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排序方式: 共有192条查询结果,搜索用时 562 毫秒
171.
172.
军队服装订货和供应系统的计算机仿真 总被引:1,自引:0,他引:1
美军服装订货和供应系统采用传统的经济订货量法和分发中心供货。由于生产厂不能预测订货周期和数量,很难计划生产;而维护分发中心也增加了开销。讨论了现行系统模型,并提出一个新的系统方案。新方案采用正常,的固定的订货量,不但直接有利于生产厂安排生产,产能减少库存。 相似文献
173.
Smallwood S 《Population trends》2011,(143):29-46
In an increasingly complex society there are a number of different population definitions that can be relevant for users, beyond the standard definition used in counting the population. This article describes the enumeration base for the 2011 Census and how alternative population outputs may be produced. It provides a background as to how the questions on the questionnaire were decided upon and how population bases can be constructed from the Census. Similarities and differences between the information collected across the three UK Censuses (England and Wales, Scotland and Northern Ireland) are discussed. Finally, issues around estimating the population on alternative bases are presented. 相似文献
174.
In the process of fabricating nano electrical device or system based on single-walled carbon nanotube (SWCNT), the controllable assembly and fabrication of SWCNT field-effect transistor (SWCNT FET) is a key issue. SWCNT FET is the most basic and important component in nano electronics. After microelectrode chip of back-gate FET is designed and fabricated, di-electrophoresis technology is adopted to realize the controllable alignment and assembly of SWCNTs, based on dispersing SWCNT by sodium dodecyl sulphate (SDS) facilitated ultra-sonication technique and removing impurities by centrifugal technique. The experiments of SWCNTs assembly demonstrate that SWCNTs are aligned and assembled uniformly at the microelectrodes gap with the alignment density nearly proportional to di-electrophoresis duration and solution concentration. After the processes of rinsing, drying and improving, metallic SWCNTs among the assembled SWCNTs are burned out and residual SDS is removed, and perfect field-effect performance of SWCNT FET is eventually obtained. 相似文献
175.
Dynein mutations impair autophagic clearance of aggregate-prone proteins 总被引:11,自引:0,他引:11
Ravikumar B Acevedo-Arozena A Imarisio S Berger Z Vacher C O'Kane CJ Brown SD Rubinsztein DC 《Nature genetics》2005,37(7):771-776
Mutations that affect the dynein motor machinery are sufficient to cause motor neuron disease. It is not known why there are aggregates or inclusions in affected tissues in mice with such mutations and in most forms of human motor neuron disease. Here we identify a new mechanism of inclusion formation by showing that decreased dynein function impairs autophagic clearance of aggregate-prone proteins. We show that mutations of the dynein machinery enhanced the toxicity of the mutation that causes Huntington disease in fly and mouse models. Furthermore, loss of dynein function resulted in premature aggregate formation by mutant huntingtin and increased levels of the autophagosome marker LC3-II in both cell culture and mouse models, compatible with impaired autophagosome-lysosome fusion. 相似文献
176.
Goetz W Bertelsen P Binau CS Gunnlaugsson HP Hviid SF Kinch KM Madsen DE Madsen MB Olsen M Gellert R Klingelhöfer G Ming DW Morris RV Rieder R Rodionov DS de Souza PA Schröder C Squyres SW Wdowiak T Yen A 《Nature》2005,436(7047):62-65
The ubiquitous atmospheric dust on Mars is well mixed by periodic global dust storms, and such dust carries information about the environment in which it once formed and hence about the history of water on Mars. The Mars Exploration Rovers have permanent magnets to collect atmospheric dust for investigation by instruments on the rovers. Here we report results from M?ssbauer spectroscopy and X-ray fluorescence of dust particles captured from the martian atmosphere by the magnets. The dust on the magnets contains magnetite and olivine; this indicates a basaltic origin of the dust and shows that magnetite, not maghemite, is the mineral mainly responsible for the magnetic properties of the dust. Furthermore, the dust on the magnets contains some ferric oxides, probably including nanocrystalline phases, so some alteration or oxidation of the basaltic dust seems to have occurred. The presence of olivine indicates that liquid water did not play a dominant role in the processes that formed the atmospheric dust. 相似文献
177.
Circadian rhythms from flies to human 总被引:34,自引:0,他引:34
In this era of jet travel, our body 'remembers' the previous time zone, such that when we travel, our sleep wake pattern, mental alertness, eating habits and many other physiological processes temporarily suffer the consequences of time displacement until we adjust to the new time zone. Although the existence of a circadian clock in humans had been postulated for decades, an understanding of the molecular mechanisms has required the full complement of research tools. To gain the initial insights into circadian mechanisms, researchers turned to genetically tractable model organisms such as Drosophila. 相似文献
178.
179.
Replacement fertility is a term commonly used by demographers when referring to levels of childbearing and yet is rarely explained. It is normally presented as being around 2.1 children per woman. Continued below replacement fertility in developed countries and fertility falling in developing countries has given the concept of replacement fertility a higher profile. This article explains how replacement level is calculated and explores the concept further. Past replacement fertility levels are calculated for England and Wales. A possible alternative definition of replacement is also presented. Simple projection scenarios are used to show the effect on population of below replacement fertility, and also of postponement of fertility. The importance and implications of below replacement fertility are discussed. 相似文献
180.
Parsons DW Wang TL Samuels Y Bardelli A Cummins JM DeLong L Silliman N Ptak J Szabo S Willson JK Markowitz S Kinzler KW Vogelstein B Lengauer C Velculescu VE 《Nature》2005,436(7052):792
Protein kinases are enzymes that are important for controlling cellular growth and invasion, and their malfunction is implicated in the development of some tumours. We analysed human colorectal cancers for genetic mutations in 340 serine/threonine kinases and found mutations in eight genes, including in three members of the phosphatidylinositol-3-OH kinase (PI(3)K) pathway. The discovery of this mutational activation of a key cell-signalling pathway may provide new targets for therapeutic intervention. 相似文献