全文获取类型
收费全文 | 8504篇 |
免费 | 318篇 |
国内免费 | 60篇 |
专业分类
化学 | 5127篇 |
晶体学 | 41篇 |
力学 | 322篇 |
数学 | 1458篇 |
物理学 | 1435篇 |
无线电 | 499篇 |
出版年
2023年 | 76篇 |
2022年 | 135篇 |
2021年 | 210篇 |
2020年 | 191篇 |
2019年 | 157篇 |
2018年 | 194篇 |
2017年 | 169篇 |
2016年 | 328篇 |
2015年 | 259篇 |
2014年 | 298篇 |
2013年 | 559篇 |
2012年 | 614篇 |
2011年 | 646篇 |
2010年 | 423篇 |
2009年 | 345篇 |
2008年 | 486篇 |
2007年 | 567篇 |
2006年 | 477篇 |
2005年 | 441篇 |
2004年 | 407篇 |
2003年 | 290篇 |
2002年 | 263篇 |
2001年 | 102篇 |
2000年 | 69篇 |
1999年 | 51篇 |
1998年 | 58篇 |
1997年 | 70篇 |
1996年 | 75篇 |
1995年 | 59篇 |
1994年 | 44篇 |
1993年 | 41篇 |
1992年 | 45篇 |
1991年 | 34篇 |
1990年 | 37篇 |
1989年 | 32篇 |
1988年 | 38篇 |
1987年 | 24篇 |
1986年 | 16篇 |
1985年 | 42篇 |
1984年 | 50篇 |
1983年 | 35篇 |
1982年 | 33篇 |
1981年 | 35篇 |
1980年 | 36篇 |
1979年 | 35篇 |
1978年 | 22篇 |
1977年 | 21篇 |
1976年 | 26篇 |
1975年 | 18篇 |
1974年 | 21篇 |
排序方式: 共有8882条查询结果,搜索用时 18 毫秒
101.
M. Düdükcü 《Research on Chemical Intermediates》2013,39(8):3641-3647
In this study, electrochemical synthesis of poly(o-phenylenediamine) (PoPDA) on 316L stainless steel and its corrosion inhibition effect were studied. Electropolymerization of o-phenylenediamine (oPDA) was carried out by a potentiodynamic method using 0.5 M H2SO4 solution containing 0.05 M oPDA monomer. The corrosion protection ability of the PoPDA in 3.5 % NaCl was investigated by potentiodynamic polarization, electrochemical impedance spectroscopy, and change of open circuit potential with immersion time (EOCP ? t). The results showed that PoPDA acted as a protective layer on stainless steel against corrosion in 3.5 % NaCl solution. 相似文献
102.
A new family of optically pure tetrathiafulvalenium and tetraselenafulvalenium salts, D(3)[M(III)(S,S-EDDS)](2)·nH(2)O (where D = TTF, TSF; M = Co, Fe, Cr; EDDS = ethylenediaminedisuccinato), were synthesized electrochemically. These phases are semiconductors with conductivities between 6.9 × 10(-6) and 1.3 × 10(-5) S·cm(-1) (E(a)ca. 0.3 eV) for TTF and 2.8 × 10(-4) to 2.8 × 10(-5) S·cm(-1) (E(a)ca. 0.1 eV) for TSF compounds. While some crystals suffer from twinning, other well resolved structures consist of TTF/TSF stacks which, under the influence of the chiral anion, exhibit a periodic undulation described by an elliptical helix. The crystallographic data, along with computational work, indicate charge localization in the semiconducting motifs. 相似文献
103.
Livieri A Boiocchi M Desimoni G Faita G 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(2):516-520
Diels–Alder and 1,3‐dipolar cycloadditions involving (E)‐3‐aryl‐1‐(pyridin‐2‐yl‐N‐oxide)prop‐2‐en‐1‐ones as the 2π components are efficiently catalysed by bis(oxazoline)–CuII complexes. The cycloadducts are obtained in quantitative yields with up to 98 % ee; absolute configurations were determined by X‐ray analysis. The structure of the reactive complex, determined by X‐ray analysis, is fully consistent with the stereochemical outcome of the catalysed process (approach of the diene or nitrone to the less hindered face of the coordinated pyridine‐N‐oxide derivative). 相似文献
104.
Chauvin J Lafolet F Chardon-Noblat S Deronzier A Jakonen M Haukka M 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(15):4313-4322
Optical excitation in the visible region of trans-(Cl)-[Os(bpy)(CO)(2)Cl(2)] (bpy=2,2'-bipyridine; C1) and trans-(Cl)-[Os(dmbpy)(CO)(2)Cl(2)] (dmbpy=4,4'-dimethyl 2,2'-bipyridine; C2) is known to induce the common CO dissociation reaction. However, the quantum yield of the reactions is less than 0.15, although C1 and C2 display pronounced photoluminescence in the visible region at room temperature with a lifetime of few tens of nanoseconds. Taking into account the characteristics of their emitting state, we have investigated the capability of C1 and C2 to act as a photosensitiser in redox reactions in different solvents (MeCN, PrCN and DMF). The efficient oxidation and reduction of both complexes under continuous irradiation in the presence of a sacrificial electron acceptor or donor is reported here. The photo-induced transformations and the nature of the resulting compounds were analysed by UV/Vis and IR spectroscopies and cyclic voltammetry. Photo-induced oxidation of C1 and C2 leads to the corresponding monocarbonyl oxidised species, whereas photo-induced reduction under argon leads mainly to the formation of the corresponding Os-bonded molecular wires P1 and P2 after exchange of two electrons associated with the loss of two chloro ligands. The chemical yield of the latter reaction (around 65%) becomes quantitative by adding [Ru(bpy)(3)](2+) as an external redox photosensitiser. This behaviour has been used to photocatalyse the two electron, two proton conversion of CO(2) to CO. Turnover numbers (TON) of 11.5 and 19.5 have been obtained respectively for C1 and C2 after 4.5 h of irradiation under CO(2) in DMF with triethanolamine as the electron donor. TON can be slightly increased by adding [Ru(bpy)(3)](2+) to the solution. 相似文献
105.
Donoli A Marcuzzo V Moretto A Toniolo C Cardena R Bisello A Santi S 《Organic letters》2011,13(6):1282-1285
Two series of 3(10)-helical peptides of different lengths and rigidity, based on the strongly foldameric α-aminoisobutyric acid and containing a terminal ferrocenyl unit, have been synthesized. Oxidation-state sensitive spectroscopic tags of helical peptides, the N-H groups, allowed mapping of the charge delocalization triggered by oxidation of the terminal ferrocenyl moiety and were monitored by IR spectroelectrochemistry. 相似文献
106.
This review describes the state of the art in the field of polyoxometalates containing noble metal atoms (ruthenium, rhodium, palladium, silver, osmium, iridium, platinum and gold). The structures of the various species are listed together with their applications (mainly in catalysis). 相似文献
107.
108.
109.
Frédérique Tellier 《合成通讯》2013,43(22):2287-2294
A stereospecific synthesis of (E,E)-9, 11, 13-tetradecatrienyl acetate and aldehyde is described. The key steps are two sequential palladium-catalyzed cross-coupling reactions between adequate organometalic reagents and the (E)-1,2-dibromoethylene. 相似文献