全文获取类型
收费全文 | 44117篇 |
免费 | 1866篇 |
国内免费 | 1448篇 |
专业分类
化学 | 31483篇 |
晶体学 | 360篇 |
力学 | 888篇 |
综合类 | 10篇 |
数学 | 6105篇 |
物理学 | 8585篇 |
出版年
2023年 | 323篇 |
2022年 | 527篇 |
2021年 | 722篇 |
2020年 | 726篇 |
2019年 | 729篇 |
2018年 | 857篇 |
2017年 | 838篇 |
2016年 | 1631篇 |
2015年 | 1304篇 |
2014年 | 1366篇 |
2013年 | 2979篇 |
2012年 | 3208篇 |
2011年 | 3494篇 |
2010年 | 1973篇 |
2009年 | 1988篇 |
2008年 | 2741篇 |
2007年 | 2678篇 |
2006年 | 2326篇 |
2005年 | 2215篇 |
2004年 | 2222篇 |
2003年 | 1670篇 |
2002年 | 1536篇 |
2001年 | 981篇 |
2000年 | 828篇 |
1999年 | 622篇 |
1998年 | 514篇 |
1997年 | 412篇 |
1996年 | 512篇 |
1995年 | 364篇 |
1994年 | 333篇 |
1993年 | 402篇 |
1992年 | 339篇 |
1991年 | 225篇 |
1990年 | 220篇 |
1989年 | 184篇 |
1988年 | 181篇 |
1987年 | 175篇 |
1986年 | 169篇 |
1985年 | 283篇 |
1984年 | 252篇 |
1983年 | 186篇 |
1982年 | 164篇 |
1981年 | 163篇 |
1980年 | 130篇 |
1979年 | 123篇 |
1978年 | 118篇 |
1977年 | 109篇 |
1976年 | 103篇 |
1975年 | 102篇 |
1973年 | 101篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
Synthesis,Electronic Properties and WOLED Devices of Planar Phosphorus‐Containing Polycyclic Aromatic Hydrocarbons 下载免费PDF全文
Dr. François Riobé Rózsa Szűcs Dr. Pierre‐Antoine Bouit Dr. Denis Tondelier Bernard Geffroy Fátima Aparicio Julia Buendía Prof. Luis Sánchez Prof. Régis Réau Prof. László Nyulászi Prof. Muriel Hissler 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(17):6547-6556
We describe the synthesis and the physical properties of polyaromatic hydrocarbons (PAHs) containing a phosphorus atom at the edge. In particular, the impact of the successive addition of aromatic rings on the electronic properties was investigated by experimental (UV/Vis absorption, fluorescence, cyclic voltammetry) and theoretical studies (DFT). The physical properties recorded in solution and in the solid state showed that the P‐containing PAHs exhibit properties expected for an emitter in white organic light‐emitting diodes (WOLEDs). 相似文献
42.
Susana Estopiñá-Durán Liam J. Donnelly Euan B. Mclean Bryony M. Hockin Prof. Alexandra M. Z. Slawin Dr. James E. Taylor 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(15):3950-3956
A combination of pentafluorophenylboronic acid and oxalic acid catalyses the dehydrative substitution of benzylic alcohols with a second alcohol to form new C−O bonds. This method has been applied to the intermolecular substitution of benzylic alcohols to form symmetrical ethers, intramolecular cyclisations of diols to form aryl-substituted tetrahydrofuran and tetrahydropyran derivatives, and intermolecular crossed-etherification reactions between two different alcohols. Mechanistic control experiments have identified a potential catalytic intermediate formed between the aryl boronic acid and oxalic acid. 相似文献
43.
44.
45.
Highly Selective Copper‐Catalyzed Asymmetric [3+2] Cycloaddition of Azomethine Ylides with Acyclic 1,3‐Dienes 下载免费PDF全文
María González‐Esguevillas Ana Pascual‐Escudero Dr. Javier Adrio Prof. Dr. Juan C. Carretero 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(12):4561-4565
The first examples of the catalytic asymmetric 1,3‐dipolar cycloaddition of azomethine ylides with acyclic activated 1,3‐dienes (and 1,3‐enynes) are described. Under copper catalysis, a selective cycloaddition at the terminal γ,δ‐C?C bond is observed. In addition, depending on the ligand used, either the exo or the endo adduct can be obtained with high selectivity. Under appropriate reaction conditions, the acyclic 1,6‐addition product is detected, suggesting a stepwise mechanism. The resulting C4‐alkenyl‐substituted pyrrolidines are suitable substrates for further access to polycyclic systems, as highlighted by the preparation of hexahydrochromeno[4,3‐b]pyrrole and the tetracyclic core of the alkaloid gracilamine. 相似文献
46.
47.
G. Montero L. Gonzlez E. Flrez M. D. García A. Surez 《Numerical Linear Algebra with Applications》2002,9(3):239-247
Parallel preconditioners are presented for the solution of general linear systems of equations. The computation of these preconditioners is achieved by orthogonal projections related to the Frobenius inner product. So, minM∈??∥AM?I∥ F and matrix M0∈?? corresponding to this minimum (?? being any vectorial subspace of ??n(?)) are explicitly computed using accumulative formulae in order to reduce computational cost when subspace ?? is extended to another one containing it. Every step, the computation is carried out taking advantage of the previous one, what considerably reduces the amount of work. These general results are illustrated with the subspace of matrices M such that AM is symmetric. The main application is developed for the subspace of matrices with a given sparsity pattern which may be constructed iteratively by augmenting the set of non‐zero entries in each column. Finally, the effectiveness of the sparse preconditioners is illustrated with some numerical experiments. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
48.
49.
50.
Marí a J. Martí n Dragan Vukotic 《Proceedings of the American Mathematical Society》2006,134(6):1701-1705
We show that every composition operator which is an isometry of the Dirichlet space is induced by a univalent full map of the disk into itself that fixes the origin. This is an analogue of the Hardy space result for inner functions due to Nordgren. The proof relies on the Stone-Weierstrass theorem and the Riesz representation theorem.