全文获取类型
收费全文 | 314355篇 |
免费 | 3752篇 |
国内免费 | 1091篇 |
专业分类
化学 | 170617篇 |
晶体学 | 4457篇 |
力学 | 13030篇 |
综合类 | 7篇 |
数学 | 36270篇 |
物理学 | 94817篇 |
出版年
2020年 | 1983篇 |
2019年 | 1955篇 |
2018年 | 1965篇 |
2017年 | 1876篇 |
2016年 | 3858篇 |
2015年 | 3235篇 |
2014年 | 4422篇 |
2013年 | 13976篇 |
2012年 | 10728篇 |
2011年 | 13363篇 |
2010年 | 8270篇 |
2009年 | 8255篇 |
2008年 | 12337篇 |
2007年 | 12572篇 |
2006年 | 12212篇 |
2005年 | 11154篇 |
2004年 | 10034篇 |
2003年 | 8848篇 |
2002年 | 8700篇 |
2001年 | 10109篇 |
2000年 | 7710篇 |
1999年 | 6115篇 |
1998年 | 4894篇 |
1997年 | 4733篇 |
1996年 | 4773篇 |
1995年 | 4364篇 |
1994年 | 4115篇 |
1993年 | 3941篇 |
1992年 | 4433篇 |
1991年 | 4293篇 |
1990年 | 4011篇 |
1989年 | 3832篇 |
1988年 | 4120篇 |
1987年 | 3785篇 |
1986年 | 3678篇 |
1985年 | 5320篇 |
1984年 | 5395篇 |
1983年 | 4377篇 |
1982年 | 4754篇 |
1981年 | 4793篇 |
1980年 | 4545篇 |
1979年 | 4663篇 |
1978年 | 4665篇 |
1977年 | 4644篇 |
1976年 | 4601篇 |
1975年 | 4512篇 |
1974年 | 4357篇 |
1973年 | 4525篇 |
1972年 | 2569篇 |
1971年 | 1879篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
161.
Dynamic stage repair policies where the stage repair probabilities are determined by the number of items in the buffer are examined through a model of a manufacturing system with two unreliable workstages connected by a minimal intermediate storage buffer. Definitions for workstage availability and line balance are extended for sequential manufacturing systems with dynamic repair policies. A measure for stage repair inputs and a general form of dynamic stage repair policies are presented. The steady-state probabilities of the resultant state-inhomogeneous Markov chain are computed by an efficient solution procedure. Insights obtained from extensive numerical studies are illustrated and discussed. 相似文献
162.
Z.J. Yang T.H. Johansen H. Bratsberg G. Helgesen A.T. Skjeltorp 《Physica C: Superconductivity and its Applications》1989,160(5-6):461-465
Based on a dipole-dipole interaction model, we discuss the levitation force and related vibration problems to understand the effects of flux pinning in type-II superconductors, and the applications of levitation in superconducting systems. 相似文献
163.
The rotational spectra of 34SO2F2 and S18O16OF2 have been measured in their ground vibrational state between 9 and 110 GHz. Accurate rotational constants have been derived. Various experimental structures including the average structure have been determined. The ab initio structure has been calculated at the CCSD(T) level of theory. The different structures are compared and the best equilibrium structure is the ab initio structure: re(SO)=1.401 (3) Å, re(SF)=1.532 (3) Å, ∠e(OSO)=124.91(20)°, ∠e(FSF)=95.53 (20)°. 相似文献
164.
J.J. Pan Xiangdong Qiu Kejian Guan Liang Dong FengQing Zhou Wei Wang Mingjie Zhang James Guo Jun Yang Chunmeng Wu 《光学学报》2003,23(Z1)
A low cost, coolerless 980nm diode pumped, gain flattened L band EDFA with fast transient control, high pump efficiency and gain clamping effect was realized by using FBGs as C band seed generators. 相似文献
165.
166.
The room temperature structure of perovskite CeAlO3 has been reinvestigated by X-ray powder diffraction. The Rietveld refinement has confirmed the tetragonal symmetry; but revealed a super cell, a=5.32489(6) Å and c=7.58976(10) Å, with the space group I4/mcm. In CeAlO3, the distortion from the ideal cubic perovskite is caused by the cooperative tilting of the AlO6 octahedra around the primitive cubic [001]p-axis. 相似文献
167.
168.
169.
170.
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