全文获取类型
收费全文 | 386篇 |
免费 | 20篇 |
国内免费 | 12篇 |
专业分类
化学 | 330篇 |
晶体学 | 2篇 |
力学 | 7篇 |
数学 | 33篇 |
物理学 | 46篇 |
出版年
2023年 | 5篇 |
2022年 | 6篇 |
2021年 | 9篇 |
2020年 | 19篇 |
2019年 | 9篇 |
2018年 | 2篇 |
2017年 | 3篇 |
2016年 | 13篇 |
2015年 | 10篇 |
2014年 | 7篇 |
2013年 | 18篇 |
2012年 | 36篇 |
2011年 | 51篇 |
2010年 | 21篇 |
2009年 | 20篇 |
2008年 | 25篇 |
2007年 | 16篇 |
2006年 | 19篇 |
2005年 | 19篇 |
2004年 | 23篇 |
2003年 | 27篇 |
2002年 | 15篇 |
2001年 | 2篇 |
1999年 | 3篇 |
1998年 | 2篇 |
1997年 | 7篇 |
1996年 | 3篇 |
1995年 | 4篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1992年 | 2篇 |
1990年 | 1篇 |
1986年 | 1篇 |
1984年 | 6篇 |
1983年 | 1篇 |
1982年 | 3篇 |
1979年 | 1篇 |
1977年 | 2篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1972年 | 1篇 |
排序方式: 共有418条查询结果,搜索用时 0 毫秒
411.
Sanctolide A (1), a 14-membered polyketide-nonribosomal peptide (PK-NRP) hybrid macrolide, was isolated from the cultured cyanobacterium Oscillatoria sancta (SAG 74.79). The planar structure was determined using various spectroscopic techniques including HRESIMS, and 1D and 2D NMR analyses. The relative configuration was assigned by J-based configurational analysis in combination with NOE correlations. The absolute configuration was determined by Mosher ester and enantioselective HPLC analyses. The structure of sanctolide A (1) features a rare N-methyl enamide and a 2-hydroxyisovaleric acid, which are incorporated to form a 14-membered macrolide ring structure, comprising a new type of cyanobacterial macrolides derived from a PKS-NRPS hybrid biosynthetic pathway. 相似文献
412.
413.
Hedin-Dahlström J Rosengren-Holmberg JP Legrand S Wikman S Nicholls IA 《The Journal of organic chemistry》2006,71(13):4845-4853
[structures: see text] A class II aldolase-mimicking synthetic polymer was prepared by the molecular imprinting of a complex of cobalt (II) ion and either (1S,3S,4S)-3-benzoyl-1,7,7-trimethylbicyclo[2.2.1]heptan-2-one (4a) or (1R,3R,4R)-3-benzoyl-1,7,7-trimethylbicyclo[2.2.1]heptan-2-one (4b) in a 4-vinylpyridine-styrene-divinylbenzene copolymer. Evidence for the formation of interactions between the functional monomer and the template was obtained from NMR and VIS titration studies. The polymers imprinted with the template demonstrated enantioselective recognition of the corresponding template structure, and induced a 55-fold enhancement of the rate of reaction of camphor (1) with benzaldehyde (2), relative to the solution reactions, and were also compared to reactions with a series of reference polymers. Substrate chirality was observed to influence reaction rate, and the reaction could be competitively inhibited by dibenzoylmethane (6). Collectively, the results presented provide the first example of the use of enantioselective molecularly imprinted polymers for the catalysis of carbon-carbon bond formation. 相似文献
414.
We present detailed studies of the relationship between ionic conductivity and segmental relaxation in polymer electrolytes. The analysis shows that the ionic conductivity can be decoupled from segmental dynamics and the strength of the decoupling correlates with the fragility but not with the glass transition temperature. These results call for a revision of the current picture of ionic transport in polymer electrolytes. We relate the observed decoupling phenomenon to frustration in packing of rigid polymers, where the loose local structure is also responsible for the increase in their fragility. 相似文献
415.
Lía S. Valencia-Chan Dafn Moreno-Lorenzana Jimmy Josu Ceballos-Cruz Sergio R. Peraza-Snchez Antonieta Chvez-Gonzlez Rosa E. Moo-Puc 《Molecules (Basel, Switzerland)》2022,27(17)
Current antineoplastic agents present multiple disadvantages, driving an ongoing search for new and better compounds. Four lupane-type triterpenes, 3α,24-dihydroxylup-20(29)-en-28-oic acid (1), 3α,23-dihydroxy-30-oxo-lup-20(29)-en-28-oic acid (2), 3α,23-O-isopropylidenyl-3α,23-dihydroxylup-20(29)-en-28-oic acid (3), and 3α,23-dihydroxylup-20(29)-en-28-oic acid (4), previously isolated from Phoradendron wattii, were evaluated on two cell lines of chronic (K562) and acute (HL60) myeloid leukemia. Compounds 1, 2, and 4 decreased cell viability and inhibit proliferation, mainly in K562, and exhibited an apoptotic effect from 24 h of treatment. Of particular interest is compound 2, which caused arrest in active phases (G2/M) of the cell cycle, as shown by in silico study of the CDK1/Cyclin B/Csk2 complex by molecular docking. This compound [3α,23-dihydroxy-30-oxo-lup-20(29)-en-28-oic acid] s a promising candidate for incorporation into cancer treatments and deserves further study. 相似文献
416.
Lía S. Valencia-Chan Neptis Estrada-Alfaro Jimmy Josu Ceballos-Cruz Luis W. Torres-Tapia Sergio R. Peraza-Snchez Rosa E. Moo-Puc 《Molecules (Basel, Switzerland)》2022,27(23)
Leukemia is one of the most frequent types of cancer. No effective treatment currently exists, driving a search for new compounds. Simple structural modifications were made to novel triterpenes isolated from Phoradendron wattii. Of the three resulting derivatives, 3α-methoxy-24-hydroxylup-20(29)-en-28-oic acid (T1m) caused a decrease in the median inhibitory concentration (IC50) on the K562 cell line. Its mode of action was apparently apoptosis, ROS generation, and loss of mitochondrial membrane potential (MMP). Molecular docking analysis showed T1m to produce lower binding energies than its precursor for the Bcl-2 and EGFR proteins. Small, simple, and viable modifications to triterpenes can improve their activity against leukemia cell lines. T1m is a potentially promising element for future research. Clarifying the targets in its mode of action will improve its applicability. 相似文献
417.
Jimmy W. Mays David Uhrig Samuel Gido Yuqing Zhu Roland Weidisch Hermis Iatrou Nikos Hadjichristidis Kunlun Hong Frederick Beyer Ralf Lach Matthias Buschnakowski 《Macromolecular Symposia》2004,215(1):111-126
Multigraft copolymers with polyisoprene backbones and polystyrene branches, having multiple regularly spaced branch points, were synthesized by anionic polymerization high vacuum techniques and controlled chlorosilane linking chemistry. The functionality of the branch points (1, 2 and 4) can be controlled, through the choice of chlorosilane linking agent. The morphologies of the various graft copolymers were investigated by transmission electron microscopy and X-ray scattering. It was concluded that the morphology of these complex architectures is governed by the behavior of the corresponding miktoarm star copolymer associated with each branch point (constituting block copolymer), which follows Milner's theoretical treatment for miktoarm stars. By comparing samples having the same molecular weight backbone and branches but different number of branches it was found that the extent of long range order decreases with increasing number of branch points. The stress-strain properties in tension were investigated for some of these multigraft copolymers. For certain compositions thermoplastic elastomer (TPE) behavior was observed, and in many instances the elongation at break was much higher (2-3X) than that of conventional triblock TPEs. 相似文献
418.
Yan Wang Prof. Yuanxing Fang Yankun Wang Haisu Wu Prof. Masakazu Anpo Prof. Jimmy C. Yu Prof. Xinchen Wang 《Angewandte Chemie (International ed. in English)》2023,62(33):e202307236
Earth's primordial atmosphere was rich in ammonia and methane. To understand the evolution of the atmosphere, these two gases were used to make photoredox-active nitrogen-doped carbon (NDC). Photocatalysts such as NDC might play an important role in the development of geological and atmospheric chemistry during the Archean era. This study describes the synthesis of NDC directly from NH3 and CH4 gases. The photocatalyst product can be used to selectively synthesize imines by photo-oxidization of amines, producing H2O2 simultaneously in the photoreduction reaction. Our findings shed light on the chemical evolution of the Earth. 相似文献