全文获取类型
收费全文 | 331篇 |
免费 | 4篇 |
国内免费 | 1篇 |
专业分类
系统科学 | 2篇 |
教育与普及 | 3篇 |
理论与方法论 | 3篇 |
现状及发展 | 51篇 |
研究方法 | 37篇 |
综合类 | 236篇 |
自然研究 | 4篇 |
出版年
2022年 | 2篇 |
2021年 | 2篇 |
2020年 | 1篇 |
2018年 | 5篇 |
2017年 | 2篇 |
2016年 | 5篇 |
2015年 | 3篇 |
2014年 | 3篇 |
2013年 | 2篇 |
2012年 | 19篇 |
2011年 | 37篇 |
2010年 | 13篇 |
2009年 | 1篇 |
2008年 | 13篇 |
2007年 | 21篇 |
2006年 | 20篇 |
2005年 | 17篇 |
2004年 | 9篇 |
2003年 | 21篇 |
2002年 | 57篇 |
2001年 | 40篇 |
2000年 | 6篇 |
1997年 | 2篇 |
1993年 | 3篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1986年 | 1篇 |
1985年 | 3篇 |
1984年 | 1篇 |
1982年 | 1篇 |
1980年 | 2篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1974年 | 1篇 |
1973年 | 3篇 |
1971年 | 1篇 |
1969年 | 2篇 |
1966年 | 2篇 |
1965年 | 2篇 |
1964年 | 4篇 |
1961年 | 2篇 |
排序方式: 共有336条查询结果,搜索用时 236 毫秒
221.
222.
223.
Luo Sanzhong Zhang Baolian Xian Ming Adam JaÑczuk Xie Wenhua Cheng Jinpei Peng George Wang 《科学通报(英文版)》2001,46(20):1673-1680
Lanthanide triflates are stable in water. It is possible for lanthanides to undergo many organic reactions in environmentally
friendly solvents. This makes lanthanides very promising in the field of green chemistry. This review describes the recent
development of the lanthanidecatalyzed organic reactions in protic solvents. Those reactions include Diels-Alder, Aldol, Allylation,
acetalization, pericyclization, radical reactions as well as some newlydeveloped lanthnidesbased catalysts. 相似文献
224.
Megan Chircop Chandra S. Malladi Audrey T. Lian Scott L. Page Michael Zavortink Christopher P. Gordon Adam McCluskey Phillip J. Robinson 《Cellular and molecular life sciences : CMLS》2010,67(21):3725-3737
Successful completion of cytokinesis requires the spatio-temporal regulation of protein phosphorylation and the coordinated
activity of protein kinases and phosphatases. Many mitotic protein kinases are well characterized while mitotic phosphatases
are largely unknown. Here, we show that the Ca2+- and calmodulin-dependent phosphatase, calcineurin (CaN), is required for cytokinesis in mammalian cells, functioning specifically
at the abscission stage. CaN inhibitors induce multinucleation in HeLa cells and prolong the time cells spend connected via
an extended intracellular bridge. Upon Ca2+ influx during cytokinesis, CaN is activated, targeting a set of proteins for dephosphorylation, including dynamin II (dynII).
At the intracellular bridge, phospho-dynII and CaN are co-localized to dual flanking midbody rings (FMRs) that reside on either
side of the central midbody ring. CaN activity and disassembly of the FMRs coincide with abscission. Thus, CaN activity at
the midbody plays a key role in regulating the completion of cytokinesis in mammalian cells. 相似文献
225.
Zhiliang Ma Adam Cardinal-Stakenas Youngser Park Michael W. Trosset Carey E. Priebe 《Journal of Classification》2010,27(3):307-321
We consider the problem of combining multiple dissimilarity representations via the Cartesian product of their embeddings. For concreteness, we choose the inferential task at hand to be classification. The high dimensionality of this Cartesian product space implies the necessity of dimensionality reduction before training a classifier. We propose a supervised dimensionality reduction method, which utilizes the class label information, to help achieve a favorable combination. The simulation and real data results show that our approach can improve classification accuracy compared to the alternatives of principal components analysis and no dimensionality reduction at all. 相似文献
226.
Adam Morton 《Studies in history and philosophy of science》2006,37(1):114-117
227.
The nuclear envelope is a selective barrier against the movement of macromolecules between the nucleus and cytoplasm. Nuclear proteins larger than relative molecular mass 20,000-40,000 are probably actively transported across the envelope through the nuclear pore complex and are directed by specific nuclear location sequences (NLS) in the proteins. NLS mediate the nuclear import of isolated nuclear proteins after microinjection into whole cells and the nuclear accumulation of chimaeric proteins or of non-nuclear proteins conjugated to synthetic peptides. The best-characterized NLS is the simian virus 40 large T-antigen sequence. We have identified two proteins of rat liver by chemical cross-linking that interact with a synthetic peptide containing this sequence: this interaction is specific for a functional NLS, is saturable, and high affinity. The binding proteins are present in a post-mitochondrial supernatant, in nuclei and in a nuclear envelope fraction, which is consistent with a role in the transport of nuclear proteins from the cytoplasm to the nucleus. 相似文献
228.
Summary The ring-E opened dihydro derivatives of tomatidine and soladulcidine give the corresponding N-chloroamines with N-chlorosuccinimide. Treatment of these compounds with sodium methoxide yields the spiroaminoketal alkaloids, tomatidine and soladulcidine respectively, in high yields, probably via instable C=N-unsaturated intermediates which undergo spontaneous stereospecific cyclisation.
Solanum-Alkaloide. XIII. Mitteilung. XII. Mitteilung:K. Schreiber undH. Ripperger, Exper.16, 536 (1960). 相似文献
Solanum-Alkaloide. XIII. Mitteilung. XII. Mitteilung:K. Schreiber undH. Ripperger, Exper.16, 536 (1960). 相似文献
229.
Chellaganesh Duraipandi Adam Khan M Winowlin Jappes J.T. Nouby M.Ghazaly Peter Madindwa Mashinini 《矿物冶金与材料学报》2021,28(7):1186-1193
Thermal barrier coatings are widely used as surface modifications to enhance the surface properties of the material and protect from surface degradations such as erosion and corrosion. Ceramic-based coatings are highly recommended to increase wear resistance in the industrial sector. In this paper, an alumina–titania ceramic powder was deposited on an aluminum alloy using an atmospheric plasma spray technique. Experimental investigations were performed to study the behavior and erosion rate of the material. Solid particle erosion studies were performed by varying the particle velocity and particle flow rate. The angle impingement and stand-off distance were constant for comparison. The base metal has a clinging effect and the mass change was negative at a maximum particle flow rate of 4 g·min?1. Under the same process conditions, the coated sample had a reduced lifetime and reached a maximum erosion rate of 0.052 (Δg/g). The solid particle erosion studies confirmed that the base metal aluminum alloy had severe surface damage with erodent reinforcement when compared to the coated samples. The influence of the particle velocity, particle flow rate, and input process parameters were also identified. 相似文献
230.
Kappelman J Rasmussen DT Sanders WJ Feseha M Bown T Copeland P Crabaugh J Fleagle J Glantz M Gordon A Jacobs B Maga M Muldoon K Pan A Pyne L Richmond B Ryan T Seiffert ER Sen S Todd L Wiemann MC Winkler A 《Nature》2003,426(6966):549-552
Afro-Arabian mammalian communities underwent a marked transition near the Oligocene/Miocene boundary at approximately 24 million years (Myr) ago. Although it is well documented that the endemic paenungulate taxa were replaced by migrants from the Northern Hemisphere, the timing and evolutionary dynamics of this transition have long been a mystery because faunas from about 32 to 24 Myr ago are largely unknown. Here we report a late Oligocene fossil assemblage from Ethiopia, which constrains the migration to postdate 27 Myr ago, and yields new insight into the indigenous faunal dynamics that preceded this event. The fauna is composed of large paenungulate herbivores and reveals not only which earlier taxa persisted into the late Oligocene epoch but also demonstrates that one group, the Proboscidea, underwent a marked diversification. When Eurasian immigrants entered Afro-Arabia, a pattern of winners and losers among the endemics emerged: less diverse taxa such as arsinoitheres became extinct, moderately species-rich groups such as hyracoids continued into the Miocene with reduced diversity, whereas the proboscideans successfully carried their adaptive radiation out of Afro-Arabia and across the world. 相似文献