全文获取类型
收费全文 | 322篇 |
免费 | 4篇 |
国内免费 | 2篇 |
专业分类
化学 | 179篇 |
力学 | 33篇 |
数学 | 42篇 |
物理学 | 74篇 |
出版年
2023年 | 1篇 |
2022年 | 1篇 |
2021年 | 3篇 |
2019年 | 2篇 |
2018年 | 4篇 |
2017年 | 2篇 |
2016年 | 7篇 |
2015年 | 2篇 |
2014年 | 5篇 |
2013年 | 12篇 |
2012年 | 11篇 |
2011年 | 21篇 |
2010年 | 21篇 |
2009年 | 28篇 |
2008年 | 25篇 |
2007年 | 19篇 |
2006年 | 18篇 |
2005年 | 10篇 |
2004年 | 7篇 |
2003年 | 7篇 |
2002年 | 12篇 |
2001年 | 3篇 |
2000年 | 5篇 |
1999年 | 8篇 |
1998年 | 12篇 |
1997年 | 10篇 |
1996年 | 11篇 |
1995年 | 2篇 |
1994年 | 5篇 |
1993年 | 10篇 |
1992年 | 12篇 |
1991年 | 7篇 |
1990年 | 4篇 |
1989年 | 3篇 |
1988年 | 4篇 |
1987年 | 1篇 |
1986年 | 3篇 |
1982年 | 2篇 |
1980年 | 4篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1968年 | 1篇 |
排序方式: 共有328条查询结果,搜索用时 15 毫秒
81.
82.
John Hannah Richard L. Tolman John D. Karkas Richard Liou Helen C. Perry A. Kirk Field 《Journal of heterocyclic chemistry》1989,26(5):1261-1271
Ganciclovir 2 and 2′-carba-ganciclovir 5a are anti-viral agents differing structurally only in the replacement of an oxygen by a methylene group and yet expressing their biological properties along mechanistically independent pathways. Methoxy, hydroxy and fluoro derivatives of 2′-carba-ganciclovir were prepared to examine the effect of re-introducing a binding site close to that in the original oxa side chain. The cyclic phosphate of carba-ganciclovir was also prepared. 相似文献
83.
Guey‐Sheng Liou Yi‐Lung Yang Yuhlong Oliver Su 《Journal of polymer science. Part A, Polymer chemistry》2006,44(8):2587-2603
A series of novel triphenylamine‐containing aromatic polyamides and polyimides having a crank and twisted noncoplanar structures were synthesized in inherent viscosities of 0.14–0.64 dL/g and 0.11–0.67 dL/g, respectively. These polymers had useful levels of thermal stability associated with relatively high glass‐transition temperatures (174–311 °C). They exhibited strong UV–Vis absorption bands at around 300 nm in NMP solutions. The PL spectra of these polymers in NMP solutions (1 × 10?5 M) showed maximum peaks around 396–479 nm. The hole‐transporting and electrochromic properties were examined by electrochemical and spectroelectrochemical methods. Cyclic voltammetry (CV) of the polymer films cast onto an indium‐tin oxide (ITO)‐coated glass substrate exhibited two reversible oxidation redox couples at potentials of 0.70–1.01 V and 1.10–1.46 V, respectively, vs. Ag/AgCl in acetonitrile solution. The polymer films revealed electrochromic characteristics, with a color change from neutral pale yellowish to green and then to a blue oxidized form at applied potentials ranging from 0.00 to 1.75 V. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2587–2603, 2006 相似文献
84.
85.
The conditions for the Pd-catalyzed cross coupling of cyclic α-iodoenones, such as 2-iodo-2-cyclohexenone, with alkynylzincs have been optimized. The use of tris(o-furyl)phosphine (TFP) as a ligand and DMF as a solvent has led to the formation of α-alkynylenones in excellent yields. This optimized procedure has been applied to the synthesis of (±)-harveynone and (±)-tricholomenyn A in high yields. Investigation of related α-alkylation reactions using alkylzincs has revealed the following. Methylzinc and primary alkylzinc derivatives readily undergo Pd-catalyzed cross coupling with α-iodoenones. Although (s-Bu)2Zn also undergoes Pd-catalyzed cross coupling, only the n-Bu-substituted products were obtained. α-Benzylation and α-homobenzylation can proceed satisfactorily, whereas allylzinc and propargylzinc derivatives undergo only addition to the carbonyl group. Although some promising results have been obtained in α-homoallylation and α-homopropargylation, these reactions need to be further improved. 相似文献
86.
We combined CdSe nanoparticles and ZnO nanowire arrays to demonstrate a wire-shaped electrode for photoelectrochemical hydrogen generation illuminated with AM 1.5 spectrum. An array of ZnO nanowires was grown vertically and radially outward from a Cu-wire mesh substrate. CdSe nanoparticles were attached to the surface of the orientated ZnO nanowires. Such wire-shaped electrode with radially outward orientated CdSe/ZnO nanowires provided improved electrolyte mass transport and minimized loss of incident photons. CdSe/ZnO nanowires were formed in all directions over the Cu wire, leading to low incident-light-angle dependence. For photoelectrochemical hydrogen generation under one-sun irradiation, the wire-shaped electrode device outperformed the planar-shaped electrode device by at least 30%. 相似文献
87.
Shu-Long Li Chong Li Yeong-Cheng Liou Jen-Chih Yao 《Nonlinear Analysis: Theory, Methods & Applications》2009,71(11):5695-5706
We establish the existence and uniqueness results for variational inequality problems on Riemannian manifolds and solve completely the open problem proposed in [S.Z. Németh, Variational inequalities on Hadamard manifolds, Nonlinear Anal. 52 (2003) 1491–1498]. Also the relationships between the constrained optimization problem and the variational inequality problems as well as the projections on Riemannian manifolds are studied. 相似文献
88.
Through the study of photodissociation events in the CS(2) molecule that originate in various selected vibrational modes, but terminate in the same final predissociation state, we looked for the evidence that photodissociation processes can depend on the initial conditions. Such dependence would not occur within RRKM theory, because of its statistical assumptions. The experimental results were compared with trajectory calculations in normal mode coordinates, in which initial conditions were given in terms of coordinates and momenta. We have found that the photodissociation rate for events originating in the combination nu(1), nu(2) mode is higher than that for events from the pure nu(2) mode, and shows a large variation along the vibrational progression. The experimental observations agree with the trajectory calculations. In addition, the trajectory calculations predict that photodissociation events initiated at small values of the vibrational coordinates result in larger dissociation rates at low excess energy above the dissociation limit, while events from large values of the coordinates result in larger dissociation rates at high excess energies. 相似文献
89.
Yonghong Yao Muhammad Aslam Noor Khalida Inayat Noor Yeong-Cheng Liou Huma Yaqoob 《Acta Appl Math》2010,110(3):1211-1224
In this paper, we introduce a new system of general variational inequalities in Banach spaces. We establish the equivalence
between this system of variational inequalities and fixed point problems involving the nonexpansive mapping. This alternative
equivalent formulation is used to suggest and analyze a modified extragradient method for solving the system of general variational
inequalities. Using the demi-closedness principle for nonexpansive mappings, we prove the strong convergence of the proposed
iterative method under some suitable conditions. 相似文献
90.
This paper presents a distance invariant manifold that preserves the neighborhood relations among data patterns. All patterns have their corresponding cells in the manifold space. The constellation of neighborhood cells closely resembles that of patterns. The manifold is invariant under the translation, rotation and scale of the pattern coordinates. The neighborhood relations among cells are adjusted and improved in each iteration according to the reduction of the distance preservation energy. 相似文献