全文获取类型
收费全文 | 536086篇 |
免费 | 6513篇 |
国内免费 | 1614篇 |
专业分类
电工技术 | 10575篇 |
综合类 | 594篇 |
化学工业 | 75910篇 |
金属工艺 | 23677篇 |
机械仪表 | 19378篇 |
建筑科学 | 12648篇 |
矿业工程 | 2490篇 |
能源动力 | 13240篇 |
轻工业 | 40912篇 |
水利工程 | 5344篇 |
石油天然气 | 7676篇 |
武器工业 | 80篇 |
无线电 | 68596篇 |
一般工业技术 | 107620篇 |
冶金工业 | 94780篇 |
原子能技术 | 10357篇 |
自动化技术 | 50336篇 |
出版年
2021年 | 3875篇 |
2020年 | 2895篇 |
2019年 | 3640篇 |
2018年 | 12943篇 |
2017年 | 13520篇 |
2016年 | 10488篇 |
2015年 | 4659篇 |
2014年 | 7483篇 |
2013年 | 21345篇 |
2012年 | 13866篇 |
2011年 | 23066篇 |
2010年 | 19421篇 |
2009年 | 20279篇 |
2008年 | 20964篇 |
2007年 | 22647篇 |
2006年 | 14009篇 |
2005年 | 15487篇 |
2004年 | 13711篇 |
2003年 | 13495篇 |
2002年 | 11955篇 |
2001年 | 11902篇 |
2000年 | 11300篇 |
1999年 | 11752篇 |
1998年 | 29047篇 |
1997年 | 20405篇 |
1996年 | 15801篇 |
1995年 | 12150篇 |
1994年 | 10834篇 |
1993年 | 10724篇 |
1992年 | 7977篇 |
1991年 | 7595篇 |
1990年 | 7320篇 |
1989年 | 6891篇 |
1988年 | 6660篇 |
1987年 | 5777篇 |
1986年 | 5609篇 |
1985年 | 6378篇 |
1984年 | 5901篇 |
1983年 | 5476篇 |
1982年 | 5135篇 |
1981年 | 5082篇 |
1980年 | 4876篇 |
1979年 | 4646篇 |
1978年 | 4309篇 |
1977年 | 5206篇 |
1976年 | 6783篇 |
1975年 | 3863篇 |
1974年 | 3776篇 |
1973年 | 3773篇 |
1972年 | 3130篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
961.
Low-loss (<6 dB), flat-top, 16-wavelength, 100-GHz channel spacing DWDM (de)multiplexers are reported. The bulk-optics architecture used allows excellent thermal stability for operating temperature [-10, 60°C] 相似文献
962.
Tsujimura T. Tokuhiro O. Morooka M. Miyamoto T. Miwa K. Yoshimura Y. Andry P. Libsch F. 《Electron Devices, IEEE Transactions on》2002,49(4):576-583
The leakage mechanism for a top-gate thin-film transistor (TFT) produced using the fewest process steps in the industry is analyzed in order to achieve a high-contrast liquid crystal display (LCD). Using a T-shaped TFT structure, the OFF and ON channel lengths are defined independently, so that the leakage can be reduced with no ON current decrease 相似文献
963.
Tonchev V.D. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》2002,48(4):975-977
It is proved that a class of q-ary (2n,n) formally self-dual codes obtained from symmetric matrices over GF (q), contains codes that meet the Varshamov-Gilbert bound. The codes are self-dual with respect to the symplectic inner product and yield quantum codes encoding one state with n q-ary qubits and having minimum distance proportional to n 相似文献
964.
Sung D. Kwon Sung J. Song Dong H. Bae Young Z. Lee 《Journal of Mechanical Science and Technology》2002,16(9):1084-1092
The frequency dependency of Rayleigh surface wave is investigated indirectly by measuring the angular dependency of the backward
radiation of the incident ultrasonic wave in two kinds of degraded specimens by scuffing or corrosion. Then, the frequency
dependency is compared with the residual stress distribution or the corrosion-fatigue characteristics for the scuffed or corroded
specimens, respectively. The width of the backward radiation profile increases with the increase of the variation in residual
stress distribution for the scuffed specimens. In the corroded specimens, the profile width decreases with the increase of
the effective aging layer thickness and is inversely proportional to the exponent, m, in the Paris’ law that can predict the
crack size increase due to fatigue. The result observed in this study demonstrates high potential of backward radiated ultrasound
as a tool for nondestructive evaluation of subsurface gradient of material degradation generated by scuffing or corrosion. 相似文献
965.
The stability of the reactive interface during the solid-state displacement reaction, Cu2O+Co1−X
Fe
X
=2Cu+(Co1−X
Fe
X
)O, is studied as a function of Co-Fe alloy composition at 1223 K. For X≤0.03, the reaction zone has a layered structure, and the cation diffusion in (Co, Fe)O is the rate-limiting step. The interface
is unstable in the early stages of the reaction; the instability decreases with time as the oxide thickness increases, and
the interface becomes planar at long times. The time required for the attainment of interface planarity increases with the
value of X. The reaction kinetics are consistent with the available cation-diffusion data in (Co, Fe)O. For X≥0.045, the product zone is a composite of Cu+(Co, Fe)O, and the rate is limited by the oxygen transport in copper. The transition
to interface instability occurs when the oxide can support a cation flux that exceeds the maximum possible oxygen flux in
copper. During the reaction, composition gradients develop in (Co, Fe)O because of higher diffusion rates for iron than for
cobalt. 相似文献
966.
This report deals with direct observations of microcrack linkage at the crack tip prior to macroscopic crack initiation. It is shown that this process is directly linked to the inclusion distribution in the material and can be considered in terms of an R curve to describe microcrack development. 相似文献
967.
A mixed K-value model allows existing computer programs for the simulation of vapor-liquid equilibrium stages to be used for three-phase vapor-liquid-liquid systems. The mixed K-value model has been implemented with a minimum effort into the Badger General Material Balance flow-sheeting program. Good convergence has been obtained with the mixed K-value model for a number of systems. A comparison is made with published literature [1, 2], showing excellent results with this generally applicable and easy-to-use method. 相似文献
968.
K.L. Johnson J.A. Greenwood J.G. Higginson 《International Journal of Mechanical Sciences》1985,27(6):383-396
A complete solution in closed form to the elastic contact of a one-dimensional sinusoidal surface with a flat surface was presented by Westergaard in 1939. This paper is concerned with the elastic contact of a two-dimensional sinusoidal surface with a flat. In this case the stress distribution within the elastic solids is three-dimensional. As the load is increased the contact areas change in shape from being circular to square and finally leave a circular region of no contact when the waves are almost squashed flat. The problem is solved in general using a numerical method due to Kalker, but asymptotic solutions in closed form have been found for light loads and also for heavy loads at which contact is almost complete. The variation of the mean separation with load, which determines the volume of the space trapped between the two surfaces, is also found. 相似文献
969.
970.
Gibbs energies of formation of CoF2 and MnF2 have been measured in the temperature range from 700 to 1100 K using Al2O3-dispersed CaF2 solid electrolyte and Ni+NiF2 as the reference electrode. The dispersed solid electrolyte has higher conductivity than pure CaF2 thus permitting accurate measurements at lower temperatures. However, to prevent reaction between Al2O3 in the solid electrolyte and NiF2 (or CoF2) at the electrode, the dispersed solid electrolyte was coated with pure CaF2, thus creating a composite structure. The free energies of formation of CoF2 and MnF2 are (± 1700) J mol−1; {fx37-1} The third law analysis gives the enthalpy of formation of solid CoF2 as ΔH° (298·15 K) = −672·69 (± 0·1) kJ mol−1, which compares with a value of −671·5 (± 4) kJ mol−1 given in Janaf tables. For solid MnF2, ΔH°(298·15 K) = − 854·97 (± 0·13) kJ mol−1, which is significantly different from a value of −803·3 kJ mol−1 given in the compilation by Barinet al. 相似文献