全文获取类型
收费全文 | 250篇 |
免费 | 7篇 |
国内免费 | 2篇 |
专业分类
系统科学 | 3篇 |
理论与方法论 | 4篇 |
现状及发展 | 78篇 |
研究方法 | 47篇 |
综合类 | 126篇 |
自然研究 | 1篇 |
出版年
2020年 | 1篇 |
2019年 | 4篇 |
2018年 | 1篇 |
2017年 | 3篇 |
2016年 | 6篇 |
2015年 | 6篇 |
2014年 | 4篇 |
2013年 | 4篇 |
2012年 | 17篇 |
2011年 | 26篇 |
2010年 | 5篇 |
2009年 | 2篇 |
2008年 | 13篇 |
2007年 | 11篇 |
2006年 | 16篇 |
2005年 | 26篇 |
2004年 | 13篇 |
2003年 | 20篇 |
2002年 | 24篇 |
2001年 | 2篇 |
2000年 | 1篇 |
1999年 | 1篇 |
1998年 | 1篇 |
1997年 | 4篇 |
1996年 | 2篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1992年 | 2篇 |
1991年 | 2篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1984年 | 3篇 |
1983年 | 4篇 |
1982年 | 4篇 |
1980年 | 2篇 |
1977年 | 3篇 |
1974年 | 1篇 |
1972年 | 4篇 |
1970年 | 1篇 |
1957年 | 1篇 |
1954年 | 1篇 |
1946年 | 5篇 |
1945年 | 2篇 |
排序方式: 共有259条查询结果,搜索用时 687 毫秒
121.
研究了由平均直径为210μm的玻璃球在硅油中加直流电场后形成的单链的导电行为,主要研究了链的轴向应变对其导电性质的影响。 相似文献
122.
Mutations in DNAH5 cause primary ciliary dyskinesia and randomization of left-right asymmetry. 总被引:19,自引:0,他引:19
Heike Olbrich Karsten H?ffner Andreas Kispert Alexander V?lkel Andreas Volz Gürsel Sasmaz Richard Reinhardt Steffen Hennig Hans Lehrach Nikolaus Konietzko Maimoona Zariwala Peadar G Noone Michael Knowles Hannah M Mitchison Maggie Meeks Eddie M K Chung Friedhelm Hildebrandt Ralf Sudbrak Heymut Omran 《Nature genetics》2002,30(2):143-144
123.
Large scale optimization problems can only be solved in an efficient way, if their special structure is taken as the basis of algorithm design. In this paper we consider a very broad class of large — scale problems with special structure, namely tree structured problems. We show how the exploitation of the structure leads to efficient decomposition algorithms and how it may be implemented in a parallel environment. 相似文献
124.
125.
126.
Hans Niels Jahnke 《Archive for History of Exact Sciences》1987,37(2):101-182
Ohne Zusammenfassung
Vorgelegt von
C. J. Scriba 相似文献
127.
Human ES-cell-derived cardiomyocytes electrically couple and suppress arrhythmias in injured hearts 总被引:1,自引:0,他引:1
Y Shiba S Fernandes WZ Zhu D Filice V Muskheli J Kim NJ Palpant J Gantz KW Moyes H Reinecke B Van Biber T Dardas JL Mignone A Izawa R Hanna M Viswanathan JD Gold MI Kotlikoff N Sarvazyan MW Kay CE Murry MA Laflamme 《Nature》2012,489(7415):322-325
Transplantation studies in mice and rats have shown that human embryonic-stem-cell-derived cardiomyocytes (hESC-CMs) can improve the function of infarcted hearts, but two critical issues related to their electrophysiological behaviour in vivo remain unresolved. First, the risk of arrhythmias following hESC-CM transplantation in injured hearts has not been determined. Second, the electromechanical integration of hESC-CMs in injured hearts has not been demonstrated, so it is unclear whether these cells improve contractile function directly through addition of new force-generating units. Here we use a guinea-pig model to show that hESC-CM grafts in injured hearts protect against arrhythmias and can contract synchronously with host muscle. Injured hearts with hESC-CM grafts show improved mechanical function and a significantly reduced incidence of both spontaneous and induced ventricular tachycardia. To assess the activity of hESC-CM grafts in vivo, we transplanted hESC-CMs expressing the genetically encoded calcium sensor, GCaMP3 (refs 4, 5). By correlating the GCaMP3 fluorescent signal with the host ECG, we found that grafts in uninjured hearts have consistent 1:1 host–graft coupling. Grafts in injured hearts are more heterogeneous and typically include both coupled and uncoupled regions. Thus, human myocardial grafts meet physiological criteria for true heart regeneration, providing support for the continued development of hESC-based cardiac therapies for both mechanical and electrical repair. 相似文献
128.
Beck PG Montalban J Kallinger T De Ridder J Aerts C García RA Hekker S Dupret MA Mosser B Eggenberger P Stello D Elsworth Y Frandsen S Carrier F Hillen M Gruberbauer M Christensen-Dalsgaard J Miglio A Valentini M Bedding TR Kjeldsen H Girouard FR Hall JR Ibrahim KA 《Nature》2012,481(7379):55-57
When the core hydrogen is exhausted during stellar evolution, the central region of a star contracts and the outer envelope expands and cools, giving rise to a red giant. Convection takes place over much of the star's radius. Conservation of angular momentum requires that the cores of these stars rotate faster than their envelopes; indirect evidence supports this. Information about the angular-momentum distribution is inaccessible to direct observations, but it can be extracted from the effect of rotation on oscillation modes that probe the stellar interior. Here we report an increasing rotation rate from the surface of the star to the stellar core in the interiors of red giants, obtained using the rotational frequency splitting of recently detected 'mixed modes'. By comparison with theoretical stellar models, we conclude that the core must rotate at least ten times faster than the surface. This observational result confirms the theoretical prediction of a steep gradient in the rotation profile towards the deep stellar interior. 相似文献
129.
130.
ter Steege H Pitman NC Phillips OL Chave J Sabatier D Duque A Molino JF Prévost MF Spichiger R Castellanos H von Hildebrand P Vásquez R 《Nature》2006,443(7110):444-447
The world's greatest terrestrial stores of biodiversity and carbon are found in the forests of northern South America, where large-scale biogeographic patterns and processes have recently begun to be described. Seven of the nine countries with territory in the Amazon basin and the Guiana shield have carried out large-scale forest inventories, but such massive data sets have been little exploited by tropical plant ecologists. Although forest inventories often lack the species-level identifications favoured by tropical plant ecologists, their consistency of measurement and vast spatial coverage make them ideally suited for numerical analyses at large scales, and a valuable resource to describe the still poorly understood spatial variation of biomass, diversity, community composition and forest functioning across the South American tropics. Here we show, by using the seven forest inventories complemented with trait and inventory data collected elsewhere, two dominant gradients in tree composition and function across the Amazon, one paralleling a major gradient in soil fertility and the other paralleling a gradient in dry season length. The data set also indicates that the dominance of Fabaceae in the Guiana shield is not necessarily the result of root adaptations to poor soils (nodulation or ectomycorrhizal associations) but perhaps also the result of their remarkably high seed mass there as a potential adaptation to low rates of disturbance. 相似文献