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Extracts of oat cultures of 53 isolates of Pythium and Phytophthora and an isolate of Achlya were tested for their ability to cause watersoaking, laminar collapse, and dehydration of excised tobacco leaves. Extracts of oat cultures of 10 of 11 isolates of P. cryptogea Pethy. & Laff., 4 of 5 isolates of P. megasperma Drechs., all 5 isolates of P. drechsleri Tucker, and 3 of 4 isolates of P. erythroseptica Pethy, were toxic to tobacco laminae. Mycelial extracts of three P. cryptogea isolates obtained from three diverse sources had properties similar to a previously studied toxin from P. cryptogea. Extracts of oat cultures of three P. cryptogea isolates and an isolate of P. megasperma caused foliar toxicity and growth reduction of tobacco transplants. Mycelial extracts of isolates of four species of Phytophthora active on excised leaves were also active in inhibiting plant growth. Most isolates of these four species of Phytophthora appear to produce identical or similar toxins. Although not parasitic to tobacco, those species are potentially detrimental to tobacco. 相似文献
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D.L. Hendrix J.R. Mauney B.A. Kimball K. Lewin J. Nagy G.R. Hendrey 《Agricultural and Forest Meteorology》1994,70(1-4)
Root, stem and leaf tissues, from cotton plants exposed to CO2 at ambient (370 μmol mol−1 (control)) or elevated (550 μmol mol−1 (FACE; free-air carbon dioxide enrichment)) levels in the field during the 1990 and 1991 growing seasons, were analyzed for nonstructural carbohydrates (glucose, fructose, sucrose and starch). Besides the FACE treatment, these plants were also exposed to two irrigation levels: 100% and 67% replacement of evapotranspiration. FACE had a greater effect upon cotton plant nonstructural carbohydrates than did irrigation treatments. Leaf carbohydrate content was increased by FACE, but this increase was much more pronounced in the stems and roots. Starch and soluble sugars in leaves in FACE plots tended to be consistently greater than in control leaves, without much change in carbohydrate content during the growing season. In contrast, root and stem, starch and soluble sugar pools were strongly increased by FACE and fluctuated strongly during the growing season. In both seasons, stem and taproot nonstructural carbohydrate content passed through a minimum during periods of heavy boll set. The fluctuations in stem and root carbohydrate content were therefore probably caused by the varying metabolic demands of the developing plant. These results suggest that a significant effect of CO2 enrichment on starch-accumulating plants is an increase of nonstructural carbohydrate, especially starch, in nonleaf storage pools. This buildup occurs somewhat independently of the water status of the plant, and these enlarged pools can be drawn upon by the growing plant to maintain growth during periods of high metabolic demand. 相似文献
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G. S. McMaster D. R. LeCain J. A. Morgan L. Aiguo D. L. Hendrix 《Journal of Agronomy and Crop Science》1999,183(2):119-128
Whole-plant responses to elevated CO2 throughout the life cycle are needed to understand future impacts of elevated atmospheric CO2. In this study, Triticum aestivum L. leaf carbon exchange rates (CER) and carbohydrates, growth, and development were examined at the tillering, booting, and grain-filling stages in growth chambers with CO2 concentrations of 350 (ambient) or 700 (high) μmol mol?1. Single-leaf CER values measured on plants grown at high CO2 were 50% greater than those measured on plants grown at ambient CO2 for all growth stages, with no photosynthetic acclimation observed at high CO2. Leaves grown in high CO2 had more starch and simple sugars at tillering and booting, and more starch at grain-filling, than those grown in ambient CO2. CER and carbohydrate levels were positively correlated with leaf appearance rates and tillering (especially third-, fourth- and fifth-order tillers). Elevated CO2 slightly delayed tiller appearance, but accelerated tiller development after appearance. Although high CO2 increased leaf appearance rates, final leaf number/culm was not effected because growth stages were reached slightly sooner. Greater plant biomass was related to greater tillering. Doubling CO2 significantly increased both shoot and root dry weight, but decreased the shoot to root ratio. High CO2 plants had more spikes plant?1 and spikelets spike?1, but a similar number of fertile spikelets spike?1. Elevated CO2 resulted in greater shoot, root and spike production and quicker canopy development by increasing leaf and tiller appearance rates and phenology. 相似文献
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C J Brunner C M Hendrix B L Blagburn L A Hanrahan 《Journal of the American Veterinary Medical Association》1988,192(10):1423-1427
In 30 random-source dogs, we determined sensitivity and specificity of 5 serologic tests for detection of canine heartworm antigens. Seventeen of the dogs were infected naturally with adult Dirofilaria immitis, and 4 of the infected dogs were amicrofilaremic. The ability of the serologic tests to predict whether a dog was infected or uninfected (overall test accuracy) ranged from 73 to 97%. Sensitivity was not affected by circulating D immitis microfilariae, but was markedly influenced by the number of adult D immitis present. False-positive reactions were rare and were not associated with intestinal parasites or Dipetalonema reconditum microfilariae. Modifications of some of the test procedures were necessary to maximize test accuracy and reproducibility. These modifications and other technical details might limit the usefulness of some of the tests in a veterinary practice. 相似文献