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排序方式: 共有111条查询结果,搜索用时 15 毫秒
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Lunar surface magnetic fields and their interaction with the solar wind: results from lunar prospector 总被引:1,自引:0,他引:1
RP Lin DL Mitchell DW Curtis KA Anderson CW Carlson J McFadden MH Acuna LL Hood A Binder 《Science (New York, N.Y.)》1998,281(5382):1480-1484
The magnetometer and electron reflectometer experiment on the Lunar Prospector spacecraft has obtained maps of lunar crustal magnetic fields and observed the interaction between the solar wind and regions of strong crustal magnetic fields at high selenographic latitude (30 degreesS to 80 degreesS) and low ( approximately 100 kilometers) altitude. Electron reflection maps of the regions antipodal to the Imbrium and Serenitatis impact basins, extending to 80 degreesS latitude, show that crustal magnetic fields fill most of the antipodal zones of those basins. This finding provides further evidence for the hypothesis that basin-forming impacts result in magnetization of the lunar crust at their antipodes. The crustal magnetic fields of the Imbrium antipode region are strong enough to deflect the solar wind and form a miniature (100 to several hundred kilometers across) magnetosphere, magnetosheath, and bow shock system. 相似文献
63.
MA Stevenson RL Sanson AO Miranda KA Lawrence RS Morris 《New Zealand veterinary journal》2013,61(6):264-272
To mitigate the effects of risks to food safety and infectious disease outbreaks in farmed animals, animal health authorities need to have systems in place to identify and trace the source of identified problems in a timely manner. In the event of emergencies, these systems will allow infected or contaminated premises (and/or animals) to be identified and contained, and will allow the extent of problems to be communicated to consumers and trading partners in a clear and unambiguous manner. The key to achieving these goals is the presence of an effective animal health decision support system that will provide the facilities to record and store detailed information about cases and the population at risk, allowing information to be reported back to decision makers when it is required. Described here are the components of an animal health decision support system, and the ways these components can be used to enhance food safety, responses to infectious disease incursions, and animal health and productivity. Examples are provided to illustrate the benefit these systems can return, using data derived from countries that have such systems (or parts of systems) in place. Emphasis is placed on the features that make particular system components effective, and strategies to ensure that these are kept up to date. 相似文献
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Antognoli MC Remmenga MD Bengtson SD Clark HJ Orloski KA Gustafson LL Scott AE 《Preventive veterinary medicine》2011,101(1-2):35-41
The goal of this study was to evaluate the test sensitivity (SE) and specificity (SP) of the gamma interferon (G-IFN) assay used for the detection of bovine tuberculosis (bTB) in U.S. cattle herds. In addition, the study assessed the association between G-IFN test results and bTB status of cattle, and explored different cut off values for classification of test results in adult cattle using receiver operating characteristics (ROC) curve analysis. Test SE was estimated using a population of 87 confirmed infected cattle from 14 herds distributed in 6 states. Test SP was estimated using a population of 4123 cattle representing 3000 premises in 3 states. These animals were from bTB free areas, accredited bTB free herds, or herds that were historically bTB free based on the absence of lesions found at slaughter and historical records of negative tests performed for bTB surveillance. The distribution of G-IFN results and its association with bTB infection status was also explored in a group of 914 exposed cattle in which infection was not confirmed. The results showed that the SE of the G-IFN for a cut-off value ≥0.1 was 83.9% (76.1, 91.6). The SP of the G-IFN was 90.7% (95% CI: 89.8, 91.6), 97% (95% CI: 96.5, 97.5), and 98.6%(95% CI: 98.2, 98.9), for cut off values of 0.1, 0.3, and 0.5, respectively. For a cut off value ≥0.1, the likelihood ratio of a positive G-IFN test was 9.03 (95% CI: 7.90, 10.31), and the likelihood ratio of a negative G-IFN test was 0.18 (95% CI: 0.11, 0.29). The area under the ROC curve was 0.976 (95% CI: 0.97, 0.98), characteristic of a highly accurate test. ROC analysis also showed that lower cut-off values, such as 0.1, have high SE with suitable SP for use in parallel testing, while cut-off values ranging between 0.3 and 0.6 provide the high SP desired in series-testing protocols with lower SE values. Findings from this study indicated that the G-IFN performs with high accuracy in the field, yielding SE and SP estimates comparable to those reported in previous evaluations (Ryan et al., 2000; Ameni et al., 2000; de la Rua-Domenech et al., 2006; Gormley et al., 2006). 相似文献
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Biosecurity risks are a major threat to the profitability of the industry as well as impacting human and animal health. Livestock producers play a crucial role in biosecurity as the first to notice changes in the health or productivity of their stock and are generally responsible for implementing protective measures. However, uptake of biosecurity measures by producers is variable. We critically appraised the current literature regarding biosecurity practices in Australian livestock industries and highlight aspects that are well understood as well as those where further research or information is needed. Findings from 12 cross-sectional studies suggest that Australian producers' knowledge of biosecurity methods and importance might have a positive influence on their willingness to implement or incorporate biosecurity practices. There is moderate evidence supportive of biosecurity being well understood by livestock producers across Australia. Barriers to producers using biosecurity practices included lack of information or communication from agricultural, veterinary or government organisations. It was found that larger stock numbers were positively correlated with biosecurity implementation and that producers used veterinarians, government and industry agencies as resources for trusted information. 相似文献
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Cost-benefit evaluation of artificial insemination for genetic improvement of wool-producing sheep 总被引:1,自引:0,他引:1
KA ABBOTT 《Australian veterinary journal》1994,71(11):353-360
SUMMARY The financial costs and benefits associated with the use of artificial insemination (AI) in commercial flocks are evaluated. Benefits are calculated in terms of net present values after summing the discounted value of benefits over 20 years. Two breeding strategies are evaluated. With the first, AI is used to produce flock ewes and wethers. The method is unlikely to be profitable unless high breeding value rams are available for AI programs with fresh semen. With the second, AI is used to produce home-bred rams, which in turn sire flock ewes and wethers. This approach is more likely to be profitable. The cost of AI per lamb weaned from laparoscopic AI programs is about $100. Benefits exceed this cost for rams of very high merit when wool prices are moderate or higher. Flock structure has a significant effect on the benefits. Flocks with low wether retention rates have benefits half that of flocks that retain most wethers to 6 years of age. AI with purchased semen also provides benefits to risk management for owners of commercial flocks who wish to breed their own replacement flock rams. 相似文献