全文获取类型
收费全文 | 36250篇 |
免费 | 6127篇 |
国内免费 | 5260篇 |
专业分类
化学 | 26897篇 |
晶体学 | 477篇 |
力学 | 2186篇 |
综合类 | 396篇 |
数学 | 3804篇 |
物理学 | 13877篇 |
出版年
2024年 | 116篇 |
2023年 | 699篇 |
2022年 | 1305篇 |
2021年 | 1388篇 |
2020年 | 1457篇 |
2019年 | 1466篇 |
2018年 | 1244篇 |
2017年 | 1221篇 |
2016年 | 1769篇 |
2015年 | 1884篇 |
2014年 | 2244篇 |
2013年 | 2855篇 |
2012年 | 3411篇 |
2011年 | 3595篇 |
2010年 | 2468篇 |
2009年 | 2307篇 |
2008年 | 2409篇 |
2007年 | 2198篇 |
2006年 | 2099篇 |
2005年 | 1651篇 |
2004年 | 1350篇 |
2003年 | 1014篇 |
2002年 | 1022篇 |
2001年 | 921篇 |
2000年 | 737篇 |
1999年 | 703篇 |
1998年 | 539篇 |
1997年 | 456篇 |
1996年 | 431篇 |
1995年 | 415篇 |
1994年 | 370篇 |
1993年 | 307篇 |
1992年 | 297篇 |
1991年 | 248篇 |
1990年 | 206篇 |
1989年 | 188篇 |
1988年 | 108篇 |
1987年 | 111篇 |
1986年 | 98篇 |
1985年 | 87篇 |
1984年 | 47篇 |
1983年 | 48篇 |
1982年 | 41篇 |
1981年 | 25篇 |
1980年 | 17篇 |
1979年 | 9篇 |
1977年 | 5篇 |
1975年 | 6篇 |
1969年 | 4篇 |
1957年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
61.
Ying Zhang Gang Hu Shigang Chen H.A. Cerdeira 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,27(3):381-384
A method of controlling global stochasticity in Hamiltonian systems by applying nonlinear perturbation is proposed. With the
well-known standard map we demonstrate that this control method can convert global stochasticity into regular motion in a
wide chaotic region for arbitrary initial condition, in which the control signal remains very weak after a few kicks. The
system in which chaos has been controlled approximates to the original Hamiltonian system, and this approach appears robust
against small external noise. The mechanism underlying this high control efficiency is intuitively explained.
Received 15 January 2002 Published online 6 June 2002 相似文献
62.
根据生产实际,综合利用并列、赋闲列和拟水平试验设计,运用多重比较进行方差分析,寻找水泥熟料的最佳工艺.不仅解决了不同水平多因素试验问题,同时还可考虑交互作用,大大减少了试验次数,从而提高经济效益. 相似文献
63.
光电效应是物理学中一个重要课问题,也是近代物理学几个重大的实验之一.一般物理学教材均要介绍光电效应.但是,在众多的教材中,对光电效应实验装置图的引入存在差异,有些有失科学性,因而引起广大物理学教育工作者的关注. 相似文献
64.
Baoqiang Li Dechang Jia Yu Zhou Qiaoling Hu Wei Cai 《Journal of magnetism and magnetic materials》2006
Chitosan/magnetite nanocomposite was synthesized induced by magnetic field via in situ hybridization in ambient condition. Results of XRD patterns and TEM micrographs indicated that magnetite particles with 10–20 nm were dispersed in chitosan homogeneously. An interesting result is that magnetite nanoparticles were assembled to form chain-like structures under the influence of the external magnetic field, which mimics the magnetite chains inside of magnetotatic bacteria. The saturated magnetization (Ms) of nano-magnetite in chitosan was 50.54 emu/g, which is as high as 54% of bulk magnetite. The remanence (Mr) and coercivity (Hc) were 4 emu/g and14.8 Oe, respectively, which indicated that magnetite nanoparticles were superparamagnetic. The key of route is that a pre-precipitated chitosan hydrogel membrane, used as chemical reactor, which controlled the precipitation of chitosan precipitation and in situ transformation of magnetite from the precursor simultaneously in the magnetic field environment. 相似文献
65.
利用关于乘积分布密度的相对熵和相对熵率的概念,建立了相依连续型随机变量序列关于参考微分熵的一类强偏差定理,证明中给出了将Laplace变换应用于微分熵强偏差定理的研究的一种途径. 相似文献
66.
Han-xing Wang Xi Hu Qin Zhang 《应用数学学报(英文版)》2007,23(2):235-244
In this paper,we present a random graph model with spatial reuse for a mobile ad hoc network(MANET) based on the dynamic source routing protocol.Many important performance parameters of theMANET are obtained,such as the average flooding distance (AFD),the probability generating function of theflooding distance,and the probability of a flooding route to be symmetric.Compared with the random graphmodel without spatial reuse,this model is much more effective because it has a smaller value of AFD and alarger probability for finding a symmetric valid route. 相似文献
67.
采用光学显微镜和扫描电子显微镜等手段,对某轻型汽车40Cr后桥半轴断裂件的组织及断口特征进行了分析结果表明:半轴在调质处理时的淬火温度不够高,使其表层和心部组织中存在较多的铁素体相,造成了工件最终的硬度和疲劳强度不足,导致半轴在使用中发生扭转疲劳断裂. 相似文献
68.
69.
Wenbing Hu Alexander Buzin Jar‐Shyong Lin Bernhard Wunderlich 《Journal of Polymer Science.Polymer Physics》2003,41(4):403-417
The annealing at 373 K of ultrastrong, gel‐spun polyethylene (PE) has been studied. At this temperature, the fibers show no significant shrinkage. Still, a significant decrease in the mechanical properties is observed. The fibers have been analyzed with differential scanning calorimetry (DSC), temperature‐modulated differential scanning calorimetry (TMDSC), atomic force microscopy (AFM), and small‐angle X‐ray scattering (SAXS). During the annealing, the glass transition of the intermediate phase is exceeded, as shown by DSC. When split for structure analysis by AFM, the annealed fibers undergo plastic deformation around the base fibrils instead of brittle fracture. The quasi‐isothermal TMDSC experiments are compared to the minor structural changes seen with SAXS and AFM. The loss of performance of the PE fibers at 373 K is suggested to be caused by the oriented intermediate phase, and not by major changes in the structure or morphology. The overall metastable, semicrystalline structure is shown by TMDSC to posses local regions that can melt reversibly. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 403–417, 2003 相似文献
70.
Gu De-shan Jing Shi-wei Sang Hai-feng Qiao Shuang Liu Yu-ren Liu Lin-mao 《Journal of Radioanalytical and Nuclear Chemistry》2004,262(2):493-496
This paper introduces the analysis method and principle of pulse fast-thermal neutron analysis (PFTNA). A system for the measurement
of low caloric power of coal by PFTNA is also presented. The 14 MeV pulse neutron generator and BGO detector and 4096 MCA
were applied in this system. A multiple linear regression method applied to the data solved the interferential problem of
multiple elements. The error of low caloric power between chemical analysis and experiment was less than 0.4 MJ/kg.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献