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   65篇
  免费   3篇
  国内免费   2篇
系统科学   3篇
现状及发展   17篇
研究方法   13篇
综合类   28篇
自然研究   9篇
  2020年   2篇
  2019年   1篇
  2018年   6篇
  2017年   3篇
  2016年   3篇
  2014年   2篇
  2013年   2篇
  2012年   2篇
  2011年   7篇
  2010年   1篇
  2008年   3篇
  2007年   2篇
  2006年   3篇
  2005年   3篇
  2004年   1篇
  2003年   1篇
  2002年   1篇
  2001年   1篇
  1999年   2篇
  1998年   4篇
  1997年   2篇
  1996年   1篇
  1995年   2篇
  1992年   1篇
  1989年   2篇
  1986年   1篇
  1979年   1篇
  1974年   2篇
  1971年   1篇
  1970年   2篇
  1969年   1篇
  1967年   2篇
  1960年   2篇
排序方式: 共有70条查询结果,搜索用时 15 毫秒
1.
将环糊精与集中人有非线性光学性质官能团的化合物相连合成相应的LB膜材料,并对它们的性质进行了初步研究。结果表明,它们既保留了环糊精类衍生物出色的成膜性,又有良好的非线性光学性质,是一类有用的LB膜材料。  相似文献   
2.
This paper undertakes an in-sample and rolling-window comparative analysis of dependence, market, and portfolio investment risks on a 10-year global index portfolio of developed, emerging, and commodity markets. We draw our empirical results by fitting vine copulas (e.g., r-vines, c-vines, d-vines), IGARCH(1,1) RiskMetrics value-at-risk (VaR), and portfolio optimization methods based on risk measures such as the variance, conditional value-at-risk, conditional drawdown-at-risk, minimizing regret (Minimax), and mean absolute deviation. The empirical results indicate that all international indices tend to correlate strongly in the negative tail of the return distribution; however, emerging markets, relative to developed and commodity markets, exhibit greater dependence, market, and portfolio investment risks. The portfolio optimization shows a clear preference towards the gold commodity for investment, while Japan and Canada are found to have the highest and lowest market risk, respectively. The vine copula analysis identifies symmetry in the dependence dynamics of the global index portfolio modeled. Large VaR diversification benefits are produced at the 95% and 99% confidence levels by the modeled international index portfolio. The empirical results may appeal to international portfolio investors and risk managers for advanced portfolio management, hedging, and risk forecasting.  相似文献   
3.
3MC syndrome has been proposed as a unifying term encompassing the overlapping Carnevale, Mingarelli, Malpuech and Michels syndromes. These rare autosomal recessive disorders exhibit a spectrum of developmental features, including characteristic facial dysmorphism, cleft lip and/or palate, craniosynostosis, learning disability and genital, limb and vesicorenal anomalies. Here we studied 11 families with 3MC syndrome and identified two mutated genes, COLEC11 and MASP1, both of which encode proteins in the lectin complement pathway (collectin kidney 1 (CL-K1) and MASP-1 and MASP-3, respectively). CL-K1 is highly expressed in embryonic murine craniofacial cartilage, heart, bronchi, kidney and vertebral bodies. Zebrafish morphants for either gene develop pigmentary defects and severe craniofacial abnormalities. Finally, we show that CL-K1 serves as a guidance cue for neural crest cell migration. Together, these findings demonstrate a role for complement pathway factors in fundamental developmental processes and in the etiology of 3MC syndrome.  相似文献   
4.
The present study summarizes additions to the known fauna of Eucharitidae of Saudi Arabia. Cherianella arabica Gadallah &; Soliman sp. nov. and the male of previously known female Eucharis (Psilogastrellus) albipennis Bou?ek, 1956 are described and illustrated. Three new records are also added to the fauna of Saudi Arabia: Eucharis (Eucharisca) intermedia Ruschka, 1924, Eucharis (Psilogastrellus) acuminata Ruschka, 1924 and Eucharis (Psilogastrellus) punctata Förster, 1859.

http:/zoobank.org/urn:lsid:zoobank.org:pub:F1B1C493-AA83-4696-AF8B-3B3F62C09B41  相似文献   
5.
Charcot-Marie-Tooth disease (CMT1) is the most common form of inherited peripheral neuropathy. Although the disease is genetically heterogeneous, it has been demonstrated that the gene defect is the most frequent type (CMT1A) is the result of a partial duplication of band 17p11.2. Recent studies suggested that the peripheral hypomyelination syndrome in the trembler (Tr) mouse, a possible animal model for CMT1 disease, is associated with a point mutation in the peripheral myelin protein-22 gene (pmp-22). Expression of pmp-22 is particularly high in Schwann cells, and the protein is found in peripheral myelin. We now report that the human PMP-22 gene is contained within the CMT1A duplication. We therefore, suggest that increased dosage of the PMP-22 gene may be the cause of CMT1A neuropathy.  相似文献   
6.
In this work, a new model reduction technique is introduced. The proposed technique is derived using the matrix reducibility concept. The eigenvalues of the reduced model are preserved; that is, the reduced model eigenvalues are a subset of the full order model eigenvalues. This preservation of the eigenvalues makes the mathematical model closer to the physical model. Finally, the outcomes of this method are fully illustrated using simulations of two numeric examples  相似文献   
7.
Zusammenfassung Nachweis der Beinregeneration bei adulten FröschenRana ridibunda ridibunda Pallas. Skelett war weitgehend verknöchert.  相似文献   
8.
9.
定义了单位圆周上的贝塞尔级数;给出其核函数的渐近表示;讨论与其相应的幂级数间的等价收敛定理及其应用.  相似文献   
10.
根据作者研制的垂直平均二维水流运动模拟的边界通用模式,给出了模式计算的程序结构,并应用于珠江三角洲一个感潮河段的潮流模拟.实际边界按相应的信息号从边界信息库中自动搜寻计算.内点和其它模拟所需的输入条件均设计为信息文件自动查询.模拟结果表明,计算程式简单易用且稳定性良好  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