首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   28篇
  免费   0篇
  国内免费   4篇
系统科学   3篇
现状及发展   7篇
研究方法   3篇
综合类   17篇
自然研究   2篇
  2020年   3篇
  2019年   3篇
  2018年   2篇
  2017年   2篇
  2016年   1篇
  2015年   1篇
  2013年   2篇
  2012年   3篇
  2011年   1篇
  2007年   3篇
  2005年   1篇
  2004年   1篇
  2003年   1篇
  2002年   2篇
  2000年   2篇
  1999年   1篇
  1987年   1篇
  1973年   1篇
  1971年   1篇
排序方式: 共有32条查询结果,搜索用时 0 毫秒
1.
A fast and accurate method based on FTIR is developed for determining the lignin content and its characteristic bands in alkali solutions. The work consisted of two main parts: 1) establishing a predictive model and 2) determination of the accuracy of the model. The model was derived by applying the partial least squares algorithm for multivariate analyses to a set of spectrum data obtained from selected IR absorption regions in the range of 1600 - 900 cm-1. The model was tested with spent liquors obtained from commercial pulp mills.The accuracy of the predictive model is extremely high suitable for commercial applications,particularly for monitoring the dynamic response of modern kraft pulping processes.  相似文献   
2.
A second generation human haplotype map of over 3.1 million SNPs   总被引:2,自引:0,他引:2  
We describe the Phase II HapMap, which characterizes over 3.1 million human single nucleotide polymorphisms (SNPs) genotyped in 270 individuals from four geographically diverse populations and includes 25-35% of common SNP variation in the populations surveyed. The map is estimated to capture untyped common variation with an average maximum r2 of between 0.9 and 0.96 depending on population. We demonstrate that the current generation of commercial genome-wide genotyping products captures common Phase II SNPs with an average maximum r2 of up to 0.8 in African and up to 0.95 in non-African populations, and that potential gains in power in association studies can be obtained through imputation. These data also reveal novel aspects of the structure of linkage disequilibrium. We show that 10-30% of pairs of individuals within a population share at least one region of extended genetic identity arising from recent ancestry and that up to 1% of all common variants are untaggable, primarily because they lie within recombination hotspots. We show that recombination rates vary systematically around genes and between genes of different function. Finally, we demonstrate increased differentiation at non-synonymous, compared to synonymous, SNPs, resulting from systematic differences in the strength or efficacy of natural selection between populations.  相似文献   
3.
We studied the feeding ecology of Eutropis multifasciata in the tropical plains of central Vietnam to understand better the foraging mode, spatiotemporal and sexual variation in dietary composition, and rarefaction curves of prey-taxon richness for males and females. Stomach contents (n = 161) were collected from October 2013 to May 2014 using a nonlethal stomach-flushing technique. A total of 680 food items (624 animal items and 56 plant items) was found in 161 stomachs of skinks, representing 19 unique animal categories. We found that the diet of E. multifasciata is composed mainly of small, sedentary and clumped prey and that this skink specialises on spiders, insect larvae, snails, grasshoppers and crickets (with a combined importance index of 60%). Dietary composition, prey size and total prey volume in E. multifasciata changed between dry and rainy seasons and among regions. The total volume of food items consumed by males was larger than that of females, and the diversity and evenness index of prey categories were larger in males than in females. However, using rarefaction curves revealed that females have the higher prey-taxon richness after points between 130 and 140 prey items for frequency, and between 160 and 170 prey items for number of items, and the differences were not statistically significant. The foraging behaviour of E. multifasciata best fits a ‘widely foraging’ model.  相似文献   
4.
5.
In legumes, root nodule organogenesis is activated in response to morphogenic lipochitin oligosaccharides that are synthesized by bacteria, commonly known as rhizobia. Successful symbiotic interaction results in the formation of highly specialized organs called root nodules, which provide a unique environment for symbiotic nitrogen fixation. In wild-type plants the number of nodules is regulated by a signalling mechanism integrating environmental and developmental cues to arrest most rhizobial infections within the susceptible zone of the root. Furthermore, a feedback mechanism controls the temporal and spatial susceptibility to infection of the root system. This mechanism is referred to as autoregulation of nodulation, as earlier nodulation events inhibit nodulation of younger root tissues. Lotus japonicus plants homozygous for a mutation in the hypernodulation aberrant root (har1) locus escape this regulation and form an excessive number of nodules. Here we report the molecular cloning and expression analysis of the HAR1 gene and the pea orthologue, Pisum sativum, SYM29. HAR1 encodes a putative serine/threonine receptor kinase, which is required for shoot-controlled regulation of root growth, nodule number, and for nitrate sensitivity of symbiotic development.  相似文献   
6.
有限单元法(FEM)及其软件是求解大型工程应用的最有效工具之一。在这类应用问题中,有效的方程和本征值求解器扮演着至关重要的角色。稀疏矩阵及其求解技术已经足够成熟并在商用软件中实现。然而,截至目前,关于稀疏系数方程求解、Lanczos域分解或FEM并行计算的详细介绍的书籍尚不多见。  相似文献   
7.
8.
抛体运动的轨迹长度与所围面积研究   总被引:1,自引:0,他引:1  
空气阻力对抛体的运动可以产生显著的影响.运用近似的方法处理超越方程,给出了考虑空气阻力时抛体运动轨迹的长度和轨迹所包围的面积的近似解析解.数值计算表明:(1)当kt/m越小时轨迹长度与所围面积的近似解析解与真实值越接近;(2)抛体运动轨迹的长度取最大值时,抛射角随空气阻力系数的增大而减小:(3)抛体运动轨迹所围面积取最大值时,抛射角随空气阻力系数的增大而增加.  相似文献   
9.

In this article we discuss how an interdisciplinary research team partnered with a variety of stakeholders concerned with and/or affected by the impacts of climate change in the Red River Delta of Vietnam. The research, undertaken from 2016 to 2018, drew upon a wide range of methods to investigate systemically these impacts – with a view to the research inputting into the development of (more) sustainable ways of living. The research solicited various accounts of the experience of climate change in the community, set up learning processes in community meetings, and created an interface with government officials positioned at commune, district, provincial, and national levels. The intention was to offer support towards developing a learning process (broadly defined as including learnings/systemic inquiry across organizational levels of the society) to pursue options for sustainable living. The article offers our post-facto reflections which render more explicit (to ourselves and for the benefit of audiences) how the research team, with Hoang as lead researcher, facilitated the inquiry process towards developing a synthesis which underscored the assets for resilience to climate change and supported interventions to strengthen such (defined) assets.

  相似文献   
10.
This paper investigates the time-varying volatility patterns of some major commodities as well as the potential factors that drive their long-term volatility component. For this purpose, we make use of a recently proposed generalized autoregressive conditional heteroskedasticity–mixed data sampling approach, which typically allows us to examine the role of economic and financial variables of different frequencies. Using commodity futures for Crude Oil (WTI and Brent), Gold, Silver and Platinum, as well as a commodity index, our results show the necessity for disentangling the short-term and long-term components in modeling and forecasting commodity volatility. They also indicate that the long-term volatility of most commodity futures is significantly driven by the level of global real economic activity as well as changes in consumer sentiment, industrial production, and economic policy uncertainty. However, the forecasting results are not alike across commodity futures as no single model fits all commodities.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号