全文获取类型
收费全文 | 2510篇 |
免费 | 147篇 |
国内免费 | 225篇 |
专业分类
化学 | 441篇 |
晶体学 | 8篇 |
力学 | 33篇 |
综合类 | 13篇 |
数学 | 2193篇 |
物理学 | 194篇 |
出版年
2024年 | 6篇 |
2023年 | 17篇 |
2022年 | 38篇 |
2021年 | 43篇 |
2020年 | 58篇 |
2019年 | 72篇 |
2018年 | 60篇 |
2017年 | 67篇 |
2016年 | 47篇 |
2015年 | 42篇 |
2014年 | 80篇 |
2013年 | 467篇 |
2012年 | 86篇 |
2011年 | 134篇 |
2010年 | 92篇 |
2009年 | 186篇 |
2008年 | 138篇 |
2007年 | 177篇 |
2006年 | 142篇 |
2005年 | 107篇 |
2004年 | 111篇 |
2003年 | 119篇 |
2002年 | 131篇 |
2001年 | 64篇 |
2000年 | 53篇 |
1999年 | 60篇 |
1998年 | 54篇 |
1997年 | 37篇 |
1996年 | 44篇 |
1995年 | 29篇 |
1994年 | 22篇 |
1993年 | 12篇 |
1992年 | 5篇 |
1991年 | 6篇 |
1990年 | 2篇 |
1989年 | 3篇 |
1988年 | 4篇 |
1987年 | 6篇 |
1986年 | 2篇 |
1985年 | 7篇 |
1984年 | 8篇 |
1983年 | 5篇 |
1982年 | 7篇 |
1981年 | 7篇 |
1980年 | 6篇 |
1979年 | 7篇 |
1978年 | 7篇 |
1973年 | 1篇 |
1970年 | 1篇 |
1966年 | 1篇 |
排序方式: 共有2882条查询结果,搜索用时 15 毫秒
61.
Giancarlo De Santis Luigi Fabbrizzi Maurizio Licchelli Piersandro Pallavicini Angelo Perotti Antonio Poggi 《Supramolecular chemistry》2013,25(2):115-125
Abstract The new ferrocene-containing water-soluble ligands 1 and 2 were synthesized and their protonation and complexation properties toward NiII and CuII studied as a function of pH, by means of potentiometric titration experiments. Electrochemical measurements were performed in aqueous solution on pure 1 and 2 and in the presence of NiII and CuII cations, in the pH range 2–12, allowing us to determine the redox potential values relative to the ferrocene oxidation in the free ligands and in their NiII and CuII complexes. 1 and 2 behave as redox switchable ligands, the former enhancing, the latter decreasing its binding ability upon oxidation of the appended ferrocene function. Besides, the CuII complex of ligand 1 and the NiII complex of ligand 2 behave as two-centre two-electron redox systems, the complexed metal cation being subject to further oxidation to MIII. 相似文献
62.
Based on the works of Gordon (1977) and Zhang and Zhou (2001) on the variational minimizing properties for Keplerian orbits and Lagrangian solutions of Newtonian 2-body and 3-body problems, we use the constrained variational principle of Ambrosetti and Coti Zelati (1990) to compute the Lagrangian actions on Keplerian and Lagrangian elliptical solutions with fixed energies. We also find an interesting relation between the period and the energy for Lagrangian elliptical solutions with Newtonian potentials. 相似文献
63.
In this paper, we develop a new mixed Mann iteration process to approximate the fixed points of mixed increasing operators in ordered Banach spaces and discuss the convergence analysis of the iterative sequences generated by the iteration process. As an application, we develop a new iterative method for solving a class of nonlinear integral equations. 相似文献
64.
《Journal of Coordination Chemistry》2012,65(2-3):169-185
Abstract The synthesis of Ti(iso)Cl2 (iso = the dianion of 2, 2′-ethylidenebis(4, 6-di-rert-butylphenol)) is described. Metathesis reactions of this complex with Grignard reagents, as well as alkali metal salts, yielded Ti(iso)X2 (X = CH3, CH, Ph, CH2SiMe3, OCMe3, or NMe2). Reactions of the Ti-C bond in Ti(iso)(CH3)2 toward halogens, active hydrogen compounds, and acetone were studied. In addition. Ti(iso)(X)(Y) (X = CI or CH3; Y = OC6H2-2, 6-tBu2-4-Me) could be prepared with the formation of only one coordination isomer. The new complexes have been thoroughly characterized by 1H and 13C NMR spectroscopies. The solid state structure of Ti(iso)Cl2 was determined via single crystal X-ray diffraction methods. The complex is monomeric, with approximately tetrahedral geometry about the titanium ion. The structure of Ti(iso)Cl2 is compared to that of Ti(ultra)Cl2 (ultra = the dianion of 2, 2′-mefhylenebis(6-tert-butyl-4-mefhylphenol)), which was redetermined to greater precision. 相似文献
65.
Based on a recursive Green's function method, we investigate the conductance of mesoscopic graphene rings in the presence of disorder, in the limit of phase coherent transport. Two models of disorder are considered: edge disorder and surface disorder. Our simulations show that the conductance decreases exponentially with the edge disorder and the surface disorder. In the presence of flux, a clear Aharonov-Bohm conductance oscillation with the period Φ0 (Φ0=h/e) is observed. The edge disorder and the surface disorder have no effect on the period of AB oscillation. The amplitudes of AB oscillations vary with gate voltage and flux, which is consistent with the previous results. Additionally, ballistic rectification and negative differential resistance are observed in I-V curves, with on/off characteristic. 相似文献
66.
Attempted reaction of indolenines (which represent rather sterically hindered cyclic imines) with a series of dicarboxylic acid anhydrides yielded no expected product, the Castagnoli-Cushman lactam. Instead, products presumably formed via N-acyliminium species trapping by a carboxylate anion. Among them, hydrolytically labile 2:2 adducts of an indolenine and a cyclic anhydride, containing a 16-membered cyclic core, are particularly intriguing. This result contradicts the recently reported successful Castagnoli-Cushman reaction of indolenines with homophthalic anhydride suggesting a mechanistic switch in the course of the reaction. 相似文献
67.
C.A. Castillo-Guillén C. Rentería-Márquez E. Sarmiento-Rosales H. Tapia-Recillas R.H. Villarreal 《Discrete Mathematics》2019,342(8):2283-2296
Over finite local Frobenius non-chain rings with nilpotency index 3 and when the length of the codes is relatively prime to the characteristic of the residue field of the ring, the structure of the dual of -constacyclic codes is established and the algebraic characterization of self-dual -constacyclic codes, reversible -constacyclic codes and -constacyclic codes with complementary dual are given. Generators for the dual code are obtained from those of the original constacyclic code. 相似文献
68.
69.
ABSTRACTIn this paper, we investigate the problem of finding a common solution to a fixed point problem involving demi-contractive operator and a variational inequality with monotone and Lipschitz continuous mapping in real Hilbert spaces. Inspired by the projection and contraction method and the hybrid descent approximation method, a new and efficient iterative method for solving the problem is introduced. Strong convergence theorem of the proposed method is established under standard and mild conditions. Our scheme generalizes and extends some of the existing results in the literature, and moreover, its computational effort is less per each iteration compared with related works. 相似文献
70.
Shibo Xu Kazutaka Takamatsu Prof. Dr. Koji Hirano Prof. Dr. Masahiro Miura 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(40):9400-9404
A NiCl2(PEt3)2-catalyzed regioselective C−H coupling of 8-aminoquinoline-derived benzamides with oxetanes has been developed. The reaction proceeds with concomitant removal of the 8-aminoquinoline auxiliary to directly form the corresponding seven-membered benzolactones, which frequently occur in natural products and bioactive molecules. Additionally, no stereochemical erosion is observed during the course of the reaction, and the use of enantioenriched and substituted oxetane thus provides a new avenue to the optically active benzolactone. 相似文献