全文获取类型
收费全文 | 1666篇 |
免费 | 48篇 |
国内免费 | 6篇 |
专业分类
化学 | 1422篇 |
晶体学 | 6篇 |
力学 | 10篇 |
数学 | 66篇 |
物理学 | 216篇 |
出版年
2023年 | 11篇 |
2022年 | 6篇 |
2021年 | 11篇 |
2020年 | 30篇 |
2019年 | 21篇 |
2018年 | 10篇 |
2017年 | 7篇 |
2016年 | 24篇 |
2015年 | 27篇 |
2014年 | 31篇 |
2013年 | 87篇 |
2012年 | 86篇 |
2011年 | 108篇 |
2010年 | 52篇 |
2009年 | 56篇 |
2008年 | 108篇 |
2007年 | 76篇 |
2006年 | 112篇 |
2005年 | 90篇 |
2004年 | 95篇 |
2003年 | 77篇 |
2002年 | 87篇 |
2001年 | 39篇 |
2000年 | 30篇 |
1999年 | 28篇 |
1998年 | 30篇 |
1997年 | 16篇 |
1996年 | 30篇 |
1995年 | 13篇 |
1994年 | 18篇 |
1993年 | 14篇 |
1992年 | 13篇 |
1991年 | 19篇 |
1990年 | 17篇 |
1989年 | 11篇 |
1988年 | 10篇 |
1987年 | 12篇 |
1986年 | 9篇 |
1985年 | 21篇 |
1984年 | 17篇 |
1983年 | 10篇 |
1982年 | 16篇 |
1981年 | 14篇 |
1980年 | 16篇 |
1979年 | 17篇 |
1978年 | 7篇 |
1976年 | 7篇 |
1975年 | 15篇 |
1974年 | 12篇 |
1973年 | 7篇 |
排序方式: 共有1720条查询结果,搜索用时 15 毫秒
1.
Homohelicity induction of a series of propylene-linked zinc bilinone (ZnBL; linear tetrapyrrople-zinc(II) complex) dimers upon complexation with chiral amine and α-amino esters was investigated. Introduction of substituents such as dimethyl and diisobutyl to the central carbon of the propylene spacer gave rise to stabilization of the homohelical (PP and MM) conformers rather than the heterohelical (PM) conformer. As bulkiness of the substituent increased, stability of the homohelical conformers was raised. The preorganization of the homohelical structures led to significantly amplified homohelicity induction upon complexation with chiral amine and α-amino esters. 相似文献
2.
3.
Frequency dependence of ac conductivity from 1 to 105 Hz and time series of the conductivity at 2 kHz were measured along c-axis of thulium nitrate crystal, Tm(NO3)36H2O at temperatures from 203.15 to 293.15 K. The meta-stability was observed. The frequency spectra of the conductivity were similar to those in disorder system. Aging effect was observed. Non-periodic instability (burst) was found. Non-linear dynamical property was characterized by 1/f noise spectrum, limit cycle in return map and dependence of correlation exponent on embedding dimension. 相似文献
4.
Md. Nur Alam Per B. Zetterlund Masayoshi Okubo 《Journal of polymer science. Part A, Polymer chemistry》2007,45(21):4995-5004
Bimolecular termination in nitroxide‐mediated radical polymerization in miniemulsion has been investigated through the heating of a polystyrene–2,2,6,6‐tetramethylpiperidinyl‐1‐oxy macroinitiator and its 4‐hydroxy‐2,2,6,6‐tetramethylpiperidinyl‐1‐oxy analogue in an aqueous toluene dispersion with sodium dodecyl benzenesulfonate as a surfactant at 125 °C. The level of bimolecular termination by combination, evaluated from the high‐molecular‐weight shoulder, was higher in miniemulsion than in solution and increased with decreasing particle size. Quantitative analysis revealed that these results cannot be rationalized solely by nitroxide partitioning to the aqueous phase. The results are explained by an interface effect, by which nitroxide is adsorbed or located at the aqueous–organic interface. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4995–5004, 2007 相似文献
5.
Takanori Ide Hiroshi Isozaki Susumu Nakata Samuli Siltanen Gunther Uhlmann 《纯数学与应用数学通讯》2007,60(10):1415-1442
Let a physical body Ω in ?2 or ?3 be given. Assume that the electric conductivity distribution inside Ω consists of conductive inclusions in a known smooth background. Further, assume that a subset Γ ? ?Ω is available for boundary measurements. It is proved using hyperbolic geometry that certain information about the location of the inclusions can be exactly recovered from static electric measurements on Γ. More precisely: given a ball B with center outside the convex hull of Ω and satisfying (B? ∩ ?Ω) ? Γ, boundary measurements on Γ with explicitly given Dirichlet data are enough to determine whether B intersects the inclusion. An approximate detection algorithm is introduced based on the theory. Numerical experiments in dimension two with simulated noisy data suggest that the algorithm finds the inclusion‐free domain near Γ and is robust against measurement noise. © 2007 Wiley Periodicals, Inc. 相似文献
6.
Susumu Ariki 《Advances in Mathematics》2004,181(1):134-159
This paper determines the representation type of the Iwahori-Hecke algebras of type B when q≠±1. In particular, we show that a single parameter non-semisimple Iwahori-Hecke algebra of type B has finite representation type if and only if q is a simple root of the Poincaré polynomial, confirming a conjecture of Uno's (J. Algebra 149 (1992) 287). 相似文献
7.
Liquid crystal lens with focus movable in focal plane 总被引:1,自引:0,他引:1
A liquid crystal lens with focus movable in the focal plane is reported. There are three electrodes in the cell. One electrode with a hole in the center is divided into four subelectrodes. The potential of each subelectrode is adjusted to produce a desired asymmetrical phase transformation resulting in off-axis movement of the focus. The potential of another electrode is adjusted to maintain the focus in the focal plane. Movements of the focus in three directions in the focal plane are demonstrated experimentally, and off-axis movement as large as approximately 800 μm is realized. 相似文献
8.
Calcium-induced alginate gel beads (Alg-Ca) containing various polysaccharides, including an alginate hydrolysate, were prepared and the drug release profiles were investigated. Hydrocortisone (HC) was gradually released from Alg-Ca into the mimic gastric fluid, while in intestinal fluid, it was quickly released with the dissolution of Alg-Ca. However, with Alg-Ca containing 5% chitin (CT), dissolution of Alg-Ca was not observed, and release of HC showed apparent zero-order kinetics. Furthermore, addition of the alginate hydrolysate altered the HC-release profile for Alg-Ca. 相似文献
9.
An antiviral nucleoside or virazole was synthesized efficiently and regioselectively starting with benzyl cyanoformate. 相似文献
10.
Influence of shell strength on shape transformation of micron-sized,monodisperse, hollow polymer particles 总被引:1,自引:0,他引:1
Micron-sized, monodisperse, non-spherical polymer particles with "rugby ball" and "red blood corpuscle"-like shapes were produced by seeded polymerization of the dispersion of (divinylbenzene/vinylbiphenyl/xylene)-swollen polystyrene particles prepared by utilizing the dynamic swelling method which the authors proposed in 1991. Their non-spherical shapes were based on buckling of the shell of the resultant hollow particles. In this article, the reversible shape transformation of the hollow composite polymer particle between spherical and such non-spherical shapes was studied in detail by controlling the shell strength. A part of the shell was buckled by external pressure which was caused by evaporation of xylene from the hollow when the shell had the tensile modulus below the critical value calculated from the pressure-buckling relationship of a spherical shell proposed by Uemura. The plasticization of the shell by a good solvent was one of key factors for the shape transformation. 相似文献