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21.
21世纪中国货运代理业的发展趋势及其对策   总被引:2,自引:0,他引:2  
根据关贸总协定乌拉圭回合签署的《服务贸易总协定》提供的总体规则框架,探讨了21世纪中国货运代理的发展趋势和应采取的对策,为中国政府参加海运谈判提供科学依据。  相似文献   
22.
Fasel R  Parschau M  Ernst KH 《Nature》2006,439(7075):449-452
The concept of chirality dates back to 1848, when Pasteur manually separated left-handed from right-handed sodium ammonium tartrate crystals. Crystallization is still an important means for separating chiral molecules into their two different mirror-image isomers (enantiomers), yet remains poorly understood. For example, there are no firm rules to predict whether a particular pair of chiral partners will follow the behaviour of the vast majority of chiral molecules and crystallize together as racemic crystals, or as separate enantiomers. A somewhat simpler and more tractable version of this phenomenon is crystallization in two dimensions, such as the formation of surface structures by adsorbed molecules. The relatively simple spatial molecular arrangement of these systems makes it easier to study the effects of specific chiral interactions; moreover, chiral assembly and recognition processes can be observed directly and with molecular resolution using scanning tunnelling microscopy. The enantioseparation of chiral molecules in two dimensions is expected to occur more readily because planar confinement excludes some bulk crystal symmetry elements and enhances chiral interactions; however, many surface structures have been found to be racemic. Here we show that the chiral hydrocarbon heptahelicene on a Cu111 surface does not undergo two-dimensional spontaneous resolution into enantiomers, but still shows enantiomorphism on a mesoscopic length scale that is readily amplified. That is, we observe formation of racemic heptahelicene domains with non-superimposable mirror-like lattice structures, with a small excess of one of the heptahelicene enantiomers suppressing the formation of one domain type. Similar to the induction of homochirality in achiral enantiomorphous monolayers by a chiral modifier, a small enantiomeric excess suffices to ensure that the entire molecular monolayer consists of domains having only one of two possible, non-superimposable, mirror-like lattice structures.  相似文献   
23.
Bico J  Roman B  Moulin L  Boudaoud A 《Nature》2004,432(7018):690
We investigated why wet hair clumps into bundles by dunking a model brush of parallel elastic lamellae into a perfectly wetting liquid. As the brush is withdrawn, pairs of bundles aggregate successively, forming complex hierarchical patterns that depend on a balance between capillary forces and the elasticity of the lamellae. This capillary-driven self-assembly of flexible structures, which occurs in the tarsi of insects and in biomimetic adhesives but which can also damage micro-electromechanical structures or carbon nanotube 'carpets', represents a new type of coalescence process.  相似文献   
24.
In the paper some applications of Gödel's incompleteness theorems to discussions of problems of computer science are presented. In particular the problem of relations between the mind and machine (arguments by J.J.C. Smart and J.R. Lucas) is discussed. Next Gödel's opinion on this issue is studied. Finally some interpretations of Gödel's incompleteness theorems from the point of view of the information theory are presented.  相似文献   
25.
Efficiency and power in genetic association studies   总被引:30,自引:0,他引:30  
We investigated selection and analysis of tag SNPs for genome-wide association studies by specifically examining the relationship between investment in genotyping and statistical power. Do pairwise or multimarker methods maximize efficiency and power? To what extent is power compromised when tags are selected from an incomplete resource such as HapMap? We addressed these questions using genotype data from the HapMap ENCODE project, association studies simulated under a realistic disease model, and empirical correction for multiple hypothesis testing. We demonstrate a haplotype-based tagging method that uniformly outperforms single-marker tests and methods for prioritization that markedly increase tagging efficiency. Examining all observed haplotypes for association, rather than just those that are proxies for known SNPs, increases power to detect rare causal alleles, at the cost of reduced power to detect common causal alleles. Power is robust to the completeness of the reference panel from which tags are selected. These findings have implications for prioritizing tag SNPs and interpreting association studies.  相似文献   
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大连港海上交通安全调研与航道锚地功能改善规划   总被引:2,自引:0,他引:2  
在对大连港航道锚地和船舶航行环境的调研和海上交通实态观测的基础上,研究了大连港海上交通系统的现状,对港口交通事故进行了预测,同时对港口交通流进行了计算机模拟,面向21世纪,提出了大连港航道锚地和船舶航行环境的规划方案,并用模糊数学最大贴近度新方法进行了方案优选。  相似文献   
29.
基于模糊算法的控制器   总被引:1,自引:0,他引:1  
在分析了液力偶合器工作特点的基础上,采用三输入单输出的模糊控制模型,提出了一种转速控制模糊算法;介绍了相应模糊控制器的设计过程;给出了微机模糊控制系统框图。该算法简单有效,具有一定的实用价值。  相似文献   
30.
Mitochondria from diverse organisms are capable of transporting large amounts of Ca(2+) via a ruthenium-red-sensitive, membrane-potential-dependent mechanism called the uniporter. Although the uniporter's biophysical properties have been studied extensively, its molecular composition remains elusive. We recently used comparative proteomics to identify MICU1 (also known as CBARA1), an EF-hand-containing protein that serves as a putative regulator of the uniporter. Here, we use whole-genome phylogenetic profiling, genome-wide RNA co-expression analysis and organelle-wide protein coexpression analysis to predict proteins functionally related to MICU1. All three methods converge on a novel predicted transmembrane protein, CCDC109A, that we now call 'mitochondrial calcium uniporter' (MCU). MCU forms oligomers in the mitochondrial inner membrane, physically interacts with MICU1, and resides within a large molecular weight complex. Silencing MCU in cultured cells or in vivo in mouse liver severely abrogates mitochondrial Ca(2+) uptake, whereas mitochondrial respiration and membrane potential remain fully intact. MCU has two predicted transmembrane helices, which are separated by a highly conserved linker facing the intermembrane space. Acidic residues in this linker are required for its full activity. However, an S259A point mutation retains function but confers resistance to Ru360, the most potent inhibitor of the uniporter. Our genomic, physiological, biochemical and pharmacological data firmly establish MCU as an essential component of the mitochondrial Ca(2+) uniporter.  相似文献   
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