全文获取类型
收费全文 | 2460篇 |
免费 | 92篇 |
国内免费 | 10篇 |
专业分类
化学 | 1971篇 |
晶体学 | 22篇 |
力学 | 31篇 |
数学 | 309篇 |
物理学 | 229篇 |
出版年
2023年 | 10篇 |
2022年 | 20篇 |
2021年 | 37篇 |
2020年 | 44篇 |
2019年 | 32篇 |
2018年 | 22篇 |
2017年 | 25篇 |
2016年 | 65篇 |
2015年 | 55篇 |
2014年 | 77篇 |
2013年 | 97篇 |
2012年 | 172篇 |
2011年 | 172篇 |
2010年 | 104篇 |
2009年 | 80篇 |
2008年 | 133篇 |
2007年 | 139篇 |
2006年 | 143篇 |
2005年 | 142篇 |
2004年 | 136篇 |
2003年 | 97篇 |
2002年 | 123篇 |
2001年 | 34篇 |
2000年 | 35篇 |
1999年 | 27篇 |
1998年 | 16篇 |
1997年 | 25篇 |
1996年 | 20篇 |
1995年 | 16篇 |
1994年 | 20篇 |
1993年 | 11篇 |
1991年 | 10篇 |
1990年 | 13篇 |
1989年 | 14篇 |
1988年 | 9篇 |
1987年 | 11篇 |
1986年 | 13篇 |
1985年 | 23篇 |
1984年 | 30篇 |
1983年 | 9篇 |
1982年 | 29篇 |
1981年 | 14篇 |
1980年 | 25篇 |
1979年 | 13篇 |
1978年 | 16篇 |
1977年 | 21篇 |
1976年 | 16篇 |
1975年 | 14篇 |
1974年 | 9篇 |
1973年 | 16篇 |
排序方式: 共有2562条查询结果,搜索用时 15 毫秒
131.
Regiospecific Formation and Unusual Optical Properties of 2,5‐Bis(arylethynyl)rhodacyclopentadienes: A New Class of Luminescent Organometallics 下载免费PDF全文
Dr. Andreas Steffen Dr. Richard M. Ward Dr. Meng Guan Tay Dr. Robert M. Edkins Dr. Fabian Seeler Magda van Leeuwen Dr. Lars‐Olof Pålsson Prof. Dr. Andrew Beeby Dr. Andrei S. Batsanov Prof. Dr. Judith A. K. Howard Prof. Dr. Todd B. Marder 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(13):3652-3666
A series of 2,5‐bis(arylethynyl)rhodacyclopentadienes has been prepared by a rare example of regiospecific reductive coupling of 1,4‐(p‐R‐phenyl)‐1,3‐butadiynes (R?H, Me, OMe, SMe, NMe2, CF3, CO2Me, CN, NO2, ?C?C‐(p‐C6H4?NHex2), ?C?C?(p‐C6H4?CO2Oct)) at [RhX(PMe3)4] ( 1 ) (X=?C?C?SiMe3 ( a ), ?C?C‐(p‐C6H4?NMe2) ( b ), ?C?C?C?C?(p‐C6H4?NPh2) ( c ) or ?C?C?{p‐C6H4‐C?C?(p‐C6H4‐N(C6H13)2)} ( d ) or Me ( e )), giving the 2,5‐bis(arylethynyl) isomer exclusively. The rhodacyclopentadienes bearing a methyl ligand in the equatorial plane (compound 1 e ) have been converted into their chloro analogues by reaction with HCl etherate. The rhodacycles thus obtained are stable to air and moisture in the solid state and the acceptor‐substituted compounds are even stable to air and moisture in solution. The photophysical properties of the rhodacyclopentadienes are highly unusual in that they exhibit, exclusively, fluorescence between 500–800 nm from the S1 state, with quantum yields of Φ=0.01–0.18 and short lifetimes (τ=0.45–8.20 ns). The triplet state formation (ΦISC=0.57 for 2 a ) is exceptionally slow, occurring on the nanosecond timescale. This is unexpected, because the Rh atom should normally facilitate intersystem crossing within femto‐ to picoseconds, leading to phosphorescence from the T1 state. This work therefore highlights that in some transition‐metal complexes, the heavy atom can play a more subtle role in controlling the photophysical behavior than is commonly appreciated. 相似文献
132.
Judith Hoffmann Prof. Dr. Uli Kazmaier 《Angewandte Chemie (International ed. in English)》2014,53(42):11356-11360
The development of a new photolabile protecting group containing an additional allyl functionality allows the synthesis of cyclic photoactivatable natural products. Cyclization occurs between the allyl moiety in the protecting group and a second double bond in the target molecule by means of ring‐closing metathesis. Cyclization should increase the metabolic stability towards proteases. On the other hand, the conformational change should cause diminished biological activity. As illustrated for tubulysin derivatives, cyclic and photoactivatable drug candidates can easily be obtained in only two steps from simple building blocks through Ugi reaction and ring‐closing metathesis. The photolabile protecting group is introduced by means of the isocyanide component during the Ugi reaction. 相似文献
133.
Tetracyanoquinodimethane Reduction by Complexed Guanidinyl‐Functionalized Aromatic Compounds 下载免费PDF全文
Hendrik Herrmann Alexandra Ziesak Ute Wild Simone Leingang David Schrempp Norbert Wagner Prof. Dr. Johannes Beck Dr. Elisabeth Kaifer Prof. Dr. Hubert Wadepohl Prof. Dr. Hans‐Jörg Himmel 《Chemphyschem》2014,15(2):351-365
In this work, we report on the reduction of tetracyanoquinodimethane (TCNQ) with dicationic complexes of guanidinyl‐functionalized aromatic (GFA) electron donors. In contrast to reduction with free GFAs, milder reduction conditions were achieved, and this led to semiconducting materials with extended TCNQ π stacking. The charge on the TCNQ units was estimated from the structural data obtained by single‐crystal X‐ray diffraction analysis and from IR spectroscopic data. The electrical conductivity was studied and the activation energy of the semiconducting materials was estimated from the temperature dependence of the conductivity. 相似文献
134.
Arnar Guðmundsson Kim Elisabeth Schlipköter Prof. Dr. Jan-E. Bäckvall 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(13):5441-5444
We report the first FeII-catalyzed biomimetic aerobic oxidation of alcohols. The principle of this oxidation, which involves several electron-transfer steps, is reminiscent of biological oxidation in the respiratory chain. The electron transfer from the alcohol to molecular oxygen occurs with the aid of three coupled catalytic redox systems, leading to a low-energy pathway. An iron transfer-hydrogenation complex was utilized as a substrate-selective dehydrogenation catalyst, along with an electron-rich quinone and an oxygen-activating Co(salen)-type complex as electron-transfer mediators. Various primary and secondary alcohols were oxidized in air to the corresponding aldehydes or ketones with this method in good to excellent yields. 相似文献
135.
Stephan Ludwig Dr. Kai Helmdach Mareike Hüttenschmidt Elisabeth Oberem Dr. Jabor Rabeah Dr. Alexander Villinger Prof. Dr. Ralf Ludwig Prof. Dr. Wolfram W. Seidel 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(70):16811-16817
A pair of diastereomeric dinuclear complexes, [Tp′(CO)BrW{μ-η2-C,C′-κ2-S,P-C2(PPh2)S}Ru(η5-C5H5)(PPh3)], in which W and Ru are bridged by a phosphinyl(thiolato)alkyne in a side-on carbon P,S-chelate coordination mode, were synthesized, separated and fully characterized. Even though the isomers are similar in their spectroscopic properties and redox potentials, the like-isomer is oxidized at W while the unlike-isomer is oxidized at Ru, which is proven by IR, NIR and EPR-spectroscopy supported by spectro-electrochemistry and computational methods. The second oxidation of the complexes was shown to take place at the metal left unaffected in the first redox step. Finally, the tipping point could be realized in the unlike isomer of the electronically tuned thiophenolate congener [Tp′(CO)(PhS)W{μ-η2-C,C′-κ2-S,P-C2(PPh2)S}Ru(η5-C5H5)-(PPh3)], in which valence trapped WIII/RuII and WII/RuIII cationic species are at equilibrium. 相似文献
136.
Jrg Schappel Kathrin Schmidt Elisabeth Klemm 《Journal of polymer science. Part A, Polymer chemistry》2005,43(16):3574-3587
A Sonogashira polycondensation reaction has been used to synthesize copolymers consisting of alternating oligo(p‐phenyleneethynylene) with a precise block length as an electron‐rich component and 1,4‐bis(2‐phenylene‐2‐cyanovinylene)benzene or 2,6‐bis(2‐pyridinylene‐ethynylene)pyridine as an electron‐poor component. The copolymers differ in the length of the phenyleneethynylene block (trimer or pentamer) and the content of the electron‐poor component. The length of the phenyleneethynylene block has no influence on the maximum wavelength. The electron‐poor cyano‐block component lowers the optical band‐gap energy of the copolymers. The value is equivalent to that of poly(cyano‐phenylenevinylene) (CN‐PPV) (2.3–2.4 eV). © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3574–3587, 2005 相似文献
137.
138.
Elisabeth Eidenberger Erich Stergar Harald Leitner Peter Staron Jürgen Spitaler Claudia Ambrosch-Draxl Helmut Clemens 《Applied Physics A: Materials Science & Processing》2009,97(2):331-340
Atom probe tomography (APT) measurements were conducted to analyze nm-sized precipitates in a Fe-25 m% Co-15 m% Mo model alloy.
Calculation of isoconcentration surfaces and application of cluster-search algorithms yielded the chemical compositions of
matrix and precipitates. Small-angle neutron scattering (SANS) was performed in order to calculate the ratio of magnetic to
nuclear scattering. This so-called A-ratio was compared with values calculated from the chemical information derived from the atom probe data. For this, the magnetism
of the precipitates has to be taken into account. Ab-initio studies have been carried out to determine the magnetic moment
of the precipitate phase. The results show that the extremely fine precipitates are ferromagnetic and exhibit near-equilibrium
composition. In the very early stage of decomposition, however, the composition is different from near-equilibrium. The influences
of the magnetism of the precipitates as well as of artifacts from atom probe measurements on the obtained results are discussed. 相似文献
139.
Quentin Ronzon Dr. Wei Zhang Dr. Nicolas Casaretto Dr. Elisabeth Mouray Prof. Dr. Isabelle Florent Dr. Bastien Nay 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(28):7764-7772
The introduction of substituents on bare heterocyclic scaffolds can selectively be achieved by directed C−H functionalization. However, such methods have only occasionally been used, in an iterative manner, to decorate various positions of a medicinal scaffold to build chemical libraries. We herein report the multiple, site selective, metal-catalyzed C−H functionalization of a “programmed” 4-hydroxyquinoline. This medicinally privileged template indeed possesses multiple reactive sites for diversity-oriented functionalization, of which four were targeted. The C-2 and C-8 decorations were directed by an N-oxide, before taking benefit of an O-carbamoyl protection at C-4 to perform a Fries rearrangement and install a carboxamide at C-3. This also released the carbonyl group of 4-quinolones, the ultimate directing group to functionalize position 5. Our study highlights the power of multiple C−H functionalization to generate diversity in a biologically relevant library, after showing its strong antimalarial potential. 相似文献
140.
Johannes Tauer Heinrich Kofler Elisabeth Schwarz Ernst Wintner 《Central European Journal of Physics》2010,8(2):242-248
Laser ignition is considered to be one of the most promising future concepts for internal combustion engines. It combines the legally required reduction of pollutant emissions and higher engine efficiencies. The igniting plasma is generated by a focused pulsed laser beam. Having pulse durations of a few nanoseconds, the pulse energy E p for reliable ignition amounts to the order of 10 mJ. Different methods of laser ignition with an emphasis on fiber-based systems will be discussed and evaluated. 相似文献