全文获取类型
收费全文 | 290290篇 |
免费 | 1708篇 |
国内免费 | 858篇 |
专业分类
化学 | 122390篇 |
晶体学 | 4059篇 |
力学 | 17160篇 |
综合类 | 5篇 |
数学 | 63556篇 |
物理学 | 85686篇 |
出版年
2018年 | 18075篇 |
2017年 | 18709篇 |
2016年 | 10260篇 |
2015年 | 2640篇 |
2014年 | 1758篇 |
2013年 | 5306篇 |
2012年 | 10767篇 |
2011年 | 25242篇 |
2010年 | 14596篇 |
2009年 | 14811篇 |
2008年 | 20070篇 |
2007年 | 25391篇 |
2006年 | 4557篇 |
2005年 | 12455篇 |
2004年 | 8458篇 |
2003年 | 8408篇 |
2002年 | 5467篇 |
2001年 | 4014篇 |
2000年 | 3280篇 |
1999年 | 2402篇 |
1998年 | 2130篇 |
1997年 | 2031篇 |
1996年 | 2144篇 |
1995年 | 2004篇 |
1994年 | 1724篇 |
1993年 | 1726篇 |
1992年 | 1902篇 |
1991年 | 1904篇 |
1990年 | 1824篇 |
1989年 | 1839篇 |
1988年 | 1845篇 |
1987年 | 1820篇 |
1986年 | 1732篇 |
1985年 | 2297篇 |
1984年 | 2434篇 |
1983年 | 2050篇 |
1982年 | 2374篇 |
1981年 | 2178篇 |
1980年 | 2237篇 |
1979年 | 2217篇 |
1978年 | 2352篇 |
1977年 | 2161篇 |
1976年 | 2221篇 |
1975年 | 2145篇 |
1974年 | 1981篇 |
1973年 | 2239篇 |
1972年 | 1349篇 |
1971年 | 1019篇 |
1968年 | 1169篇 |
1967年 | 1145篇 |
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
991.
Z.J. Liu H.H. Long W.C. Ye X.X. Zou Z.L. Qin E.P. Li J.S. Chen 《Journal of magnetism and magnetic materials》2006
In this paper, specific issues related to high-density perpendicular magnetic recording processes, such as transition noise properties and cross-track correlation lengths, were investigated with the help of micromagnetic analysis. The effects of media parameters were taken into consideration, including intergranular exchange coupling, and exchange distribution, irregular grain shapes, magnetization saturation distribution, and anisotropy distribution. The micromagnetic simulation results showed that the effect of anisotropy distribution on transition noise is more significant than magnetization saturation distribution, and it is crucial to reduce this effect to achieve a high signal-to-noise ratio. Additionally, a new method to further estimate the partial erasure threshold was proposed to approximate the partial erasure effects, and the relation between the microtrack jitter and total track jitter was investigated. 相似文献
992.
Axel Ruhe 《BIT Numerical Mathematics》2007,47(2):239-240
993.
Y. Zhang T. M. Benson P. Sewell A. Vukovic D. Zhang W. J. Pan A Loni D. Furniss A. B. Seddon 《Optical and Quantum Electronics》2006,38(1-3):97-110
This paper presents our recent simulation results and novel designs of single mode large cross-section glass-based waveguides for photonic integrated circuits (PICs). Simulations were performed using an in-house Finite Difference (FD) based mode solver and the FD Beam propagation Method (FD-BPM). Our simulation results show that this innovative technology could provide a simplified means to couple optical energy efficiently between optical components in a single chip. This would provide the base for the future large-scale integration of optical components in PICs. The novel idea of using single mode large cross-section glass-based waveguides as an optical integration platform is an evolutionary innovative solution for the monolithic integration of optical components, in which the glass-based structures act both as waveguides and as an optical bench for integration. This allows easy and efficient optical coupling between optical components and optical fibres, removing costly and tedious alignment problems and considerably reducing optical coupling losses in PICs. We expect that the glass-based waveguide PICs technology will enable the emergence of a new generation of compact, reliable, high speed, and multifunctional devices. 相似文献
994.
995.
We demonstrate that the 3-power torsion points of the Jacobians of the principal modular curves X(3n) are fixed by the kernel of the canonical outer Galois representation of the pro-3 fundamental group of the projective line
minus three points. The proof proceeds by demonstrating the curves in question satisfy a two-part criterion given by Anderson
and Ihara. Two proofs of the second part of the criterion are provided; the first relies on a theorem of Shimura, while the
second uses the moduli interpretation.
Received: 30 September 2005 相似文献
996.
Lanju Xu 《Discrete and Computational Geometry》2007,37(3):485-491
The lower bounds for the translative kissing numbers of superballs are studied in this note. We improve the bound given by
Larman and Zong. Furthermore, we give a constructive bound based on algebraic-geometry codes that also improves the bound
by Larman and Zong in almost all cases. 相似文献
997.
Labour scheduling plays an important and critical role in Sainsburys day to day operations and profitability. The integrated
workforce management solution for Sainsburys is an intelligent solution for the operational deployment of human resources,
integrated business forecasting, generation and calculation of workload and staff scheduling. The workforce management technology
has provided Sainsburys with a fully web-based and centralised system that produces optimised schedules for all employees
satisfying the forecasted demand of work with granularity of fifteen minutes. The system is configured to respect all operational
and business requirements as well as employee contractual constraints. This paper introduces the workforce management solution
system designed, developed and implemented for Sainsburys. We concentrate on two modelling structures, namely the work pattern
model and optimisation model, and briefly discuss the optimisation process. 相似文献
998.
We report a highly-efficient, high-power, single-frequency Nd:YVO4 master-oscillator power-amplifier with near-diffraction-limited output beam quality. A diode-pumped Nd:YVO4 ring laser incorporating a passive method for suppressing axial-mode-hopping was employed as the master-oscillator, and was amplified by a three-stage diode-end-pumped Nd:YVO4 amplifier, yielding 79 W of output with an extraction efficiency of 29%. The overall power gain was 15 dB for an input power from the master-oscillator of 2.4 W, and the M2 parameter was less than 1.5 at the maximum power. The prospects for a further increase of power and brightness via this approach are considered. PACS 42.55.Xi; 42.60.Da; 42.60.Jf 相似文献
999.
De Ming ZHU Ying SUN 《数学学报(英文版)》2007,23(8):1495-1504
In this paper, we study the dynamical behavior for a 4-dimensional reversible system near its heteroclinic loop connecting a saddle-focus and a saddle. The existence of infinitely many reversible 1-homoclinic orbits to the saddle and 2-homoclinic orbits to the saddle-focus is shown. And it is also proved that, corresponding to each 1-homoclinic (resp. 2-homoclinic) orbit F, there is a spiral segment such that the associated orbits starting from the segment are all reversible 1-periodic (resp. 2-periodic) and accumulate onto F. Moreover, each 2-homoclinic orbit may be also accumulated by a sequence of reversible 4-homoclinic orbits. 相似文献
1000.