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   8482篇
  免费   743篇
  国内免费   194篇
系统科学   1285篇
丛书文集   96篇
教育与普及   51篇
理论与方法论   302篇
现状及发展   902篇
研究方法   10篇
综合类   6771篇
自然研究   2篇
  2024年   10篇
  2023年   37篇
  2022年   75篇
  2021年   83篇
  2020年   75篇
  2019年   50篇
  2018年   764篇
  2017年   775篇
  2016年   495篇
  2015年   127篇
  2014年   122篇
  2013年   117篇
  2012年   396篇
  2011年   1103篇
  2010年   907篇
  2009年   600篇
  2008年   668篇
  2007年   912篇
  2006年   156篇
  2005年   179篇
  2004年   245篇
  2003年   236篇
  2002年   172篇
  2001年   132篇
  2000年   129篇
  1999年   129篇
  1998年   78篇
  1997年   96篇
  1996年   85篇
  1995年   77篇
  1994年   72篇
  1993年   59篇
  1992年   51篇
  1991年   45篇
  1990年   27篇
  1989年   39篇
  1988年   40篇
  1987年   22篇
  1986年   11篇
  1985年   1篇
  1984年   1篇
  1981年   1篇
  1980年   1篇
  1973年   2篇
  1972年   8篇
  1971年   1篇
  1970年   2篇
  1968年   4篇
  1967年   2篇
排序方式: 共有9419条查询结果,搜索用时 609 毫秒
971.
It is important to reduce data redundancy of stereo video in practical applications. In this paper,first,a data embedding method for stereo video(DEMSV) is investigated by embedding the encoding data into the reference frame to encode stereo video. It can use only one channel to transfer all the video data and the receiver can choose a monocular video decoder or stereo video decoder adaptively. Then,introducing the joint prediction scheme in the coding process of DEMSV,we propose a novel data embedding meth...  相似文献   
972.
An efficient method for the synthesis of tetrahydroquinoline derivatives via lanthanide halides catalyzed domino reactions of arylamines with dihydropyran is described. Either the cis or the trans isomer can be obtained as the major product in good yield by changing the catalyst and reaction conditions.  相似文献   
973.
974.
The present article considers Giulio Racah’s contributions to general physical theory and his establishment of theoretical physics as a discipline in Israel. Racah developed mathematical methods that are based on tensor operators and continuous groups. These methods revolutionized spectroscopy. Currently, these are essential research tools in atomic, nuclear and elementary particle physics. He himself applied them to modernizing theoretical atomic spectroscopy. Racah laid the foundations of theoretical physics in Israel. He educated several generations of Israeli physicists, and put Israel on the world map of physics.  相似文献   
975.
A dragonfly wing consists of membranes and both longitudinal and cross veins. We observed the microstructure cross-section at several locations in the dragonfly wing using environmental scanning electron microscopy (ESEM). The organic nature of the junction between the vein and the membrane was clearly identifiable. The membrane was divided into two layers, the upper epidermis and the lower epidermis. These layers extend around the sandwich structure vein, and combine with the adjacent membrane at a symmetrical location along the vein. Thus, we defined this as an organic junction between the vein and the membranes. The organic junction is able to form a tight corrugation angle, which dramatically increases both the warping rigidity and the strength of the wing, but not the torsional rigidity. The torsional deformation is primarily controlled by the microstructure of the longitudinal veins, and is based on the relative rotation angle between the epidermal layer and the inner layer of the vein that forms the zigzag section.  相似文献   
976.
Neuronal hyperpolarization-activated cyclic nucleotide-gated (HCN) channels are known to modulate spontaneous activity, resting membrane potential, input resistance, afterpotential, rebound activity, and dendritic integration. To evaluate the role of HCN2 for hippocampal synaptic plasticity, we recorded long-term potentiation (LTP) in the direct perforant path (PP) to CA1 pyramidal cells. LTP was enhanced in mice carrying a global deletion of the channel (HCN2−/−) but not in a pyramidal neuron-restricted knockout. This precludes an influence of HCN2 located in postsynaptic pyramidal neurons. Additionally, the selective HCN blocker zatebradine reduced the activity of oriens-lacunosum moleculare interneurons in wild-type but not HCN2−/− mice and decreased the frequency of spontaneous inhibitory currents in postsynaptic CA1 pyramidal cells. Finally, we found amplified LTP in the PP of mice carrying an interneuron-specific deletion of HCN2. We conclude that HCN2 channels in inhibitory interneurons modulate synaptic plasticity in the PP by facilitating the GABAergic output onto pyramidal neurons.  相似文献   
977.
We give a “direction for use” of the scale relativity theory and apply it to an example of spontaneous multiscale integration including four embedded levels of organization (intracellular, cell, tissue and organism-like levels). We conclude by an update of our analysis of the arctic sea ice melting.  相似文献   
978.
Modeling a business to match its customer perceived (and customer desired) outcomes, remains an on-going task. This paper considers shows how a service value networks (SVNs) approach may be engaged to model, and deliver, understanding of the front-end business and its direct engagement with its immediate (or front-end) customers. These front-end customers may be either: (1) its off-line, in-store customers - engaging directly with the business sales staff (or representative), or-(2) its on-line, virtual customers - engaging with the business via internet or remote access. In this situation, both the business, and the customer draw upon their respective viewpoints, and both sides influence the interaction. External to these business and customer influences are additional factors that capture the immediate and broader global effects - termed environmental effects. These three business-customer engagement areas of influence are captured by a SVN SEM approach.
Without a business-customer encounter of some kind the likelihood of a services business, and a prospecting customer, successfully engaging in an exchange process is reduced. This exchange may be a physical, and/or services exchange, and/or an information and/or ideas exchange. To the business, this encounter is, in effect, a trade, and as a result, the business targets acquiring an economic exchange that will ultimately deliver a net positive economic outcome. To the customer, external and internal information feeds, servicing, perceived value, and satisfaction, are key encounter drivers. SVNs offers a new way to understand the business-customer encounter, and to then utilize this acquired knowledge to either: (1) build a strategic management model, or (2) reengineer its business networks, and to then create a re-positioned, more customer-aligned business operation - one that is capable of delivering win - win, competitive business-customer solutions.  相似文献   
979.
扬子鳄肌肉组织成份测试和营养评价   总被引:1,自引:0,他引:1  
古医籍早有记载,鳄肉可食。根据江苏省理化测试中心和南京大学现代化分析中心的测定,本文在国内首次发表了鳄肉中所含脂肪、蛋白质、氨基酸、维生素、宏量及微量元素的全部资料,说明鳄肉营养丰富,胜过猪、牛、羊、鸡、鸭肉,并具有海洋生物特有的DHA(脑黄金)。对进一步研究怀开发我省特产扬子鳄有重要意义。  相似文献   
980.
量子点,又称“人造原子”,它是纳米科技研究的重要组成部分。由于载流子在半导体量子点中受到三维限制而具有的独特性能,构成了量子器件和电路的基础,在未来的纳米电子学、光电子学,光子、量子计算和生命科学等方面有着重要的应用前景,受到人们广泛重视。文章介绍了半导体量子点结构的制备和性质以及量子点器件的可能应用。  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