全文获取类型
收费全文 | 678篇 |
免费 | 6篇 |
国内免费 | 5篇 |
专业分类
系统科学 | 6篇 |
教育与普及 | 3篇 |
理论与方法论 | 8篇 |
现状及发展 | 98篇 |
研究方法 | 103篇 |
综合类 | 441篇 |
自然研究 | 30篇 |
出版年
2022年 | 1篇 |
2021年 | 2篇 |
2020年 | 2篇 |
2019年 | 3篇 |
2018年 | 2篇 |
2017年 | 6篇 |
2016年 | 10篇 |
2015年 | 4篇 |
2014年 | 5篇 |
2013年 | 18篇 |
2012年 | 86篇 |
2011年 | 113篇 |
2010年 | 18篇 |
2009年 | 7篇 |
2008年 | 74篇 |
2007年 | 56篇 |
2006年 | 36篇 |
2005年 | 48篇 |
2004年 | 37篇 |
2003年 | 51篇 |
2002年 | 47篇 |
2000年 | 4篇 |
1999年 | 7篇 |
1998年 | 5篇 |
1996年 | 2篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1990年 | 2篇 |
1988年 | 3篇 |
1987年 | 4篇 |
1985年 | 3篇 |
1983年 | 3篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1974年 | 2篇 |
1972年 | 2篇 |
1971年 | 2篇 |
1970年 | 1篇 |
1969年 | 2篇 |
1967年 | 2篇 |
1965年 | 6篇 |
1964年 | 2篇 |
1963年 | 1篇 |
1958年 | 1篇 |
排序方式: 共有689条查询结果,搜索用时 15 毫秒
101.
102.
103.
R Sanchis-Ojeda DC Fabrycky JN Winn T Barclay BD Clarke EB Ford JJ Fortney JC Geary MJ Holman AW Howard JM Jenkins D Koch JJ Lissauer GW Marcy F Mullally D Ragozzine SE Seader M Still SE Thompson 《Nature》2012,487(7408):449-453
The Sun's equator and the planets' orbital planes are nearly aligned, which is presumably a consequence of their formation from a single spinning gaseous disk. For exoplanetary systems this well-aligned configuration is not guaranteed: dynamical interactions may tilt planetary orbits, or stars may be misaligned with the protoplanetary disk through chaotic accretion , magnetic interactions or torques from neighbouring stars. Indeed, isolated 'hot Jupiters' are often misaligned and even orbiting retrograde. Here we report an analysis of transits of planets over starspots on the Sun-like star Kepler-30 (ref. 8), and show that the orbits of its three planets are aligned with the stellar equator. Furthermore, the orbits are aligned with one another to within a few degrees. This configuration is similar to that of our Solar System, and contrasts with the isolated hot Jupiters. The orderly alignment seen in the Kepler-30 system suggests that high obliquities are confined to systems that experienced disruptive dynamical interactions. Should this be corroborated by observations of other coplanar multi-planet systems, then star-disk misalignments would be ruled out as the explanation for the high obliquities of hot Jupiters, and dynamical interactions would be implicated as the origin of hot Jupiters. 相似文献
104.
105.
106.
107.
108.
109.
The Amazon basin in transition 总被引:7,自引:0,他引:7
Davidson EA de Araújo AC Artaxo P Balch JK Brown IF C Bustamante MM Coe MT DeFries RS Keller M Longo M Munger JW Schroeder W Soares-Filho BS Souza CM Wofsy SC 《Nature》2012,481(7381):321-328
Agricultural expansion and climate variability have become important agents of disturbance in the Amazon basin. Recent studies have demonstrated considerable resilience of Amazonian forests to moderate annual drought, but they also show that interactions between deforestation, fire and drought potentially lead to losses of carbon storage and changes in regional precipitation patterns and river discharge. Although the basin-wide impacts of land use and drought may not yet surpass the magnitude of natural variability of hydrologic and biogeochemical cycles, there are some signs of a transition to a disturbance-dominated regime. These signs include changing energy and water cycles in the southern and eastern portions of the Amazon basin. 相似文献
110.
Wu X Northcott PA Dubuc A Dupuy AJ Shih DJ Witt H Croul S Bouffet E Fults DW Eberhart CG Garzia L Van Meter T Zagzag D Jabado N Schwartzentruber J Majewski J Scheetz TE Pfister SM Korshunov A Li XN Scherer SW Cho YJ Akagi K MacDonald TJ Koster J McCabe MG Sarver AL Collins VP Weiss WA Largaespada DA Collier LS Taylor MD 《Nature》2012,482(7386):529-533
Medulloblastoma, the most common malignant paediatric brain tumour, arises in the cerebellum and disseminates through the cerebrospinal fluid in the leptomeningeal space to coat the brain and spinal cord. Dissemination, a marker of poor prognosis, is found in up to 40% of children at diagnosis and in most children at the time of recurrence. Affected children therefore are treated with radiation to the entire developing brain and spinal cord, followed by high-dose chemotherapy, with the ensuing deleterious effects on the developing nervous system. The mechanisms of dissemination through the cerebrospinal fluid are poorly studied, and medulloblastoma metastases have been assumed to be biologically similar to the primary tumour. Here we show that in both mouse and human medulloblastoma, the metastases from an individual are extremely similar to each other but are divergent from the matched primary tumour. Clonal genetic events in the metastases can be demonstrated in a restricted subclone of the primary tumour, suggesting that only rare cells within the primary tumour have the ability to metastasize. Failure to account for the bicompartmental nature of metastatic medulloblastoma could be a major barrier to the development of effective targeted therapies. 相似文献