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61.
62.
Successful vaccination of sheep against footrot and attempts to eradicate the disease depend on there being a limit to the antigenic diversity of the causative bacterium, Bacteroides nodosus. Fimbrial antigenic variation was therefore investigated in vivo, both under conditions of chronic infection and under the pressure of a vaccine-induced immune response, to ascertain whether this represented an obstacle to such goals. Material was available from 5 experiments and although B. nodosus appeared to have undergone changes in its fimbrial antigens in one of these, the possibility that superinfection was responsible for the variation detected could not be ruled out because all sheep in this case were maintained at pasture. Overall, the results provided no evidence of fimbrial antigenic shift in B. nodosus in vivo and in conclusion, the survival of the organism in the sheep's foot, both in long-term natural infection and following vaccination, must therefore be related to factors other than the ability to undergo antigenic variation in order to evade the host's immune response. 相似文献
63.
Bull K.R. Achermann B. Bashkin V. Chrast R. Fenech G. Forsius M. Gregor H.-D. Guardans R. Haubmann T. Hayes F. Hettelingh J.-P. Johannessen T. Krzyzanowski M. Kucera V. Kvaeven B. Lorenz M. Lundin L. Mills G. Posch M. Skjelkvåle B. L. Ulstein M. J. 《Water, air, and soil pollution》2001,130(1-4):119-130
For 20 years the Convention on Long-range Transboundary Air Pollution has worked to control air pollutant emissions in Europe and North America. Its Working Group on Effects (WGE) has been responsible for much of the underpinning science. The WGE's six International Cooperative Programmes (ICPs) on Waters, Natural Vegetation and Crops, Forests, Materials and Cultural Heritage, Integrated Monitoring, and Modelling and Mapping, together with a Joint Task Force on Human Health with WHO, quantify air pollution effects on the environment through monitoring, modelling and scientific review. Early work found evidence to support the need for decreases in emissions of sulphur and nitrogen pollutants. More recently, monitoring results and models have provided the scientific basis, e.g. critical loads and levels, for effects-based Protocols and for evaluating their effectiveness. ICP studies on trends show recovery from acidification effects in keeping with the fall in sulphur emissions. Steady-state models provide an indication of long-term improvements. Recent increased emphasis on developing dynamic models will enable better links between recovery rates and abatement strategies. The scientific network of the ICPs and the monitoring and modelling results have been key to the development of the Convention and are an essential component for its success in the future. 相似文献
64.
Hasselmann K Latif M Hooss G Azar C Edenhofer O Jaeger CC Johannessen OM Kemfert C Welp M Wokaun A 《Science (New York, N.Y.)》2003,302(5652):1923-1925
Climate policy needs to address the multidecadal to centennial time scale of climate change. Although the realization of short-term targets is an important first step, to be effective climate policies need to be conceived as long-term programs that will achieve a gradual transition to an essentially emission-free economy on the time scale of a century. This requires a considerably broader spectrum of policy measures than the primarily market-based instruments invoked for shorter term mitigation policies. A successful climate policy must consist of a dual approach focusing on both short-term targets and long-term goals. 相似文献
65.
Ice-edge eddies in the fram strait marginal ice zone 总被引:1,自引:0,他引:1
Johannessen OM Johannessen JA Svendsen E Shuchman RA Campbell WJ Josberger E 《Science (New York, N.Y.)》1987,236(4800):427-429
Five prominent ice-edge eddies in Fram Strait on the scale of 30 to 40 kilometers were observed over deep water within 77 degrees N to 79 degrees N and 5 degrees W to 3 degrees E. The use of remote sensing, a satellite-tracked buoy, and in situ oceanographic measurements showed the presence of eddies with orbital speeds of 30 to 40 centimeters per second and lifetimes of at least 20 days. Ice ablation measurements made within one of these ice-ocean eddies indicated that melting, which proceeded at rates of 20 to 40 centimeters per day, is an important process in determining the ice-edge position. These studies give new insight on the formation, propagation, and dissipation of ice-edge eddies. 相似文献