全文获取类型
收费全文 | 168570篇 |
免费 | 1172篇 |
国内免费 | 193篇 |
专业分类
电工技术 | 2553篇 |
综合类 | 119篇 |
化学工业 | 26612篇 |
金属工艺 | 9472篇 |
机械仪表 | 5720篇 |
建筑科学 | 3008篇 |
矿业工程 | 1889篇 |
能源动力 | 2704篇 |
轻工业 | 8819篇 |
水利工程 | 2729篇 |
石油天然气 | 8692篇 |
武器工业 | 12篇 |
无线电 | 14505篇 |
一般工业技术 | 38259篇 |
冶金工业 | 27812篇 |
原子能技术 | 6933篇 |
自动化技术 | 10097篇 |
出版年
2018年 | 2977篇 |
2017年 | 3092篇 |
2016年 | 3346篇 |
2015年 | 1672篇 |
2014年 | 2954篇 |
2013年 | 6339篇 |
2012年 | 4317篇 |
2011年 | 5398篇 |
2010年 | 4422篇 |
2009年 | 4898篇 |
2008年 | 4943篇 |
2007年 | 4870篇 |
2006年 | 4142篇 |
2005年 | 3821篇 |
2004年 | 3635篇 |
2003年 | 3522篇 |
2002年 | 3450篇 |
2001年 | 3463篇 |
2000年 | 3361篇 |
1999年 | 3213篇 |
1998年 | 7021篇 |
1997年 | 5150篇 |
1996年 | 3822篇 |
1995年 | 2916篇 |
1994年 | 2593篇 |
1993年 | 2720篇 |
1992年 | 2254篇 |
1991年 | 2306篇 |
1990年 | 2410篇 |
1989年 | 2316篇 |
1988年 | 2313篇 |
1987年 | 2191篇 |
1986年 | 2246篇 |
1985年 | 2292篇 |
1984年 | 2208篇 |
1983年 | 2135篇 |
1982年 | 1982篇 |
1981年 | 2193篇 |
1980年 | 2053篇 |
1979年 | 2271篇 |
1978年 | 2431篇 |
1977年 | 2430篇 |
1976年 | 3095篇 |
1975年 | 2246篇 |
1974年 | 2307篇 |
1973年 | 2342篇 |
1972年 | 2155篇 |
1971年 | 1911篇 |
1970年 | 1702篇 |
1969年 | 1633篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
391.
We have used x-ray phase analysis to study the composition of the products of reaction between oxygen and nanocrystalline
powders with particle sizes 15, 40, 55, and 80 nm, and also specimens pressed (and sintered) from them. The powders were oxidized
in air at 100°C (400 h) to 500°C (5 min), while the sintered specimens were oxidized at 600–900°C for 15, 120, and 240 min.
In all cases, in the initial oxidation step the oxynitride Ti(OxNy) is formed, which over time is oxidized to TiO, Ti2O3, Ti3O5, TiO2 (anatase) and TiO2 (rutile). In the range 600–800°C, formation of a continuous oxide layer and conversion of anatase to rutile slows down diffusion
of oxygen in the scale. We have established that at 900°C, the growth rate of the scale thickness increases and so the reflections
from the oxynitride are barely noticeable on the diffraction patterns taken from the surface of the oxidized specimen. In
these diffraction patterns, along with strong reflections from the rutile, we also observed weak reflections from lower oxides
and anatase, which may be due to reaction between oxygen and the titanium ions diffused to the scale surface. We have concluded
that at T > 850°C, the mechanism for oxidation of TiN changes. This is due to superposition of counterdiffusion of titanium
ions on the diffusion of oxygen.
__________
Translated from Poroshkovaya Metallurgiya, Nos. 3–4(448), pp. 72–78, March–April, 2006. 相似文献
392.
393.
A systematic approach for product families formation in Reconfigurable Manufacturing Systems 总被引:2,自引:0,他引:2
The aim of this work is to establish a methodology for an effective working of Reconfigurable Manufacturing Systems (RMSs). These systems are the next step in manufacturing, allowing the production of any quantity of highly customised and complex products together with the benefits of mass production. In RMSs, products are grouped into families, each of which requires a system configuration. The system is configured to produce the first family of products. Once it is finished, the system is reconfigured in order to produce the second family, and so forth. Therefore, the effectiveness of a RMS depends on the formation of the best set of product families. Therefore, a methodology for grouping products into families, which takes into account the requirements of products in RMSs, is an issue of core importance. These requirements are modularity, commonality, compatibility, reusability, and product demand. The methodology starts by calculating, for each product requirement, a matrix that summarises the similarity between pairs of products. Then, through the use of the AHP methodology, a unique matrix that comprises the similarity values between products is obtained. The Average Linkage Clustering algorithm is applied to this matrix in order to obtain a dendogram that shows the diverse sets of product families that may be formed. 相似文献
394.
395.
The paper briefly reviews the major forms of optical bistability in active optical devices compatible for use in gigabit optical communication systems, and reports an entirely new optical bistability for the first time. Unlike previous devices, the two bistable states of the optical device are each a series of picosecond optical pulses at 1 GHz or greater repetition rates, and are distinguished by a half period temporal shift between their temporal positions in relation to a clock pulse. The bistable device is based on a gain switched semiconductor laser. Theoretical studies suggest 100-ps switching speeds might be achieved, and experimental results are reported indicating optically triggered switching times of 500 ps. 相似文献
396.
397.
398.
399.
A. V. Shchedrin V. V. Ul’yanov V. M. Skoromnov A. A. Bekaev Z. I. Egorova 《Metallurgist》2006,50(9-10):542-547
Results are presented from extensive comparison studies of drawing operations performed with the use of drawplates whose working surfaces have an irregular or regular microroughness. Regularizing the microroughness of the working part of the drawplate makes it possible to control the dimensional accuracy of the resulting products within broad ranges of values. 相似文献
400.
A circuit design is proposed and the possibilities for incorporation of an input double-notch low-frequency ripple filter are considered. Recommendations regarding the use of mathematical models for the calculation of transient processes in a DC electric-traction network are given. An analysis of the simulation of processes in a low-frequency filter shows that the emission of interference by the electric rolling stock should be estimated using the wavelet analysis since this approach best suits the studies of nonstationary signals. 相似文献