全文获取类型
收费全文 | 1680篇 |
免费 | 41篇 |
国内免费 | 6篇 |
专业分类
化学 | 737篇 |
晶体学 | 22篇 |
力学 | 91篇 |
数学 | 179篇 |
物理学 | 496篇 |
无线电 | 202篇 |
出版年
2023年 | 12篇 |
2022年 | 27篇 |
2021年 | 31篇 |
2020年 | 38篇 |
2019年 | 42篇 |
2018年 | 38篇 |
2017年 | 41篇 |
2016年 | 49篇 |
2015年 | 31篇 |
2014年 | 61篇 |
2013年 | 114篇 |
2012年 | 102篇 |
2011年 | 104篇 |
2010年 | 62篇 |
2009年 | 70篇 |
2008年 | 85篇 |
2007年 | 66篇 |
2006年 | 51篇 |
2005年 | 50篇 |
2004年 | 39篇 |
2003年 | 42篇 |
2002年 | 26篇 |
2001年 | 16篇 |
2000年 | 16篇 |
1999年 | 16篇 |
1998年 | 12篇 |
1997年 | 11篇 |
1996年 | 20篇 |
1995年 | 20篇 |
1994年 | 24篇 |
1993年 | 25篇 |
1992年 | 13篇 |
1991年 | 14篇 |
1990年 | 18篇 |
1989年 | 21篇 |
1988年 | 23篇 |
1987年 | 14篇 |
1986年 | 13篇 |
1985年 | 10篇 |
1984年 | 20篇 |
1983年 | 11篇 |
1982年 | 11篇 |
1981年 | 16篇 |
1980年 | 10篇 |
1979年 | 16篇 |
1978年 | 11篇 |
1976年 | 10篇 |
1975年 | 11篇 |
1973年 | 10篇 |
1936年 | 13篇 |
排序方式: 共有1727条查询结果,搜索用时 31 毫秒
61.
Pranab Kumar Som Amar Nath Banerjee 《Journal of polymer science. Part A, Polymer chemistry》1993,31(4):1007-1012
Isatoic anhydride (IA) alone did not initiate photopolymerization of methyl metacrylate (MMA) at 40°C when exposed to visible light for about 180 min. But IA, when used in combination with bromine (Br2) as the initiator, initiated the photopolymerization of MMA readily under the same conditions. This behavior was explained by the formation of a donor-acceptor type of complex between IA and Br2 in the presence of MMA. The polymerization was found to proceed via a free radical mechanism and the radical generation process was considered to follow an initial complexation reaction between the initiator components and monomer. The complex initiator showed nonideal kinetics for the present system (initiator exponent < 0.5) and was analyzed. The monomer exponents varied from 0.83 to 1.15 normally depending on the nature of solvent used. Initiator-dependent chain termination was significant as well as the bimolecular mode of chain termination. © 1993 John Wiley & Sons, Inc. 相似文献
62.
The kinetics of oxidation of ethyldigol by vanadium(V) in aqueous acidic medium has been carried out. The reaction is first order with respect to vanadium(V) and the substrate and is acid catalysed.Hammett acidity function (H
0) andBunnett hypothesis have been applied. The formation of free radicals during the course of the reaction has been indicated. A probable reaction mechanism is proposed.
Die Kinetik der Oxidation von Ethyldigol mit Vanadium(V) in wäßrigem saurem Medium
Zusammenfassung Es wurde die Kinetik der Oxidation von Ethyldigol mittels Vanadium(V) in wäßriger saurer Lösung untersucht. Die Reaktion ist erster Ordnung bezüglich Vanadium(V) und Substrat und ist säurekatalysiert. Es wurden dieHammett-Aciditätsfunktion (H 0) und dieBunnett-Hypothese angewandt. Die Bildung von freien Radikalen während der Reaktion konnte bestätigt werden. Es wird ein Reaktionsmechanismus vorgeschlagen.相似文献
63.
Viscosity behaviour of several samples ofGraham's salt with varying molecular weight has been studied. Reduced viscosity (η sp /c) versus concentration curves were found to be characteristic of polyelectrolytes. They are dependent on the molecular weight and can be reduced to straight lines by plotting the reciprocal of the reduced viscosity against the square root of concentration. The intrinsic viscosities obtained by extrapolation were found to be proportional to the square of molecular weights. The value of reduced viscosity at any particular concentration in the concentration range between 0.25% and 4.0% was linearly related to the molecular weight. Reduced viscosities were found to decrease considerably on addition of electrolytes. Reduced viscosity versus added salt concentration curves were remarkably molecular weight dependent. The pH of the medium seemed to have no effect at all. Bivalent salts reduce the viscosity to a much greater extent than monovalent ones. By keeping the concentration of the added salt constant and varying that ofGraham's salt, curves showing hump which disappeared at higher concentration of the added salt, were obtained. In the action of electrolytes the more important factor is the valency of cation rather than the ionic strength of the medium. Most observations confirm the already well-establishedFolding-Chain Theory of polyelectrolytes developed byKatchalsky, Fuoss and others. 相似文献
65.
66.
67.
Corrigendum: Triazole‐Tailored Guanosine Dinucleosides as Biomimetic Ion Channels to Modulate Transmembrane Potential 下载免费PDF全文
68.
Structure‐cytotoxicity relationship of di?/tri‐organotin(IV) derivatives of mandelic acid ( 1 – 4 ), L‐proline ( 5 – 7, 15, 16 ), and mixed ligand complexes of latter with 1,10‐phenanthroline ( 8 – 14 ) investigated on the basis of MTT assay against human cancer cell lines, viz. MCF‐7 (mammary cancer), HepG2 (liver cancer) and PC‐3 (prostate cancer) in vitro indicated that all complexes except methyl‐ and octyl‐ analogues displayed potential cytotoxicity. The most active one is dibutyltin(IV) mandelate ( 2 ) exhibiting IC50 2.03 ± 0.40, 0.98 ± 0.23 and 3.86 ± 1.68 μM against MCF‐7, HepG2 and PC‐3, respectively, which is ≈ 15 and 2.5 times against MCF‐7, 20 and 5 times against HepG2 and 5 and ≈ 3 times against PC‐3 more cytotoxic than cis‐platin and 5‐fluorouracil, respectively. Diorganotin(IV) derivatives of mandelic acid are more cytotoxic than triorganotin analogues. Organotin(IV) derivatives of L‐proline (except Bu3Sn(Pro) 16 ) are less cytotoxic than those of mandelic acid but their cytotoxicity is enhanced by complexion with 1,10‐phenanthroline. This may be due to the structural planarity and extended π system of 1,10‐phenanthroline which facilitates their transportation across the cell membrane and enhances the possibility of DNA intercalation over the planar L‐proline ring, and eventually, their DNA binding affinity so as to interfere with the cellular functions of DNA leading to apoptosis. Various biophysical experiments such as DNA fragmentation, acridine orange and comet assays, and flow cytometry assay using annexin V–fluorescein isothiocyanate (FITC) and propidium iodide (PI) have been carried out in order to ascertain their mode of action. The observed results indicated that the major cause of cancer cell death is apoptosis, but a minor role played by necrosis cannot be excluded. It is concluded on the basis of the observed results that the nature and number of organic groups bonded to tin as well as the nature of counter anions play an important role in determining the cytotoxicity of organotin(IV) compounds. 相似文献
69.
Dr. Jakov Ivkovic Dr. Shalinee Jha Dipl.-Ing. Christian Lembacher-Fadum Dipl.-Ing. Johannes Puschnig Dr. Prashant Kumar Dr. Viktoria Reithofer Prof. Dr. Karl Gruber Prof. Dr. Peter Macheroux Prof. Dr. Rolf Breinbauer 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(56):14108-14120
Dipeptidyl peptidase III (DPP3) is a ubiquitously expressed Zn-dependent protease, which plays an important role in regulating endogenous peptide hormones, such as enkephalins or angiotensins. In previous biophysical studies, it could be shown that substrate binding is driven by a large entropic contribution due to the release of water molecules from the closing binding cleft. Here, the design, synthesis and biophysical characterization of peptidomimetic inhibitors is reported, using for the first time an hydroxyethylene transition-state mimetic for a metalloprotease. Efficient routes for the synthesis of both stereoisomers of the pseudopeptide core were developed, which allowed the synthesis of peptidomimetic inhibitors mimicking the VVYPW-motif of tynorphin. The best inhibitors inhibit DPP3 in the low μM range. Biophysical characterization by means of ITC measurement and X-ray crystallography confirm the unusual entropy-driven mode of binding. Stability assays demonstrated the desired stability of these inhibitors, which efficiently inhibited DPP3 in mouse brain homogenate. 相似文献
70.
A semiempirical method has been used to study the electronic structures of some π-bonded purely organic materials that are either known or proposed to have multiplet ground states. These materials are the precursors of organic ferromagnets. Narrow energy bands formed from the radical π-orbitals of these materials are necessary for the π-electrons to be unpaired. Favorable topological arrangements of atoms in these materials are needed to enable the spins of these electrons to align parallel, and hence yield macroscopic ferromagnetic ordering. Following ideas based on these studies, a new model for a possible organic ferromagnet is proposed and studied. 相似文献