全文获取类型
收费全文 | 4693篇 |
免费 | 1479篇 |
国内免费 | 305篇 |
专业分类
化学 | 169篇 |
晶体学 | 15篇 |
力学 | 449篇 |
综合类 | 19篇 |
数学 | 63篇 |
物理学 | 3379篇 |
无线电 | 2383篇 |
出版年
2024年 | 20篇 |
2023年 | 46篇 |
2022年 | 77篇 |
2021年 | 116篇 |
2020年 | 123篇 |
2019年 | 105篇 |
2018年 | 132篇 |
2017年 | 134篇 |
2016年 | 180篇 |
2015年 | 169篇 |
2014年 | 329篇 |
2013年 | 313篇 |
2012年 | 349篇 |
2011年 | 402篇 |
2010年 | 317篇 |
2009年 | 309篇 |
2008年 | 403篇 |
2007年 | 399篇 |
2006年 | 373篇 |
2005年 | 286篇 |
2004年 | 251篇 |
2003年 | 222篇 |
2002年 | 178篇 |
2001年 | 168篇 |
2000年 | 167篇 |
1999年 | 142篇 |
1998年 | 122篇 |
1997年 | 115篇 |
1996年 | 115篇 |
1995年 | 71篇 |
1994年 | 89篇 |
1993年 | 54篇 |
1992年 | 47篇 |
1991年 | 42篇 |
1990年 | 35篇 |
1989年 | 17篇 |
1988年 | 14篇 |
1987年 | 15篇 |
1986年 | 5篇 |
1985年 | 4篇 |
1984年 | 6篇 |
1982年 | 8篇 |
1981年 | 4篇 |
1980年 | 1篇 |
1975年 | 2篇 |
1957年 | 1篇 |
排序方式: 共有6477条查询结果,搜索用时 15 毫秒
1.
硅微机械梳齿静电谐振器的建模与分析 总被引:5,自引:2,他引:3
基于参数化的计算机辅助设计(CAD)软件,对硅微机械梳齿静电谐振器进行了实体建模,以有限元分析软件为工具,进行了谐振器的模态分析,静态分析和谐响应分析,初步揭示了谐振器的静、动态特性,有助于改善设计效率和质量,展示了计算机辅助工程(CAE)技术在微机电系统(MEMS)研究中的重要作用。 相似文献
2.
V. I. Dashkevich 《Journal of Applied Spectroscopy》2002,69(6):862-870
Based on a semiclassical theory, investigations were made of the dynamics and spectral composition of pulsed generation with self-injection of priming radiation from the active part of a three-mirror linear resonator, the passive part of which contains an active loss modulator and serves as the output reflector of the laser. It is shown that there exists a range of resonator parameters at which pulsed lasing has virtually a single frequency irrespective of the detuning of the frequencies of the priming radiation and of the nearest eigenmode of the composite resonator. Considering graphically the phase conditions of generation, it is established that among pulsed lasers with self-injection of priming radiation which are constructed on the basis of three-mirror linear and branched resonators, the most efficient for creating single-frequency generation are those in which the length of the main resonator, where generation of the pulse occurs, is larger than the length of the additional one intended for forming the priming radiation. With an inverse ratio of the lengths of the resonators, the conditions of single-frequency pulsed generation becomes dependent on the priming radiation frequency. 相似文献
3.
4.
5.
6.
A novel and simple two-frequency Brillouin fiber laser is presented. It is based on a fiber Fabry-Perot cavity with fiber Bragg gratings as reflectors. The model of stimulated Brillouin scattering in fiber grating-based Fabry-Perot resonator is investigated. The laser allows conversion efficiency of close to 100% and suppresses the higher-order Stokes waves. The theoretical prediction is presented and the experimental demonstration is realized. 相似文献
7.
The paper presents a new formulation of the integral boundary element method (BEM) using subdomain technique. A continuous approximation of the function and the function derivative in the direction normal to the boundary element (further ‘normal flux’) is introduced for solving the general form of a parabolic diffusion‐convective equation. Double nodes for normal flux approximation are used. The gradient continuity is required at the interior subdomain corners where compatibility and equilibrium interface conditions are prescribed. The obtained system matrix with more equations than unknowns is solved using the fast iterative linear least squares based solver. The robustness and stability of the developed formulation is shown on the cases of a backward‐facing step flow and a square‐driven cavity flow up to the Reynolds number value 50 000. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
8.
Santwana Mukhopadhyay 《Mechanics Research Communications》2004,31(1):81-89
The present work is concerned with the thermally induced vibration in a homogeneous and isotropic unbounded body with a spherical cavity. The Green and Nagdhi model of thermoelasticity without energy dissipation is employed. The closed form solutions for distributions of displacement, temperature and stresses are obtained. The solutions valid in the case of small frequency are deduced and the results are compared with the corresponding results obtained in other generalized thermoelasticity theories. Numerical results applicable to a copper-like material are also presented graphically and the nature of variations of the physical quantities with radial coordinate and with frequency of vibration is analyzed. 相似文献
9.
K. P. O. Mahesh M. Sivakumar Y. Yamamoto Y. Tsujita H. Yoshimizu S. Okamoto 《Journal of Polymer Science.Polymer Physics》2004,42(18):3439-3446
A crystalline δ form of a syndiotactic polystyrene (sPS) membrane was prepared from a solution of sPS (1 wt %) and p‐chlorotoluene (p‐CT) by a solution‐casting method. The mesophase (δ empty form) of sPS was obtained by the extraction of the guest solvent from the δ form of sPS by a stepwise solvent‐extraction method. The sPS/p‐CT mesophase membrane [p‐CT (A‐M)] was used for the sorption of 1 mol % p‐CT for different times and for the sorption of different concentrations of p‐CT, chlorobenzene (CB), p‐xylene (p‐X), toluene, and chloroform for 48 h. The presence of solvents in the sPS membrane was confirmed by IR analysis. A thermal study revealed that the sorption amount of 1 mol % p‐CT increased with increasing immersion time, and the sorption amounts of different solvents increased with increasing solvent concentration. Differential scanning calorimetry results showed that the desorption peak temperature increased as the amount of the solvent increased in the clathrated sPS membrane. Wide‐angle X‐ray diffraction results showed that 2θ at 8.25° was slightly shifted toward 8°, and there was no change in the peak position at 10° for p‐CT (A‐M), which was immersed in different solvents (1 mol %); however, the intensity of 2θ at 10° was not similar for all the samples. Among the solvents used for the sorption studies at 1 mol %, p‐CT (A‐M) could sorb more p‐CT and CB than p‐X, toluene, and chloroform. The solvent sorption isotherm was the Langmuir sorption mechanism. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3439–3446, 2004 相似文献
10.