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   2614篇
  免费   9篇
  国内免费   25篇
系统科学   44篇
丛书文集   2篇
教育与普及   11篇
理论与方法论   41篇
现状及发展   291篇
研究方法   363篇
综合类   1797篇
自然研究   99篇
  2022年   4篇
  2021年   9篇
  2020年   4篇
  2019年   6篇
  2018年   25篇
  2017年   16篇
  2016年   29篇
  2015年   22篇
  2014年   22篇
  2013年   44篇
  2012年   205篇
  2011年   352篇
  2010年   73篇
  2009年   10篇
  2008年   222篇
  2007年   231篇
  2006年   222篇
  2005年   251篇
  2004年   253篇
  2003年   187篇
  2002年   242篇
  2001年   6篇
  2000年   16篇
  1999年   11篇
  1998年   6篇
  1997年   7篇
  1996年   9篇
  1995年   9篇
  1994年   5篇
  1993年   6篇
  1992年   5篇
  1991年   3篇
  1990年   4篇
  1989年   7篇
  1986年   3篇
  1985年   3篇
  1984年   4篇
  1983年   9篇
  1982年   10篇
  1981年   10篇
  1980年   4篇
  1979年   14篇
  1978年   10篇
  1977年   8篇
  1974年   5篇
  1973年   7篇
  1972年   6篇
  1971年   6篇
  1970年   7篇
  1967年   5篇
排序方式: 共有2648条查询结果,搜索用时 593 毫秒
21.
22.
23.
The purpose of the paper is to present a framework that enables action researchers to create quality action research projects within the organization development (OD) domain using the broad criteria of being rigorous, reflective and relevant and so contribute to the realm of practical knowing. What constitutes good quality action research within OD is a difficult question, given the broad range of approaches that operates in a wide variety of settings and with great diversity. It advances specific dimensions by which action researchers can create, review and assess quality in action research work. This integrative framework and criteria are practical tools to enable action researchers to create quality action research in OD.  相似文献   
24.
25.
Calorie restriction extends lifespan and produces a metabolic profile desirable for treating diseases of ageing such as type 2 diabetes. SIRT1, an NAD+-dependent deacetylase, is a principal modulator of pathways downstream of calorie restriction that produce beneficial effects on glucose homeostasis and insulin sensitivity. Resveratrol, a polyphenolic SIRT1 activator, mimics the anti-ageing effects of calorie restriction in lower organisms and in mice fed a high-fat diet ameliorates insulin resistance, increases mitochondrial content, and prolongs survival. Here we describe the identification and characterization of small molecule activators of SIRT1 that are structurally unrelated to, and 1,000-fold more potent than, resveratrol. These compounds bind to the SIRT1 enzyme-peptide substrate complex at an allosteric site amino-terminal to the catalytic domain and lower the Michaelis constant for acetylated substrates. In diet-induced obese and genetically obese mice, these compounds improve insulin sensitivity, lower plasma glucose, and increase mitochondrial capacity. In Zucker fa/fa rats, hyperinsulinaemic-euglycaemic clamp studies demonstrate that SIRT1 activators improve whole-body glucose homeostasis and insulin sensitivity in adipose tissue, skeletal muscle and liver. Thus, SIRT1 activation is a promising new therapeutic approach for treating diseases of ageing such as type 2 diabetes.  相似文献   
26.
Cdk1 is sufficient to drive the mammalian cell cycle   总被引:1,自引:0,他引:1  
  相似文献   
27.
Conover DO 《Nature》2007,450(7167):179-180
  相似文献   
28.
Partridge L  Gems D 《Nature》2007,450(7167):165-167
  相似文献   
29.
30.
Colombe Y  Steinmetz T  Dubois G  Linke F  Hunger D  Reichel J 《Nature》2007,450(7167):272-276
An optical cavity enhances the interaction between atoms and light, and the rate of coherent atom-photon coupling can be made larger than all decoherence rates of the system. For single atoms, this 'strong coupling regime' of cavity quantum electrodynamics has been the subject of many experimental advances. Efforts have been made to control the coupling rate by trapping the atom and cooling it towards the motional ground state; the latter has been achieved in one dimension so far. For systems of many atoms, the three-dimensional ground state of motion is routinely achieved in atomic Bose-Einstein condensates (BECs). Although experiments combining BECs and optical cavities have been reported recently, coupling BECs to cavities that are in the strong-coupling regime for single atoms has remained an elusive goal. Here we report such an experiment, made possible by combining a fibre-based cavity with atom-chip technology. This enables single-atom cavity quantum electrodynamics experiments with a simplified set-up and realizes the situation of many atoms in a cavity, each of which is identically and strongly coupled to the cavity mode. Moreover, the BEC can be positioned deterministically anywhere within the cavity and localized entirely within a single antinode of the standing-wave cavity field; we demonstrate that this gives rise to a controlled, tunable coupling rate. We study the heating rate caused by a cavity transmission measurement as a function of the coupling rate and find no measurable heating for strongly coupled BECs. The spectrum of the coupled atoms-cavity system, which we map out over a wide range of atom numbers and cavity-atom detunings, shows vacuum Rabi splittings exceeding 20 gigahertz, as well as an unpredicted additional splitting, which we attribute to the atomic hyperfine structure. We anticipate that the system will be suitable as a light-matter quantum interface for quantum information.  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