全文获取类型
收费全文 | 3157篇 |
免费 | 131篇 |
国内免费 | 19篇 |
专业分类
化学 | 2034篇 |
晶体学 | 67篇 |
力学 | 74篇 |
数学 | 516篇 |
物理学 | 616篇 |
出版年
2023年 | 21篇 |
2022年 | 44篇 |
2021年 | 61篇 |
2020年 | 59篇 |
2019年 | 66篇 |
2018年 | 57篇 |
2017年 | 75篇 |
2016年 | 119篇 |
2015年 | 70篇 |
2014年 | 140篇 |
2013年 | 224篇 |
2012年 | 194篇 |
2011年 | 216篇 |
2010年 | 133篇 |
2009年 | 117篇 |
2008年 | 182篇 |
2007年 | 166篇 |
2006年 | 153篇 |
2005年 | 111篇 |
2004年 | 116篇 |
2003年 | 102篇 |
2002年 | 80篇 |
2001年 | 48篇 |
2000年 | 43篇 |
1999年 | 41篇 |
1998年 | 26篇 |
1997年 | 26篇 |
1996年 | 43篇 |
1995年 | 42篇 |
1994年 | 33篇 |
1993年 | 33篇 |
1992年 | 33篇 |
1991年 | 24篇 |
1990年 | 24篇 |
1989年 | 32篇 |
1988年 | 25篇 |
1987年 | 23篇 |
1986年 | 23篇 |
1985年 | 29篇 |
1984年 | 24篇 |
1983年 | 16篇 |
1982年 | 33篇 |
1981年 | 15篇 |
1980年 | 26篇 |
1979年 | 17篇 |
1978年 | 18篇 |
1976年 | 15篇 |
1975年 | 11篇 |
1974年 | 12篇 |
1972年 | 13篇 |
排序方式: 共有3307条查询结果,搜索用时 203 毫秒
11.
Leong‐Huat Gan Palaniswamy Ravi Bao Wei Mao Kam‐Chiu Tam 《Journal of polymer science. Part A, Polymer chemistry》2003,41(17):2688-2695
Polymerization of 2‐(diethylamino)ethyl methacrylate (DEAEMA) via homogeneous atom transfer radical polymerization under various reaction conditions is described. The effects of the initiators and solvents were examined. With 1,1,4,7,10,10‐hexamethyl triethylenetetramine/copper(I) chloride/p‐toluenesulfonyl chloride as the ligand/catalyst/initiator system in methanol, poly(DEAEMA) with a polydispersity index as low as 1.07 was synthesized. Kinetic studies demonstrated the polymerization was very well controlled and exhibited the living characteristic of the process. Well‐defined block copolymers of DEAEMA and tert‐butyl methacrylate (tBMA) were successfully synthesized. The copolymers could be synthesized with equally good results by starting with either p(DEAEMA) or p(tBMA) as the macroinitiators. However, only the macroinitiators terminated with chlorine should be used. The corresponding macroinitiators with bromine as a transferable group did not yield well‐defined copolymers. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2688–2695, 2003 相似文献
12.
13.
We have given design of a very small residual dispersion fiber system consisting of a small dispersion fiber(SDF) with flat modal field and a corresponding dual core coaxial dispersion compensating fiber (DCF). 相似文献
14.
Govindarajan Sankar A. Sultan Nasar 《Journal of polymer science. Part A, Polymer chemistry》2007,45(8):1557-1570
A series of substituted N‐methylaniline‐blocked polyisocyanates based on 4,4′‐methylenebis(phenyl isocyanate) and poly(tetrahydrofuran) were prepared and characterized thoroughly with FTIR, 1H NMR, and 13C NMR spectroscopy methods. Compared with unsubstituted N‐methylaniline, a blocking agent with an electron‐releasing substituent at the para position took a shorter time, whereas those with an electron‐releasing substituent at the ortho position or an electron‐withdrawing substituent at the ortho and para positions took longer times for the blocking reaction. The thermal dissociation reactions of blocked polyisocyanates were carried out with an FTIR spectrophotometer attached to hot‐stage accessories under dynamic and isothermal conditions. The dynamic method was used to determine the deblocking temperature, and the isothermal method was used to calculate the deblocking kinetics and activation parameters. The cure times of blocked polyisocyanates with hydroxyl‐terminated polybutadiene were also determined. The deblocking temperatures, the results of cure‐time studies, and the kinetic parameters revealed that the thermal dissociation of the N‐methylaniline‐blocked polyisocyanates was retarded by electron‐donating substituents and facilitated by electron‐withdrawing substituents. The action of N‐methylanilines as blocking agents for isocyanate was explained by the formation of a four‐center, intramolecularly hydrogen‐bonded ring structure during the thermal dissociation of the blocked polyisocyanates. The formation of such a hydrogen‐bonded ring structure was confirmed and supported by variable‐temperature 1H NMR studies and entropy parameters, respectively. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1557–1570, 2007 相似文献
15.
Prapti Saxena Sankar P. Sanyal 《Physica E: Low-dimensional Systems and Nanostructures》2004,24(3-4):244-248
We report a detailed study of the phonon properties of hexagonal boron nitride (BN) monolayers as well as nanotubes by using De Launay type of angular force model. The force constants used for calculation of phonon dispersion relations of the nanotube are derived from those for the monolayers of hexagonal by employing force constant method. These force constants have been modified to include the effect of curvature of the tubule. The results are then used to derive the phonon dispersion relations for (10,10) BN nanotubes using ‘zone-folding’ method. Calculated phonon modes are in good agreement with the experimental values obtained so far, for (10,10) armchair BN nanotubes. 相似文献
16.
S Uma Sankar 《Pramana》2006,67(4):655-663
In this talk I review the physics possible at India-based Neutrino Observatory (INO). I discuss the improvement in the precision
of currently known quantities and the possibility measuring the presently unknown quantities. 相似文献
17.
18.
A graphite electrode modified with cobalt hexacyanoferrate by mechanical immobilization was used for amperometric determination of hydrazine. The modified electrode exhibits good catalytic activity for the oxidation of hydrazine at a reduced overpotential with remarkable sensitivity. The modified electrode showed a linear response for hydrazine in the concentration range of 2.0 × 10–5 to 2.8 × 10–4 M. The detection limit was 9.8 × 10–6 M (S/N = 3). The proposed modified electrode was simple, sensitive, rapid, stable and promising. 相似文献
19.
D. M. Bhardwaj D. C. Jain S. Dalela Ravi Kumar N. L. Saini K. B. Garg 《Physica B: Condensed Matter》2004,350(4):366-374
We have made the XAFS measurements at the Cr–K-edge on natural Indian ruby single crystals (corundum) and its two irradiated samples with fluence 1×1012 Ni6+ and 5×1012 Ni6+ ions/cm2. Irradiated samples show interesting changes in their physical appearance. XANES measurements show progressive decrease in Δoct value on increase of Ni fluence in irradiated samples. EXAFS measurements on these samples show decrease in Cr–O distance on increase of Ni fluence. Lowering of Δoct value is correlated with the increase of Cr–O distance. 相似文献
20.