全文获取类型
收费全文 | 905篇 |
免费 | 2篇 |
国内免费 | 4篇 |
专业分类
系统科学 | 42篇 |
丛书文集 | 1篇 |
教育与普及 | 1篇 |
理论与方法论 | 4篇 |
现状及发展 | 180篇 |
研究方法 | 132篇 |
综合类 | 517篇 |
自然研究 | 34篇 |
出版年
2021年 | 4篇 |
2020年 | 5篇 |
2018年 | 4篇 |
2017年 | 6篇 |
2016年 | 6篇 |
2014年 | 8篇 |
2013年 | 11篇 |
2012年 | 44篇 |
2011年 | 104篇 |
2010年 | 18篇 |
2009年 | 4篇 |
2008年 | 59篇 |
2007年 | 53篇 |
2006年 | 50篇 |
2005年 | 45篇 |
2004年 | 37篇 |
2003年 | 34篇 |
2002年 | 42篇 |
2001年 | 33篇 |
2000年 | 24篇 |
1999年 | 12篇 |
1995年 | 5篇 |
1992年 | 21篇 |
1991年 | 7篇 |
1990年 | 6篇 |
1989年 | 3篇 |
1988年 | 5篇 |
1987年 | 10篇 |
1986年 | 8篇 |
1985年 | 12篇 |
1984年 | 7篇 |
1983年 | 5篇 |
1982年 | 7篇 |
1980年 | 9篇 |
1978年 | 15篇 |
1977年 | 10篇 |
1976年 | 13篇 |
1975年 | 9篇 |
1974年 | 8篇 |
1973年 | 8篇 |
1972年 | 9篇 |
1971年 | 17篇 |
1970年 | 27篇 |
1969年 | 10篇 |
1968年 | 15篇 |
1967年 | 12篇 |
1966年 | 9篇 |
1965年 | 12篇 |
1964年 | 3篇 |
1963年 | 3篇 |
排序方式: 共有911条查询结果,搜索用时 15 毫秒
1.
We compare forecasts of recessions using four different specifications of the probit model: a time invariant conditionally independent version; a business cycle specific conditionally independent model; a time invariant probit with autocorrelated errors; and a business cycle specific probit with autocorrelated errors. The more sophisticated versions of the model take into account some of the potential underlying causes of the documented predictive instability of the yield curve. We find strong evidence in favour of the more sophisticated specification, which allows for multiple breakpoints across business cycles and autocorrelation. We also develop a new approach to the construction of real time forecasting of recession probabilities. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
2.
3.
High-frequency generalised transduction by bacteriophage T4 总被引:30,自引:0,他引:30
4.
Summary The crucial functional groups of phorbol-12-myristate-13-acetate (PMA) are superimposable with those of the glucocorticoid cortisol in a unique manner which suggests a mechanism for PMA activity, i.e. the alkylation of a cortisol receptor. 相似文献
5.
6.
Wilson J. E. M. Costa Axel M. Katz José Leonardo O. Mattos Pedro F. Amorim Beatrizz O. Mesquita Paulo J. Vilardo 《Journal of Natural History》2019,53(47-48):2905-2928
ABSTRACT This study is primarily directed to the most poorly known species of the genus Trichomycterus, comprising five nominal species (T. florensis, T. immaculatus, T. nigricans, T. paquequerensis and T. santaeritae) endemic to south-eastern Brazil. One of them, T. nigricans, is the type species of the genus, involved in taxonomic problems for over 150 years. A detailed historical review, accompanied by examination of type specimens and recent collections, revealed that the correct type locality of T. nigricans is in the vicinity of Rio de Janeiro, not Santa Catarina as commonly appears in the literature; specimens previously misidentified as T. nigricans from Santa Catarina belong to a possibly undescribed species of the genus Cambeva; T. paquequerensis is a synonym of T. immaculatus, and T. florensis is a synonym of T. santaeritae; and the hypothesis that T. santaeritae is closely related to the Amazon Sarcoglanidinae is refuted. The three valid species are redescribed. These species are members of a clade also including T. caipora that is highly supported by molecular data, diagnosed by a pronounced posterior maxillary process and caudal fin emarginate at least in larger specimens. A subclade comprising T. caipora, T. nigricans and T. santaeritae is diagnosed by a long maxilla and a bifid anterior extremity of hypobranchial 3. 相似文献
7.
Douglas A. Wilson Victoria Raish Alison Carr-Chellman 《Systemic Practice and Action Research》2017,30(3):277-293
The paper explores cinematic films as a pedagogical tool to promote critical thinking and student discussions in a doctoral-level learning, design, and technology seminar course at a major U.S. research university. These discussions focused on systemic change and systemic thinking concepts. The authors offer evidence from the literature that supports films’ power as a visual metaphor and neurocognitive stimulator to promote development of new perspectives in graduate students on case studies through articulation, reflection, and explanation of their thought processes on change and diffusion of innovation. There are theoretical, political, social, and technological issues that create tensions during any systemic change effort. The goal of using film in this seminar is to equip students with the requisite skills, theoretical frameworks, and interpersonal experiences needed to address these issues within organizations and communities. The change expected from systemic thinking is for students to think more deeply about the interconnectedness of systems and the importance of bottom-up change efforts that consider the perspective of all stakeholders. 相似文献
8.
How People Use Rich Pictures to Help Them Think and Act 总被引:1,自引:1,他引:0
Groups of all kinds are complex organisations. To understand them and to facilitate them in process terms is a matter of rich and diverse discourse in varied fields from sustainable development to coastal ecology; from bandwidth in rural communities to health service provision. How to allow groups to discourse, problem solve and review their own issues and concerns? Diagrams in general and rich pictures in particular can be great means to allow groups to explore their subconscious, their occult sentiments and conflicted understandings. This paper explores and explains diverse use of pictures and shows how they can be applied and understood in group processes of all kinds. 相似文献
9.
Piccioni G Drossart P Sanchez-Lavega A Hueso R Taylor FW Wilson CF Grassi D Zasova L Moriconi M Adriani A Lebonnois S Coradini A Bézard B Angrilli F Arnold G Baines KH Bellucci G Benkhoff J Bibring JP Blanco A Blecka MI Carlson RW Di Lellis A Encrenaz T Erard S Fonti S Formisano V Fouchet T Garcia R Haus R Helbert J Ignatiev NI Irwin PG Langevin Y Lopez-Valverde MA Luz D Marinangeli L Orofino V Rodin AV Roos-Serote MC Saggin B Stam DM Titov D Visconti G 《Nature》2007,450(7170):637-640
Venus has no seasons, slow rotation and a very massive atmosphere, which is mainly carbon dioxide with clouds primarily of sulphuric acid droplets. Infrared observations by previous missions to Venus revealed a bright 'dipole' feature surrounded by a cold 'collar' at its north pole. The polar dipole is a 'double-eye' feature at the centre of a vast vortex that rotates around the pole, and is possibly associated with rapid downwelling. The polar cold collar is a wide, shallow river of cold air that circulates around the polar vortex. One outstanding question has been whether the global circulation was symmetric, such that a dipole feature existed at the south pole. Here we report observations of Venus' south-polar region, where we have seen clouds with morphology much like those around the north pole, but rotating somewhat faster than the northern dipole. The vortex may extend down to the lower cloud layers that lie at about 50 km height and perhaps deeper. The spectroscopic properties of the clouds around the south pole are compatible with a sulphuric acid composition. 相似文献
10.