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91.
Chih-Wei HuangMuthian Shanmugasundaram Hao-Ming ChangChien-Hong Cheng 《Tetrahedron》2003,59(20):3635-3641
An efficient method for the preparation of various monosubstituted arylallenes, disubstituted allenes and alkenylallenes via palladium-catalyzed coupling of allenylstannanes with aryl iodides or alkenyl iodides is described. The coupling reaction was carried out in the presence of Pd(PPh3)4 and LiCl using DMF as solvent. The possible role of LiCl in this coupling process is discussed based on the 119Sn NMR studies. 相似文献
92.
Koji Nakabayashi Masaki Kawano Prof. Dr. Tatsuhisa Kato Prof. Dr. Ko Furukawa Dr. Shin‐ichi Ohkoshi Prof. Dr. Toshiya Hozumi Dr. Makoto Fujita Prof. Dr. 《化学:亚洲杂志》2007,2(1):164-170
We show a new approach to manipulating the through‐space spin–spin interaction by utilizing the confined cavity of a self‐assembled M6L4 coordination cage. The coordination cage readily encapsulates stable organic radicals in solution, which brings the spin centers of the radicals closer to each other. In sharp contrast to the fact that the radical in solution in the absence of the cage is in a doublet state, in the presence of the cage through‐space spin–spin interaction is induced through cage‐encapsulation effects in solution as well as in the solid state, resulting in the triplet state of the complex. These results were confirmed by ESR spectroscopy and X‐ray crystallography. The quantity of triplet species generated by encapsulation in the cage increases with increasing affinity of the radicals to the cage. We estimated the affinity between several types of guests and the cage in solution by cyclic voltammetry. We also demonstrate that the through‐space interaction of organic radicals within the self‐assembled coordination cage can be controlled by external stimuli such as heat or pH. 相似文献
93.
A new process for the Pd/Cu co-catalyzed homocoupling reaction of terminal alkynes was developed. The reaction was carried out in aqueous media with sodium percarbonate as both a clean oxidant and a base. Meanwhile, a palladium complex immobilized on a synthetic PS-PEG400-PPh2 resin was used as the catalyst, which may be recovered by simple filtration and reused for several times with high activity. 相似文献
94.
Kremzow D Seidel G Lehmann CW Fürstner A 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(6):1833-1853
Oxidative insertion of [Pd(PPh3)4] or [Ni(cod)2]/PPh3 into the C-Cl bond of various 2-chloroimidazolinium- and other -amidinium salts affords metal-diaminocarbene complexes in good to excellent yields. This procedure is complementary to existing methodology in which the central metal does not change its oxidation state, and therefore allows to incorporate carbene fragments that are difficult to access otherwise. The preparation of a variety of achiral as well as enantiomerically pure, chiral metal-NHC complexes (NHC = N-heterocyclic carbene) and metal complexes with acyclic diaminocarbene ligands illustrates this aspect. Furthermore it is shown that oxidative insertion also paves a way to prototype Fischer carbenes of Pd(II). Since the required starting materials are readily available from urea- or thiourea derivatives, this novel approach allows for substantial structural variations of the ligand backbone. The catalytic performance of the resulting library of nickel- and palladium-carbene complexes has been evaluated by applications to prototype Suzuki-, Heck-, and Kumada-Corriu cross-coupling reactions as well as Buchwald-Hartwig aminations. It was found that even Fischer carbenes show appreciable catalytic activity. Moreover, representative examples of all types of neutral and cationic metal-carbene complexes formed in this study have been characterized by X-ray crystallography. 相似文献
95.
Anusuya Choudhury Michael E. Pierce Dieu Nguyen Louis Storace Pat N. Confalone 《Tetrahedron letters》2005,46(47):8099-8102
D-D4FC (1) is an anti-HIV agent currently under phase II clinical trial (Pharmaset Inc). Its molecular architecture is suitable for a Ferrier rearrangement kind of operation on a furanoid glycal to fix the position of the double bond and the relative stereochemistry. Despite the fact that classical Ferrier rearrangement does not work on furanoid glycals, a palladium mediated modified protocol has been developed for the glycosidation of an aromatization prone xylo-furanoid glycal (5) for the synthesis of D-D4FC. 相似文献
96.
A. A. Bezrukova V. S. Khandkarova P. V. Petrovskii A. Z. Rubezhov Ya. S. Vygodskii K. P. Butin T. V. Magdesieva G. A. Pirogova 《Russian Chemical Bulletin》1995,44(5):941-945
Binuclear RhIII and RuII complexes of the [M1-CN-M2]+BF
4
–
(M1 and/or M2 are (5-Cp)(3-C3H5)Rh and (6-C6H6)(3-C3H5)Ru) type, heteronuclear organometallic compound (5-Cp)(3-C3H5)RhCNPd(3-C3H5)Cl, and mononuclear RhIII and RuII complexes [(3-C3H5)LM(MeCN)]+
BF4
–
(M = Rh, L = 5-Cp; M = Ru, L = 6-C6H6) were synthesized. An electrochemical study of these compounds in solutions demonstrates that the bond between the bridged CN ligand and the metal atoms is rather strong, and there is no dissociation into mononuclear fragments in solutions. The kinetics of the reaction of [(5-Cp)(3-C3H5)Rh(MeCN)]+
BF4
–
with halide ions was studied by electrochemical methods. The ligand exchange proceeds by a bimolecular dissociative-exchange mechanism.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 968–973, May, 1995. 相似文献
97.
Yi-min HuJie Zhou Xiang-tian LongJian-lin Han Chen-jian ZhuYi Pan 《Tetrahedron letters》2003,44(27):5009-5010
Reaction of benzyl halides with N-allyl-N-(2-butenyl)-p-toluenesulfonamide 1 in the presence of a palladium catalyst afforded dihydropyrroles 3 in moderate to excellent yields. It is proposed that the cyclic products were formed via a palladium-catalyzed cascade cyclization-coupling process. 相似文献
98.
Mauleón P Núñez AA Alonso I Carretero JC 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(7):1511-1520
Unlike traditionally used acyclic 1,2-disubstituted alkenes, the reaction of alpha,beta-unsaturated phenyl sulfones with aryl iodides under Heck reaction conditions (Pd(OAc)(2) as catalyst, Ag(2)CO(3) as base in DMF at 120 (0)C) takes place mainly by a cascade process, involving one unit of the alkene and three units of the aryl iodide, to afford a substituted 9-phenylsulfonyl-9,10-dihydrophenanthrene. The dominant formation of this 3:1 coupling product, instead of the Heck trisubstituted olefin, shows that aromatic C-H bond activation processes can compete with the usually fast syn beta-hydrogen elimination step in the Heck arylation of an acyclic olefin. The structural scope of this palladium-catalyzed cascade arylation of alpha,beta-unsaturated sulfones has proved to be wide with regard to substitution at the beta-position (alkyl, aryl, or alkenyl substitution), substitution at the sulfone unit (alkyl or phenyl sulfones), and configuration at the CdoublebondC bond (trans or cis). Moreover, although less favored than in the case of the arylation of alpha,beta-unsaturated sulfones, similarly substituted 9,10-dihydrophenanthrenes have also been obtained in the case of alpha,beta-unsaturated phosphine oxides and alpha,beta-unsaturated phosphonate esters. A Pd(0)-Pd(II)-Pd(IV) mechanistic pathway involving the successive formation of highly electrophilic sigma-alkylpalladium intermediates and palladacycles is proposed for this multicomponent arylation. 相似文献
99.
载体和担载酸对乙烯直接氧化合成乙酸反应的影响 总被引:3,自引:0,他引:3
在固定床流动反应器上研究了Pd-酸/载体体系催化乙烯直接氧\r\n化合成乙酸的反应,并对载体相同但担载酸强度不同的催化剂的催化活\r\n性进行了比较.结果表明,担载酸的强度明显影响催化剂的活性,酸强\r\n度越大其催化活性越高.用NH3-TPD和异丙醇脱水探针反应表征了二氧\r\n化硅、活性碳和酸性白土三种载体担载的Pd-H4SiW12催化剂的酸性,\r\n并测试了三种催化剂的催化活性.结果表明,载体通过影响担载酸的强\r\n度而影响催化剂的活性,载体上的强酸中心越多,催化剂的活性越高.\r\n测定了二氧化硅、活性碳和酸性白土三种载体担载的Pd-H4SiW12催化\r\n剂上Pd的分散度,并与其催化活性相关联.结果表明,决定乙烯直接氧\r\n化生成乙酸反应活性的主要因素是催化剂的酸强度而不是Pd的分散度. 相似文献
100.
Werner Unterberger Bernd Jenewein Bernhard Kl?tzer Simon Penner Wolfgang Reichl Günther Rupprechter Di Wang Di Wang Robert Schl?gl Konrad Hayek 《Reaction Kinetics and Catalysis Letters》2006,87(2):215-234
Summary The effect of hydrogen reduction on the structure and catalytic properties of “thin film”and “inverse”model systems for supported
metal catalysts is discussed. Thin film model catalysts were obtained by epitaxial growth of Pt and Rh nanoparticles on NaCl(001),
which were coated with amorphous or crystalline supports of alumina, silica, titania, ceria and vanadia. Structural and morphological
changes upon hydrogen reduction between 473 and 973 K were examined by high resolution electron microscopy. Metal-oxide interaction
sets in at a specific reduction temperature and is characterized by an initial “wetting”stage, followed by alloy formation
at increasing temperature, in the order VOx< TiOx< SiO2< CeOx< Al2O3. “Inverse”model systems were prepared by deposition of oxides on a metal substrate, e.g. VOx/Rh and VOx/Pd. Reduction of inverse systems at elevated temperature induces subsurface alloy formation. In contrast to common bimetallic
surfaces, the stable subsurface alloys of V/Rh and V/Pd have a purely noble metal-terminated surface, with V positioned in
near-surface layers. The uniform composition of the metallic surface layer excludes catalytic ensemble effects in favor of
ligand effects. Activity and selectivity, e.g. for CO and CO2methanation and for partial oxidation of ethene, are mainly controlled by the temperature of annealing or reduction. Reduction
above 573 K turned out to be beneficial for the catalytic activity of the subsurface alloys, but not for the corresponding
thin film systems which tend to deactivate viaparticle encapsulation.</o:p> 相似文献