全文获取类型
收费全文 | 7589篇 |
免费 | 1116篇 |
国内免费 | 540篇 |
专业分类
化学 | 1896篇 |
晶体学 | 50篇 |
力学 | 1477篇 |
综合类 | 60篇 |
数学 | 903篇 |
物理学 | 2220篇 |
无线电 | 2639篇 |
出版年
2024年 | 18篇 |
2023年 | 106篇 |
2022年 | 212篇 |
2021年 | 282篇 |
2020年 | 324篇 |
2019年 | 213篇 |
2018年 | 218篇 |
2017年 | 279篇 |
2016年 | 338篇 |
2015年 | 295篇 |
2014年 | 453篇 |
2013年 | 542篇 |
2012年 | 445篇 |
2011年 | 504篇 |
2010年 | 422篇 |
2009年 | 455篇 |
2008年 | 406篇 |
2007年 | 425篇 |
2006年 | 389篇 |
2005年 | 353篇 |
2004年 | 279篇 |
2003年 | 289篇 |
2002年 | 234篇 |
2001年 | 190篇 |
2000年 | 206篇 |
1999年 | 176篇 |
1998年 | 178篇 |
1997年 | 150篇 |
1996年 | 111篇 |
1995年 | 107篇 |
1994年 | 111篇 |
1993年 | 106篇 |
1992年 | 80篇 |
1991年 | 75篇 |
1990年 | 59篇 |
1989年 | 41篇 |
1988年 | 31篇 |
1987年 | 20篇 |
1986年 | 16篇 |
1985年 | 27篇 |
1984年 | 13篇 |
1983年 | 10篇 |
1982年 | 16篇 |
1981年 | 4篇 |
1980年 | 5篇 |
1979年 | 7篇 |
1978年 | 4篇 |
1976年 | 3篇 |
1971年 | 5篇 |
1957年 | 6篇 |
排序方式: 共有9245条查询结果,搜索用时 421 毫秒
11.
12.
13.
P.A. Ramachandran 《Numerical Methods for Partial Differential Equations》2006,22(4):831-846
Time‐dependent differential equations can be solved using the concept of method of lines (MOL) together with the boundary element (BE) representation for the spatial linear part of the equation. The BE method alleviates the need for spatial discretization and casts the problem in an integral format. Hence errors associated with the numerical approximation of the spatial derivatives are totally eliminated. An element level local cubic approximation is used for the variable at each time step to facilitate the time marching and the nonlinear terms are represented in a semi‐implicit manner by a local linearization at each time step. The accuracy of the method has been illustrated on a number of test problems of engineering significance. © 2005 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 2006 相似文献
14.
R. S. Martynov Yu. M. Nechepurenko 《Computational Mathematics and Mathematical Physics》2006,46(7):1155-1167
For a discrete linear stochastic dynamical system, computation of the response matrix to the external action from a subspace using given observational data is examined. An algorithm is proposed and substantiated that makes it possible to improve the numerical accuracy and to reduce the amount of observational data compared to the general case where an arbitrary external action is allowed. As an illustration, a discrete system arising in the analysis of a linear stochastic dynamical continuous-time system is considered more thoroughly. Some numerical results are presented. 相似文献
15.
Hong-Xing Zheng Dao-Yin Yu 《International Journal of Infrared and Millimeter Waves》2005,26(9):1343-1353
In this paper, a very useful numerical technique has been developed for analyzing the transient characteristics of a planar-spiral inductor on-chip. A locally conformal technique and an alternating-direction implicit scheme are applied to the finite-difference time-domain method. A formulation for solving three dimensional Maxwell’s equations is proposed. Using the proposed method, various parameters of the planar-spiral inductors have been analyzed and an equivalent circuit, which includes frequency-independent circuit elements, has been introduced. Highly computational efficiency is implemented. Numerical results show excellent agreement with the measured data over a wide frequency range. 相似文献
16.
富勒烯 (C60 /C70 )与N ,N ,N′ ,N′ 四 (对甲苯基 ) 4,4′ 二胺 1,1′ 二苯硒醚 (TPDASe)间在激光光诱导条件下 ,发生了分子间的电子转移过程 .在可见 -近红外区 ( 60 0~ 12 0 0nm) ,观测到了TPDASe阳离子自由基、富勒烯 (C60 /C70 )激发三线态和阴离子自由基 ,在苯腈溶液中 ,观测瞬态谱测定了电子从TPDASe转移到富勒烯 (C60 /C70 )激发三线态的量子转化产率(ΦTet)和电子转移常数 (Ket) . 相似文献
17.
18.
通过分析PHS网络中各寻呼区的统计指标,剖析指标劣化的根本原因,采取修改相应的参数配置、移站、调整天线等措施进行网络优化,优化实施后再次收集统计指标做对比分析,总结经验。 相似文献
19.
用于强磁场的快响应真空规的研制进展 总被引:2,自引:2,他引:0
研制了能在强磁场、强干扰环境下工作的快响应真空电离规(快规),用于对HL 2A装置偏滤器室和等离子体附近的中性粒子密度和通量进行原位测量。介绍了快规的结构、工作原理、设计要点以及实验结果。在无磁场的情况下,快规对气体压强的测量范围为6.4×10-6~0.15Pa,在1×10-5~0.15Pa范围内,快规收集极离子流与发射电子流之比与气压保持良好线性关系;在0 15T的磁场下,快规的规管常数未发生显著变化,在规管对称轴与磁力线的夹角小于15o时,规管常数的变化小于10%。 相似文献
20.
N. Fitier 《国际流体数值方法杂志》2003,42(12):1345-1361
There is a growing interest in developing numerical tools to investigate the onset of physical instabilities observed in experiments involving viscoelastic flows, which is a difficult and challenging task as the simulations are very sensitive to numerical instabilities. Following a recent linear stability analysis carried out in order to better understand qualitatively the origin of numerical instabilities occurring in the simulation of flows viscoelastic fluids, the present paper considers a possible extension for more complex flows. This promising method could be applied to track instabilities in complex (i.e. essentially non‐parallel) flows. In addition, results related to transient growth mechanism indicate that it might be responsible for the development of numerical instabilities in the simulation of viscoelastic fluids. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献