贵南县高寒草地荒漠化及其控制技术与措施   总被引：8，自引：0，他引：8  

拉元林  梁珠英  班玛多杰 《青海草业》2002,11(1):41-45

通过简述贵南县高寒干旱区草地类型、分布区域及荒漠化特征 ,从气候变化、鼠害、盲目开垦及超载过牧等自然、人为因素方面 ,分析总结了草地荒漠化引发机理 ,提出了防止草地荒漠化的对策及治理技术。  相似文献   

In vitro activity of chloramphenicol,florfenicol and enrofloxacin against Chlamydia pecorum isolated from koalas (Phascolarctos cinereus)          下载免费PDF全文

LA Black  DP Higgins  M Govendir 《Australian veterinary journal》2015,93(11):420-423

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干旱条件下墨西哥中部高地不同耕作措施和农作物残留物管理对玉米产量和净收益的影响     

R. ROMERO-PEREZGROVAS  N. VERHULST  D. DE LA ROSA  V. HERNÁNDEZ  M. MAERTENS  J. DECKERS  B. GOVAERTS 《土壤圈》2014,24(4):476-486

In the subtropical highlands of Central Mexico, where the main crop is maize （Zea mays）, the conventional practice （CP） involves tillage, monoculture and residue removal, leading to soil degradation and unsustainable use of natural resources and agricultural inputs. Conservation agriculture （CA） has been proposed as a viable alternative in the region, based on reduction in tillage, retention of adequate levels of crop residues and soil surface cover and use of crop rotation. This study began in 2009 when the highlands of Central Mexico suffered from a prolonged drought during vegetative maize growth in July-August, providing an opportunity for the on-farm comparison of CA with CP under severe drought conditions which 21 climate change models projected to become more frequent. Under dry conditions, CA resulted in higher yields and net returns per hectare as early as the first and second years after adoption by farmers. As an average of 27 plots under farmers＇ management in 2009, the maize yields were 26% higher under CA （6.3 t ha-1） than under CP （5.0 t ha-l）. 2010 was close to a normal year in terms of rainfall so yields were higher than in 2009 for both practices; in addition, the yield difference between the practices was reduced to 19% （6.8 t ha-1 for CA vs. 5.7 t ha-1 for CP）. When all the 2009 and 2010 observations were analyzed in a modified stability analysis, CA had an overall positive effect of 3 838 Mexican Pesos ha-1 （320 $US ha-1） on net return and 1.3 t ha-1 on yield. After only one to two years of adoption by farmers on their fields, CA had higher yields and net returns under dry conditions that were even drier than those predicted by the analyzed 21 climate change models under a climate change scenario, emission scenario A2.  相似文献   

Encounter with saturn: voyager 1 imaging science results     

Smith BA  Soderblom L  Beebe R  Boyce J  Briggs G  Bunker A  Collins SA  Hansen CJ  Johnson TV  Mitchell JL  Terrile RJ  Carr M  Cook AF  Cuzzi J  Pollack JB  Danielson GE  Ingersoll A  Davies ME  Hunt GE  Masursky H  Shoemaker E  Morrison D  Owen T  Sagan C  Veverka J  Strom R  Suomi VE 《Science (New York, N.Y.)》1981,212(4491):163-191

As Voyager 1 flew through the Saturn system it returned photographs revealing many new and surprising characteristics of this complicated community of bodies. Saturn's atmosphere has numerous, low-contrast, discrete cloud features and a pattern of circulation significantly different from that of Jupiter. Titan is shrouded in a haze layer that varies in thickness and appearance. Among the icy satellites there is considerable variety in density, albedo, and surface morphology and substantial evidence for endogenic surface modification. Trends in density and crater characteristics are quite unlike those of the Galilean satellites. Small inner satellites, three of which were discovered in Voyager images, interact gravitationally with one another and with the ring particles in ways not observed elsewhere in the solar system. Saturn's broad A, B, and C rings contain hundreds of "ringlets," and in the densest portion of the B ring there are numerous nonaxisymmetric features. The narrow F ring has three components which, in at least one instance, are kinked and crisscrossed. Two rings are observed beyond the F ring, and material is seen between the C ring and the planet.  相似文献   

The evolution of Titan's mid-latitude clouds     

Griffith CA  Penteado P  Baines K  Drossart P  Barnes J  Bellucci G  Bibring J  Brown R  Buratti B  Capaccioni F  Cerroni P  Clark R  Combes M  Coradini A  Cruikshank D  Formisano V  Jaumann R  Langevin Y  Matson D  McCord T  Mennella V  Nelson R  Nicholson P  Sicardy B  Sotin C  Soderblom LA  Kursinski R 《Science (New York, N.Y.)》2005,310(5747):474-477

Spectra from Cassini's Visual and Infrared Mapping Spectrometer reveal that the horizontal structure, height, and optical depth of Titan's clouds are highly dynamic. Vigorous cloud centers are seen to rise from the middle to the upper troposphere within 30 minutes and dissipate within the next hour. Their development indicates that Titan's clouds evolve convectively; dissipate through rain; and, over the next several hours, waft downwind to achieve their great longitude extents. These and other characteristics suggest that temperate clouds originate from circulation-induced convergence, in addition to a forcing at the surface associated with Saturn's tides, geology, and/or surface composition.  相似文献   

In situ evidence for an ancient aqueous environment at Meridiani Planum, Mars     

Squyres SW  Grotzinger JP  Arvidson RE  Bell JF  Calvin W  Christensen PR  Clark BC  Crisp JA  Farrand WH  Herkenhoff KE  Johnson JR  Klingelhöfer G  Knoll AH  McLennan SM  McSween HY  Morris RV  Rice JW  Rieder R  Soderblom LA 《Science (New York, N.Y.)》2004,306(5702):1709-1714

Sedimentary rocks at Eagle crater in Meridiani Planum are composed of fine-grained siliciclastic materials derived from weathering of basaltic rocks, sulfate minerals (including magnesium sulfate and jarosite) that constitute several tens of percent of the rock by weight, and hematite. Cross-stratification observed in rock outcrops indicates eolian and aqueous transport. Diagenetic features include hematite-rich concretions and crystal-mold vugs. We interpret the rocks to be a mixture of chemical and siliciclastic sediments with a complex diagenetic history. The environmental conditions that they record include episodic inundation by shallow surface water, evaporation, and desiccation. The geologic record at Meridiani Planum suggests that conditions were suitable for biological activity for a period of time in martian history.  相似文献   

Flash X-ray Microscopy     

McCorkle R  Angilello J  Coleman G  Feder R  LA Placa SJ 《Science (New York, N.Y.)》1979,205(4404):401-402

Soft x-ray contact microscopy, utilizing single-shot exposures of approximately 60 nanoseconds duration in polymethyl methacrylate, has been realized with a resolution of 300 angstroms. The radiation spectrum is intense in the "window" between 23 and 44 angstroms where water is transparent compared to biological materials, and therefore permits viewing of wet samples.  相似文献   

SOIL TRANSECT CORRELOGRAMS OF NORTH OXFORDSHIRE AND THEIR INTERPRETATION   总被引：2，自引：1，他引：2  

R. WEBSTER  H. E. CUANALO DE LA C 《European Journal of Soil Science》1975,26(2):176-194

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Frequency of a FAS ligand gene variant associated with inherited feline autoimmune lymphoproliferative syndrome in British shorthair cats in New Zealand     

D Aberdein  JS Munday  KE Dittmer  RW Heathcott  LA Lyons 《New Zealand veterinary journal》2013,61(6):327-331

Abstract