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   199篇
  免费   2篇
系统科学   2篇
教育与普及   2篇
理论与方法论   1篇
现状及发展   55篇
研究方法   23篇
综合类   114篇
自然研究   4篇
  2017年   3篇
  2016年   1篇
  2015年   1篇
  2014年   1篇
  2013年   4篇
  2012年   13篇
  2011年   16篇
  2010年   4篇
  2009年   3篇
  2008年   13篇
  2007年   13篇
  2006年   14篇
  2005年   7篇
  2004年   13篇
  2003年   9篇
  2002年   12篇
  2001年   6篇
  2000年   4篇
  1999年   5篇
  1998年   1篇
  1994年   2篇
  1992年   5篇
  1991年   4篇
  1990年   1篇
  1989年   1篇
  1988年   2篇
  1987年   3篇
  1986年   2篇
  1985年   1篇
  1982年   3篇
  1981年   1篇
  1980年   2篇
  1979年   1篇
  1978年   1篇
  1977年   2篇
  1976年   1篇
  1975年   4篇
  1974年   4篇
  1973年   2篇
  1972年   2篇
  1971年   5篇
  1970年   2篇
  1969年   2篇
  1967年   1篇
  1966年   2篇
  1965年   1篇
  1946年   1篇
排序方式: 共有201条查询结果,搜索用时 31 毫秒
91.
本书提供了一个对解析的电子结构的说明,以便与计算的电子结构相互区分。这两者都是建立在单电子近似、局部密度理论和量子机理电子态确定的基础之上的。这两种方法都是以这些状态为基础。寻求合成的固体或者分子性质的预测。本书是1999年出版的教课书《固体的电子结构与性质》一书的修订版。书中增加了有关玻璃的一章,并且重新撰写了有关旋转轨道耦合、磁合金与锕系元素的章节。  相似文献   
92.
非线性嗅觉生理模型在一维序列识别中的应用   总被引:8,自引:1,他引:7  
Water J Freeman教授在生理实验的基础上建立了一套基于嗅觉系统的神经网络模型。这套模型运用非线性动力学的方法较好的模拟了人体的嗅觉系统,并能够产生类似脑电的非周期背景信号。利用这个的基于嗅觉系统而建立的模型--K系列模型可以实现模式识别。本文首先从原理上介绍了K系列模型的拓扑结构和数学基础,然后通过实际的计算机数值模拟介绍了KII网络和KIII模型在实现一维序列识别时的方法和结果,简单说明了这个模型在模式识别上的特点。  相似文献   
93.
Mapping copy number variation by population-scale genome sequencing   总被引:1,自引:0,他引:1  
Genomic structural variants (SVs) are abundant in humans, differing from other forms of variation in extent, origin and functional impact. Despite progress in SV characterization, the nucleotide resolution architecture of most SVs remains unknown. We constructed a map of unbalanced SVs (that is, copy number variants) based on whole genome DNA sequencing data from 185 human genomes, integrating evidence from complementary SV discovery approaches with extensive experimental validations. Our map encompassed 22,025 deletions and 6,000 additional SVs, including insertions and tandem duplications. Most SVs (53%) were mapped to nucleotide resolution, which facilitated analysing their origin and functional impact. We examined numerous whole and partial gene deletions with a genotyping approach and observed a depletion of gene disruptions amongst high frequency deletions. Furthermore, we observed differences in the size spectra of SVs originating from distinct formation mechanisms, and constructed a map of SV hotspots formed by common mechanisms. Our analytical framework and SV map serves as a resource for sequencing-based association studies.  相似文献   
94.
Hepatitis C virus (HCV) remains a major medical problem. Antiviral treatment is only partially effective and a vaccine does not exist. Development of more effective therapies has been hampered by the lack of a suitable small animal model. Although xenotransplantation of immunodeficient mice with human hepatocytes has shown promise, these models are subject to important challenges. Building on the previous observation that CD81 and occludin comprise the minimal human factors required to render mouse cells permissive to HCV entry in vitro, we attempted murine humanization via a genetic approach. Here we show that expression of two human genes is sufficient to allow HCV infection of fully immunocompetent inbred mice. We establish a precedent for applying mouse genetics to dissect viral entry and validate the role of scavenger receptor type B class I for HCV uptake. We demonstrate that HCV can be blocked by passive immunization, as well as showing that a recombinant vaccinia virus vector induces humoral immunity and confers partial protection against heterologous challenge. This system recapitulates a portion of the HCV life cycle in an immunocompetent rodent for the first time, opening opportunities for studying viral pathogenesis and immunity and comprising an effective platform for testing HCV entry inhibitors in vivo.  相似文献   
95.
Lately there has been a growing interest in evolutionary studies concerning how the regularities and patterns found in the living cell could have emerged spontaneously by way of self-assembly and self-organization. It is reasonable to postulate that the chemical compounds found in the primitive Earth would have mostly been very simple in nature, and would have been immersed in the natural dynamics of the physical world, some of which would have involved self-organization. It seems likely that some molecular processes self-organized spontaneously into a hierarchy of complex behaviours. Our conceptual search herein reaches back to the time when prebiotic phenomena began to take shape. This was before the origin of life, so in this paper we hope to shed new light on some of the theoretical issues that surround the ways in which cellular organization might have evolved without the aid of replicated information.  相似文献   
96.
我们对柏拉图之前的希腊情况知之甚少,然而公元前6世纪出现的一种特殊文学样式留下了宝贵的历史资料。在这个时期曾经有一些视野较为宽阔的关于宇宙及其起源的书籍问世,它们在特殊的环境中获得繁荣。这些书籍主要由两条支流——思想和文学汇集而成,它们超越了狭小的地域边界,广为流传的是:智慧的宣言和宇宙开创的神话。到目前为止,我们没有理由将希腊人——荷马,赫西俄德或俄耳甫斯神话的宇宙发生论从其东方副本(极相似的人或物)中分离出来。很明显,它们出自同一个家庭,而且有不少证据显示出前苏格拉底的哲学家们依然在步东方宇宙发生论的后尘。  相似文献   
97.
Road track surveys were a poor index of cougar density in southern Utah. The weak relationship we found between track finding frequency and cougar density undoubtedly resulted in part from the fact that available roads do not sample properly from the nonuniformly distributed cougar population. However, the significantly positive relationship ( r 2 = .73) we found between track-finding frequency and number of cougar home ranges crossing the survey road suggested the technique may be of use in monitoring cougar populations where road abundance and location allow the population to be sampled properly. The amount of variance in track-finding frequency unexplained by number of home ranges overlapping survey roads indicates the index may be useful in demonstrating only relatively large changes in cougar population size.  相似文献   
98.
Retraction of mesenchymal stromal cells supports the invasion of colorectal cancer cells (CRC) into the adjacent compartment. CRC-secreted 12(S)-HETE enhances the retraction of cancer-associated fibroblasts (CAFs) and therefore, 12(S)-HETE may enforce invasivity of CRC. Understanding the mechanisms of metastatic CRC is crucial for successful intervention. Therefore, we studied pro-invasive contributions of stromal cells in physiologically relevant three-dimensional in vitro assays consisting of CRC spheroids, CAFs, extracellular matrix and endothelial cells, as well as in reductionist models. In order to elucidate how CAFs support CRC invasion, tumour spheroid-induced CAF retraction and free intracellular Ca2+ levels were measured and pharmacological- or siRNA-based inhibition of selected signalling cascades was performed. CRC spheroids caused the retraction of CAFs, generating entry gates in the adjacent surrogate stroma. The responsible trigger factor 12(S)-HETE provoked a signal, which was transduced by PLC, IP3, free intracellular Ca2+, Ca2+-calmodulin-kinase-II, RHO/ROCK and MYLK which led to the activation of myosin light chain 2, and subsequent CAF mobility. RHO activity was observed downstream as well as upstream of Ca2+ release. Thus, Ca2+ signalling served as central signal amplifier. Treatment with the FDA-approved drugs carbamazepine, cinnarizine, nifedipine and bepridil HCl, which reportedly interfere with cellular calcium availability, inhibited CAF-retraction. The elucidation of signalling pathways and identification of approved inhibitory drugs warrant development of intervention strategies targeting tumour–stroma interaction.  相似文献   
99.
Knowing how bats select different habitats in response to environmental changes provides a framework for anticipating the likely consequences of changes in climate or vegetation. In this study we assessed the presence of greater horseshoe bats (Rhinolophus ferrumequinum) and their foraging behavior. This study depicts an effective approach for seasonal responses of habitat selection by Chiroptera.  相似文献   
100.
Calorie restriction (CR), a reduction of 10–40% in intake of a nutritious diet, is often reported as the most robust non-genetic mechanism to extend lifespan and healthspan. CR is frequently used as a tool to understand mechanisms behind ageing and age-associated diseases. In addition to and independently of increasing lifespan, CR has been reported to delay or prevent the occurrence of many chronic diseases in a variety of animals. Beneficial effects of CR on outcomes such as immune function, motor coordination and resistance to sarcopenia in rhesus monkeys have recently been reported. We report here that a CR regimen implemented in young and older age rhesus monkeys at the National Institute on Aging (NIA) has not improved survival outcomes. Our findings contrast with an ongoing study at the Wisconsin National Primate Research Center (WNPRC), which reported improved survival associated with 30% CR initiated in adult rhesus monkeys (7–14?years) and a preliminary report with a small number of CR monkeys. Over the years, both NIA and WNPRC have extensively documented beneficial health effects of CR in these two apparently parallel studies. The implications of the WNPRC findings were important as they extended CR findings beyond the laboratory rodent and to a long-lived primate. Our study suggests a separation between health effects, morbidity and mortality, and similar to what has been shown in rodents, study design, husbandry and diet composition may strongly affect the life-prolonging effect of CR in a long-lived nonhuman primate.  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