全文获取类型
收费全文 | 9041篇 |
免费 | 1271篇 |
国内免费 | 1396篇 |
专业分类
化学 | 8029篇 |
晶体学 | 178篇 |
力学 | 313篇 |
综合类 | 58篇 |
数学 | 370篇 |
物理学 | 2760篇 |
出版年
2024年 | 19篇 |
2023年 | 109篇 |
2022年 | 255篇 |
2021年 | 312篇 |
2020年 | 362篇 |
2019年 | 318篇 |
2018年 | 314篇 |
2017年 | 375篇 |
2016年 | 493篇 |
2015年 | 422篇 |
2014年 | 537篇 |
2013年 | 1040篇 |
2012年 | 637篇 |
2011年 | 694篇 |
2010年 | 496篇 |
2009年 | 633篇 |
2008年 | 604篇 |
2007年 | 600篇 |
2006年 | 514篇 |
2005年 | 409篇 |
2004年 | 383篇 |
2003年 | 336篇 |
2002年 | 295篇 |
2001年 | 174篇 |
2000年 | 175篇 |
1999年 | 137篇 |
1998年 | 140篇 |
1997年 | 113篇 |
1996年 | 116篇 |
1995年 | 99篇 |
1994年 | 99篇 |
1993年 | 78篇 |
1992年 | 68篇 |
1991年 | 36篇 |
1990年 | 35篇 |
1989年 | 38篇 |
1988年 | 32篇 |
1987年 | 22篇 |
1986年 | 21篇 |
1985年 | 26篇 |
1984年 | 17篇 |
1983年 | 9篇 |
1982年 | 17篇 |
1981年 | 13篇 |
1980年 | 14篇 |
1979年 | 17篇 |
1978年 | 15篇 |
1977年 | 9篇 |
1976年 | 11篇 |
1973年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
Peixiang Xing Gilles P. Robertson Michael D. Guiver Serguei D. Mikhailenko Serge Kaliaguine 《Journal of polymer science. Part A, Polymer chemistry》2004,42(12):2866-2876
A series of sulfonated poly(aryl ether ketone)s (SPAEKs) were prepared by aromatic nucleophilic polycondensation of 2,6‐dihydroxynaphthalene with 5,5′‐carbonyl‐bis(2‐fluorobenzenesulfonate) and 4,4′‐difluorobenzophenone. The structure and degree of sulfonation (DS) of the SPAEKs were characterized using 1H NMR spectroscopy. The experimentally observed DS values were close to the expected values derived from the starting material ratios. The thermal stabilities of the SPAEKs were characterized by thermogravimetric analysis, which showed that in acid and sodium salt forms they were thermally stable in air up to about 240 and 380 °C, respectively. Transparent membranes cast from the directly polymerized SPAEKs exhibited good mechanical properties in both dry and hydrated states. The dependence of water uptake and of membrane swelling on the DS at different temperatures was studied. SPAEK membranes with a DS from 0.72 to 1.60 maintained adequate mechanical properties after immersion in water at 80 °C for 24 h. The proton conductivity of SPAEK membranes with different degrees of sulfonation was measured as a function of temperature. The proton conductivity of the SPAEK films increased with increased DS, and the highest room temperature conductivity (4.2 × 10?2 S/cm) was recorded for a SPAEK membrane with a DS of 1.60, which further increased to 1.1 × 10?1 S/cm at 80 °C. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2866–2876, 2004 相似文献
22.
Tadeusz Biedro Przemysaw Kubisa 《Journal of polymer science. Part A, Polymer chemistry》2004,42(13):3230-3235
The cationic polymerization of styrene in a neutral ionic liquid, 1‐butyl‐3‐methylimidazolium hexafluorophosphate, with a 1‐phenetyl chloride/TiCl4 initiating system is reported. The polymerization proceeds to a high conversion, but an analysis of the matrix‐assisted laser desorption/ionization time‐of‐flight spectra of the polymers indicates that chain transfer is significant, leading to a lack of control over the molecular weight and molecular weight distribution. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3230–3235, 2004 相似文献
23.
24.
25.
26.
Hiromichi Kurosu Mizuyo Kikuchi Isao Ando 《Journal of Polymer Science.Polymer Physics》1995,33(5):769-775
The solid-state 15N CP/MAS NMR spectra and 15N spin-lattice relaxation times (T1) of doped and dedoped 15N-labeled polypyrroles prepared by electrochemical polymerization, have been measured by means of high-resolution solid-state 15N NMR. The 15N signal of polypyrrole consists of four peaks decomposed by line shape analysis. The four peaks obtained have been assigned to the various structures of polypyrrole. Further, the half-width of the 15N NMR spectra of polypyrroles is discussed as related to the electrical conductivity. © 1995 John Wiley & Sons, Inc. 相似文献
27.
28.
In this paper, the impact of optical beat noise on the performance of optical fast frequency-hopping code-division multiple-access (FFH OCDMA) networks is analyzed. BCH/FFH-OCDMA to reduce the impact of optical beat noise is proposed. It is shown that, BCH/FFH-OCDMA has much better performance under the same bit rate, same chip time and same number of available wavelengths. Another advantage for BCH/FFH-OCDMA is that the code length of one-coincidence sequence will be shorter, which can greatly reduce the difficulty of fabrication for fiber gratings. 相似文献
29.
Chen Hao 《中国科学A辑(英文版)》2006,49(5):715-720
In this paper, for the the primes p such that 3 is a divisor of p − 1, we prove a result which reduces the computation of the linear complexity of a sequence over GF(p
m) (any positive integer m) with the period 3n (n and p
m − 1 are coprime) to the computation of the linear complexities of three sequences with the period n. Combined with some known algorithms such as generalized Games-Chan algorithm, Berlekamp-Massey algorithm and Xiao-Wei-Lam-Imamura
algorithm, we can determine the linear complexity of any sequence over GF(p
m) with the period 3n (n and p
m
− 1 are coprime) more efficiently. 相似文献
30.
建立了电子隧穿电导模型,推导了一维无序体系新的直流电导公式.通过计算20000格点无序体系的直流电导率,分析了直流电导率和温度及外场电压的关系,讨论了无序度对直流电导的影响.计算结果表明,无序体系的直流电导率随无序度的增加而减小;外加电场较小时,电导率相对较大,且出现一系列峰值,电压较大时,电导率反而较小;无序体系在低温区出现了负微分电阻特性,电导率随温度的升高而增大,在高温区电导率随温度的升高而减小.计算结果和实验符合很好
关键词:
无序体系
电子隧穿
直流电导率 相似文献