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71.
Competitive Gold‐Promoted Meyer–Schuster and oxy‐Cope Rearrangements of 3‐Acyloxy‐1,5‐enynes: Selective Catalysis for the Synthesis of (+)‐(S)‐γ‐Ionone and (−)‐(2S,6 R)‐cis‐γ‐Irone 下载免费PDF全文
Dr. Serena Bugoni Dr. Valentina Merlini Dr. Alessio Porta Dr. Sylvain Gaillard Prof. Giuseppe Zanoni Prof. Dr. Steven P. Nolan Prof. Giovanni Vidari 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(40):14068-14074
We report a simple, highly stereoselective synthesis of (+)‐(S)‐γ‐ionone and (‐)‐(2S,6R)‐cis‐γ‐irone, two characteristic and precious odorants; the latter compound is a constituent of the essential oil obtained from iris rhizomes. Of general interest in this approach are the photoisomerization of an endo trisubstituted cyclohexene double bond to an exo vinyl group and the installation of the enone side chain through a [(NHC)AuI]‐catalyzed Meyer–Schuster‐like rearrangement. This required a careful investigation of the mechanism of the gold‐catalyzed reaction and a judicious selection of reaction conditions. In fact, it was found that the Meyer–Schuster reaction may compete with the oxy‐Cope rearrangement. Gold‐based catalytic systems can promote either reaction selectively. In the present system, the mononuclear gold complex [Au(IPr)Cl], in combination with the silver salt AgSbF6 in 100:1 butan‐2‐one/H2O, proved to efficiently promote the Meyer–Schuster rearrangement of propargylic benzoates, whereas the digold catalyst [{Au(IPr)}2(μ‐OH)][BF4] in anhydrous dichloromethane selectively promoted the oxy‐Cope rearrangement of propargylic alcohols. 相似文献
72.
Muhammed Üçüncü Erman Karakuş Prof. Dr. Mustafa Emrullahoğlu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(38):13201-13205
A fluorescent probe that displays a ratiometric fluorescence response towards gold and mercury ions has been devised. Emitting at a relatively longer wavelength, the conjugated form of the fluorescent dye transforms in the presence of the gold or mercury ions into a new dye, the molecular structure of which lacks the conjugation and consequently emits at a distinctly shorter wavelength. 相似文献
73.
Synthesis and Catalytic Use of Gold(I) Complexes Containing a Hemilabile Phosphanylferrocene Nitrile Donor 下载免费PDF全文
Karel Škoch Dr. Ivana Císařová Prof. Dr. Petr Štěpnička 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(45):15998-16004
Removal of the chloride ligand from [AuCl( 1 ‐κP)] ( 2 ) containing a P‐monodentate 1′‐(diphenylphosphanyl)‐1‐cyanoferrocene ligand ( 1 ), by using silver(I) salts affords cationic complexes of the type [Au( 1 )]X, which exist either as cyclic dimers [Au( 1 )]2X2 ( 3 a , X=SbF6; 3 c , X=NTf2) or linear coordination polymers [Au( 1 )]nXn ( 3 a′ , X=SbF6; 3 b′ , X=ClO4), depending on anion X and the isolation procedure. As demonstrated for 3 a′ , the polymers can be readily cleaved by the addition of donors, such as Cl?, tetrahydrothiophene (tht) or 1 , giving rise to the parent compound 2 , [Au(tht)( 1 ‐κP)][SbF6] ( 5 a ) or [Au( 1 ‐κP)2][SbF6] ( 4 a ), respectively, of which the last two compounds can also be prepared by stepwise replacement of tht in [Au( 1 ‐κP)2][SbF6]. The particular combination of a firmly coordinated (phosphane) and a dissociable (nitrile) donor moieties renders complexes 3/3′ attractive for catalysis because they can serve as shelf‐stable precursors of coordinatively unsaturated AuI fragments, analogous to those that result from the widely used [Au(PR3)(RCN)]X catalysts. The catalytic properties of the Au‐ 1 complexes were evaluated in model annulation reactions, such as the synthesis of 2,3‐dimethylfuran from (Z)‐3‐methylpent‐2‐en‐4‐yn‐1‐ol and oxidative cyclisation of alkynes with nitriles to produce 2,5‐disubstituted 1,3‐oxazoles. Of the compounds tested ( 2 , 3 a′ , 3 b′ , 3 a , 4 a and 5 a ), the best results were consistently achieved with dimer 3 c , which has good solubility in organic solvents and only one firmly bound donor at the gold atom. This compound was advantageously used in the key steps of annuloline and rosefuran syntheses. 相似文献
74.
75.
Frontispiece: Surface Segregated AgAu Tadpole‐Shaped Nanoparticles Synthesized Via a Single Step Combined Galvanic and Citrate Reduction Reaction 下载免费PDF全文
76.
Reversible Modulation of Surface Plasmons in Gold Nanoparticles Enabled by Surface Redox Chemistry 下载免费PDF全文
Dr. Zheng Li Dr. Jonathan J. Foley IV Dr. Sheng Peng Dr. Cheng‐Jun Sun Dr. Yang Ren Dr. Gary P. Wiederrecht Dr. Stephen K. Gray Dr. Yugang Sun 《Angewandte Chemie (International ed. in English)》2015,54(31):8948-8951
Switchable surface redox chemistry is demonstrated in gold@iron/iron oxide core–shell nanoparticles with ambient oxidation and plasmon‐mediated reduction to modulate the oxidation state of shell layers. The iron shell can be oxidized to iron oxide through ambient oxidation, leading to an enhancement and red‐shift of the gold surface plasmon resonance (SPR). This enhanced gold SPR can drive reduction of the iron oxide shell under broadband illumination to reversibly blue‐shift and significantly dampen gold SPR absorption. The observed phenomena provide a unique mechanism for controlling the plasmonic properties and surface chemistry of small metal nanoparticles. 相似文献
77.
78.
Gold(I)‐Catalyzed Tandem Transformation with Diynes: Rapid Access to Linear Cyclopentenone‐Fused Polycyclic Molecules 下载免费PDF全文
Congjun Yu Bin Chen Tian Zhou Qingshan Tian Prof. Dr. Guozhu Zhang 《Angewandte Chemie (International ed. in English)》2015,54(37):10903-10907
An efficient and convenient synthesis of useful linear cyclopentenone‐fused polycyclic compounds has been achieved through a novel gold(I)‐catalyzed transformation of diynes. The method demonstrates high product yields and tolerates of a wide variety of important functional groups. Gold‐vinylidene formation, methoxy group migration, and Nazarov‐type cyclization are proposed to be the key steps in the reaction pathway. The synthetic utility of this method is demonstrated by converting the product to eight‐membered‐ring‐fused compound. 相似文献
79.
Dr. Concha Bosch‐Navarro Zachary P. L. Laker Helen R. Thomas Alexander J. Marsden Dr. Jeremy Sloan Dr. Neil R. Wilson Dr. Jonathan P. Rourke 《Angewandte Chemie (International ed. in English)》2015,54(33):9560-9563
Atomic‐resolution transmission electron microscopy was used to identify individual Au9 clusters on a sulfur‐functionalized graphene surface. The clusters were preformed in solution and covalently attached to the surface without any dispersion or aggregation. Comparison of the experimental images with simulations allowed the rotational motion, without lateral displacement, of individual clusters to be discerned, thereby demonstrating a robust covalent attachment of intact clusters to the graphene surface. 相似文献
80.
Songyi Ham Hee‐Jeong Jang Yookyung Song Prof. Kevin L. Shuford Prof. Sungho Park 《Angewandte Chemie (International ed. in English)》2015,54(31):9025-9028
Herein, we report a general synthetic pathway to various shapes of three‐dimensional (3D) gold nanoframes (NFs) embedded with a Pt skeleton for structural rigidity. The synthetic route comprises three steps: site‐specific (edge and vertex) deposition of Pt, etching of inner Au, and regrowth of Au on the Pt framework. Site‐specific reduction of Pt on Au nanoparticles (NPs) led to the high‐quality of 3D Au NFs with good structural rigidity, which allowed the detailed characterization of the corresponding 3D metal NFs. The synthetic method described here will open new avenues toward many new kinds of 3D metal NFs. 相似文献