全文获取类型
收费全文 | 18614篇 |
免费 | 3306篇 |
国内免费 | 2815篇 |
专业分类
化学 | 14023篇 |
晶体学 | 333篇 |
力学 | 1130篇 |
综合类 | 193篇 |
数学 | 2313篇 |
物理学 | 6743篇 |
出版年
2024年 | 50篇 |
2023年 | 374篇 |
2022年 | 754篇 |
2021年 | 683篇 |
2020年 | 792篇 |
2019年 | 791篇 |
2018年 | 669篇 |
2017年 | 629篇 |
2016年 | 862篇 |
2015年 | 932篇 |
2014年 | 1080篇 |
2013年 | 1366篇 |
2012年 | 1642篇 |
2011年 | 1745篇 |
2010年 | 1218篇 |
2009年 | 1249篇 |
2008年 | 1413篇 |
2007年 | 1239篇 |
2006年 | 1102篇 |
2005年 | 891篇 |
2004年 | 644篇 |
2003年 | 551篇 |
2002年 | 591篇 |
2001年 | 501篇 |
2000年 | 453篇 |
1999年 | 386篇 |
1998年 | 281篇 |
1997年 | 247篇 |
1996年 | 294篇 |
1995年 | 236篇 |
1994年 | 162篇 |
1993年 | 152篇 |
1992年 | 126篇 |
1991年 | 107篇 |
1990年 | 97篇 |
1989年 | 85篇 |
1988年 | 53篇 |
1987年 | 52篇 |
1986年 | 48篇 |
1985年 | 36篇 |
1984年 | 29篇 |
1983年 | 36篇 |
1982年 | 19篇 |
1981年 | 12篇 |
1980年 | 6篇 |
1979年 | 8篇 |
1974年 | 5篇 |
1972年 | 4篇 |
1971年 | 4篇 |
1957年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 281 毫秒
71.
Xiao‐Hui Liu Yan‐Guo Li Ying Lin Yue‐Sheng Li 《Journal of polymer science. Part A, Polymer chemistry》2007,45(7):1272-1281
The reversible addition–fragmentation chain transfer (RAFT) polymerization of acrylonitrile (AN) mediated by 2‐cyanoprop‐2‐yl dithiobenzoate was first applied to synthesize polyacrylonitrile (PAN) with a high molecular weight up to 32,800 and a polydispersity index as low as 1.29. The key to success was ascribed to the optimization of the experimental conditions to increase the fragmentation reaction efficiency of the intermediate radical. In accordance with the atom transfer radical polymerization of AN, ethylene carbonate was also a better solvent candidate for providing higher controlled/living RAFT polymerization behaviors than dimethylformamide and dimethyl sulfoxide. The various experimental parameters, including the temperature, the molar ratio of dithiobenzoate to the initiator, the molar ratio of the monomer to dithiobenzoate, the monomer concentration, and the addition of the comonomer, were varied to improve the control of the molecular weight and polydispersity index. The molecular weights of PANs were validated by gel permeation chromatography along with a universal calibration procedure and intrinsic viscosity measurements. 1H NMR analysis confirmed the high chain‐end functionality of the resultant polymers. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1272–1281, 2007 相似文献
72.
Jiangen Huang Guiqin Zhang Yuanhe Huang Decai Fang Deqing Zhang 《Journal of magnetism and magnetic materials》2006
A one-dimensional (1D) silver (I) complex of nitronyl nitroxide with fairly strong antiferromagnetic interaction, in which the metal ions are diamagnetic, is investigated by means of the ab initio crystal orbital method based on the density functional theory. The calculated values of the magnetic coupling constant (J) are close to the experimental measured J value in the periodic system. The magneto-structural correlation reveals that the existence of an antiferromagnetic coupling pathway along nitronyl nitroxide units via silver (I) ion in this system. The spin population distribution also shows the existence of spin delocalization along the ONCNO–Ag–ONCNO, which affords a rational interpretation for the antiferromagnetic interaction mechanism. 相似文献
73.
74.
Xi Nian FANG Jian Hua WANG 《数学学报(英文版)》2006,22(6):1819-1824
In this paper, we study the extension of isometries between the unit spheres of normed space E and C(Ω). We obtain that any surjective isometry between the unit spheres of normed space E and C(Ω) can be extended to be a linear isometry on the whole space E and give an affirmative answer to the corresponding Tingley's problem (where Ω be a compact metric space). 相似文献
75.
In this paper, we study a micro‐macro model for polymeric fluid. The system involves coupling between the macroscopic momentum equation and a microscopic evolution equation describing the combined effects of the microscopic potential and thermofluctuation. We employ an energetic variation procedure to explore the relation between the macroscopic transport of the particles and the induced elastic stress due to the microscopic structure. For the initial data not far from the equilibrium, we prove the global existence and uniqueness of classical solutions to the system. © 2006 Wiley Periodicals, Inc. 相似文献
76.
本文根据1978—2003年中国农村居民现金消费支出数据,综合考虑影响消费的主要因素来研究中国农村居民的现金消费行为。与以往研究不同的是,对于影响消费支出的不确定性因素,本文不是采用某个具体变量进行近似替代,而是采用刻画不确定性的条件异方差来描述。文章的结论是农村居民现金消费支出的主要影响因素并非收入,而是利率和不确定性因素,不确定性因素在1996年后表现得尤为突出。 相似文献
77.
Gold in ores was determined by flame atomic absorption spectrometry following on-line preconcentration by sorbent extraction in a flow-injection system. The medium polarity adsorption resin Amberlite XAD-8 packed in a 220-μl micro-column was used to collect gold(III) from hydrochloric acid sample solutions for 40 s at 7.6 ml/min. Ethanol was used to elute the adsorbed analytes into the nebulizer. Optimization studies were made on sample loading rate, elution rate and sample acidity. Some possible interferences on the determination are discussed. A 35-fold enrichment was achieved at a sampling frequency of 60 h?1 and with an RSD of 1.4%. The detection limit (3σ) and 2 μg l?1. Results for gold in ore samples showed good agreement with those obtained using activated carbon adsorption preconcentration. The recoveries were 97–108%. 相似文献
78.
本文介绍了利用喷油脉宽大小的变化来分析电控发动机电控系统、燃油供给等系统故障的一种方法,在汽车故障检测与诊断中有着广泛的应用。 相似文献
79.
Features of the total disintegration events of heavyemulsion targets caused by 4.5A GeV/c16O
下载免费PDF全文
![点击此处可从《中国物理》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Total disintegration events produced by 4.5\,A GeV/c $^{16}$O--AgBr interactions are
analysed to investigate the characteristics of secondary charged particles produced
in such collisions. The multiplicity distributions of grey, black, and relativistic
charged particles can be well represented by Gaussian distribution. The average
multiplicity of grey particles is found to increase with the mass of projectile
increasing, while that of black particles is found to decrease with the mass of
projectile increasing. This result is in good agreement with the prediction of
fireball model. Finally, the linear dependence between grey and black particles is
observed, but there is no distinct dependence between the production of relativistic
charged particles and the target excitation. 相似文献
80.
提出了一种基于增强现实的室内漫游系统,在这个系统中用户通过HMD观察增强的视景。在这个视景中不但包含真实布景的图像,还包含有计算机生成的虚拟物体的图像。为了实现虚实场景之间的注册,在HMD上安装有两个摄像机:场景摄像机与跟踪摄像机。并且在用户所在房间的顶部安装了一系列的红外标志点,这些标志点的图像由跟踪摄像机获取,并通过位置估计算法计算用户头部的位置和姿态。另外,通过一对安装有ARtoolKit标志点的手套,实现用户与虚拟环境之间的交互。最后,一套海底漫系统被开发出来,以验证整个漫游系统的可用性 相似文献