Export of north american ozone pollution to the north atlantic ocean     

Parrish DD  Holloway JS  Trainer M  Murphy PC  Fehsenfeld FC  Forbes GL 《Science (New York, N.Y.)》1993,259(5100):1436-1439

Measurement of the levels of ozone and carbon monoxide (a tracer of anthropogenic pollution) at three surface sites on the Atlantic coast of Canada allow the estimation of the amount of ozone photochemically produced from anthropogenic precursors over North America and transported to the lower troposphere over the temperate North Atlantic Ocean. This amount is greater than that injected from the stratosphere, the primary natural source of ozone. This conclusion supports the contention that ozone derived from anthropogenic pollution has a hemisphere-wide effect at northern temperate latitudes.  相似文献   

In situ Sampler for Marine Sedimentary Pore Waters: Evidence for Potassium Depletion and Calcium Enrichment     

Sayles FL  Wilson TR  Hume DN  Mangelsdorf PC 《Science (New York, N.Y.)》1973,181(4095):154-156

A device for sampling the interstitial waters of deep-sea sediments in situ has been developed and tested. The sampler collects a series of samples over a depth of 1.5 meters in the sediment and thus makes possible the accurate delineation of chemical gradients existing in the pore waters. Samples collected in the North Atlantic indicate that significant gradients of K(+) and Ca(2+) exist in the sediments sampled. Interstitial solutions sampled between Ireland and Cape Cod, Massachusetts, are characterized by the depletion of K(+) and the enrichment of Ca(2+).  相似文献   

Direct Oxidation by Adsorbed Oxygen during Acidic Mine Drainage     

Smith EE  Shumate KS  Singer PC  Stumm W 《Science (New York, N.Y.)》1970,169(3940):98

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Hormology in nutrition     

LUCKEY TD  STONE PC 《Science (New York, N.Y.)》1960,132(3443):1891-1893

Discrepancies in the growth curves for the sodium requirement of the cricket indicate that hormology may play an important role in the response to essential nutrients as well as to toxic compounds. Differentiation between stimulation of growth by a nonnutritive action and support of growth by an essential nutrient is difficult.  相似文献   

General acid-base catalysis in the mechanism of a hepatitis delta virus ribozyme     

Nakano S  Chadalavada DM  Bevilacqua PC 《Science (New York, N.Y.)》2000,287(5457):1493-1497

Many protein enzymes use general acid-base catalysis as a way to increase reaction rates. The amino acid histidine is optimized for this function because it has a pK(a) (where K(a) is the acid dissociation constant) near physiological pH. The RNA enzyme (ribozyme) from hepatitis delta virus catalyzes self-cleavage of a phosphodiester bond. Reactivity-pH profiles in monovalent or divalent cations, as well as distance to the leaving-group oxygen, implicate cytosine 75 (C75) of the ribozyme as the general acid and ribozyme-bound hydrated metal hydroxide as the general base in the self-cleavage reaction. Moreover, C75 has a pK(a) perturbed to neutrality, making it "histidine-like." Anticooperative interaction is observed between protonated C75 and a metal ion, which serves to modulate the pK(a) of C75. General acid-base catalysis expands the catalytic repertoire of RNA and may provide improved rate acceleration.  相似文献   

广东银杏资源调查初报   总被引：5，自引：0，他引：5  

梁红  冯颖竹  王英强  潘伟明  洪梅 《农业与技术》2002,22(6):75-79

对广东省各地银杏资源进行调查发现，广东100年以上的老银杏树主要分布在北纬24°以上的北部山区。根据种子和种核的形态特征，它们分别属于“圆子”、“佛手”和“梅核”类品种，主导品种是圆子类品种，尚未发现“马铃”类品种。在广东顺德市清晖园内发现1株类似于佛手银杏的150年以上雌树，是广东境内仅有的一株在北纬23°以南，年平均温度22℃以上仍能开花结实的银杏树。对广东银杏品种特性的形成条件，顺德银杏的资源开发以及广东银杏产业发展进行了讨论。  相似文献   

Newsgathering     

Hirschberg E  Joseph Fu SC  Frisell WR  Farber E  Potter VR  Rusch HP  Saffiotti U  Shimkin MB  Brennan MJ  Nowell PC  Creech HJ  Taylor RM  Schabel FM  Frei E  Lepage GA  Weinhouse S  Hall TC 《Science (New York, N.Y.)》1972,176(4041):1288-1289

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Role of brain insulin receptor in control of body weight and reproduction     

Brüning JC  Gautam D  Burks DJ  Gillette J  Schubert M  Orban PC  Klein R  Krone W  Müller-Wieland D  Kahn CR 《Science (New York, N.Y.)》2000,289(5487):2122-2125

Insulin receptors (IRs) and insulin signaling proteins are widely distributed throughout the central nervous system (CNS). To study the physiological role of insulin signaling in the brain, we created mice with a neuron-specific disruption of the IR gene (NIRKO mice). Inactivation of the IR had no impact on brain development or neuronal survival. However, female NIRKO mice showed increased food intake, and both male and female mice developed diet-sensitive obesity with increases in body fat and plasma leptin levels, mild insulin resistance, elevated plasma insulin levels, and hypertriglyceridemia. NIRKO mice also exhibited impaired spermatogenesis and ovarian follicle maturation because of hypothalamic dysregulation of luteinizing hormone. Thus, IR signaling in the CNS plays an important role in regulation of energy disposal, fuel metabolism, and reproduction.  相似文献   

Organic matter in a coal ball: peat or coal?     

Hatcher PG  Lyons PC  Thompson CL  Brown FW  Maciel GE 《Science (New York, N.Y.)》1982,217(4562):831-833

Chemical analyses of morphologically preserved organic matter in a Carboniferous coal ball reveal that the material is coalified to a rank approximately equal to that of the surrounding coal. Hence, the plant tissues in the coal ball were chemically altered by coalification processes and were not preserved as peat.  相似文献   

Response     

Sereno PC  Wilson JA  Larsson HC  Dutheil DB  Sues HD 《Science (New York, N.Y.)》1995,267(5205):1752-1753

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