全文获取类型
收费全文 | 4575篇 |
免费 | 645篇 |
国内免费 | 384篇 |
专业分类
化学 | 3267篇 |
晶体学 | 52篇 |
力学 | 237篇 |
综合类 | 23篇 |
数学 | 526篇 |
物理学 | 1499篇 |
出版年
2024年 | 7篇 |
2023年 | 110篇 |
2022年 | 173篇 |
2021年 | 185篇 |
2020年 | 167篇 |
2019年 | 148篇 |
2018年 | 141篇 |
2017年 | 108篇 |
2016年 | 203篇 |
2015年 | 207篇 |
2014年 | 248篇 |
2013年 | 283篇 |
2012年 | 349篇 |
2011年 | 389篇 |
2010年 | 241篇 |
2009年 | 237篇 |
2008年 | 283篇 |
2007年 | 258篇 |
2006年 | 238篇 |
2005年 | 199篇 |
2004年 | 169篇 |
2003年 | 152篇 |
2002年 | 127篇 |
2001年 | 103篇 |
2000年 | 90篇 |
1999年 | 114篇 |
1998年 | 100篇 |
1997年 | 90篇 |
1996年 | 90篇 |
1995年 | 78篇 |
1994年 | 54篇 |
1993年 | 33篇 |
1992年 | 37篇 |
1991年 | 32篇 |
1990年 | 23篇 |
1989年 | 17篇 |
1988年 | 20篇 |
1987年 | 19篇 |
1986年 | 13篇 |
1985年 | 9篇 |
1984年 | 15篇 |
1983年 | 4篇 |
1982年 | 4篇 |
1981年 | 3篇 |
1980年 | 9篇 |
1978年 | 2篇 |
1976年 | 7篇 |
1975年 | 3篇 |
1974年 | 2篇 |
1972年 | 2篇 |
排序方式: 共有5604条查询结果,搜索用时 0 毫秒
1.
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
2.
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
3.
A convergent-barrel (CB) cold spray nozzle was designed through numerical simulation. It was found that the main factors influencing significantly particle velocity and temperature include the length and diameter of the barrel section, the nature of the accelerating gas and its pressure and temperature, and the particle size. Particles can achieve a relatively low velocity but a high temperature under the same gas pressure using a CB nozzle compared to a convergent-divergent (CD) nozzle. The experiment results with Cu powder using the designed CB nozzle confirmed that particle deposition can be realized under a lower gas pressure with a CB nozzle. 相似文献
4.
Sung‐Fu Hsu Tzong‐Ming Wu Chien‐Shiun Liao 《Journal of Polymer Science.Polymer Physics》2006,44(23):3337-3347
Poly(3‐hydroxybutyrate) (PHB)/layered double hydroxides (LDHs) nanocomposites were prepared by mixing PHB and poly(ethylene glycol) phosphonates (PEOPAs)‐modified LDH (PMLDH) in chloroform solution. Both X‐ray diffraction data and TEM micrographs of PHB/PMLDH nanocomposites indicate that the PMLDHs are randomly dispersed and exfoliated into the PHB matrix. In this study, the effect of PMLDH on the isothermal crystallization behavior of PHB was investigated using a differential scanning calorimeter (DSC) and polarized optical microscopy. Isothermal crystallization results of PHB/PMLDH nanocomposites show that the addition of 2 wt % PMLDH into PHB induced more heterogeneous nucleation in the crystallization significantly increasing the crystallization rate and reducing their activation energy. By adding more PMLDH into the PHB probably causes more steric hindrance of the diffusion of PHB, reducing the transportation ability of polymer chains during crystallization, thus increasing the activation energy. The correlation among crystallization kinetics, melting behavior and crystalline structure of PHB/PMLDH nanocomposites can also be discussed. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3337–3347, 2006 相似文献
5.
A novel Y-branch waveguide with two reflectors is proposed. The normalized transmitted power for the branching angle of 50°is greater than 70%, which is higher than conventional Y-branch with such wide angle. 相似文献
6.
Tm3+/Yb3+-codoped germanate-niobic (GN) and germanium-bismuth (GB) glasses have been synthesized by conventional melting and quenching method. Intense blue and weak red emissions centered at 477 and 650 nm, corresponding to the transitions 1G4→3H6 and 1G4→3H4, respectively, were observed at room temperature. The possible up-conversion mechanisms are discussed and estimated. GN glass showed a weaker up-conversion emission than GB glass, which is inconsistent with the prediction from the difference of maximum phonon energy between GN and GB glasses. In this paper, Raman spectroscopy was employed to investigate the origin of the difference in up-conversion luminescence in the two glasses. Compared with phonon side-band spectroscopy, Raman spectroscopy extracts more information including both phonon energy and phonon density. For the first time, our results reveal that, besides the maximum phonon energy, the phonon density of host glasses is also an important factor in determining the up-conversion efficiency. 相似文献
7.
8.
机器人焊接已成为焊接自动化技术现代化的主要标志。文中通过阐述机器人离线编程系统的组成原理和主流软件,认为须在焊接自动化专业构筑起机器人离线编程的相关课程体系,才可将机器人离线编程技术引入焊接自动化专业。以此提升焊接自动化的理论和实践教学,提高学生的职业技能。 相似文献
9.
共轴均匀带电薄圆盘间的相互作用力 总被引:3,自引:0,他引:3
本文利用静电场的高斯定律和环路定律巧妙地求出了均匀带电圆盘在空间任一点所产生的电场 ,进而计算出了共轴均匀带电薄圆盘之间的相互作用力 相似文献
10.
In this paper we obtain some sufficient conditions for the existence of non-constant periodic solutions of the following planar system with six delaysOur approach is based on the continuation theorem of the coincidence degree. 相似文献