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991.
Devin H. A. Boom Ewoud J. J. de Boed Emmanuel Nicolas Martin Nieger Andreas W. Ehlers Andrew R. Jupp J. Chris Slootweg 《无机化学与普通化学杂志》2020,646(13):586-592
The reaction of the intramolecular frustrated Lewis pair (FLP) tBu2PCH2BPh2 with the amine-boranes NH3 · BH3 and Me2NH · BH3 leads to the formation of the corresponding FLP-H2 adducts as well as novel five-membered heterocycles that result from capturing the in situ formed amino-borane by a second equivalent of FLP. The sterically more demanding tBu2PCH2BMes2 does not form such a five-membered heterocycle when reacted with Me2NH · BH3 and its H2 adduct liberates dihydrogen at elevated temperatures, promoting the metal-free catalytic dehydrogenation of amine-boranes. 相似文献
992.
Dr. Daisuke Uraguchi Fumito Ueoka Dr. Naoya Tanaka Dr. Tomohito Kizu Wakana Takahashi Prof. Dr. Takashi Ooi 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(28):11553-11558
Catalysis by chiral weakly-coordinating anions (WCAs) remains underdeveloped due to the lack of a molecular design strategy for exploiting their characteristics, such as the non-nucleophilic nature. Here, we report the development of a chiral borate ion comprising an O,N,N,O-tetradentate backbone, which ensures hitherto unattainable structural robustness. Upon pairing with a proton, the hydrogen borate acts as an effective catalyst for the asymmetric Prins-type cyclization of vinyl ethers, providing access to structurally and stereochemically defined dihydropyrans. The key to selectivity control is the distinct ability of the borate ion to discriminate the prochiral faces of the acyclic oxonium ion intermediate and dictate the regiochemical outcome. We anticipate that this study paves the way for exploring the untapped potential of WCA catalysis for selective chemical synthesis. 相似文献
993.
Zhenghong Zhou Zhaoming Li Kangying Li Zhuohong Yang Guofeng Zhao Lixin Wang 《Phosphorus, sulfur, and silicon and the related elements》2013,188(8):1771-1779
New chiral Schiff base ligands 1-4 were synthesized starting from (+)-camphor and (+)-1-(4-nitrophenyl)-2-amino-1,3-propanediol, and their application in asymmetric ring-opening of cyclohexene oxide using mercaptan (thiophenols) as nucleophiles was investigated. The aymmetric ring-opening of cylohexene oxide catalyzed respectively by chiral Schiff bases 1-4 /Ti(OPr- i ) 4 and ( m )-(S)-1,1'-binaphthalene-2,2'-diol 5 /Ti(OPr- i ) 4 complex afforded the corresponding chiral g -hydroxysulfides 6-10 in lower to good yield with lower to moderate ee values. Moreover, the using of ( m )-(S)-1,1'-binaphthalene-2,2'-diol as ligand led to better chiral induction effect. 相似文献
994.
995.
996.
A. Sankaranarayanan 《Lithuanian Mathematical Journal》2007,47(3):277-310
We study the sixth-power moments of certain L-functions belonging to a sub-class of the Selberg’s class on the critical line and, using this, we conclude an upper bound
for the fourth-power moments of certain L-functions related to GL
3 on the critical line. This is an analogue of the upper bound for the twelfth-power moment of the Riemann zeta-function on
the critical line.
Published in Lietuvos Matematikos Rinkinys, Vol. 47, No. 3, pp. 341–380, July–September, 2007. 相似文献
997.
David Milovich 《Topology and its Applications》2008,156(2):443-464
The Noetherian type of a space is the least κ such that it has a base that is κ-like with respect to reverse inclusion. Just as all known homogeneous compacta have cellularity at most c, they satisfy similar upper bounds in terms of Noetherian type and related cardinal functions. We prove these and many other results about these cardinal functions. For example, every homogeneous dyadic compactum has Noetherian type ω. Assuming GCH, every point in a homogeneous compactum X has a local base that is c(X)-like with respect to containment. If every point in a compactum has a well-quasiordered local base, then some point has a countable local π-base. 相似文献
998.
999.
Dr. Alessandro Bismuto Dr. Gary S. Nichol Dr. Fernanda Duarte Dr. Michael J. Cowley Dr. Stephen P. Thomas 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(31):12831-12835
The reaction of a Lewis acidic borane with an alkyne is a key step in a diverse range of main group transformations. Alkyne 1,1-carboboration, the Wrackmeyer reaction, is an archetypal transformation of this kind. 1,1-Carboboration has been proposed to proceed through a zwitterionic intermediate. We report the isolation and spectroscopic, structural and computational characterization of the zwitterionic intermediates generated by reaction of B(C6F5)3 with alkynes. The stepwise reactivity of the zwitterion provides new mechanistic insight for 1,1-carboboration and wider B(C6F5)3 catalysis. Making use of intramolecular stabilization by a ferrocene substituent, we have characterized the zwitterionic intermediate in the solid state and diverted reactivity towards alkyne cyclotrimerization. 相似文献
1000.
This paper classifies dual pairs (F,G′) in complex G2 where F is finite and G′ is infinite complex reductive. 相似文献