全文获取类型
收费全文 | 551442篇 |
免费 | 3695篇 |
国内免费 | 921篇 |
专业分类
化学 | 257954篇 |
晶体学 | 8273篇 |
力学 | 30838篇 |
综合类 | 11篇 |
数学 | 84369篇 |
物理学 | 174613篇 |
出版年
2020年 | 4671篇 |
2019年 | 5459篇 |
2018年 | 12717篇 |
2017年 | 13150篇 |
2016年 | 13042篇 |
2015年 | 5769篇 |
2014年 | 9725篇 |
2013年 | 20294篇 |
2012年 | 18555篇 |
2011年 | 26319篇 |
2010年 | 18870篇 |
2009年 | 18972篇 |
2008年 | 24288篇 |
2007年 | 26361篇 |
2006年 | 16655篇 |
2005年 | 17669篇 |
2004年 | 15337篇 |
2003年 | 14664篇 |
2002年 | 13740篇 |
2001年 | 13172篇 |
2000年 | 10607篇 |
1999年 | 7866篇 |
1998年 | 7200篇 |
1997年 | 7068篇 |
1996年 | 6700篇 |
1995年 | 6018篇 |
1994年 | 6168篇 |
1993年 | 5893篇 |
1992年 | 6293篇 |
1991年 | 6615篇 |
1990年 | 6495篇 |
1989年 | 6403篇 |
1988年 | 6278篇 |
1987年 | 6244篇 |
1986年 | 5799篇 |
1985年 | 7324篇 |
1984年 | 7755篇 |
1983年 | 6583篇 |
1982年 | 6819篇 |
1981年 | 6522篇 |
1980年 | 6318篇 |
1979年 | 6680篇 |
1978年 | 7042篇 |
1977年 | 6972篇 |
1976年 | 7193篇 |
1975年 | 6657篇 |
1974年 | 6560篇 |
1973年 | 6865篇 |
1972年 | 5278篇 |
1971年 | 4584篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
V. Z. Kasimov O. V. Ushakova Yu. P. Khomenko 《Journal of Applied Mechanics and Technical Physics》2003,44(5):612-619
An improved procedure for modeling the operation of a light-gas gun is proposed. The motion of working bodies in both the firing chamber and the light-gas chamber is studied within the framework of the mechanics of heterogeneous media. The problem of barrel heating taking into account its melting and removal of thermal ablation products into the medium inside the bore is solved in a coupled formulation. Heat and mass transfer and friction on the barrel surface are calculated using empirical dependences. The deformable piston is considered compressible and elastoviscoplastic. Allowance is made for the presence of a clearance between the lateral surface of the piston and the barrel bore walls and the associated gas flow between the firing and the light-gas chamber. Calculation results are given. 相似文献
992.
S. Mancini D. Vitali V. Giovannetti P. Tombesi 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,22(3):417-422
We show that the optomechanical coupling between an optical cavity mode and two movable cavity mirrors is able to entangle
two different macroscopic oscillation modes of the mirrors. This continuous variable entanglement is maintained by the light
bouncing between the mirrors and is robust against thermal noise. In fact, it could be experimentally demonstrated using present
technology.
Received 2 September 2002 / Received in final form 10 October 2002 Published online 7 January 2003 相似文献
993.
Zavarzin I. V. Smirnova N. G. Chernoburova E. I. Yarovenko V. N. Krayushkin M. M. 《Russian Chemical Bulletin》2004,53(6):1257-1260
A method for syntheses of previously unknown derivatives of thieno[2,3-d]pyrimidines and quinazolines from monothiooxamides was proposed. 相似文献
994.
Let K be ? or an imaginary quadratic number field, and q ∈ K an integer with ¦q¦ > 1. We give a quantitative version of Σn≥1 an/(qn ? 1) ? K for non-zero periodic sequences (an) in K of period length ≤ 2. As a corollary, we get a quantitative version of the linear independence over K of 1, the q-harmonic series, and a q-analogue of log 2. A similar result on 1, the q-harmonic series, and a q-analogue of ζ(2) is also proved. Mathematics Subject Classification (2000): 11J72, 11J82 相似文献
995.
996.
The first stage in a multi-attribute value analysis is the development of a hierarchical structure of the attributes of the problem. This paper reports the process of developing such a structure for the problem of choosing a suitable mode of transport for radioactive waste. The initial hierarchy of attributes went through several stages of development as new insights emerged about the nature of the problem. Some of the reasons behind this restructuring are discussed, and several important questions about the structuring process are formulated. 相似文献
997.
The ultraviolet band systemsA
1Π-X
1Σ+ of P14N and P15N were excited in an electrodeless tube containing traces of phosphorus specpure nitrogen and neon using a microwave discharge
(2450 MHz). Bands of the isotopic species, P15N, were obtained using15N2 enriched to 95.5%. Rotational analyses of eleven bands of P14N and sixteen bands of P15N were carried out. Three perturbing statese
3Σ−,d
3Δ andb
3Π, arising from the lower valence configurations were identified from the observed perturbations in thev′=0–4 levels of theA
1Π state. Deperturbation studies led to the determination of molecular constants of the perturbing states. Vibrational assignments
of the perturbing states were made from isotope shift studies. 相似文献
998.
J. Berkemeier T. Dirksmeyer G. Klempt H. G. Purwins 《Zeitschrift für Physik B Condensed Matter》1986,65(2):255-258
It is observed experimentally that a periodic array of resistively coupled LC-oscillators with ans-shaped nonlinearity exhibits stable non-uniform voltage and current distributions. The dependence of the resulting structure on the coupling resistance and the boundary conditions is investigated. The structure is rather insensitive to variations of the boundary values. The experiments are well described by a two-variable reaction-diffusion equation. 相似文献
999.
We develop a theory of the magnetic-zenith effect (MZE) observed upon the ionosphere modification by powerful radio waves.
The dependences of MZE on main parameters, such as the magnetic-field inclination angle, pump-wave frequency and power, and
angular width of HF beam are obtained. The optimal elevation angle of pump-wave beam is predicted.
__________
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 48, No. 9, pp. 772–787, September 2005. 相似文献
1000.