全文获取类型
收费全文 | 2312篇 |
免费 | 47篇 |
国内免费 | 14篇 |
专业分类
化学 | 1363篇 |
晶体学 | 24篇 |
力学 | 57篇 |
数学 | 303篇 |
物理学 | 626篇 |
出版年
2021年 | 16篇 |
2020年 | 18篇 |
2019年 | 16篇 |
2018年 | 17篇 |
2017年 | 13篇 |
2016年 | 32篇 |
2015年 | 24篇 |
2014年 | 33篇 |
2013年 | 104篇 |
2012年 | 124篇 |
2011年 | 129篇 |
2010年 | 58篇 |
2009年 | 41篇 |
2008年 | 118篇 |
2007年 | 107篇 |
2006年 | 85篇 |
2005年 | 94篇 |
2004年 | 89篇 |
2003年 | 71篇 |
2002年 | 66篇 |
2001年 | 41篇 |
2000年 | 46篇 |
1999年 | 28篇 |
1998年 | 20篇 |
1997年 | 23篇 |
1996年 | 38篇 |
1995年 | 33篇 |
1994年 | 32篇 |
1993年 | 38篇 |
1992年 | 40篇 |
1991年 | 20篇 |
1990年 | 29篇 |
1989年 | 32篇 |
1988年 | 37篇 |
1987年 | 24篇 |
1986年 | 16篇 |
1985年 | 43篇 |
1984年 | 42篇 |
1983年 | 28篇 |
1982年 | 39篇 |
1981年 | 29篇 |
1980年 | 36篇 |
1979年 | 30篇 |
1978年 | 39篇 |
1977年 | 31篇 |
1976年 | 34篇 |
1975年 | 20篇 |
1974年 | 29篇 |
1973年 | 30篇 |
1972年 | 15篇 |
排序方式: 共有2373条查询结果,搜索用时 11 毫秒
41.
N.S. Allen G.P. Marshall C. Vasiliou L.M. Moore J.L. Kotecha J. Luc-Gardette B. Valange 《Polymer Degradation and Stability》1988,20(3-4):315-324
The thermal, hydrolytic and photochemical oxidation of blue water pipe material has been studied using Fourier Transform infra-red microscopy, differential scanning calorimetry (DSC) and hydroperoxide analysis. The results indicate that oxidation of the pipe occurs predominantly on the outer surface and to a lesser extent on the bore, often with little or no change in the middle layers, FTIR analysis of microtomed sections of the pipe supports the DSC analysis (oxidation induction time at 200°C—OIT) and indicates leaching and consumption of the polymer antioxidants at the outer surface of the pipe. Oxidation profiles at 80°C in water, as measured using carbonyl index, indicate an unusual hydrolytic oxidation and extraction of the carbonylic oxidation products only at the outer pipe surface to a depth of about 0·5 mm resulting in high hydroperoxidation levels. These oxidation analyses are consistent with density profile changes through the pipe wall. Whilst water is concluded to have an important influence in controlling pipe stability, which, in turn, is governed by the temperature and extractability of the polymer antioxidants, ultraviolet light is also seen to have a similar detrimental effect. The influence of these various degradative parameters on the long-term stability of pipe is discussed with a view to elucidating the mechanisms involved. 相似文献
42.
Protein phosphorylation is a major mechanism of post-translational protein modification used to control cellular signaling. A challenge in phosphoproteomics is to identify the direct substrates of each protein kinase. Herein, we describe a chemical strategy for delivery of a bio-orthogonal affinity tag to the substrates of an individual protein kinase. The kinase of interest is engineered to transfer a phosphorothioate moiety to phosphoacceptor hydroxyl groups on direct substrates. In a second nonenzymatic step, the introduced phosphorothioate is alkylated with p-nitrobenzylmesylate (PNBM). Antibodies directed against the alkylated phosphorothioate epitope recognize these labeled substrates, but not alkylation products of other cellular nucleophiles. This strategy is demonstrated with Cdk1/cyclinB substrates using ELISA, western blotting, and immunoprecipitation in the context of whole cell lysates. 相似文献
43.
Boyd DR Sharma ND King AW Shepherd SD Allen CC Holt RA Luckarift HR Dalton H 《Organic & biomolecular chemistry》2004,2(4):554-561
Direct and indirect evidence, of unexpected stereoselective reductase-catalysed deoxygenations of sulfoxides, was found. The deoxygenations proceeded simultaneously, with the expected dioxygenase-catalysed asymmetric sulfoxidation of sulfides, during some biotransformations with the aerobic bacterium Pseudomonas putida UV4. Stereoselective reductase-catalysed asymmetric deoxygenation of racemic alkylaryl, dialkyl and phenolic sulfoxides was observed, without evidence of the reverse sulfoxidation reaction, using anaerobic bacterial strains. A purified dimethyl sulfoxide reductase, obtained from the intact cells of the anaerobic bacterium Citrobacter braakii DMSO 11, yielded, from the corresponding racemates, enantiopure alkylaryl sulfoxide and thiosulfinate samples. 相似文献
44.
It has been suggested [F. H. Stillinger, J. Chem. Phys. 112, 9711 (2000)] that the convergence or divergence of M?ller-Plesset perturbation theory is determined by a critical point at a negative value of the perturbation parameter z at which an electron cluster dissociates from the nuclei. This conjecture is examined using configuration-interaction computations as a function of z and using a quadratic approximant analysis of the high-order perturbation series. Results are presented for the He, Ne, and Ar atoms and the hydrogen fluoride molecule. The original theoretical analysis used the true Hamiltonian without the approximation of a finite basis set. In practice, the singularity structure depends strongly on the choice of basis set. Standard basis sets cannot model dissociation to an electron cluster, but if the basis includes diffuse functions then it can model another critical point corresponding to complete dissociation of all the valence electrons. This point is farther from the origin of the z plane than is the critical point for the electron cluster, but it is still close enough to cause divergence of the perturbation series. For the hydrogen fluoride molecule a critical point is present even without diffuse functions. The basis functions centered on the H atom are far enough from the F atom to model the escape of electrons away from the fluorine end of the molecule. For the Ar atom a critical point for a one-electron ionization, which was not previously predicted, seems to be present at a positive value of the perturbation parameter. Implications of the existence of critical points for quantum-chemical applications are discussed. 相似文献
45.
The effect of certain aromatic compounds on the PMR spectrum of methyl methacrylate (MMA) was investigated. The magnitude of observed aromatic-induced shifts decreased in the order benzene ? styrene > chlorobenzene ≈ bromobenzene.Assuming that the interaction arises from a stoichiometric 1:1 complex, equilibrium parameters for the MMA-benzene interaction have been estimated. ΔH ± S.E. (ΔH) = ?(8 ± 4) kJ mol?1. These effects are likely to have a small influence on the kinetics of copolymerization with aromatic monomers and polymerization in aromatic solvent. The stereochemistry of the solute-solvent interactions suggests that MMA takes a cis-conformation in solution, which is relevant to the mechanism of stereoregular polymerizations of this monomer. 相似文献
46.
D. Fennell Evans Martin Allen B. W. Ninham Abdel Fouda 《Journal of solution chemistry》1984,13(2):87-101
Critical micelle concentrations were determined by conductance measurements for decyl-, dodecyl-, tetradecyl- and hexadecyltrimethylammonium bromide in water at 25, 60, 95, 130, and 160°C. The results are discussed in terms of the equilibrium model and the nonlinear Poisson-Boltzmann model for micelle formation. The free energies of transferring a methylene group from water to the oil-like interior of the micelle are found to be –781 at 25°C, –796 at 60°C, –819 at 95°C, –815 at 130°C, and –787 at 160°C cal-mol–1. 相似文献
47.
Abe K Abt I Ahn CJ Akagi T Allen NJ Ash WW Aston D Baird KG Baltay C Band HR Barakat MB Baranko G Bardon O Barklow T Bazarko AO Ben-David R Benvenuti AC Bienz T Bilei GM Bisello D Blaylock G Bogart JR Bolton T Bower GR Brau JE Breidenbach M Bugg WM Burke D Burnett TH Burrows PN Busza W Calcaterra A Caldwell DO Calloway D Camanzi B Carpinelli M Cassell R Castaldi R Castro A Cavalli-Sforza M Church E Cohn HO Coller JA Cook V Cotton R Cowan RF Coyne DG D'Oliveira A Damerell CJ Daoudi M 《Physical review D: Particles and fields》1995,52(7):4240-4244
48.
49.
50.