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161.
162.
辽宁热河生物群小龙虾化石形态特征及分类之甄别 总被引:1,自引:0,他引:1
通过上侏罗统义县组61块龙虾标本的12种形态特征统计分析,分别论述了其构造分类意义。利用这些保存良好的新材料,对环足虾科(Cricoidoscelosidae)特征作了重要补充和修订。雄性第1腹足呈棱状,第2腹足无特化现象,是这一科的重要特征。从环足虾(Xricoidoscelosus)和古La蛄属(Palaeocambarus)雌性都具有腹环沟构造来看,它们与古La蛄科的关系最密切。海相的化石原 相似文献
163.
Large-scale forest girdling shows that current photosynthesis drives soil respiration. 总被引:124,自引:0,他引:124
P H?gberg A Nordgren N Buchmann A F Taylor A Ekblad M N H?gberg G Nyberg M Ottosson-L?fvenius D J Read 《Nature》2001,411(6839):789-792
The respiratory activities of plant roots, of their mycorrhizal fungi and of the free-living microbial heterotrophs (decomposers) in soils are significant components of the global carbon balance, but their relative contributions remain uncertain. To separate mycorrhizal root respiration from heterotrophic respiration in aboreal pine forest, we conducted a large-scale tree-girdling experiment, comprising 9 plots each containing about 120 trees. Tree-girdling involves stripping the stem bark to the depth of the current xylem at breast height terminating the supply of current photosynthates to roots and their mycorrhizal fungi without physically disturbing the delicate root-microbe-soil system. Here we report that girdling reduced soil respiration within 1-2 months by about 54% relative to respiration on ungirdled control plots, and that decreases of up to 37% were detected within 5 days. These values clearly show that the flux of current assimilates to roots is a key driver of soil respiration; they are conservative estimates of root respiration, however, because girdling increased the use of starch reserves in the roots. Our results indicate that models of soil respiration should incorporate measures of photosynthesis and of seasonal patterns of photosynthate allocation to roots. 相似文献
164.
A I Taylor 《Nature》1970,227(5254):163-164
165.
Fluorescence ratio imaging of cyclic AMP in single cells. 总被引:24,自引:0,他引:24
Fluorescence imaging is perhaps the most powerful technique currently available for continuously observing the dynamic intracellular biochemistry of single living cells. However, fluorescent indicator dyes have been available only for simple inorganic ions such as Ca2+, H+, Na+, K+, Mg2+ and Cl-. We now report a fluorescent indicator for the adenosine 3',5'-cyclic monophosphate (cAMP) signalling pathway. The sensor consists of cAMP-dependent protein kinase in which the catalytic (C) and regulatory (R) subunits are each labelled with a different fluorescent dye such as fluorescein or rhodamine capable of fluorescence resonance energy transfer in the holoenzyme complex R2C2. When cAMP molecules bind to the R subunits, the C subunits dissociate, thereby eliminating energy transfer. The change in shape of the fluorescence emission spectrum allows cAMP concentrations and the activation of the kinase to be nondestructively visualized in single living cells microinjected with the labelled holoenzyme. 相似文献
166.
Depression of polymorph counts by various scrapie agents 总被引:1,自引:0,他引:1
167.
Summary Extensive copulatory experiences at a younger age provoked chronic changes in the reproductive physiology of old male rats. Continuous access to females was not necessary, sperm numbers were elevated in the 22-month-old males 7 months after a final sexual interaction. 相似文献
168.
Structure of ferroverdin 总被引:2,自引:0,他引:2
169.
Résumé Nous proposons un mode uniforme de numérotation pour le squelette des alcaloïdes indoliques complexes. Il est basé sur le fait que tous ces composés sont susceptibles d'être coupés en éléments identiques.
This is a precis of a suggestion discussed at the fifth annual meeting, American Society of Pharmacognosy, Symposium on the Chemistry and Biological Activity of Catharanthus, Vinca and Related Indole Alkaloids, Pittsburgh (Pennsylvania), June, 1964. 相似文献
This is a precis of a suggestion discussed at the fifth annual meeting, American Society of Pharmacognosy, Symposium on the Chemistry and Biological Activity of Catharanthus, Vinca and Related Indole Alkaloids, Pittsburgh (Pennsylvania), June, 1964. 相似文献
170.
Gating currents associated with potassium channel activation 总被引:7,自引:0,他引:7