全文获取类型
收费全文 | 416328篇 |
免费 | 31945篇 |
国内免费 | 17762篇 |
专业分类
电工技术 | 24091篇 |
技术理论 | 50篇 |
综合类 | 29100篇 |
化学工业 | 69336篇 |
金属工艺 | 23820篇 |
机械仪表 | 26403篇 |
建筑科学 | 32055篇 |
矿业工程 | 13636篇 |
能源动力 | 11449篇 |
轻工业 | 27817篇 |
水利工程 | 7583篇 |
石油天然气 | 27578篇 |
武器工业 | 3185篇 |
无线电 | 44829篇 |
一般工业技术 | 46444篇 |
冶金工业 | 21689篇 |
原子能技术 | 4194篇 |
自动化技术 | 52776篇 |
出版年
2024年 | 1659篇 |
2023年 | 6363篇 |
2022年 | 11278篇 |
2021年 | 15833篇 |
2020年 | 11969篇 |
2019年 | 9869篇 |
2018年 | 11469篇 |
2017年 | 12928篇 |
2016年 | 11663篇 |
2015年 | 15908篇 |
2014年 | 20152篇 |
2013年 | 24255篇 |
2012年 | 26099篇 |
2011年 | 29032篇 |
2010年 | 25655篇 |
2009年 | 24238篇 |
2008年 | 23773篇 |
2007年 | 22773篇 |
2006年 | 23227篇 |
2005年 | 20552篇 |
2004年 | 13868篇 |
2003年 | 12468篇 |
2002年 | 11493篇 |
2001年 | 10245篇 |
2000年 | 10327篇 |
1999年 | 11126篇 |
1998年 | 8699篇 |
1997年 | 7358篇 |
1996年 | 7008篇 |
1995年 | 5831篇 |
1994年 | 4740篇 |
1993年 | 3260篇 |
1992年 | 2557篇 |
1991年 | 1948篇 |
1990年 | 1526篇 |
1989年 | 1228篇 |
1988年 | 1034篇 |
1987年 | 652篇 |
1986年 | 519篇 |
1985年 | 348篇 |
1984年 | 260篇 |
1983年 | 200篇 |
1982年 | 168篇 |
1981年 | 102篇 |
1980年 | 120篇 |
1979年 | 56篇 |
1978年 | 20篇 |
1977年 | 30篇 |
1976年 | 36篇 |
1970年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
31.
网络安全事件的关联分析方法的比较研究 总被引:2,自引:0,他引:2
随着当前攻击手段和技术的日益复杂化,一次入侵事件往往需要多个步骤才能完成,这些步骤都是彼此相关的。但是传统的入侵检测集中于检测底层的入侵或异常,所检测到的结果也仅仅是一次完整入侵的一部分,所以不能将不同的报警结合起来以发现入侵的逻辑步骤或者入侵背后的攻击策略。关联分析技术将不同分析器上产生的报警进行融合与关联分析,极大地减少了报警的数量,降低了入侵检测的误报率,并且适当的减少了入侵检测的漏报率。文中在对网络安全事件关联分析方法的系统结构进行分析后,着重介绍了当前比较流行的几种网络安全事件关联分析方法,最后对各种方法进行了比较研究。 相似文献
32.
信息系统灾难恢复能力评估方法研究 总被引:1,自引:0,他引:1
论文提出了一种信息系统灾难恢复能力评估方法:信息资产分析方法、本地灾难恢复和远程灾难恢复等级的划分方法,并在此基础上,利用AHP层次分析法,构建了一套灾难恢复能力评估指标体系。该方法可以使评估结果具有更好的针对性和全面性。 相似文献
33.
34.
35.
Chong D. Y. R. Lim B. K. Rebibis K. J. Pan S. J. Sivalingam K. Kapoor R. Sun A. Y. S. Tan H. B. 《Advanced Packaging, IEEE Transactions on》2006,29(4):674-682
The recent advancement in high- performance semiconductor packages has been driven by the need for higher pin count and superior heat dissipation. A one-piece cavity lid flip chip ball grid array (BGA) package with high pin count and targeted reliability has emerged as a popular choice. The flip chip technology can accommodate an I/O count of more than five hundreds500, and the die junction temperature can be reduced to a minimum level by a metal heat spreader attachment. None the less, greater expectations on these high-performance packages arose such as better substrate real estate utilization for multiple chips, ease in handling for thinner core substrates, and improved board- level solder joint reliability. A new design of the flip chip BGA package has been looked into for meeting such requirements. By encapsulating the flip chip with molding compound leaving the die top exposed, a planar top surface can be formed. A, and a flat lid can then be mounted on the planar mold/die top surface. In this manner the direct interaction of the metal lid with the substrate can be removed. The new package is thus less rigid under thermal loading and solder joint reliability enhancement is expected. This paper discusses the process development of the new package and its advantages for improved solder joint fatigue life, and being a multichip package and thin core substrate options. Finite-element simulations have been employed for the study of its structural integrity, thermal, and electrical performances. Detailed package and board-level reliability test results will also be reported 相似文献
36.
37.
结合工程实例,介绍了我国第一座可拆装高架火炬的基本原理及组成,并对可拆装高架火炬与普通高架火炬在安全、技术、安装、维修、占地面积、投资等方面进行了比较,还分析了高架火炬未来的发展趋势. 相似文献
38.
H. L. Du S. R. Rose Z. D. Xiang P. K. Datta X. Y. Li 《Materialwissenschaft und Werkstofftechnik》2003,34(4):421-426
The oxidation/sulphidation behaviour of a Ti‐46.7Al‐1.9W‐0.5Si alloy with a TiAl3 diffusion coating was studied in an environment of H2/H2S/H2O at 850oC. The kinetic results demonstrate that the TiAl3 coating significantly increased the high temperature corrosion resistance of Ti‐46.7Al‐1.9W‐0.5Si. The SEM, EDX, XRD and TEM analysis reveals that the formation of an Al2O3 scale on the surface of the TiAl3‐coated sample was responsible for the enhancement of the corroison resistance. The Ti‐46.7Al‐1.9W‐0.5Si alloy was also modified by Nb ion implantation. The Nb ion implanted and as received sampels were subjected to cyclic oxidation in an open air at 800oC. The Nb ion implantation not only increased the oxidation resistance but also substantially improved the adhesion of scale to the substrate. 相似文献
39.
40.
Feng-Wen Sun Yimin Jiang Baras J.S. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》2003,49(1):180-190
Many issues in signal processing involve the inverses of Toeplitz matrices. One widely used technique is to replace Toeplitz matrices with their associated circulant matrices, based on the well-known fact that Toeplitz matrices asymptotically converge to their associated circulant matrices in the weak sense. This often leads to considerable simplification. However, it is well known that such a weak convergence cannot be strengthened into strong convergence. It is this fact that severely limits the usefulness of the close relation between Toeplitz matrices and circulant matrices. Observing that communication receiver design often needs to seek optimality in regard to a data sequence transmitted within finite duration, we define the finite-term strong convergence regarding two families of matrices. We present a condition under which the inverses of a Toeplitz matrix converges in the strong sense to a circulant matrix for finite-term quadratic forms. This builds a critical link in the application of the convergence theorems for the inverses of Toeplitz matrices since the weak convergence generally finds its usefulness in issues associated with minimum mean squared error and the finite-term strong convergence is useful in issues associated with the maximum-likelihood or maximum a posteriori principles. 相似文献