全文获取类型
收费全文 | 3214篇 |
免费 | 101篇 |
国内免费 | 25篇 |
专业分类
化学 | 1996篇 |
晶体学 | 22篇 |
力学 | 71篇 |
数学 | 654篇 |
物理学 | 597篇 |
出版年
2023年 | 14篇 |
2022年 | 25篇 |
2021年 | 74篇 |
2020年 | 71篇 |
2019年 | 89篇 |
2018年 | 72篇 |
2017年 | 62篇 |
2016年 | 130篇 |
2015年 | 110篇 |
2014年 | 136篇 |
2013年 | 233篇 |
2012年 | 204篇 |
2011年 | 228篇 |
2010年 | 155篇 |
2009年 | 157篇 |
2008年 | 198篇 |
2007年 | 184篇 |
2006年 | 156篇 |
2005年 | 124篇 |
2004年 | 99篇 |
2003年 | 76篇 |
2002年 | 87篇 |
2001年 | 41篇 |
2000年 | 41篇 |
1999年 | 29篇 |
1998年 | 19篇 |
1997年 | 22篇 |
1996年 | 39篇 |
1995年 | 27篇 |
1994年 | 26篇 |
1993年 | 23篇 |
1992年 | 34篇 |
1991年 | 14篇 |
1990年 | 21篇 |
1989年 | 20篇 |
1988年 | 22篇 |
1987年 | 14篇 |
1986年 | 9篇 |
1985年 | 15篇 |
1984年 | 25篇 |
1983年 | 15篇 |
1982年 | 15篇 |
1981年 | 17篇 |
1980年 | 15篇 |
1979年 | 14篇 |
1978年 | 23篇 |
1977年 | 22篇 |
1976年 | 14篇 |
1970年 | 8篇 |
1968年 | 10篇 |
排序方式: 共有3340条查询结果,搜索用时 31 毫秒
991.
992.
M. Caprosu M. Roman I. Olariu S. T. Dima I. Mangalagiu M. Petrovanu 《Journal of heterocyclic chemistry》2001,38(2):495-498
In this paper we present a study concerning the basicity of some new carbanion monosubstituted pyridazinium, 3‐methyl‐pyridazinium, 3‐(p‐halogenophenyl)‐pyridazinium and phtalazinium ylids. The pka values of the conjugated acids (salts) of ylids have been experimentaly determinated. Consequently, we have evaluated their basicity (kb,) using the titration curves. The basicity depends mainly on the structure of the ylids carbanion itself, however the heterocycle's structures also has some influence on bacisity. Having in view the basicity, we have established certain correlations between basicity, structure and stability of the analised ylids. 相似文献
993.
Serdiuk Katarzyna Gancarz Roman Cieślak-Golonka Maria 《Transition Metal Chemistry》2001,26(4-5):538-543
The interaction of an aqueous MoO3 solution with H2O2, and glycine, serine, lysine, histidine or methionine, results in the precipitation of mononuclear MoO(O2)2LH2O (L = glycine), dinuclear Mo2O4(O2)2L(H2O)4 (L = methionine, serine) and trinuclear Mo3O7(O2)2L(H2O)6 (L = lysine, histidine) species. A detailed analysis of the electronic spectra has been performed using the digital filter method. It was found that the polynuclear complexes preserve the individuality of the molybdenum oxo peroxo core. 相似文献
994.
Orest Hevus Ananiy Kohut Roman Fleychuk Natalija Mitina Oleksandr Zaichenko 《Macromolecular Symposia》2007,254(1):117-121
Summary: New anion surfmers of the family of maleic acid asymmetrical esters have been synthesized. Some of its features in the process of emulsion copolymerization with styrene have been studied. The characteristics of covering, obtained on the basis of such latexes of new generation have been investigated as well. 相似文献
995.
Jose E. Roman 《PAMM》2007,7(1):1141703-1141704
SLEPc is a software library for the solution of large, sparse eigenvalue problems on parallel computers. We have recently extended its functionality by incorporating a Krylov-Schur eigensolver and a module for singular value computation. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
996.
New Q-conditional symmetries for two classes of reaction-diffusion-convection equations with power diffusivities are derived. The symmetries obtained for constructing exact solutions of the relevant nonlinear equations are successfully applied. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
997.
Borja Cirera Alexander Riss Pingo Mutombo Jos I. Urgel Jos Santos Marco Di Giovannantonio Roland Widmer Samuel Stolz Qiang Sun Max Bommert Roman Fasel Pavel Jelínek Willi Auwrter Nazario Martín David cija 《Chemical science》2021,12(38):12806
The design of organometallic complexes is at the heart of modern organic chemistry and catalysis. Recently, on-surface synthesis has emerged as a disruptive paradigm to design previously precluded compounds and nanomaterials. Despite these advances, the field of organometallic chemistry on surfaces is still at its infancy. Here, we introduce a protocol to activate the inner diacetylene moieties of a molecular precursor by copper surface adatoms affording the formation of unprecedented organocopper metallacycles on Cu(111). The chemical structure of the resulting complexes is characterized by scanning probe microscopy and X-ray photoelectron spectroscopy, being complemented by density functional theory calculations and scanning probe microscopy simulations. Our results pave avenues to the engineering of organometallic compounds and steer the development of polyyne chemistry on surfaces.The diacetylene skeletons of DNBD precursors are attacked on Cu(111) by copper adatoms resulting in the synthesis of organocopper metallacycles. 相似文献
998.
Roman O. Grigoriev 《Physica D: Nonlinear Phenomena》2000,140(3-4):171-192
In a recent paper [Phys. Rev. E 57 (1998) 1550] it was demonstrated that the symmetries of the evolution equation and the target state have a profound effect on controlling the chaotic behavior. In the present paper we extend these results to the cases of time-periodic target trajectories and inexact symmetries, and apply the developed formalism to the problem of controlling spatiotemporal chaos. We use the example of a lattice dynamical system in arbitrary spatial dimension to show that there exists an intimate relationship between the geometry of an extended system and the geometry of feedback control. 相似文献
999.
1000.
Miroslav Novák Marek Bouška Dr. Libor Dostál Dr. Aleš Růžička Dr. Alexander Hoffmann Prof. Dr. Sonja Herres‐Pawlis Dr. Roman Jambor 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(21):7820-7829
We report here the synthesis of new C,N‐chelated chlorostannylenes and germylenes L3MCl (M=Sn( 1 ), Ge ( 2 )) and L4MCl (M=Sn( 3 ), Ge ( 4 )) containing sterically demanding C,N‐chelating ligands L3, 4 (L3=[2,4‐di‐tBu‐6‐(Et2NCH2)C6H2]?; L4=[2,4‐di‐tBu‐6‐{(C6H3‐2′,6′‐iPr2)N=CH}C6H2]?). Reductions of 1 – 4 yielded three‐coordinate C,N‐chelated distannynes and digermynes [L3, 4M ]2 for the first time ( 5 : L3, M=Sn, 6 : L3, M=Ge, 7 : L4, M=Sn, 8 : L4, M=Ge). For comparison, the four‐coordinate distannyne [L5Sn]2 ( 10 ) stabilized by N,C,N‐chelate L5 (L5=[2,6‐{(C6H3‐2′,6′‐Me2)N?CH}2C6H3]?) was prepared by the reduction of chlorostannylene L5SnCl ( 9 ). Hence, we highlight the role of donor‐driven stabilization of tetrynes. Compounds 1 – 10 were characterized by means of elemental analysis, NMR spectroscopy, and in the case of 1 , 2 , 5 – 7 , and 10 , also by single‐crystal X‐ray diffraction analysis. The bonding situation in either three‐ or four‐coordinate distannynes 5 , 7 , and 10 was evaluated by DFT calculations. DFT calculations were also used to compare the nature of the metal–metal bond in three‐coordinate C,N‐chelating distannyne [L3Sn]2 ( 5 ) and related digermyme [L3Ge]2 ( 6 ). 相似文献