全文获取类型
收费全文 | 2840篇 |
免费 | 13篇 |
国内免费 | 26篇 |
专业分类
系统科学 | 46篇 |
丛书文集 | 2篇 |
教育与普及 | 11篇 |
理论与方法论 | 44篇 |
现状及发展 | 342篇 |
研究方法 | 393篇 |
综合类 | 1938篇 |
自然研究 | 103篇 |
出版年
2022年 | 6篇 |
2021年 | 11篇 |
2020年 | 5篇 |
2019年 | 6篇 |
2018年 | 30篇 |
2017年 | 18篇 |
2016年 | 34篇 |
2015年 | 25篇 |
2014年 | 25篇 |
2013年 | 46篇 |
2012年 | 213篇 |
2011年 | 382篇 |
2010年 | 83篇 |
2009年 | 11篇 |
2008年 | 232篇 |
2007年 | 245篇 |
2006年 | 239篇 |
2005年 | 261篇 |
2004年 | 262篇 |
2003年 | 195篇 |
2002年 | 255篇 |
2001年 | 45篇 |
2000年 | 22篇 |
1999年 | 11篇 |
1997年 | 9篇 |
1996年 | 9篇 |
1995年 | 9篇 |
1994年 | 5篇 |
1993年 | 9篇 |
1992年 | 5篇 |
1989年 | 8篇 |
1985年 | 6篇 |
1984年 | 5篇 |
1983年 | 9篇 |
1982年 | 11篇 |
1981年 | 10篇 |
1980年 | 6篇 |
1979年 | 14篇 |
1978年 | 10篇 |
1977年 | 8篇 |
1975年 | 4篇 |
1974年 | 6篇 |
1973年 | 10篇 |
1972年 | 4篇 |
1971年 | 7篇 |
1970年 | 6篇 |
1969年 | 4篇 |
1967年 | 5篇 |
1965年 | 4篇 |
1964年 | 4篇 |
排序方式: 共有2879条查询结果,搜索用时 15 毫秒
21.
Curie’s Principle says that any symmetry property of a cause must be found in its effect. In this article, I consider Curie’s Principle from the point of view of graphical causal models, and demonstrate that, under one definition of a symmetry transformation, the causal modeling framework does not require anything like Curie’s Principle to be true. On another definition of a symmetry transformation, the graphical causal modeling formalism does imply a version of Curie’s Principle. These results yield a better understanding of the logical landscape with respect to the relationship between Curie’s Principle and graphical causal modeling. 相似文献
22.
23.
24.
The ability to improve out-of-sample forecasting performance by combining forecasts is well established in the literature. This paper advances this literature in the area of multivariate volatility forecasts by developing two combination weighting schemes that exploit volatility persistence to emphasise certain losses within the combination estimation period. A comprehensive empirical analysis of the out-of-sample forecast performance across varying dimensions, loss functions, sub-samples and forecast horizons show that new approaches significantly outperform their counterparts in terms of statistical accuracy. Within the financial applications considered, significant benefits from combination forecasts relative to the individual candidate models are observed. Although the more sophisticated combination approaches consistently rank higher relative to the equally weighted approach, their performance is statistically indistinguishable given the relatively low power of these loss functions. Finally, within the applications, further analysis highlights how combination forecasts dramatically reduce the variability in the parameter of interest, namely the portfolio weight or beta. 相似文献
25.
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
26.
Thomas Söderqvist Adam Bencard Camilla Mordhorst 《Studies in history and philosophy of science》2009,40(4):431-438
The acquisition and display of material artefacts is the raison d’être of museums. But what constitutes a museum artefact? Contemporary medicine (biomedicine) is increasingly producing artefacts that do not fit the traditional museological understanding of what constitutes a material, tangible artefact. Museums today are therefore caught in a paradox. On the one hand, medical science and technologies are having an increasing pervasive impact on the way contemporary life is lived and understood and is therefore a central part of the contemporary world. On the other hand, the objects involved in medical diagnostics and therapies are becoming increasingly invisible and intangible and therefore seem to have no role to play as artefacts in a museum context. Consequently, museums are at risk of becoming alienated from an increasingly important part of contemporary society. This essay elaborates the paradox by employing Gumbrecht’s (2004) distinction between ‘presence’ and ‘meaning’. 相似文献
27.
28.
Milne JC Lambert PD Schenk S Carney DP Smith JJ Gagne DJ Jin L Boss O Perni RB Vu CB Bemis JE Xie R Disch JS Ng PY Nunes JJ Lynch AV Yang H Galonek H Israelian K Choy W Iffland A Lavu S Medvedik O Sinclair DA Olefsky JM Jirousek MR Elliott PJ Westphal CH 《Nature》2007,450(7170):712-716
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
29.
Cdk1 is sufficient to drive the mammalian cell cycle 总被引:1,自引:0,他引:1
Santamaría D Barrière C Cerqueira A Hunt S Tardy C Newton K Cáceres JF Dubus P Malumbres M Barbacid M 《Nature》2007,448(7155):811-815
30.