全文获取类型
收费全文 | 47512篇 |
免费 | 344篇 |
国内免费 | 1087篇 |
专业分类
电工技术 | 648篇 |
综合类 | 312篇 |
化学工业 | 4862篇 |
金属工艺 | 1108篇 |
机械仪表 | 2582篇 |
建筑科学 | 3035篇 |
矿业工程 | 1115篇 |
能源动力 | 253篇 |
轻工业 | 10793篇 |
水利工程 | 803篇 |
石油天然气 | 878篇 |
武器工业 | 165篇 |
无线电 | 2513篇 |
一般工业技术 | 16164篇 |
冶金工业 | 839篇 |
原子能技术 | 510篇 |
自动化技术 | 2363篇 |
出版年
2023年 | 72篇 |
2022年 | 103篇 |
2021年 | 130篇 |
2020年 | 93篇 |
2019年 | 93篇 |
2018年 | 95篇 |
2017年 | 73篇 |
2016年 | 99篇 |
2015年 | 142篇 |
2014年 | 240篇 |
2013年 | 288篇 |
2012年 | 4814篇 |
2011年 | 6030篇 |
2010年 | 1249篇 |
2009年 | 641篇 |
2008年 | 4277篇 |
2007年 | 4007篇 |
2006年 | 3580篇 |
2005年 | 3121篇 |
2004年 | 2630篇 |
2003年 | 2217篇 |
2002年 | 2116篇 |
2001年 | 1650篇 |
2000年 | 1643篇 |
1999年 | 1051篇 |
1998年 | 581篇 |
1997年 | 559篇 |
1996年 | 496篇 |
1995年 | 497篇 |
1994年 | 463篇 |
1993年 | 346篇 |
1992年 | 456篇 |
1991年 | 407篇 |
1990年 | 450篇 |
1989年 | 404篇 |
1988年 | 334篇 |
1987年 | 380篇 |
1986年 | 344篇 |
1985年 | 411篇 |
1984年 | 356篇 |
1983年 | 311篇 |
1982年 | 298篇 |
1981年 | 259篇 |
1980年 | 200篇 |
1979年 | 153篇 |
1978年 | 106篇 |
1977年 | 49篇 |
1976年 | 52篇 |
1975年 | 59篇 |
1974年 | 55篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
231.
An interferometric technique for automated profilometry of diffuse objects has been proposed. It is based on the Fourier-fringe analysis of spatiotemporal specklegrams produced by a wavelength-shift interferometer with a laser diode as a frequency-tunable light source. Unlike conventional moiré techniques the proposed technique permits the objects to have discontinuous height steps and/or surfaces spatially isolated from one another. Experimental results are presented that demonstrate the validity of the principle. 相似文献
232.
Chemical-vapor-deposited silicon-carbide mirrors were exposed to bombardment by 95-keV electrons and 100-keV protons with accumulated fluxes comparable with those expected in low-altitude Earth orbit for simulated periods of as many as 5 years. The reflectances of four mirrors were measured at five wavelengths (58.4, 73.6, 104.8, 121.6, and 161 nm) and at 11 angles of incidence from 5° to 80°. The electron and proton exposure resulted in no significant change in the reflectances of the mirrors. 相似文献
233.
Fabrication of planar microlens arrays by silver-sodium ion exchange is possible by using a new glass type, optimized for this technology. Because of its nonlinear diffusion response it is well suited to the fabrication of microlens arrays. We show that the diffusion coefficient can be described theoretically by an exponential concentration dependence. The parameters of the planar microlenses are measured interferometrically and by imaging experiments. Because of the specific index distribution, new evaluation techniques for the determination of lens parameters from interferometric measurements have been applied. We also present a simple model that relates the achievable lens parameters to the diffusion conditions. 相似文献
234.
Schäfer M 《Applied optics》1994,33(28):6591-6596
The optical properties of highly chirped gratings of broadband reflection-type volume phase holograms are evaluated by a ray-tracing approach. The deformation of the fringes as well as the change of refractive index is attributed to swelling during processing. For high-efficiency holograms the problem can be reduced to geometric optics. The power density distribution in the focus of an on-axis mirror is calculated by a Monte Carlo integration. The results are discussed for replay conditions that are relevant for photovoltaic applications. 相似文献
235.
Sjödahl M 《Applied optics》1994,33(28):6667-6673
Electronic speckle photography offers a simple and fast technique for measuring in-plane displacement fields in solid and fluid mechanics. An improved algorithm is presented and analyzed by use of both computer-simulated speckle patterns and real experiments. The idea of the improved algorithm is to maximize the correlation between correlated subimages from different images by shifting one of them by nonintegral pixel values. The improved algorithm was found to determine displacement components with an uncertainty of less than 1% of a pixel and with negligible systematic errors in ideal experimental conditions. 相似文献
236.
We experimentally investigate the birefringence of bare and coated substrates for magneto-optical recording, using ellipsometry at wavelengths of 632.8 and 780 nm. The polarization rotation and ellipticity of reflected or transmitted light are measured for different incident angles and for different orientations of the incident linear polarization. The measured data are then fitted by the MULTILAYER computer program, which solves the Maxwell equations for a plane wave propagating in a multilayer structure. This approach makes it possible to determine, with high accuracy, the orientations of the principal axes of the substrate and the corresponding refractive indices. The results show that one of the principal axes is always along the substrate's normal direction, but the orientations of the in-plane principal axes can be much different from the radial and track directions. A special feature of the ellipsometers that were used is that a glass hemisphere is placed in contact with the substrate to eliminate refraction of the incident beam. This enables a maximum propagation angle of 70° (with respect to the normal) in the substrate and hence increases the measurement sensitivity. Certain anomalies have been observed, which we believe are associated with the variation of birefringence properties along the thickness direction. 相似文献
237.
A recent paper [Appl. Opt. 32, 269-274 (1993)) contained an analysis of the conditions required to suppress mode hops when one is tuning a Littrow grating-loaded laser cavity. Although the model was correct, an algebraic mistake led to a wrong conclusion. The corrected results are given and tend to recommend a previously investigated configuration. 相似文献
238.
A novel-type Raman cell especially suitable for the generation of tunable vacuum ultraviolet (VUV) radiation with pump radiation from a frequency-doubled dye laser is described. This hydrogen-filled Raman cell permits the generation of narrow-bandwidth radiation to below 114 nm. Absolute VUV energies in the various anti-Stokes orders and measurements of pulse durations and pressure dependences are given. 相似文献
239.
The effects of a portable back support, the Back-Up, were tested in 28 variables. Both subjective and objective physical load measures were recorded during sitting with and without Back-Up, most of them during VDU work. The main result was that the posture of the upper back and neck/head was improved by the Back-Up. However, the knee straps induced unacceptable high pressure and increased significantly the discomfort in the legs. Based on these results the Back-Up was modified: the contact area between the strap and the knee was enlarged. This modified Back-Up was tested again for 13 variables with 10 new subjects. The knee pressure turned out to be acceptable and the discomfort was equal to sitting without the Back-Up. Based on this research the Back-Up is considered as a possible addition to more fundamental ergonomic improvements such as adjustable furniture and variation between sitting, standing and walking tasks, especially for improvement of the neck load. However, the Back-Up should not replace proper ergonomic workstation and work organization design or a backrest on the chair. Furthermore, the Back-Up should not be made obligatory, and it should be worn only for a part of the day, because it limits variation in postures. 相似文献
240.
This note describes the results of research into the anthropometric measurements of women in Taiwan, for use in pantihose design. 相似文献