全文获取类型
收费全文 | 1586篇 |
免费 | 20篇 |
国内免费 | 18篇 |
专业分类
化学 | 1109篇 |
晶体学 | 25篇 |
力学 | 24篇 |
数学 | 253篇 |
物理学 | 213篇 |
出版年
2023年 | 9篇 |
2022年 | 8篇 |
2021年 | 10篇 |
2020年 | 19篇 |
2019年 | 8篇 |
2017年 | 8篇 |
2016年 | 22篇 |
2015年 | 18篇 |
2014年 | 20篇 |
2013年 | 72篇 |
2012年 | 62篇 |
2011年 | 86篇 |
2010年 | 46篇 |
2009年 | 52篇 |
2008年 | 103篇 |
2007年 | 106篇 |
2006年 | 91篇 |
2005年 | 68篇 |
2004年 | 72篇 |
2003年 | 81篇 |
2002年 | 83篇 |
2001年 | 28篇 |
2000年 | 33篇 |
1999年 | 23篇 |
1998年 | 21篇 |
1997年 | 19篇 |
1996年 | 40篇 |
1995年 | 14篇 |
1994年 | 22篇 |
1993年 | 16篇 |
1992年 | 22篇 |
1991年 | 13篇 |
1989年 | 14篇 |
1987年 | 6篇 |
1986年 | 11篇 |
1985年 | 21篇 |
1984年 | 17篇 |
1983年 | 7篇 |
1982年 | 20篇 |
1981年 | 30篇 |
1980年 | 17篇 |
1979年 | 21篇 |
1978年 | 23篇 |
1977年 | 12篇 |
1976年 | 16篇 |
1975年 | 19篇 |
1974年 | 17篇 |
1973年 | 13篇 |
1972年 | 9篇 |
1971年 | 6篇 |
排序方式: 共有1624条查询结果,搜索用时 15 毫秒
991.
Rajesh Chitta Tibor Macko Robert Brüll Gerard Van Doremaele Lars‐Christian Heinz 《Journal of polymer science. Part A, Polymer chemistry》2011,49(8):1840-1846
Ethylene‐propylene‐diene terpolymers (EPDM) are generally amorphous and, therefore, do not crystallize from solution. Consequently, fractionation techniques based on crystallization, such as crystallization analysis fractionation or temperature rising elution fractionation, cannot be used to analyze their chemical composition distribution. Moreover, no suitable chromatographic system was known, which would enable to separate them according to their chemical composition. In this study, two different sorbent/solvent systems are tested with regard to the capability to separate EPDM‐terpolymers and ethylene‐propylene (EP)‐copolymers according to chemical composition. While porous graphite/1‐decanol system is selective towards ethylene and ethylidene‐2‐norbornene, carbon coated zirconia/2‐ethyl‐1‐hexanol is preferentially selective towards ethylene. Consequently, the earlier system enables to separate both EP copolymers and EPDM according to the chemical composition and the latter mainly according to the ethylene content. The results prove that the chromatographic separation in both sorbent/solvent systems is not influenced by molar mass of a sample or by its long chain branching. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011 相似文献
992.
Ruthenium trichloride (RuCl3 or RuIII) catalyzed polymerization of methylmethacrylate (MMA) initiated with n‐butylamine (BA) in the presence of carbon tetrachloride (CCl4) by a charge‐transfer mechanism has been investigated in a dimethylsulfoxide (DMSO) medium by employing a dilatometric technique at 60°C. The rate of polymerization (Rp) has been obtained under the conditions [CCl4]/[BA] ? 1 and [CCl4]/[BA] ? 1. The kinetic data indicate the possible participation of the charge‐transfer complex formed between the amine–RuIII complex and CCl4 in the polymerization of MMA. In the absence of either CCl4 or BA, no polymerization of MMA is observed under the present experimental conditions. The rate of polymerization is inhibited by hydroquinone, suggesting a free‐radical initiation. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 43: 70–77, 2011 相似文献
993.
994.
Maryluz Moreno Gerard Lligadas Joan C. Ronda Marina Galià Virginia Cádiz 《Journal of polymer science. Part A, Polymer chemistry》2012,50(15):3206-3213
A novel phosphorus‐containing vegetable oil (PETR) was prepared through phospha‐Michael addition of a diphenyl phosphine oxide to the enone derivative of high‐oleic sunflower oil (ETR). The reaction was investigated using the enone derivative of methyl oleate under conventional thermal heating and microwave irradiation. The kinetic study showed a great enhancement of reaction rate for the microwave‐initiated addition. The crosslinking of ETR with diaminodiphenylmethane (DDM) via aza‐Michael addition was also investigated under microwave irradiation, showing a noticeable acceleration of the curing. The new phosphorus‐containing triglyceride was crosslinked with DDM to obtain phosphorus‐containing vegetable oil‐based thermosets of different phosphorus contents. Limiting oxygen index values from 26.4 to 35.0 for the final materials were obtained, demonstrating that the flame retardant properties of vegetable oil‐based thermosets can be improved by adding covalently bonded phosphorus to the polymer. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012 相似文献
995.
996.
Abstract Published [11,12] proton nuclear magnetic resonance data for two substituted biphenyl molecules dissolved in nematic solvents are analysed in terms of the single conformation model and compared with the results of the maximum entropy analysis of [11]. It is shown that (i) this model, in which the number of adjustable parameters is less than the number of data, can describe very well the data for both molecules and (ii) the results of the maximum entropy analysis provide global support for this model. It is argued that the ultimate support of the single conformation model would be that introduction of a sufficiently large number of additional data in the maximum entropy analysis leads to a distribution for the dihedral angle between the two phenyl rings with two symmetrical very sharp peaks. 相似文献
997.
Gaft Michael Shoval Shlomo Panczer Gerard Champagnon Bernard Rabinowitz Jimmy 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1-4)
Abstract Apatite of various genesis accommodates trace elements by diverse ways: the structural substitution is preferencial in magmatic type, while the adsorption of independent phases is the main form in sedimentary one. 相似文献
998.
999.
de la Lande A Salahub DR Maddaluno J Scemama A Pilme J Parisel O Gerard H Caffarel M Piquemal JP 《Journal of computational chemistry》2011,32(6):1178-1182
Although potentially powerful, molecular oxygen is an inert oxidant due to the triplet nature of its ground state. Therefore, many enzymesse various metal cations (M) to produce singlet active species M(n) O(2) . In this communication we investigate the topology of the Electron Localization Function (ELF) within five biomimetic complexes which are representative of the strategies followed by metalloenzymes to activate O(2) . Thanks to its coupling to the constrained DFT methods the ELF analysis reveals the tight connection between the spin state of the adduct and the spatial organization of the oxygen lone pairs. We suggest that enzymes could resort to spin state control to tune the regioselectivity of substrate oxidations. 相似文献
1000.
Krzemiński Ł Ndamba L Canters GW Aartsma TJ Evans SD Jeuken LJ 《Journal of the American Chemical Society》2011,133(38):15085-15093
A combined fluorescence and electrochemical method is described that is used to simultaneously monitor the type-1 copper oxidation state and the nitrite turnover rate of a nitrite reductase (NiR) from Alcaligenes faecalis S-6. The catalytic activity of NiR is measured electrochemically by exploiting a direct electron transfer to fluorescently labeled enzyme molecules immobilized on modified gold electrodes, whereas the redox state of the type-1 copper site is determined from fluorescence intensity changes caused by Fo?rster resonance energy transfer (FRET) between a fluorophore attached to NiR and its type-1 copper site. The homotrimeric structure of the enzyme is reflected in heterogeneous interfacial electron-transfer kinetics with two monomers having a 25-fold slower kinetics than the third monomer. The intramolecular electron-transfer rate between the type-1 and type-2 copper site changes at high nitrite concentration (≥520 μM), resulting in an inhibition effect at low pH and a catalytic gain in enzyme activity at high pH. We propose that the intramolecular rate is significantly reduced in turnover conditions compared to the enzyme at rest, with an exception at low pH/nitrite conditions. This effect is attributed to slower reduction rate of type-2 copper center due to a rate-limiting protonation step of residues in the enzyme's active site, gating the intramolecular electron transfer. 相似文献