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V.A.帕瑟根 《国外科技新书评介》2007,(2):7-7
分子间的范德华力是十分微弱的,但可以说普遍的存在着,在很多体系中起着巨大的作用,在物理学、化学、生物学等学科中得到了广泛的研究。但怎样计算范德华力?如何考虑各种条件对范德华力的影响? 相似文献
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Samuel Portmann Adrian Wüthrich 《Studies in History and Philosophy of Science Part B: Studies in History and Philosophy of Modern Physics》2007,38(4):844-862
According to Bell's theorem a large class of hidden-variable models obeying Bell's notion of local causality (LC) conflict with the predictions of quantum mechanics. Recently, a Bell-type theorem has been proven using a weaker notion of LC, yet assuming the existence of perfectly correlated event types. Here we present a similar Bell-type theorem without this latter assumption. The derived inequality differs from the Clauser–Horne inequality by some small correction terms, which render it less constraining. 相似文献
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Existential risks, particularly those arising from emerging technologies, are a complex, obstinate challenge for scientific study. This should motivate studying how the relevant scientific communities might be made more amenable to studying such risks. I offer an account of scientific creativity suitable for thinking about scientific communities, and provide reasons for thinking contemporary science doesn't incentivise creativity in this specified sense. I'll argue that a successful science of existential risk will be creative in my sense. So, if we want to make progress on those questions we should consider how to shift scientific incentives to encourage creativity. The analysis also has lessons for philosophical approaches to understanding the social structure of science. I introduce the notion of a ‘well-adapted’ science: one in which the incentive structure is tailored to the epistemic situation at hand. 相似文献
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The significance of nitrification for oceanic new production 总被引:1,自引:0,他引:1
The flux of organic material sinking to depth is a major control on the inventory of carbon in the ocean. To first order, the oceanic system is at equilibrium such that what goes down must come up. Because the export flux is difficult to measure directly, it is routinely estimated indirectly by quantifying the amount of phytoplankton growth, or primary production, fuelled by the upward flux of nitrate. To do so it is necessary to take into account other sources of biologically available nitrogen. However, the generation of nitrate by nitrification in surface waters has only recently received attention. Here we perform the first synthesis of open-ocean measurements of the specific rate of surface nitrification and use these to configure a global biogeochemical model to quantify the global role of nitrification. We show that for much of the world ocean a substantial fraction of the nitrate taken up is generated through recent nitrification near the surface. At the global scale, nitrification accounts for about half of the nitrate consumed by growing phytoplankton. A consequence is that many previous attempts to quantify marine carbon export, particularly those based on inappropriate use of the f-ratio (a measure of the efficiency of the 'biological pump'), are significant overestimates. 相似文献
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One of the most important journeys of exploration to Arctic Russia was the so-called 1909 Kara Expedition, to the polar area north of the Ural Mountains. Among the scientific papers resulting from this expedition, that on the Diptera gives only the vaguest locality data, such as ‘Kara tundra’ or ‘polar Urals’, with a date. From the separately published Russian expedition narrative, we present a table giving the day-by-day stops of the expedition, so far as possible with named localities and coordinates. As a result, localities, and especially type-localities of new species, can be precisely located for the Diptera and for other taxonomic groups. 相似文献
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Accurate business failure prediction models would be extremely valuable to many industry sectors, particularly financial investment and lending. The potential value of such models is emphasised by the extremely costly failure of high‐profile companies in the recent past. Consequently, a significant interest has been generated in business failure prediction within academia as well as in the finance industry. Statistical business failure prediction models attempt to predict the failure or success of a business. Discriminant and logit analyses have traditionally been the most popular approaches, but there are also a range of promising non‐parametric techniques that can alternatively be applied. In this paper, the relatively new technique of decision trees is applied to business failure prediction. The numerical results suggest that decision trees could be superior predictors of business failure as compared to discriminant analysis. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献