全文获取类型
收费全文 | 1027篇 |
免费 | 27篇 |
国内免费 | 1篇 |
专业分类
化学 | 791篇 |
晶体学 | 18篇 |
力学 | 18篇 |
数学 | 93篇 |
物理学 | 135篇 |
出版年
2023年 | 5篇 |
2021年 | 5篇 |
2020年 | 10篇 |
2019年 | 10篇 |
2018年 | 10篇 |
2016年 | 14篇 |
2015年 | 13篇 |
2014年 | 21篇 |
2013年 | 42篇 |
2012年 | 50篇 |
2011年 | 66篇 |
2010年 | 33篇 |
2009年 | 38篇 |
2008年 | 65篇 |
2007年 | 75篇 |
2006年 | 76篇 |
2005年 | 58篇 |
2004年 | 64篇 |
2003年 | 40篇 |
2002年 | 60篇 |
2001年 | 11篇 |
2000年 | 6篇 |
1999年 | 10篇 |
1998年 | 11篇 |
1997年 | 16篇 |
1996年 | 21篇 |
1995年 | 19篇 |
1994年 | 13篇 |
1991年 | 4篇 |
1990年 | 5篇 |
1989年 | 6篇 |
1988年 | 3篇 |
1987年 | 9篇 |
1985年 | 8篇 |
1984年 | 14篇 |
1983年 | 3篇 |
1982年 | 20篇 |
1981年 | 12篇 |
1980年 | 8篇 |
1979年 | 11篇 |
1978年 | 10篇 |
1977年 | 7篇 |
1976年 | 8篇 |
1975年 | 7篇 |
1974年 | 13篇 |
1973年 | 5篇 |
1972年 | 3篇 |
1971年 | 6篇 |
1969年 | 4篇 |
1968年 | 4篇 |
排序方式: 共有1055条查询结果,搜索用时 687 毫秒
61.
Glenn H. Miller 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(8):1237-1253
Poly(dimethylbutadiene) popcorn polymer oxidizes readily in the presence of oxygen at room temperature. Quantitative data are presented for the production of the major volatile product, 2,5-hexanedione, as well as for the secondary products: water, acetic acid, and acetaldehyde. Three reaction mechanisms formerly proposed for polyisoprene oxidation are considered for their applicability to poly(dimethylbutadiene) popcorn oxidation. Of these, one that assumes the formation of a Bevilacquatype peroxyalkoxy radical followed by hydrogen abstraction to form an alcohol group, double bond migration, formation of a peroxide radical adjacent to the alcohol, then elimination of a hydroxy radical and scission, can explain the experimental data. 相似文献
62.
Stereospecific Palladium-Catalyzed Acylation of Enantioenriched Alkylcarbastannatranes: A General Alternative to Asymmetric Enolate Reactions 下载免费PDF全文
Chao-Yuan Wang Glenn Ralph Joseph Derosa Prof. Dr. Mark R. Biscoe 《Angewandte Chemie (International ed. in English)》2017,56(3):856-860
We report the development of a Pd-catalyzed process for the cross coupling of unactivated primary, secondary, and tertiary alkylcarbastannatrane nucleophiles with acyl electrophiles. Reactions involving optically active alkylcarbastannatranes occur with exceptional stereofidelity and with net retention of absolute configuration. Because the stereochemistry of the resulting products is entirely reagent-controlled, this process may be viewed as a general, alternative approach to the preparation of products typically accessed via asymmetric enolate methodologies. Additionally, we report a new method for the preparation of optically active alkylcarbastannatranes, which should facilitate their future use in stereospecific reactions. 相似文献
63.
The syntheses of boronates derived from the reaction of dioxaborolanes and dioxaborinanes with either organolithium or organomagnesium reagents are investigated along with their subsequent use in the palladium cross coupling reaction. The intrinsic stability of these cyclic esters contributes to their facile reaction with both lithium and magnesium nucleophiles at mild and safe conditions. We have found that many of the reactions proceed at room temperature which is a significant improvement over the traditional routes which require cryogenic temperatures. The scope of these reactions and their practical application to large scale process synthesis is described. 相似文献
64.
The preparation of 7-ethoxy-5-fluoroquinazolin-4-one, starting from 3,5-difluorophenol, is described. Further reaction with alkoxide then gives differentially substituted 5,7-dialkoxyquinazolin-4-ones. 相似文献
65.
Glenn Mangelinckx Jeroen Beeckman Olga Chojnowska Jungsoon Shin James D.K. Kim Roman Dąbrowski 《Liquid crystals》2013,40(11):1553-1558
This paper describes a novel implementation of a dual-frequency liquid crystal optical shutter of the guest–host type. The transmissive state of the filter is obtained by applying a low-frequency electric field that brings the dichroic dye in a homeotropic orientation. The light-absorbing state is realised by a twisted planar configuration for which the absorption is quasi-independent of the polarisation. Switching between the two states occurs in about 1 ms and the devices show no scattering for wavelengths inside or outside the absorption band of the dichroic dye. Simulations and experiments reveal how a twisted state is obtained through the backflow phenomenon. 相似文献
66.
Dr. Christina I. Schroeder Dr. Lachlan D. Rash Xavier Vila‐Farrés Dr. K. Johan Rosengren Dr. Mehdi Mobli Prof. Glenn F. King Prof. Paul F. Alewood Prof. David J. Craik Dr. Thomas Durek 《Angewandte Chemie (International ed. in English)》2014,53(4):1017-1020
Mambalgins are a novel class of snake venom components that exert potent analgesic effects mediated through the inhibition of acid‐sensing ion channels (ASICs). The 57‐residue polypeptide mambalgin‐2 (Ma‐2) was synthesized by using a combination of solid‐phase peptide synthesis and native chemical ligation. The structure of the synthetic toxin, determined using homonuclear NMR, revealed an unusual three‐finger toxin fold reminiscent of functionally unrelated snake toxins. Electrophysiological analysis of Ma‐2 on wild‐type and mutant ASIC1a receptors allowed us to identify α‐helix 5, which borders on the functionally critical acidic pocket of the channel, as a major part of the Ma‐2 binding site. This region is also crucial for the interaction of ASIC1a with the spider toxin PcTx1, thus suggesting that the binding sites for these toxins substantially overlap. This work lays the foundation for structure–activity relationship (SAR) studies and further development of this promising analgesic peptide. 相似文献
67.
Dr. Kang Cheng Lars I. van der Wal Dr. Hideto Yoshida Jogchum Oenema Dr. Justine Harmel Dr. Zhaorong Zhang Dr. Glenn Sunley Dr. Jovana Zečević Prof. Krijn P. de Jong 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(9):3620-3628
Improving product selectivity by controlling the spatial organization of functional sites at the nanoscale is a critical challenge in bifunctional catalysis. We present a series of composite bifunctional catalysts consisting of one-dimensional zeolites (ZSM-22 and mordenite) and a γ-alumina binder, with platinum particles controllably deposited either on the alumina binder or inside the zeolite crystals. The hydroisomerization of n-heptane demonstrates that the catalysts with platinum particles on the binder, which separates platinum and acid sites at the nanoscale, leads to a higher yield of desired isomers than catalysts with platinum particles inside the zeolite crystals. Platinum particles within the zeolite crystals impose pronounced diffusion limitations on reaction intermediates, which leads to secondary cracking reactions, especially for catalysts with narrow micropores or large zeolite crystals. These findings extend the understanding of the “intimacy criterion” for the rational design of bifunctional catalysts for the conversion of low-molecular-weight reactants. 相似文献
68.
Shoichi Maeda Shunta Chikami Glenn Villena Latag Subin Song Norio Iwakiri Tomohiro Hayashi 《Molecules (Basel, Switzerland)》2022,27(7)
In this paper, we propose a new spectroscopic method to explore the behavior of molecules near polymeric molecular networks of water-containing soft materials such as hydrogels. We demonstrate the analysis of hydrogen bonding states of water in the vicinity of hydrogels (soft contact lenses). In this method, we apply force to hydrated contact lenses to deform them and to modulate the ratio between the signals from bulk and vicinal regions. We then collect spectra at different forces. Finally, we extracted the spectra of the vicinal region using the multivariate curve resolution-alternating least square (MCR-ALS) method. We report the hydration states depending on the chemical structures of hydrogels constituting the contact lenses. 相似文献
69.
70.
Nicewarner Peña SR Raina S Goodrich GP Fedoroff NV Keating CD 《Journal of the American Chemical Society》2002,124(25):7314-7323
We have investigated the impact of steric effects on the hybridization and enzymatic extension of oligonucleotides bound to 12-nm colloidal Au particles. In these experiments, a nanoparticle-bound 12-mer sequence is hybridized either to its solution phase 12-mer complement or to an 88-mer template sequence. The particle-bound oligonucleotide serves as a primer for enzymatic extension reactions, in which covalent incorporation of nucleotides to form the complement of the template is achieved by the action of DNA polymerase. Primers were attached via-C(6)H(12)SH, -C(12)H(24)SH, and -TTACAATC(6)H(12)SH linkers attached at the 5' end. Primer coverage on the nanoparticles was varied by dilution with (5')HSC(6)H(12)AAA AAA(3'). Hybridization efficiencies were determined as a function of linker length, primer coverage, complement length (12-mer vs 88-mer), and primer:complement concentration ratio. In all cases, hybridization for the 88-mer was less efficient than for the 12-mer. Low primer surface coverage, greater particle-primer separation, and higher primer:complement ratios led to optimal hybridization. Hybridization efficiencies as high as 98% and 75% were observed for the 12-mer and 88-mer, respectively. Enzymatic extension of particle-bound primers was observed under all conditions tested; however, the efficiency of the reaction was strongly affected by linker length and primer coverage. Extension of primers attached by the longest linker was as efficient as the solution-phase reaction. 相似文献