全文获取类型
收费全文 | 344027篇 |
免费 | 5778篇 |
国内免费 | 2510篇 |
专业分类
化学 | 193001篇 |
晶体学 | 4664篇 |
力学 | 13597篇 |
综合类 | 17篇 |
数学 | 40885篇 |
物理学 | 100151篇 |
出版年
2021年 | 2293篇 |
2020年 | 2552篇 |
2019年 | 2535篇 |
2018年 | 2652篇 |
2017年 | 2524篇 |
2016年 | 5109篇 |
2015年 | 4210篇 |
2014年 | 5457篇 |
2013年 | 16161篇 |
2012年 | 13114篇 |
2011年 | 15930篇 |
2010年 | 9765篇 |
2009年 | 9763篇 |
2008年 | 14252篇 |
2007年 | 14402篇 |
2006年 | 13796篇 |
2005年 | 12699篇 |
2004年 | 11712篇 |
2003年 | 10012篇 |
2002年 | 9803篇 |
2001年 | 10604篇 |
2000年 | 8160篇 |
1999年 | 6480篇 |
1998年 | 5210篇 |
1997年 | 4996篇 |
1996年 | 5117篇 |
1995年 | 4571篇 |
1994年 | 4316篇 |
1993年 | 4204篇 |
1992年 | 4644篇 |
1991年 | 4431篇 |
1990年 | 4141篇 |
1989年 | 3925篇 |
1988年 | 4205篇 |
1987年 | 3887篇 |
1986年 | 3772篇 |
1985年 | 5477篇 |
1984年 | 5522篇 |
1983年 | 4471篇 |
1982年 | 4839篇 |
1981年 | 4886篇 |
1980年 | 4621篇 |
1979年 | 4722篇 |
1978年 | 4722篇 |
1977年 | 4699篇 |
1976年 | 4644篇 |
1975年 | 4559篇 |
1974年 | 4395篇 |
1973年 | 4585篇 |
1972年 | 2599篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
D. Chithrani R. L. Williams J. Lefebvre P. J. Poole G. C. Aers 《Physica E: Low-dimensional Systems and Nanostructures》2004,21(2-4):290
We discuss the preparation and spectroscopic characterisation of a single InAs/InP quantum dot suitable for long-distance quantum key distribution applications around λ=1.55 μm. The dot is prepared using a site-selective growth technique which allows a single dot to be deposited in isolation at a controlled spatial location. Micro-photoluminescence measurements as a function of exciton occupation are used to determine the electronic structure of the dot. Biexciton emission, shell filling and many-body re-normalization effects are observed for the first time in single InAs/InP quantum dots. 相似文献
992.
J. Wang J. Kono A. Oiwa H. Munekata C. J. Stanton 《Superlattices and Microstructures》2003,34(3-6):563
We have carried out an ultrafast time-resolved differential reflectivity study of a ferromagnetic semiconductor InGaMnAs and made a systematic comparison with low-temperature grown and high-temperature grown InGaAs reference films. Very short carrier lifetimes (2 ps) were observed in InGaMnAs and the low-temperature grown InGaAs film, but not in the high-temperature grown InGaAs film. We attribute the short lifetimes to carrier trapping by mid-gap states introduced during low-temperature MBE growth. Furthermore, at long times, we observed periodic oscillations in the differential reflectivity signal with period 20 ps, which we interpret as coherent acoustic phonons. 相似文献
993.
Nonlinear susceptibility of a quantum dot (QD) embedded in a two-sided cavity, is studied theoretically from a weak-coupling to a strong-coupling regime. In the relevance of a quantum logic gate, the corresponding nonlinear phase shifts (Kerr effect) are estimated for coherent wavepackets including one photon on average. In the weak-coupling regime, the phase shift enhances strongly as a function of a coupling constant between the cavity photon and QD, and eventually saturates in the strong-coupling regime. We also show transmission spectra to evaluate the efficiency of the phase shift. Although the efficiency decreases monotonically in the weak-coupling regime, it rises in the strong-coupling regime. 相似文献
994.
J. Kidawa-Kukla 《Journal of sound and vibration》2003,262(4):865-876
This paper considers the problem of the transverse vibrations of a beam induced by a mobile heat source. The formulation of the problem is based on the differential equations of heat conduction and transverse vibrations of the beam, which are complemented by suitable initial and boundary conditions. The effect of internal and external damping on the vibrations of the beam is considered. The solution to the problem in analytical form is obtained by using the properties of the Green functions. A time partitioning method has been used to avoid the difficulties associated with the slow convergence of the series occurring in the solution to the heat conduction problem. The numerical results of the thermally induced vibration of the beam are presented. 相似文献
995.
Summary. We consider the spline collocation method for a class of parabolic pseudodifferential operators. We show optimal order convergence
results in a large scale of anisotropic Sobolev spaces. The results cover the classical boundary integral equations for the
heat equation in the general case where the spatial domain has a smooth boundary in the plane. Our proof is based on a localization
technique for which we use our recent results proved for parabolic pseudodifferential operators. For the localization we need
also some special spline approximation results in anisotropic Sobolev spaces.
Received May 17, 2001 / Revised version received February 19, 2002 / Published online April 17, 2002 相似文献
996.
A. M. Yakunin A. Yu. Silov P. M. Koenraad W. Van Roy J. De Boeck J. H. Wolter 《Superlattices and Microstructures》2003,34(3-6):539
An individual Mn acceptor in GaAs is mapped by cross-sectional scanning tunneling microscopy (X-STM) at room temperature and a strongly anisotropic shape of the acceptor state is observed. An acceptor state manifests itself as a cross-like feature which we attribute to a valence hole weakly bound to the Mn ion forming the (Mn2+3d5+hole) complex. We propose that the observed anisotropy of the Mn acceptor wavefunction is due to the d-wave present in the acceptor ground state. 相似文献
997.
Jacques Rouzaud MatthewD. Jones Robert Raja BrianF.G. Johnson John MeurigThomas MelindaJ. Duer 《Helvetica chimica acta》2003,86(5):1753-1759
A set of new, air‐stable, RhI‐based heterogeneous asymmetric hydrogenation catalysts have been synthesised, characterised, and tested. Individual members of this new family all exhibit good enantioselectivity. 相似文献
998.
999.
对不同的本底真空条件下,采用甚高频等离子体增强化学气相沉积技术沉积的氢化微晶硅(μc_Si∶H)薄膜中的氧污染问题进行了比较研究.对不同氧污染条件下制备的薄膜样品的x射线光电子能谱与傅里叶变换红外吸收光谱测量结果表明:μc_Si∶H薄膜中,氧以Si—O,O—O和O—H三种不同的键合模式存在,不同的键合模式源自不同的物理机理.μc_Si∶H薄膜的Raman光谱、电导率与激活能的测量结果进一步显示:沉积过程中氧污染程度的不同,对μc_Si∶H薄膜的结构特性与电学特性产生显著影响;而不同氧污染对μc_Si∶H薄膜电学特性的影响不同于氢化非晶硅(a_Si:H)薄膜.
关键词:
氢化微晶硅薄膜
甚高频等离子体增强化学气相沉积
氧污染 相似文献
1000.
Maximiliano A. Burgos Paci Gustavo A. Argüello Plcido García Helge Willner 《国际化学动力学杂志》2003,35(1):15-19
Thermal decomposition of bis(trifluoromethyl) peroxydicarbonate has been studied. The mechanism of decomposition is a simple bond fission, homogeneous first‐order process when the reaction is carried out in the presence of inert gases such as N2 or CO. An activation energy of 28.5 kcal mol?1 was determined for the temperature range of 50–90°C. Decomposition is accelerated by nitric oxide because of a chemical attack on the peroxide forming substances different from those formed with N2 or CO. An interpretation on the influence of the substituents in different peroxides on the O? O bond is given. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 35: 15–19, 2003 相似文献