全文获取类型
收费全文 | 832篇 |
免费 | 57篇 |
专业分类
林业 | 52篇 |
农学 | 19篇 |
基础科学 | 1篇 |
192篇 | |
综合类 | 70篇 |
农作物 | 78篇 |
水产渔业 | 59篇 |
畜牧兽医 | 321篇 |
园艺 | 30篇 |
植物保护 | 67篇 |
出版年
2024年 | 3篇 |
2023年 | 23篇 |
2022年 | 27篇 |
2021年 | 41篇 |
2020年 | 33篇 |
2019年 | 46篇 |
2018年 | 38篇 |
2017年 | 38篇 |
2016年 | 32篇 |
2015年 | 32篇 |
2014年 | 27篇 |
2013年 | 43篇 |
2012年 | 66篇 |
2011年 | 99篇 |
2010年 | 56篇 |
2009年 | 34篇 |
2008年 | 40篇 |
2007年 | 38篇 |
2006年 | 32篇 |
2005年 | 29篇 |
2004年 | 25篇 |
2003年 | 18篇 |
2002年 | 15篇 |
2001年 | 4篇 |
2000年 | 2篇 |
1999年 | 2篇 |
1998年 | 1篇 |
1997年 | 1篇 |
1996年 | 5篇 |
1995年 | 1篇 |
1991年 | 1篇 |
1990年 | 5篇 |
1988年 | 1篇 |
1987年 | 4篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1984年 | 5篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1976年 | 1篇 |
1974年 | 2篇 |
1970年 | 2篇 |
1967年 | 1篇 |
1963年 | 1篇 |
1945年 | 1篇 |
排序方式: 共有889条查询结果,搜索用时 15 毫秒
71.
Sara Ellinor Cederl?f Nils Toft Bent Aalbaek Ilka Christine Klaas 《Acta veterinaria Scandinavica》2012,54(1):65
Background
Staphylococcus aureus is one of the most common causes of intramammary infections in dairy cows at dry off. Reliable identification is important for disease management on herd level and for antimicrobial treatment of infected animals. Our objective was to evaluate the test characteristics of PathoProof ™ Mastitis PCR Assay and bacteriological culture (BC) in diagnosing bovine intramammary infections caused by S. aureus at dry off at different PCR cycle threshold (Ct)-value cut-offs.Methods
Sterile quarter samples and non-sterile composite samples from 140 animals in seven herds were collected in connection with the dairy herd improvement (DHI) milk recording. All quarter samples were analyzed using BC whereas all composite samples were analyzed with PathoProof ™ Mastitis PCR Assay. Latent class analysis was used to estimate test properties for PCR and BC in the absence of a perfect reference test. The population was divided into two geographically divided subpopulations and the Hui-Walter 2-test 2-populations model applied to estimate Se, Sp for the two tests, and prevalence for the two subpopulations.Results
The Se for PCR increased with increasing Ct-value cut-off, accompanied by a small decrease in Sp. For BC the Se decreased and Sp increased with increasing Ct-value cut-off. Most optimal test estimates for the real-time PCR assay were at a Ct-value cut-off of 37; 0.93 [95% posterior probability interval (PPI) 0.60-0.99] for Se and 0.95 [95% PPI 0.95-0.99] for Sp. At the same Ct-value cut-off, Se and Sp for BC were 0.83 [95% PPI 0.66-0.99] and 0.97 [95% PPI 0.91-0.99] respectively. Depending on the chosen PCR Ct-value cut-off, the prevalence in the subpopulations varied; the prevalence increased with increasing PCR Ct-value cut-offs.Conclusion
Neither BC nor real-time PCR is a perfect test in detecting IMI in dairy cows at dry off. The changes in sensitivity and prevalence at different Ct-value cut-offs for both PCR and BC may indicate a change in the underlying disease definition. At low PCR Ct-value cut-offs the underlying disease definition may be a truly/heavily infected cow, whereas at higher PCR Ct-value cut-offs the disease definition may be a S. aureus positive cow. 相似文献72.
Sara Granström Christian Bressen Pipper Rasmus Møgelvang Peter Sogaard Jakob Lundgren Willesen Jørgen Koch 《Journal of Veterinary Cardiology》2012,14(4):479-488
ObjectivesThe aims of this study were to compare the effect of sample volume (SV) size settings and sampling method on measurement variability and peak systolic (s′), and early (e′) and late (a′) diastolic longitudinal myocardial velocities using color tissue Doppler imaging (cTDI) in cats.AnimalsTwenty cats with normal echocardiograms and 20 cats with hypertrophic cardiomyopathy.MethodsWe quantified and compared empirical variance and average absolute values of s′, e′ and a′ for three cardiac cycles using eight different SV settings (length 1,2,3 and 5 mm; width 1 and 2 mm) and three methods of sampling (end-diastolic sampling with manual tracking of the SV, end-systolic sampling without tracking, and random-frame sampling without tracking).ResultsNo significant difference in empirical variance could be demonstrated between most of the tested SVs. However, the two settings with a length of 1 mm resulted in a significantly higher variance compared with all settings where the SV length exceeded 2 mm (p < 0.001). There was an overall significant effect of sampling method on the variability of measurements (p = 0.003) and manual tracking obtained the lowest variance. No difference in average values of s′, e′ or a′ could be found between any of the SV settings or sampling methods.ConclusionWithin the tested range of SV settings, an SV length of 1 mm resulted in higher measurement variability compared with an SV length of 3 and 5 mm, and should therefore be avoided. Manual tracking of the sample volume is recommended. 相似文献
73.
This report presents the case of a 21-year-old Warmblood mare referred to the clinic with neurological dysfunctions and considerable signs of discomfort. A fracture of the caudal vertebral body of C2 with a very unusual radiographic appearance was diagnosed, and the mare was euthanized due to deterioration in neurological status. Histology revealed no evidence of neoplasia or pathological fracture. 相似文献
74.
75.
Sara König Ulrich Weller Bibiana Betancur-Corredor Birgit Lang Thomas Reitz Martin Wiesmeier Ute Wollschläger Hans-Jörg Vogel 《European Journal of Soil Science》2023,74(5):e13411
The increasing demand for biomass for food, animal feed, fibre and bioenergy requires optimization of soil productivity, while at the same time, protecting other soil functions such as nutrient cycling and buffering, carbon storage, habitat for biological activity and water filter and storage. Therefore, one of the main challenges for sustainable agriculture is to produce high yields while maintaining all the other soil functions. Mechanistic simulation models are an essential tool to fully understand and predict the complex interactions between physical, biological and chemical processes of soils that generate those functions. We developed a soil model to simulate the impact of various agricultural management options and climate change on soil functions by integrating the relevant processes mechanistically and in a systemic way. As a special feature, we include the dynamics of soil structure induced by tillage and biological activity, which is especially relevant in arable soils. The model operates on a 1D soil profile consisting of a number of discrete layers with dynamic thickness. We demonstrate the model performance by simulating crop growth, root growth, nutrient and water uptake, nitrogen cycling, soil organic matter turnover, microbial activity, water distribution and soil structure dynamics in a long-term field experiment including different crops and different types and levels of fertilization. The model is able to capture essential features that are measured regularly including crop yield, soil organic carbon, and soil nitrogen. In this way, the plausibility of the implemented processes and their interactions is confirmed. Furthermore, we present the results of explorative simulations comparing scenarios with and without tillage events to analyse the effect of soil structure on soil functions. Since the model is process-based, we are confident that the model can also be used to predict quantities that have not been measured or to estimate the effect of management measures and climate states not yet been observed. The model thus has the potential to predict the site-specific impact of management decisions on soil functions, which is of great importance for the development of a sustainable agriculture that is currently also on the agenda of the ‘Green Deal’ at the European level. 相似文献
76.
77.
78.
79.
Mahdi Najafi-Ghiri Soodabeh Rezabigi Sara Hosseini Hamid Reza Boostani Hamid Reza Owliaie 《Archives of Agronomy and Soil Science》2019,65(7):897-910
This investigation was done to determine the release of potassium (K) from five calcareous soils of southern Iran using 0.025 M CaCl2, HCl and citric acid during six successive extractions and to study the K fixation capacity of the soils after K release experiment. Mineralogical study indicated that Vertisols and Mollisols were dominated with smectites; while other soils had illite, chlorite, palygorskite and smectite. Results indicated that citric acid extracted more K than CaCl2 and HCl (137 vs. 111 and 113 mg kg?1, respectively). The analysis of calcium (Ca), magnesium (Mg) and K concentrations in the solutions suggests that the exchange of K with soluble Ca and Mg (originated from dissolution of carbonates by acidic solutions) is the main mechanism of K release, but citrate is able to dissolve K-bearing minerals and release K in slightly calcareous soils. Soils with more illite released more K. Potassium fixation capacity of soils increased after extractions of soils with different extractants from 324 to 471 mg kg?1, with no significant difference. It is suggested to apply more K fertilizers in K-depleted calcareous soils and use of different solutions for extracting K from soil minerals may be a temporary and short term solution. 相似文献
80.
The influence of field shape, area and surrounding landscape on plant species richness in grazed ex-fields 总被引:1,自引:0,他引:1
Over the past 100 years species-rich semi-natural grasslands have decreased dramatically in Western Europe, where former arable fields (ex-fields) are used instead as pasture. The disappearance of semi-natural grasslands has caused a threat to the biodiversity in agricultural landscapes. Many typical grassland plants are dispersal limited, thus grazed ex-fields can be used to investigate if species spontaneously colonise these new grassland habitats. We examined the relationship between surrounding landscape, field area, shape, distance between edge and centre, and plant species diversity in ex-fields that had been grazed for 15-18 years. The results showed that there were 35% more plant species in fields surrounded by commercial forestry production compared to those surrounded by open agricultural landscape. Area and shape did not influence species richness, although there was increasing number of species in the centre with decreasing distance from the edge. Twenty-five percent of the species where typical grassland species, and ex-fields surrounded by forest had 91% more grassland species compared to those in the open landscape. It is possible to increase grassland plant occurrences by grazing ex-fields surrounded by forest or other grassland remnant habitats, particularly in landscapes where grazed semi-natural grasslands are scarce. 相似文献