全文获取类型
收费全文 | 17053篇 |
免费 | 2903篇 |
国内免费 | 2911篇 |
专业分类
化学 | 13689篇 |
晶体学 | 363篇 |
力学 | 808篇 |
综合类 | 255篇 |
数学 | 1902篇 |
物理学 | 5850篇 |
出版年
2024年 | 37篇 |
2023年 | 306篇 |
2022年 | 541篇 |
2021年 | 603篇 |
2020年 | 674篇 |
2019年 | 682篇 |
2018年 | 619篇 |
2017年 | 628篇 |
2016年 | 787篇 |
2015年 | 895篇 |
2014年 | 1046篇 |
2013年 | 1311篇 |
2012年 | 1480篇 |
2011年 | 1623篇 |
2010年 | 1265篇 |
2009年 | 1182篇 |
2008年 | 1311篇 |
2007年 | 1205篇 |
2006年 | 1018篇 |
2005年 | 880篇 |
2004年 | 694篇 |
2003年 | 591篇 |
2002年 | 625篇 |
2001年 | 537篇 |
2000年 | 418篇 |
1999年 | 339篇 |
1998年 | 254篇 |
1997年 | 199篇 |
1996年 | 213篇 |
1995年 | 166篇 |
1994年 | 141篇 |
1993年 | 82篇 |
1992年 | 81篇 |
1991年 | 76篇 |
1990年 | 52篇 |
1989年 | 40篇 |
1988年 | 38篇 |
1987年 | 43篇 |
1986年 | 26篇 |
1985年 | 27篇 |
1984年 | 24篇 |
1983年 | 14篇 |
1982年 | 14篇 |
1981年 | 6篇 |
1980年 | 12篇 |
1979年 | 9篇 |
1978年 | 7篇 |
1976年 | 12篇 |
1975年 | 6篇 |
1971年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
21.
In the interaction of laser-plasma the system of Zakharov equation plays an important role.This system attracted many scientists' wide interest and attention.And the formation, evolution and interaction of the Langmuir solutions differ from solutions of the KDV equation. Here we consider the following generalized Zakharov system 相似文献
22.
ZHONG Hui WAN Mingxi JIANG Yifeng WANG Supin 《声学学报:英文版》2006,25(2):104-115
The present study was to investigate the differential imaging method for detecting HIFU (High Intensity Focused Ultrasound)-induced lesions and the estimation of variation of attenuation for lesion evaluation with log spectral difference algorithm. Experiment results of bovine muscle and liver in vitro were acquired. Several algorithms for lesion detection - Absolute Difference (AD), Sum Absolute Differences (SAD) and Sum Squared Differences (SSD) - were analyzed with several window sizes and threshold values. Then three attenuation parameters were compared to evaluate the degree of tissue damage. It was found that variation of the mean attenuation △α was an effective parameter to evaluate lesions. 相似文献
23.
Fiber-optic reflex sensor for in-line production measurement 总被引:1,自引:0,他引:1
The paper describes experiments concerning distance measurement with fiber-optic sensor and improvement of the measurement principle. The sensor probe was well-designed with a small structure and multi-function. The novel optical fiber probe arrangement as well as the possibilities of use for complex measurement problems are explained using the measurement of an internal screw thread as an example. The experimental results show that the measurement uncertainty of the thread minor diameter can reach ±10 μm, and the stability of the measurement system is better than 0.07%. 相似文献
24.
基于同步辐射加速器的康普顿背散射γ射线源(Ⅰ)产生MeV量级γ光子的数值计算 总被引:1,自引:0,他引:1
提出在筹建的上海同步辐射装置上建造一条MeV量级γ射线束及应用站,采用μm波长的红外(或远红外)激光与储存环中3.5GeV电子束进行康普顿背散射,从而获得能区为1—25MeV的康普顿背散射γ光子束,该光子束具有高强度、高极化度(线和圆极化)、准单色、方向性好的优点,可以广泛地应用于核物理和核天体物理基础研究及相关的应用研究领域.介绍了康普顿背散射的基本原理,并结合储存环参数给出了光子束性能的数值计算结果. 相似文献
25.
By using the quasi-Lyapunov function, some sufficient conditions of global exponential stability for impulsive systems are established, which is the basis for the following discussion. Then, by employing Riccati inequality and Hamilton-Jacobi inequality approach, some sufficient conditions of robust exponential stability for uncertain linear/nonlinear impulsive systems are derived, respectively. Finally, some examples are given to illustrate the applications of the theory. 相似文献
26.
27.
Wang Qing-Lun Zhao Bin Liao Dai-Zheng Yan Shi-Ping Cheng Peng Jiang Zong-Hui 《Transition Metal Chemistry》2003,28(3):326-330
The copper(II) complex Na2[Cu(pba)] · 6H2O has been synthesized and its structure determined. It consists of a novel two-dimensional network of [Cu(pba)]2– anions connected to each other through the sodium ion as a bridge. Spectroscopic and magnetic properties have been measured and a spin distribution calculation has been carried out with the GAUSSIAN-94. Theoretical calculations indicate the rather larger spin density on nitrogen atoms should be responsible for the satellite lines appearing beside the main hyperfine coupling signs of copper(II). The antiferromagnetic interaction may be due to the intermolecular interaction and/or different copper(II) ions through the Na+ bridge in the same layer. 相似文献
28.
Liang Liao Yi Pang Liming Ding Frank E. Karasz 《Journal of polymer science. Part A, Polymer chemistry》2003,41(20):3149-3158
A soluble cyano‐substituted poly[(1,3‐phenylene vinylene)‐alt‐(1,4‐phenylene vinylene)] derivative ( 9 ) was synthesized and characterized. Comparison between 9 and its model compound ( 10 ) showed that the chromophore in 9 remained to be well defined as a result of a π‐conjugation interruption at adjacent m‐phenylene units. The attachment of a cyano substituent only at the β position of the vinylene allowed the maximum electronic impact of the cyano group on the optical properties of the poly(p‐phenylene vinylene) material. At a low temperature (?108 or ?198 °C), the vibronic structures of 9 and 10 were partially resolved. The absorption and emission spectra of a film of 9 were less temperature‐dependent than those of a film of 10 , indicating that the former had a lower tendency to aggregate. A light‐emitting diode (LED) based on 9 emitted yellow light (λmax ≈ 578 nm) with an external quantum efficiency of 0.03%. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3149–3158, 2003 相似文献
29.
Ching Sum Hui Lillian Sze Man Lam Chun Yin Wai Kin Chan Aleksandra B. Djurii 《Journal of polymer science. Part A, Polymer chemistry》2003,41(11):1708-1715
Polyurethanes incorporated with rhenium diimine complexes were synthesized. The polymers exhibited interesting morphologies and solution properties. Results from gel permeation chromatography suggested the formation of polymer aggregates in solutions. The polymers could act as probes for metal ions. The addition of metal ions to polymer solutions led to significant changes in the electronic absorption properties of the polymer solutions. This was attributed to the interactions between the polyether moieties and metal ions. The metal complexes could also act as efficient photosensitizers. After doping with charge‐transport viologens, the photoconductivity of the polymers was greatly enhanced. The experimental quantum efficiency was simulated with Onsager's theory. The thermalization distances and the primary yields were typically 12–14 Å and 10?3, respectively. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1708–1715, 2003 相似文献
30.
In mononuclear HgI2[(C5H4N)3N], mercury is tetrahedrally coordinated by two nitrogen atoms of a tris(2‐pyridyl)amine ligand and two iodides. The coordination moieties are connected by weak intermolecular Hg(II)···I interactions to give a one‐dimensional structure. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献