全文获取类型
收费全文 | 854篇 |
免费 | 111篇 |
专业分类
化学 | 847篇 |
晶体学 | 2篇 |
力学 | 7篇 |
数学 | 39篇 |
物理学 | 70篇 |
出版年
2024年 | 2篇 |
2023年 | 14篇 |
2022年 | 14篇 |
2021年 | 29篇 |
2020年 | 38篇 |
2019年 | 47篇 |
2018年 | 31篇 |
2017年 | 13篇 |
2016年 | 53篇 |
2015年 | 66篇 |
2014年 | 58篇 |
2013年 | 61篇 |
2012年 | 91篇 |
2011年 | 83篇 |
2010年 | 45篇 |
2009年 | 33篇 |
2008年 | 50篇 |
2007年 | 40篇 |
2006年 | 40篇 |
2005年 | 28篇 |
2004年 | 15篇 |
2003年 | 13篇 |
2002年 | 11篇 |
2001年 | 7篇 |
2000年 | 14篇 |
1999年 | 8篇 |
1998年 | 6篇 |
1997年 | 5篇 |
1996年 | 5篇 |
1995年 | 7篇 |
1994年 | 3篇 |
1993年 | 6篇 |
1992年 | 1篇 |
1991年 | 4篇 |
1990年 | 5篇 |
1988年 | 2篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1973年 | 1篇 |
1969年 | 1篇 |
1959年 | 2篇 |
1958年 | 1篇 |
1957年 | 1篇 |
1943年 | 1篇 |
1937年 | 2篇 |
1936年 | 2篇 |
1925年 | 1篇 |
排序方式: 共有965条查询结果,搜索用时 23 毫秒
91.
Holger Braunschweig Manuela Gross Katharina Kraft 《Journal of organometallic chemistry》2011,696(2):568-571
The paramagnetic ansa-niobocene [(Me2Si)2(η5-C5H4)2NbCl2] (1) was obtained from the reaction of Li2[(Me2Si)2(C5H4)2] with [NbCl4(thf)2]. Further treatment with Li[AlH4] yielded [(Me2Si)2(η5-C5H4)2NbH3] (3), which is prone to decomposition within a few days at room temperature both in solution and in the solid-state, thus affording primarily an insoluble black material. However, after heating or irradiation of a solution of 3 small quantities of the dimeric niobium hydride species, [(Me2Si)2{μ-(η1:η5-C5H3)}(η5-C5H4)NbH]2 (4), were isolated and characterized by X-ray diffraction. 相似文献
92.
Davenport JR Musa OM Paterson MJ Piepenbrock MO Fucke K Steed JW 《Chemical communications (Cambridge, England)》2011,47(35):9891-9893
A dimeric model compound gives structural insight into the mode of interaction of low dosage hydrate inhibitors with water. 相似文献
93.
94.
95.
96.
Georgios Papazoglou Jorge Sierra Katharina Homberger Armin Guggisberg Wolf-Dietrich Woggon Manfred Hesse 《Helvetica chimica acta》1991,74(3):565-571
Aphelandrine ( 1 ) is shown to be biosynthesized in the root cells of Aphelandra tetragona (VAHL ) NEES from labelled putrescine ( 4 ), spermidine ( 5 ), and cinnamic acid ( 3 ). Whether spermine ( 6 ) and the (p-hydroxycinnamoyl)spermidine 8 are precursors of 1 is uncertain, since the latter is hydrolysed to a large extent before incorporation, and the former is metabolized to 4 and 5 . Methionine ( 7 ) is the source of the 3-aminopropyl unit of 5 and 6 . 相似文献
97.
Andreas Dress Katharina T. Huber Alice Lesser Vincent Moulton 《Annals of Combinatorics》2006,10(1):63-76
One of the main problems in phylogenetics is to find good approximations of metrics by weighted trees. As an aid to solving this problem, it could be tempting to consider
optimal realizations of metrics—the guiding principle being that, the (necessarily unique) optimal realization of a tree metric is the weighted tree that realizes this metric. And, although optimal realizations of arbitrary metrics are, in general,
not trees, but rather weighted networks, one could still hope to obtain a phylogenetically informative representation of a
given metric, maybe even more informative than the best approximating tree. However, optimal realizations are not only difficult
to compute, they may also be non-unique. Here we focus on one possible way out of this dilemma: hereditarily optimal realizations. These are essentially unique, and can be described in a rather explicit way. In this paper, we recall what a hereditarily
optimal realization of a metric is and how it is related to the 1-skeleton of the tight span of that metric, and we investigate under what conditions it coincides with this 1-skeleton. As a consequence, we will show
that hereditarily optimal realizations for consistent metrics, a large class of phylogentically relevant metrics, can be computed in a straight-forward fashion.
Received August 26, 2004 相似文献
98.
99.
For the first time in Ag coordination chemistry, two supramolecular isomers, a ring and a helix, are isolated from the same mother liquor as a result of concentration effects. 相似文献
100.
Selle H Lamerz J Buerger K Dessauer A Hager K Hampel H Karl J Kellmann M Lannfelt L Louhija J Riepe M Rollinger W Tumani H Schrader M Zucht HD 《Combinatorial chemistry & high throughput screening》2005,8(8):801-806
The objective of this work was the application of peptidomics technologies for the detection and identification of reliable and robust biomarkers for Alzheimer's disease (AD) contributing to facilitate and further improve the diagnosis of AD. Using a new method for the comprehensive and comparative profiling of peptides, the differential peptide display (DPD), 312 cerebrospinal fluid (CSF) samples from AD patients, cognitively unimpaired subjects and from patients suffering from other primary dementia disorders were analysed as four independent analytical sets. By combination with a cross validation procedure, candidates were selected from a total of more than 6,000 different peptide signals based on their discriminating power. Twelve candidates were identified using mass-spectrometric techniques as fragments of the possibly neuroprotective neuroendocrine protein VGF and another one as the complement factor C3 descendent C3f. The combination of peptide profiling and cross validation resulted in the detection of novel potential biomarkers with remarkable robustness and a close relation to AD pathophysiology. 相似文献