全文获取类型
收费全文 | 76092篇 |
免费 | 739篇 |
国内免费 | 692篇 |
专业分类
电工技术 | 1447篇 |
综合类 | 47篇 |
化学工业 | 11394篇 |
金属工艺 | 3477篇 |
机械仪表 | 2674篇 |
建筑科学 | 1726篇 |
矿业工程 | 504篇 |
能源动力 | 1898篇 |
轻工业 | 6490篇 |
水利工程 | 856篇 |
石油天然气 | 2304篇 |
武器工业 | 41篇 |
无线电 | 7296篇 |
一般工业技术 | 16657篇 |
冶金工业 | 12746篇 |
原子能技术 | 2637篇 |
自动化技术 | 5329篇 |
出版年
2022年 | 576篇 |
2021年 | 919篇 |
2020年 | 705篇 |
2019年 | 790篇 |
2018年 | 1564篇 |
2017年 | 1581篇 |
2016年 | 1781篇 |
2015年 | 965篇 |
2014年 | 1584篇 |
2013年 | 3618篇 |
2012年 | 2400篇 |
2011年 | 2870篇 |
2010年 | 2409篇 |
2009年 | 2697篇 |
2008年 | 2668篇 |
2007年 | 2613篇 |
2006年 | 2229篇 |
2005年 | 1959篇 |
2004年 | 1885篇 |
2003年 | 1822篇 |
2002年 | 1741篇 |
2001年 | 1698篇 |
2000年 | 1699篇 |
1999年 | 1595篇 |
1998年 | 3784篇 |
1997年 | 2665篇 |
1996年 | 1989篇 |
1995年 | 1562篇 |
1994年 | 1353篇 |
1993年 | 1376篇 |
1992年 | 1011篇 |
1991年 | 1064篇 |
1990年 | 1085篇 |
1989年 | 1058篇 |
1988年 | 951篇 |
1987年 | 887篇 |
1986年 | 887篇 |
1985年 | 951篇 |
1984年 | 781篇 |
1983年 | 775篇 |
1982年 | 685篇 |
1981年 | 704篇 |
1980年 | 669篇 |
1979年 | 657篇 |
1978年 | 624篇 |
1977年 | 789篇 |
1976年 | 944篇 |
1975年 | 586篇 |
1974年 | 555篇 |
1973年 | 546篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
A holographic setup that involves the use of a multicore optical fiber as an in situ recording medium has been developed. The hologram is transmitted to a CCD camera for electronic processing, and the image is reconstructed numerically, providing more flexibility to the holographic process. The performances of this imaging system have been evaluated in terms of the resolution limit and robustness relative to noise. The experimental cutoff frequency has been measured experimentally over a range of observation distances (4-10 mm) and presents a very good agreement with the predictions made by simulation. The system features a resolution of 5-μm objects for a 4-mm observation distance. The different sources of noise have been analyzed, and their influence on resolution has been proved to be nonrelevant. 相似文献
992.
993.
994.
Yu. I. Frishter O. A. Kogodovskii 《Power Technology and Engineering (formerly Hydrotechnical Construction)》1995,29(12):694-706
1. | When constructing earth dams the inclusion of foreign members in the form of reinforced-concrete galleries, shafts, etc., in the body of the structure is impermissible. It is also desirable to eliminate the construction of a grouting gallery under the dam. The foundation should be grouted either before or after constructing the dam. |
2. | Installation of monitoring and measuring equipment for observations during operation must be done after completing construction of the dam. Installation of MME during construction leads to its complete disturbance, holds up the rate of filling, and affects the quality of the works. |
995.
996.
The relationships for the backscattering cross sections are derived within the scope of the physical-optics method for the case in which polarized optical radiation interacts with an oriented semitransparent circular plate. Theoretical investigation of the depolarization relation is carried out for the polarization signal backscattered from a set of oriented circular plates. An algorithm is suggested for the calculation of the orientation angles of the plates in the scattering volume. 相似文献
997.
A study of the use of millimeter-wavelength spectral transitions to investigate the atmosphere of Mars is presented. In the model experiments investigated it is assumed that a spectrometer in the frequency range from 100 to 260 GHz looks into a modest-sized telescope of from 30 to 50 cm aperture from a near-Mars orbit. The molecules H(2)O, CO, O(2), O(3), and H(2)O(2) all have intense spectral lines in the Mars atmosphere in this frequency range and in addition are all very important in understanding the water cycle, the photochemistry, and the circularization in that atmosphere. It is shown that the altitude and the zonal distribution of H(2)O can be mapped even in atmospheric columns as dry as 0.25 precipital μm. Ozone can be mapped over the entire planet, independent of solar-lighting conditions, dust loading, or clouds in the atmosphere, because millimeter waves are insensitive to any particles that can be suspended in the Mars atmosphere. Because the signal-receiving techniques use superheterodyne devices and narrow spectral lines, zonal and meridional winds can be measured at altitudes above 10 km with a precision approaching approximately 3 m/s by the use of Doppler shifts. Temperature-pressure profiles can be measured to altitudes of 100 km by the use of CO lines in the limb-sounding mode. 相似文献
998.
A new type of a swinging interferometer, the carousel interferometer, is presented, and its properties are studied and compared with other swinging interferometers. The new interferometer is built with five plane mirrors. The optical path difference is accomplished by rotation of a system that consists of four mirrors. The modulation is almost independent of the scanning of the interferometer. It is not sensitive to external perturbations such as bending or other deformations of the mount. The construction is very compact. Because of its stability and low cost it is very applicable to small Fourier-transform spectrometers for any wave-number region from the far infrared down to the ultraviolet. 相似文献
999.
A scheme for the design of diffractive phase elements (DPE's) that integrates several optical functions is presented in a consistent sense based on the general theory of amplitude-phase retrieval and the Yang-Gu algorithm [Appl. Opt. 33, 209 (1994)]. We extend the original Yang-Gu algorithm to treat a system illuminated by a beam of incident light whose components are at different wavelengths, and a set of equations for determining the phase distribution of the DPE is derived. The profile of a surface-relief DPE can be designed with an iterative algorithm. Numerical simulations are carried out for the design of one-dimensional DPE's capable of both demultiplexing different wavelength components and focusing each partial wave at predetermined positions. The influence of the extension of sampling points in the DPE's from ideal geometric points to physical spots on design results is also investigated. The numerical simulation results show that the new algorithm can be used successfully to design the desired DPE's. It is therefore expected to be useful in the design of DPE's for micro-optical systems. 相似文献
1000.
Various properties of submicronic silver-palladium powders (70/30 and 75/25 Ag/Pd % wt/wt), recently obtained by a new process of precipitation in aqueous solution, are described. These powders are intended to be used in the multilayer ceramic capacitor industry. The morphology of the particles has been analysed through various measurements, such as SEM images, tap density, BET surface area, and the size distribution by a sedimentation technique. The powders were found to be made of spherical shaped particles of mean diameter close to 0.3 m with a narrow size distribution. The individual grains were agglomerated only to a small extent. After being conditioned as a paste by blending with an organic binder, screen-printed and fired, the particles sintered into a conductive layer of low resistivity (15–30 Wcm for 2 m thickness) with only a few remaining voids, as observed by SEM. Thermal measurements indicated no melting of a pure silver phase at 960 °C, thus indicating that alloying was achieved before this temperature. 相似文献