全文获取类型
收费全文 | 546篇 |
免费 | 3篇 |
国内免费 | 7篇 |
专业分类
化学 | 333篇 |
晶体学 | 4篇 |
力学 | 19篇 |
数学 | 77篇 |
物理学 | 123篇 |
出版年
2022年 | 4篇 |
2021年 | 4篇 |
2020年 | 7篇 |
2019年 | 6篇 |
2018年 | 3篇 |
2017年 | 6篇 |
2016年 | 6篇 |
2015年 | 5篇 |
2014年 | 12篇 |
2013年 | 31篇 |
2012年 | 17篇 |
2011年 | 15篇 |
2010年 | 12篇 |
2009年 | 16篇 |
2008年 | 13篇 |
2007年 | 15篇 |
2006年 | 18篇 |
2005年 | 24篇 |
2004年 | 23篇 |
2003年 | 17篇 |
2002年 | 25篇 |
2001年 | 10篇 |
2000年 | 13篇 |
1999年 | 10篇 |
1998年 | 16篇 |
1997年 | 7篇 |
1996年 | 13篇 |
1995年 | 18篇 |
1994年 | 18篇 |
1993年 | 18篇 |
1992年 | 8篇 |
1991年 | 10篇 |
1990年 | 6篇 |
1989年 | 13篇 |
1988年 | 11篇 |
1987年 | 11篇 |
1986年 | 8篇 |
1985年 | 5篇 |
1984年 | 9篇 |
1983年 | 13篇 |
1982年 | 11篇 |
1980年 | 6篇 |
1978年 | 3篇 |
1977年 | 8篇 |
1973年 | 3篇 |
1971年 | 5篇 |
1969年 | 3篇 |
1968年 | 2篇 |
1967年 | 4篇 |
1966年 | 2篇 |
排序方式: 共有556条查询结果,搜索用时 15 毫秒
11.
The paper presents a short review on the synthesis, characterisation and selected medical applications of poly(styrene/α-tert-butoxy-ω-vinylbenzyl-polyglycidol) (P(S/PGL)) microspheres. The soap-free emulsion-polymerisation of styrene and α-tert-butoxy-ω-vinylbenzyl-polyglycidol macromonomer (PGL) in water yielded core-shell microspheres with a low particle-diameter dispersity (ratio of the weight average particle diameter and the number average particle diameter). The interfacial fraction of PGL units, estimated by XPS, was in the range of 0–42 mole % depending on the concentration of the macromonomer in the polymerisation feed. The studies of adsorption of model proteins showed that the surface fraction of adsorbed protein was significantly reduced when the PGL interfacial fraction was higher than 40 mole %. The P(S/PGL) particles with covalently immobilised proteins were used for the preparation of photonic crystal assemblies suitable for applications in optical biosensors and the medical diagnostic test for the detection of Helicobacter pylori antibodies in the blood serum. 相似文献
12.
It has previously been proposed (Ref. 1) that in the cationic vinyl polymerizations, proceeding with termination due to the collapse of ion pairs, addition of bases increases “livingness”, because of the fast convertion of the otherwise dead (within the time of polymerization) covalent species into the onium ions; these, in turn, fast convert into carbenium ions, the actually propagating species. Equilibria between carbenium ions (CH3OCH2+A− has been used as a model) and their onium counterparts ((CH3)2O taken as a model base) as well as between covalent species (CH3OCH2OSO2CF3) and the corresponding oxonium ion (with a (CH3)2O ligand) have been studied by dynamic 1H and 19F NMR. Total ionization of methoxymethyl triflate (CH3OCH2OSO2CF3) has been shown to increase indeed from 104 (-10°C) to 106 (-70°C) times when 1,0 mol·L−1 of (CH3)2O is added. Although this model system better describes polymerization of cyclic acetals than that of vinyl ethers, it shows at least qualitatively the importance of bases in ionization of covalent species, which may be responsible for reinitiation in the cationic polymerization of vinyl ethers. 相似文献
13.
14.
Stanislaw Penczek Tadeusz Biela Pawel Klosinski Grzegorz Lapienis 《Macromolecular Symposia》1986,6(1):123-153
The mechanism of polymerization is discussed, in which cyclic esters of phosphoric acid, and related compounds are converted into linear macromolecules, modelling nucleic and teichoic acid backbones. Structures like deoxyribose polyphosphate and glycerol polyphosphate were prepared from the corresponding cyclic compounds. These polymerizations involve heterolytic breaking of the P-O bond in the cyclic monomer and proceed by ionic mechanism. Both 5- and 6-membered monomers have been polymerized. The thermodynamic parameters of the ring-chain interconversion were determined; the 5-membered rings polymerization is driven by the exothermicity of the ring-opening, whereas polymerization of several 6-membered rings is endothermic and allowed because of the positive change of entropy. Anionic polymerization, and particularly the pseudo(coordinate)anionic polymerization provides, in contrast to the cationic process, high-molecular-weight polymers with more uniform structure. Anionic polymerization proceeds mostly (at the applied conditions) on the macroion – -pairs. The elementary reactions consist of the nucleophilic attack of the paired macroanions on the phosphorus atom in the cyclic monomer molecule. Rate constants of the elementary reactions for the model monomers will be presented. Stereochemistry of the propagation steps is shown to be governed by the statistical ring-opening, leading to the three kinds of polymer units (head-to-tail and two symmetrical units). Apart from the ring-opening, the polyaddition of diepoxides to phosphorous and phosphoric acids is described. Finally, a few examples of preparation of models of biopolymers are given, namely poly(deoxyribose phosphate) and poly(glycerol phosphate). 相似文献
15.
16.
G. A. Kolesnik 《Mathematical Notes》1969,6(5):784-791
New bounds are obtained for the remainder term in the divisors problem.Translated from Matematicheskie Zametki, Vol. 6, No. 5, pp. 545–554, November, 1969. 相似文献
17.
A Merck molecular force field classical potential combined with Poisson-Boltzmann electrostatics (MMFF/PB) has been used to estimate the binding free energy of seven guest molecules (six tertiary amines and one primary amine) into a synthetic receptor (acyclic cucurbit[4]uril congener) and two benzimidazoles into cyclic cucurbit[7]uril (CB[7]) and cucurbit[8]uril (CB[8]) hosts. In addition, binding enthalpies for the benzimidazoles were calculated with density functional theory (DFT) using the B3LYP functional and a polarizable continuum model (PCM). Although in most cases the MMFF/PB approach returned reasonable agreements with the experiment (±2 kcal/mol), significant, much larger deviations were reported in the case of three host-guest pairs. All four binding enthalpy predictions with the DFT/PCM method suffered 70% or larger deviations from the calorimetry data. Results are discussed in terms of the molecular models used for guest-host complexation and the quality of the intermolecular potentials. 相似文献
18.
N. M. Shcheglova V. D. Kolesnik R. V. Ashirov E. A. Krasnokutskaya 《Russian Chemical Bulletin》2016,65(2):490-497
New ruthenium carbene complexes with chelating N- and S-benzylidene ligands were synthesized by the reactions of second- and third-generation Grubbs catalysts with ortho-vinylbenzyl-substituted amines or sulfides. These complexes were shown to exhibit catalytic activity in ring-opening metathesis polymerization and ring-closing metathesis. 相似文献
19.
Leszek Czuchajowski Jan Habdas Stanislaw A. Kucharski Krystyna Rogosz 《Journal of organometallic chemistry》1978,155(2):185-193
All the fundamental frequencies observed in IR and Raman spectra have been assigned to the normal modes of the molecule (C3H5)4Pb (C3H5 = cyclopropyl). The calculated force field is compared to that of (C3H5)2Hg and the Cmetal stretching force constants are discussed along with those of Me4Pb and Me2Hg; The similarity of the spectra of cyclopropyllead and cyclopropyl-mercury proves that the vibrations of cyclopropyl structural units are isolated in both molecules. 相似文献
20.
Thermolysis of a 2'-[(16)O]-O-benzoyl-[(17)O]-5'-O-(tert-butyldimethylsilyl)-O(2),3'-cyclouridine derivative gave the more stable 3'-[(17)O]-O-benzoyl-[(16)O]- 5'-O-(tert-butyldimethylsilyl)-O(2),2'-cyclouridine isomer, which was converted into 3'-[(17)O]-2'-azido-2'-deoxyuridine by deprotection and nucleophilic ring opening at C2' with lithium azide. The 5'-diphosphate was prepared by nucleophilic displacement of the 5'-O-tosyl group with tris(tetrabutylammonium) hydrogen pyrophosphate. Model reactions gave (16)O and (18)O isotopomers, and base-promoted hydrolysis of an O(2),2'-cyclonucleoside gave stereodefined access to 3'-[(18)O]-1-(beta-D-arabinofuranosyl)uracil. Inactivation of ribonucleoside diphosphate reductase with 2'-azido-2'-deoxynucleotides results in appearance of EPR signals for a nitrogen-centered radical derived from azide, and 3'-[(17)O]-2'-azido-2'-deoxyuridine 5'-diphosphate provides an isotopomer to perturb EPR spectra in a predictable manner. 相似文献