全文获取类型
收费全文 | 1272篇 |
免费 | 77篇 |
国内免费 | 1篇 |
专业分类
化学 | 1100篇 |
晶体学 | 1篇 |
力学 | 8篇 |
数学 | 107篇 |
物理学 | 134篇 |
出版年
2023年 | 16篇 |
2022年 | 35篇 |
2021年 | 48篇 |
2020年 | 29篇 |
2019年 | 39篇 |
2018年 | 24篇 |
2017年 | 27篇 |
2016年 | 56篇 |
2015年 | 53篇 |
2014年 | 57篇 |
2013年 | 91篇 |
2012年 | 73篇 |
2011年 | 90篇 |
2010年 | 50篇 |
2009年 | 50篇 |
2008年 | 73篇 |
2007年 | 81篇 |
2006年 | 63篇 |
2005年 | 57篇 |
2004年 | 52篇 |
2003年 | 40篇 |
2002年 | 31篇 |
2001年 | 14篇 |
2000年 | 10篇 |
1999年 | 11篇 |
1998年 | 15篇 |
1997年 | 7篇 |
1996年 | 15篇 |
1995年 | 10篇 |
1994年 | 11篇 |
1993年 | 11篇 |
1992年 | 6篇 |
1991年 | 6篇 |
1990年 | 9篇 |
1988年 | 4篇 |
1987年 | 9篇 |
1986年 | 7篇 |
1985年 | 5篇 |
1984年 | 3篇 |
1982年 | 8篇 |
1981年 | 6篇 |
1978年 | 7篇 |
1977年 | 3篇 |
1921年 | 3篇 |
1919年 | 4篇 |
1918年 | 2篇 |
1917年 | 2篇 |
1916年 | 2篇 |
1914年 | 2篇 |
1913年 | 2篇 |
排序方式: 共有1350条查询结果,搜索用时 15 毫秒
131.
132.
Ayhan S. Demir Thomas Dünnwald Hans Iding Martina Pohl Michael Müller 《Tetrahedron: Asymmetry》1999,10(24):162-4774
Aromatic aldehydes are converted into benzoins by benzoylformate decarboxylase catalyzed C–C bond formation. The reaction affords (R)-benzoins with high enantiomeric excess and in good chemical yields. A broad range of aromatic aldehydes can be used as substrates in aqueous buffer or buffer/DMSO-solutions. 相似文献
133.
134.
Martin Jesberger Leonie Barner Martina H. Stenzel Eva Malmstrm Thomas P. Davis Christopher Barner‐Kowollik 《Journal of polymer science. Part A, Polymer chemistry》2003,41(23):3847-3861
Polydisperse hyperbranched polyesters were modified for use as novel multifunctional reversible addition–fragmentation chain‐transfer (RAFT) agents. The polyester‐core‐based RAFT agents were subsequently employed to synthesize star polymers of n‐butyl acrylate and styrene with low polydispersity (polydispersity index < 1.3) in a living free‐radical process. Although the polyester‐core‐based RAFT agent mediated polymerization of n‐butyl acrylate displayed a linear evolution of the number‐average molecular weight (Mn) up to high monomer conversions (>70%) and molecular weights [Mn > 140,000 g mol?1, linear poly(methyl methacrylate) equivalents)], the corresponding styrene‐based system reached a maximum molecular weight at low conversions (≈30%, Mn = 45,500 g mol?1, linear polystyrene equivalents). The resulting star polymers were subsequently used as platforms for the preparation of star block copolymers of styrene and n‐butyl acrylate with a polyester core with low polydispersities (polydispersity index < 1.25). The generated polystyrene‐based star polymers were successfully cast into highly regular honeycomb‐structured microarrays. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3847–3861, 2003 相似文献
135.
T.L. Uyen Nguyen Mohammad H. Pourgholami Thomas P. Davis Martina H. Stenzel 《European Polymer Journal》2007,43(5):1754-1767
It has been demonstrated that 1,25 dihydroxyvitamin D3 (1,25(OH)2VD3) can inhibit the proliferation of cancer cells, including colorectal and hepatocellular cells which are mainly responsible for liver cancer. However, the use of 1,25(OH)2VD3 is hampered due to the development of hypercalcaemia. We hereby report a promising technique in liver cancer treatment by utilizing crosslinked microspheres prepared by polymerization as a carrier to control the release of 1,25(OH)2VD3 or hydrophobic drug in general at targeted sites over a long period. Microspheres in the size range of 35 μm were prepared and the drug was loaded to these poly(vinyl neodecanoate-crosslinked-ethyleneglycol dimethacrylate) microspheres after polymerization. The release study has shown that up to 1% of the drug was released after 40 days. MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay and direct contact cytotoxicity assay using HT-20 and L929 confirm the non-toxicity of these spheres. 相似文献
136.
Martina Astrová Ladislav Kurc Libor erveny 《Reaction Kinetics and Catalysis Letters》2006,89(2):311-318
Summary Condensation of ephedrine with benzaldehyde, an acid catalyzed reversible reaction, producing 3,4-dimethyl-2,5-diphenyl-1,3-oxazolidine,
was studied. If the starting reaction mixture contained acetic acid, it quantitatively reacted with ephedrine and produced
a salt functioning as an acid catalyst. On the contrary, ephedrine hydrochloride had no catalytic effect. 相似文献
137.
Martina Mazzoni Lorenzo Franco Alberta Ferrarini Carlo Corvaja Giovanni Zordan Gianfranco Scorrano Michele Maggini 《Liquid crystals》2002,29(2):203-208
A nitroxide [60]fullerene adduct containing a pyrrolidine-1-oxyl group has been synthesized. Its orientational order in the nematic phase of the liquid crystal solvent 4,4'-azoxyanisole (PAA) has been measured from the variation of the EPR spectral parameters on passing from the isotropic to the nematic phase. Highly resolved EPR lines allow for precise evaluation of the shifts of the g , a N and a H values. Since the g and the hyperfine tensors are known, the order matrix could be obtained. This is compared with the one calculated with a theoretical model based on short range solute-solvent interactions, which predicts a considerable degree of orientation of the molecular axes, despite the almost spherical shape of the molecule. The agreement with experimental findings is quite good and it is further improved if a bent structure of the pyrrolidine ring is taken into account. 相似文献
138.
The behavior of copper precipitation in cast multicrystalline silicon (mc-Si) annealed at different temperatures under air cooling (30 K/s) or slow cooling (0.3 K/s) was investigated by scanning infrared microscopy (SIRM). Comparing to Czochralski-grown silicon (Cz-Si), copper precipitated more easily in mc-Si, and the lowest temperature of copper precipitation in mc-Si was about 700 °C, lower than that in Cz-Si. It was also observed that copper preferably precipitated on grain boundaries so that near the grain boundaries the denuded zone formed. The results indicate that the defects including dislocations, grain boundaries and microdefects, as the heteronucleation sites, enhanced copper precipitation. Moreover, cooling rates had a great influence on the copper precipitation, especially at lower annealing temperatures. Generally air cooling led to the formation of high density of copper-precipitate colonies. 相似文献
139.
Polymersomes Prepared from Thermoresponsive Fluorescent Protein–Polymer Bioconjugates: Capture of and Report on Drug and Protein Payloads 下载免费PDF全文
Chin Ken Wong Alistair J. Laos Dr. Alexander H. Soeriyadi Prof. Jörg Wiedenmann Prof. Paul M. G. Curmi Prof. J. Justin Gooding Dr. Christopher P. Marquis Prof. Martina H. Stenzel Assoc. Prof. Pall Thordarson 《Angewandte Chemie (International ed. in English)》2015,54(18):5317-5322
Polymersomes provide a good platform for targeted drug delivery and the creation of complex (bio)catalytically active systems for research in synthetic biology. To realize these applications requires both spatial control over the encapsulation components in these polymersomes and a means to report where the components are in the polymersomes. To address these twin challenges, we synthesized the protein–polymer bioconjugate PNIPAM‐b‐amilFP497 composed of thermoresponsive poly(N‐isopropylacrylamide) (PNIPAM) and a green‐fluorescent protein variant (amilFP497). Above 37 °C, this bioconjugate forms polymersomes that can (co‐)encapsulate the fluorescent drug doxorubicin and the fluorescent light‐harvesting protein phycoerythrin 545 (PE545). Using fluorescence lifetime imaging microscopy and Förster resonance energy transfer (FLIM‐FRET), we can distinguish the co‐encapsulated PE545 protein inside the polymersome membrane while doxorubicin is found both in the polymersome core and membrane. 相似文献
140.
Arrival time distributions of product ions reveal isomeric ratio of deprotonated molecules in ion mobility–mass spectrometry of hyaluronan‐derived oligosaccharides 下载免费PDF全文
Martina Hermannová Andreea‐Maria Iordache Kristína Slováková Vladimír Havlíček Helena Pelantová Karel Lemr 《Journal of mass spectrometry : JMS》2015,50(6):854-863
Hyaluronic acid is a naturally occurring linear polysaccharide with substantial medical potential. In this work, discrimination of tyramine‐based hyaluronan derivatives was accessed by ion mobility–mass spectrometry of deprotonated molecules and nuclear magnetic resonance spectroscopy. As the product ion mass spectra did not allow for direct isomer discrimination in mixture, the reductive labeling of oligosaccharides as well as stable isotope labeling was performed. The ion mobility separation of parent ions together with the characteristic fragmentation for reduced isomers providing unique product ions allowed us to identify isomers present in a mixture and determine their mutual isomeric ratio. The determination used simple recalculation of arrival time distribution areas of unique ions to areas of deprotonated molecules. Mass spectrometry data were confirmed by nuclear magnetic resonance spectroscopy. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献