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991.
A series of differently substituted Chugaev‐type palladium bis(acyclic diaminocarbene) complexes was screened to identify the most active catalyst for Mizoroki–Heck coupling reactions of aryl bromides with styrene. The best catalyst, which contains three methyl groups on the bis(carbene) ligand, gives excellent coupling yields at 120 °C for both activated and deactivated aryl bromides. However, activity with aryl chlorides is limited to electron‐deficient examples. The optimized catalyst demonstrates limited air and moisture stability, giving reduced yields in couplings of activated aryl bromides in open‐flask conditions. The modular synthesis of this class of catalysts should allow further fine‐tuning of activity in Mizoroki–Heck and related coupling reactions. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
992.
The development of catalytic metal carbene transformations for the construction of macrocyclic lactones has dramatically increased their synthetic advantages. This is the first review of this Developing methodology. The research described in this review has been supported by the National Science Foundation, National Institutes of Health, and the Petroleum Research Fund of the American Chemical Society. 相似文献
993.
994.
Quasi‐living copolymerization of ethylene with 1‐hexene by heteroligated (salicylaldiminato β‐enaminoketonato) titanium complexes 下载免费PDF全文
Ying‐Yun Long Yong‐Xia Wang Bai‐Xiang Li Yan‐Guo Li Yue‐Sheng Li 《Journal of polymer science. Part A, Polymer chemistry》2017,55(17):2787-2797
A series of heteroligated (salicylaldiminato)(β‐enaminoketonato)titanium complexes [3‐But‐2‐OC6H3CH = N(C6F5)] [PhN = C(R1)CHC(R2)O]TiCl2 [ 3a : R1 = CF3, R2 = tBu; 3b : R1 = Me, R2 = CF3; 3c : R1 = CF3, R2 = Ph; 3d : R1 = CF3, R2 = C6H4Ph(p ); 3e : R1 = CF3, R2 = C6H4Ph(o ); 3f : R = CF3, R2 = C6H4Cl(p ); 3g : R1 = CF3; R2 = C6H3Cl2(2,5); 3h : R1 = CF3, R2 = C6H4Me(p )] were investigated as catalysts for ethylene (co)polymerization. In the presence of modified methylaluminoxane as a cocatalyst, these complexes showed activities about 50%–1000% and 10%–100% higher than their corresponding bis(β‐enaminoketonato) titanium complexes for ethylene homo‐ and ethylene/1‐hexene copolymerization, respectively. They produced high or moderate molecular weight copolymers with 1‐hexene incorporations about 10%–200% higher than their homoligated counterpart pentafluorinated FI‐Ti complex. Among them, complex 3b displayed the highest activity [2.06 × 106 g/molTi?h], affording copolymers with the highest 1‐hexene incorporations of 34.8 mol% under mild conditions. Moreover, catalyst 3h with electron‐donating group not only exhibited much higher 1‐hexene incorporations (9.0 mol% vs. 3.2 mol%) than pentafluorinated FI‐Ti complex but also generated copolymers with similar narrow molecular weight distributions (M w/M n = 1.20–1.26). When the 1‐hexene concentration in the feed was about 2.0 mol/L and the hexene incorporation of resultant polymer was about 9.0 mol%, a quasi‐living copolymerization behavior could be achieved. 1H and 13C NMR spectroscopic analysis of their resulting copolymers demonstrated the possible copolymerization mechanism, which was related with the chain initiation, monomer insertion style, chain transfer and termination during the polymerization process. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55 , 2787–2797 相似文献
995.
cis‐1,4‐specific carbocationic polymerization and copolymerization of 1,3‐dienes initiated by (S,S)‐bis(oxazolinylphenyl)amine chromium complexes 下载免费PDF全文
Yingda Huang Jianyun He Guilong Cai Zhanxiong Liu Tingting Li Tingting Du Shaowen Zhang Bo Yao Xiaofang Li 《Journal of polymer science. Part A, Polymer chemistry》2017,55(7):1250-1259
Two new chiral (S,S)‐bis(oxazolinylphenyl)amine chromium dichloride complexes have been synthesized and structurally characterized. In combination with 2 equiv. of borate and an excess of AlR3, such Cr complexes serve as effective cationic initiators in the stereoregular carbocationic polymerization of 1,3‐dienes such as isoprene (IP) and myrcene (MY), affording cyclized cis‐1,4‐PIPs/PMys (cis‐1,4‐selectivity up to 96%) with cyclic sequence contents ranging from 26% to 87%. Moreover, these Cr initiator systems also exhibit an unprecedented control over sequence distribution of comonomers in the carbocationic copolymerization of IP and MY, preparing novel copolymers with different microstructures from mainly cyclized cis‐1,4‐specific statistical copolymers to cyclic olefin copolymers. The nature of Cr complex, borate, AlR3, temperature, molar ratio of comonomers has considerable effect on the (co)polymer's yield, stereoselectivity, cyclization, and comonomer sequence distribution. A plausible mechanism is suggested, which gives a new strategy for biomimetic synthesis of natural rubber. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 55, 1250–1259 相似文献
996.
Activity of 20wt% MO2/Al2O3 catalysts, where M = Mn, Ce and Zr has been studied in ketonisation of the mixtures of propanoic/pentanoic, ethanoic/10-undecenoic and hexanoic/(Z)-9-octadecenoic (oleic) acids. Irrespective of the molecular weights and molar ratios of reacting acids, high yields of ketones were obtained over Mn and Ce oxide catalysts at approximately 673 K. Isomerization of C=C double bonds and partial pyrolysis occurred during catalytic ketonization of 10-undecenoic and oleic acids, diminishing slightly the yield of ketones. The preparation of (Z)-14-tricosen-6-one has been performed, being the starting material for the synthesis of (Z)-9-tricosene - sex attractant of male house fly. 相似文献
997.
Synthesis of poly(1‐chloro‐2‐arylacetylene)s with high cis‐content and examination of their absorption/emission properties 下载免费PDF全文
Jesus Rodriguez Castanon Natsuhiro Sano Masashi Shiotsuki Fumio Sanda 《Journal of polymer science. Part A, Polymer chemistry》2017,55(3):382-388
A series of 1‐chloro‐2‐arylacetylenes [Cl‐C?C‐Ar, Ar = C6H5 ( 1 ), C6H4‐p‐i Pr ( 2 ), C6H4‐p‐Oi Pr ( 3 ), C6H4‐p‐NHC(O)Ot Bu ( 4 ), and C6H4‐o‐i Pr ( 5 )] were polymerized using (tBu3P)PdMeCl/silver trifluoromethanesulfonate (AgOTf) and MoCl5/SnBu4 catalysts. The corresponding polymers [poly( 1 )–poly( 5 )] with weight‐average molecular weights of 6,500–690,000 were obtained in 10–91% yields. THF‐insoluble parts, presumably high‐molecular weight polymers, were formed together with THF‐soluble polymers by the Pd‐catalyzed polymerization. The Pd catalyst polymerized nonpolar monomers 1 and 2 to give the polymers in yields lower than the Mo catalyst, while the Pd catalyst polymerized polar monomers 3 and 4 to give the corresponding polymers in higher yields. The 1H NMR and UV–vis absorption spectra of the polymers indicated that the cis‐contents of the Pd‐based polymers were higher than those of the Mo‐based polymers, and the conjugation length of the Pd‐based polymers was shorter than that of the Mo‐based polymers. Pd‐based poly( 5 ) emitted fluorescence most strongly among poly( 1 )–poly( 5 ). © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55 , 382–388 相似文献
998.
Highly Active and Robust Metalloporphyrin Catalysts for the Synthesis of Cyclic Carbonates from a Broad Range of Epoxides and Carbon Dioxide 下载免费PDF全文
Dr. Chihiro Maeda Junta Shimonishi Ray Miyazaki Prof. Jun‐ya Hasegawa Prof. Tadashi Ema 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(19):6556-6563
Bifunctional metalloporphyrins with quaternary ammonium bromides (nucleophiles) at the meta, para, or ortho positions of meso‐phenyl groups were synthesized as catalysts for the formation of cyclic carbonates from epoxides and carbon dioxide under solvent‐free conditions. The meta‐substituted catalysts exhibited high catalytic performance, whereas the para‐ and ortho‐substituted catalysts showed moderate and low activity, respectively. DFT calculations revealed the origin of the advantage of the meta‐substituted catalyst, which could use the flexible quaternary ammonium cation at the meta position to stabilize various anionic species generated during catalysis. A zinc(II) porphyrin with eight nucleophiles at the meta positions showed very high catalytic activity (turnover number (TON)=240 000 at 120 °C, turnover frequency (TOF)=31 500 h?1 at 170 °C) at an initial CO2 pressure of 1.7 MPa; catalyzed the reaction even at atmospheric CO2 pressure (balloon) at ambient temperature (20 °C); and was applicable to a broad range of substrates, including terminal and internal epoxides. 相似文献
999.
Surfactant‐Assisted Nanocrystalline Zinc Coordination Polymers: Controlled Particle Sizes and Synergistic Effects in Catalysis 下载免费PDF全文
Chao Huang Huarui Wang Xiaolu Wang Kuan Gao Prof. Jie Wu Prof. Hongwei Hou Prof. Yaoting Fan 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(18):6389-6396
Different morphologies and particle sizes of two crystalline zinc‐based coordination polymers (CPs), [Zn(pytz)H2O]n ( 1 ; H2pytz=2,6‐bis(tetrazole)pyridine) and [Zn2(pytz)24 H2O] ( 2 ), from the bulk scale to the nanoscale, could be obtained under solvothermal conditions with different surfactants (polyvinylpyrrolidone (PVP) or polyethylene glycol (PEG) 2000) as templates. PVP and PEG 2000 could act as capping and structure‐directing agents, respectively, to influence the growth of crystalline particles and control their sizes. CP 1 exhibits a two‐dimensional framework with window‐like units and 2 shows a bimetallic structure. Nanocrystalline 1 and 2 were used as heterogeneous catalysts to study how adjacent catalytic active sites synergistically effected their catalytic reactivities in the direct catalytic conversion of aromatic dinitriles into oxazolines. The results showed that 1 produced bis‐oxazolines as the sole products, whereas 2 gave the mono‐oxazolines as the major products under the same reaction conditions. 相似文献
1000.
Thomas J. Colacot 《Journal of Chemical Sciences》2000,112(3):197-207
The chiral dirhodium(II) carboxamidates are a unique class of chiral catalysts useful for asymmetric inter- and intramolecular
cyclopropanation, cyclopropenation and C-H insertion reactions with excellent enantioselectivities. The broad applications
of these catalysts in organic syntheses are briefly reviewed. 相似文献