-based decisions. The generalized likelihood uncertainty estimation (GLUE) method is a Bayesian Monte Carlo parameter estimation technique that makes use of a likelihood function to measure the closeness-of-fit of modeled and observed data. Various likelihood functions and methods of combining likelihood values have been used in previous studies. This research was conducted to determine the effects of using previously reported likelihood functions in a GLUE procedure for estimating parameters in a widely-used crop simulation model. A factorial computer experiment was conducted with synthetic measurement data to compare four likelihood functions and three methods of combining likelihood values using the CERES-Maize model of the Decision Support System for Agrotechnology Transfer (DSSAT). The procedure used an arbitrarily-selected parameter set as the known “true parameter set” and the CERES-Maize model to generate true output values. Then synthetic observations of crop variables were randomly generated (four replicates) by using the simulated true output values (dry yield, anthesis date, maturity date, leaf nitrogen concentration, soil nitrate concentration, and soil moisture) and adding a random observation error based on the variances of corresponding field measurements. The environmental conditions were obtained from a sweet corn (Zea mays L.) experiment conducted in 2005 in northern Florida. Results showed that the method of combining likelihood values had a strong influence on parameter estimates. The combination method based on the product of the likelihoods associated with each set of observations reduced the uncertainties in posterior distributions of parameter estimates most significantly. It was also found that the likelihood function based on Gaussian probability density function was the best among those tested. This combination accurately estimated the true parameter values, suggesting that it can be used when estimating CERES-Maize model parameters for real experiments. 相似文献
198.
199.
Peter Graham Coulson Jeffery Vincent Norriss Gary Jackson David Victor Fairclough 《Fisheries Management and Ecology》2019,26(3):236-248
The reproductive biology of Centroberyx gerrardi (Günther) was investigated across ~2,000 km of its southern Australian distribution, encompassing different jurisdictions and varying environmental features. Greater gonad mass and prevalence of spawning fish, along with lower ratios of lengths at maturity:maximum lengths and ages at maturity:maximum ages, were identified at the western‐most (Capes) and eastern‐most (Great Australian Bight; GAB) regions. Across the study region, spawning peaks in summer/autumn, when water temperatures are warmest. Regional differences in potential “reproductive output,” while not consistent with the eastward decline in mean monthly water temperature, may instead be related to summer upwelling in the Capes and GAB, driving greater oceanic productivity prior to peak spawning, supporting larval survival. In autumn, the prevailing southward and eastward flowing, downwelling Leeuwin Current (LC) strengthens, providing a dispersal mechanism along the west and south Australian coasts, but limiting upwelling effects. Predicted changes in environmental conditions and their potential impacts on C. gerrardi are discussed, in particular how these factors may affect recruitment to stocks and fisheries, requiring a better understanding of source‐sink relationships for this species. As environmental changes occur, management strategies to sustain fish resources must adapt to spatially variable and changing reproductive output and be collaborative across jurisdictions. 相似文献
200.
Christopher J. Fulton Charlotte Berkstrm Shaun K. Wilson Rene A. Abesamis Michael Bradley Carolina kerlund Luke T. Barrett Abner A. Bucol Dinorah H. Chacin Karen M. Chong‐Seng Darren J. Coker Martial Depczynski Linda Eggertsen Maria Eggertsen David Ellis Richard D. Evans Nicholas A. J. Graham Andrew S. Hoey Thomas H. Holmes Michel Kulbicki Priscilla T. Y. Leung Paul K. S. Lam Joshua van Lier Paloma A. Matis Mae M. Noble Alejandro Prez‐Matus Camilla Piggott Ben T. Radford Stina Tano Paul Tinkler 《Fish and Fisheries》2020,21(4):700-717
Canopy‐forming macroalgae can construct extensive meadow habitats in tropical seascapes occupied by fishes that span a diversity of taxa, life‐history stages and ecological roles. Our synthesis assessed whether these tropical macroalgal habitats have unique fish assemblages, provide fish nurseries and support local fisheries. We also applied a meta‐analysis of independent surveys across 23 tropical reef locations in 11 countries to examine how macroalgal canopy condition is related to the abundance of macroalgal‐associated fishes. Over 627 fish species were documented in tropical macroalgal meadows, with 218 of these taxa exhibiting higher local abundance within this habitat (cf. nearby coral reef) during at least one life‐history stage. Major overlap (40%–43%) in local fish species richness among macroalgal and seagrass or coral reef habitats suggest macroalgal meadows may provide an important habitat refuge. Moreover, the prominence of juvenile fishes suggests macroalgal meadows facilitate the triphasic life cycle of many fishes occupying diverse tropical seascapes. Correlations between macroalgal canopy structure and juvenile abundance suggests macroalgal habitat condition can influence levels of replenishment in tropical fish populations, including the majority of macroalgal‐associated fishes that are targeted by commercial, subsistence or recreational fisheries. While many macroalgal‐associated fishery species are of minor commercial value, their local importance for food and livelihood security can be substantial (e.g. up to 60% of landings in Kenyan reef fisheries). Given that macroalgal canopy condition can vary substantially with sea temperature, there is a high likelihood that climate change will impact macroalgal‐associated fish and fisheries. 相似文献