全文获取类型
收费全文 | 506篇 |
免费 | 59篇 |
国内免费 | 1篇 |
专业分类
化学 | 422篇 |
晶体学 | 7篇 |
力学 | 8篇 |
数学 | 31篇 |
物理学 | 98篇 |
出版年
2023年 | 11篇 |
2022年 | 10篇 |
2021年 | 17篇 |
2020年 | 16篇 |
2019年 | 20篇 |
2018年 | 18篇 |
2017年 | 19篇 |
2016年 | 32篇 |
2015年 | 23篇 |
2014年 | 35篇 |
2013年 | 18篇 |
2012年 | 52篇 |
2011年 | 44篇 |
2010年 | 24篇 |
2009年 | 25篇 |
2008年 | 43篇 |
2007年 | 22篇 |
2006年 | 15篇 |
2005年 | 11篇 |
2004年 | 3篇 |
2003年 | 6篇 |
2002年 | 5篇 |
2001年 | 7篇 |
2000年 | 5篇 |
1999年 | 7篇 |
1998年 | 2篇 |
1996年 | 2篇 |
1995年 | 5篇 |
1994年 | 3篇 |
1992年 | 5篇 |
1991年 | 3篇 |
1990年 | 5篇 |
1989年 | 5篇 |
1988年 | 4篇 |
1987年 | 3篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1982年 | 2篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 6篇 |
1977年 | 4篇 |
1976年 | 4篇 |
1975年 | 3篇 |
1974年 | 1篇 |
1973年 | 3篇 |
1972年 | 1篇 |
1970年 | 2篇 |
1967年 | 1篇 |
1966年 | 2篇 |
排序方式: 共有566条查询结果,搜索用时 15 毫秒
81.
Lea Kremer Elisabeth Hennes Alexandra Brause Andrei Ursu Lucas Robke Hideaki T. Matsubayashi Yuta Nihongaki Jana Flegel Ivana Mejdrov Jan Eickhoff Matthias Baumann Radim Nencka Petra Janning Susanne Kordes Hans R. Schler Jared Sterneckert Takanari Inoue Slava Ziegler Herbert Waldmann 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(46):16770-16781
82.
Dr. Toshiro Takao Dr. Yuta Takahashi Masataka Kai 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(29):e202200327
A dicationic triruthenium complex containing a μ3-η3-C3 ring, [(Cp*Ru)3(μ3-η3-C3MeH2−)(μ3-CH)(μ-H)]2+ ( 1 a , Cp*=η5-C5Me5), reacted with ammonia to yield a μ-amido complex, [(Cp*Ru)3(μ3-η3-CHCMeCH) (μ3-CH)(μ-NH2)]2+ ( 5 ), via N−H bond scission. Subsequent treatment with base resulted in C−N bond formation to yield a μ3-η2:η2-1-azabutadien-4-yl complex, [(Cp*Ru)3(μ3-CH)(μ3-η2:η2-NH=CH−CMe=CH−)]+ ( 6 a ). The azaruthenacyclopentadiene skeleton was alternatively synthesized by the photolysis of mono-cationic complex [(Cp*Ru)3(μ3-η3-C3RH2−)(μ3-CH)]+ ( 2 a ; R=Me, 2 b ; R=H) in the presence of ammonia. The C3 ring skeleton was broken via the electron transfer to the π*(C−C) orbital in the C3 ring, and a transiently generated unsaturated μ3-allylic species can take up ammonia, resulting in N−H bond scission followed by C−N bond formation. 相似文献
83.
Devika Sasikumar Prof. Dr. Yuta Takano Prof. Dr. Vasudevanpillai Biju 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(9):2060-2066
The conversion of solar energy to thermal, chemical, or electrical energy attracts great attention in chemistry and physics. There has been a considerable effort for the efficient extraction of photons throughout the entire solar spectrum. In this work light energy was efficiently harvested by using a long-lived betaine photogenerated from an acridinium-based electron donor–acceptor dyad. The photothermal energy-conversion efficiency of the dyad is significantly enhanced by simultaneous illumination with blue (420–440 nm) and yellow (>480 nm) light in comparison with the sum of the conversion efficiencies for individual illumination with blue or yellow light. The enhanced photothermal effect is due to the photogenerated betaine, which absorbs longer-wavelength light than the dyad, and thus the dyad–betaine combination is promising for efficient photothermal energy conversion. The mechanisms of betaine generation and energy conversion are discussed on the basis of steady-state and transient spectral measurements. 相似文献
84.
The Liebeskind-Srogl coupling/intramolecular Diels-Alder (IMDA) reaction cascade that stereoselectively affords a tricarbocyclic compound with a trans–trans-cis fused ring system including an all-carbon quaternary stereogenic center at the ring junction is described. The cascade reactions proceed quickly and stereoselectively afford the products within 2?h at room temperature in the presence of a suitable thioester. The developed protocol as well as the prepared chiral compounds are useful for the enantioselective total synthesis of terpenoids with the trans–trans-cis fused ring system. 相似文献
85.
Izumi Sakamoto Kazuya Iwaoka Yuta Kawada Takanori Naito Kazuyoshi Makida Yuki Takeuchi Takeshi Nishii Mitsuyo Horikawa Hiroto Kaku Tetsuto Tsunoda 《Tetrahedron》2018,74(24):3052-3060
3,3-Dimethoxypropylsulfonyl (Dimps) chloride was prepared and used as a new versatile sulfonating agent for ammonia, primary and secondary amines to afford corresponding Dimps-amides in excellent yields. The resulting N-nonsubstituted and N-monosubstituted Dimps-amides, activated amines, were alkylated satisfactorily under new Mitsunobu conditions. The Dimps group was removed by treatment in aqueous solution under acidic followed by basic conditions. Furthermore, epilachnene, the defensive droplets from the Mexican bean beetle, Epilachna varivestis, was synthesized utilizing this Dimps methodology in short steps. 相似文献
86.
Hayakawa I Ueda M Yamaura M Ikeda Y Suzuki Y Yoshizato K Kigoshi H 《Organic letters》2008,10(9):1859-1862
Second-generation total synthesis of haterumalide NA, a potent cytotoxic marine macrolide, was achieved by using B-alkyl Suzuki-Miyaura coupling and Nozaki-Hiyama-Kishi coupling as key steps (1.2% in 33 steps). Compared to our first-generation approach, the second-generation synthesis is much improved in the yield of key intermediate. 相似文献
87.
The authors have demonstrated the Hf(OTf)4-doped Me3SiCl system-catalyzed aminomethylation of electron-rich aromatic compounds, such as indoles and anilines, with new types of N,O-acetals having a variety of functional groups, such as cyano, ester, bis(trimethylsilyl)amino, diallylamino, and cyclic amino moieties, for the preparation of non-natural aromatic amino acid derivatives. Aminomethylation using an N,O-acetal with a bis(trimethylsilyl)amino group was particularly successful in the direct preparation of an N-unsubstituted α-indolylglycine derivative, which required only a standard aqueous workup. 相似文献
88.
Inukai J Miyatake K Ishigami Y Watanabe M Hyakutake T Nishide H Nagumo Y Watanabe M Tanaka A 《Chemical communications (Cambridge, England)》2008,(15):1750-1752
A luminescent porphyrin dye film has been coated onto a transparent separator on the cathode side of a direct methanol fuel cell (DMFC) to visualise clearly oxygen distribution under operating conditions by analysing emission from the dye. 相似文献
89.
The first synthetically useful catalytic enantioselective conjugate addition of cyanide to enones is described. The optimized conditions involved a Gd catalyst (5 or 10 mol %) derived from ligands 3 or 4 and a 1:1 ratio of TBSCN and 2,6-dimethylphenol. The reaction exhibited excellent to high enantioselectivity and a wide substrate scope. Moreover, the 1,4-adduct was exclusively produced over the 1,2-adduct. The complete regioselectivity was due both to stabilization of the 1,4-selective silylated polymetallic catalyst (7) using a TBS group and the ability of the asymmetric catalyst to promote retro-cyanation from the 1,2-adduct. 相似文献
90.
For polymer electrolyte membrane fuel membrane cell (PEMFC) applications, the effect of electron-withdrawing groups on the properties of sulfonated poly(arylene ether) (SPE) ionomer membranes was investigated. A series of poly(arylene ether)s containing fluorenyl groups and electron-withdrawing groups (sulfone, nitrile, or fluorine) was synthesized, which were sulfonated with chlorosulfonic acid using a flow reactor to obtain the title ionomers. The ionomers had high molecular weight (Mn > 77 kDa, Mw > 238 kDa) and gave tough, ductile membranes by solution casting. The ion exchange capacity (IEC) of the membranes ranged from 1.6 to 3.5 mequiv/g as determined by titration. The electron-withdrawing groups did not appear to affect the thermal properties (decomposition temperature higher than 200 °C). The presence of nitrile groups, especially at positions meta to the ether linkages, improved the oxidative stability of the SPE membranes, while it led to a deterioration of the hydrolytic stability. The perfluorinated biphenylene groups were effective in providing high mechanical strength with reasonable dimensional change, probably due to a somewhat decreased water absorbability. The SPE membrane containing sulfone groups showed the highest proton conductivity (10−3-10−1 S/cm) at 20-93% RH (relative humidity) and 80 °C. The nitrile-containing SPE membrane showed smaller apparent activation energies for oxygen and hydrogen permeability and is thus considered to be a possible candidate for applications in PEMFCs. 相似文献