全文获取类型
收费全文 | 258680篇 |
免费 | 31292篇 |
国内免费 | 10817篇 |
专业分类
电工技术 | 14984篇 |
技术理论 | 16篇 |
综合类 | 17353篇 |
化学工业 | 51798篇 |
金属工艺 | 12810篇 |
机械仪表 | 14611篇 |
建筑科学 | 19417篇 |
矿业工程 | 6348篇 |
能源动力 | 7151篇 |
轻工业 | 24984篇 |
水利工程 | 4536篇 |
石油天然气 | 12402篇 |
武器工业 | 1903篇 |
无线电 | 30707篇 |
一般工业技术 | 35216篇 |
冶金工业 | 10031篇 |
原子能技术 | 2428篇 |
自动化技术 | 34094篇 |
出版年
2024年 | 1025篇 |
2023年 | 3643篇 |
2022年 | 6881篇 |
2021年 | 9365篇 |
2020年 | 8279篇 |
2019年 | 8585篇 |
2018年 | 8962篇 |
2017年 | 10298篇 |
2016年 | 9821篇 |
2015年 | 12659篇 |
2014年 | 14808篇 |
2013年 | 17796篇 |
2012年 | 17380篇 |
2011年 | 18255篇 |
2010年 | 16765篇 |
2009年 | 15924篇 |
2008年 | 15304篇 |
2007年 | 14438篇 |
2006年 | 14138篇 |
2005年 | 11774篇 |
2004年 | 8700篇 |
2003年 | 7949篇 |
2002年 | 8070篇 |
2001年 | 7067篇 |
2000年 | 6281篇 |
1999年 | 5456篇 |
1998年 | 4009篇 |
1997年 | 3296篇 |
1996年 | 2998篇 |
1995年 | 2501篇 |
1994年 | 2019篇 |
1993年 | 1439篇 |
1992年 | 1185篇 |
1991年 | 922篇 |
1990年 | 659篇 |
1989年 | 569篇 |
1988年 | 441篇 |
1987年 | 320篇 |
1986年 | 228篇 |
1985年 | 129篇 |
1984年 | 85篇 |
1983年 | 76篇 |
1982年 | 86篇 |
1981年 | 65篇 |
1980年 | 69篇 |
1979年 | 23篇 |
1978年 | 9篇 |
1976年 | 6篇 |
1965年 | 5篇 |
1959年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
32.
近两年.IP电话又叫网络电话的发展受到全球的关注。随着宽带接入的发展,基于宽带接入提供的网络电话具有了更大的生命力。从宽带电话的经营模式出发,探究这类业务的出现时现有话音业务市场的影响,进而分析这类业务的发展前景。 相似文献
33.
Object segmentation and labeling by learning from examples 总被引:1,自引:0,他引:1
We propose a system that employs low-level image segmentation followed by color and two-dimensional (2-D) shape matching to automatically group those low-level segments into objects based on their similarity to a set of example object templates presented by the user. A hierarchical content tree data structure is used for each database image to store matching combinations of low-level regions as objects. The system automatically initializes the content tree with only "elementary nodes" representing homogeneous low-level regions. The "learning" phase refers to labeling of combinations of low-level regions that have resulted in successful color and/or 2-D shape matches with the example template(s). These combinations are labeled as "object nodes" in the hierarchical content tree. Once learning is performed, the speed of second-time retrieval of learned objects in the database increases significantly. The learning step can be performed off-line provided that example objects are given in the form of user interest profiles. Experimental results are presented to demonstrate the effectiveness of the proposed system with hierarchical content tree representation and learning by color and 2-D shape matching on collections of car and face images. 相似文献
34.
随着各高校校园网络规模的不断扩大和各种应用的急剧增加,各种新的网络问题也在不断出现。Sniffer是网络管理员进行网络管理的有效工具,可以有效地对网络进行实时监控,及时发现网络中存在的各种问题。本文首先介绍了Sniffer的工作原理,其次给出了实现Sniffer功能的编程流程图,并用C语言给出了编程所需的关键代码。 相似文献
35.
36.
37.
Polyaryloxydiphenylsilanes were prepared from phosphorus‐containing diols and diphenydichlorolsilane through solution polymerization. With a stoichiometric imbalance in feed monomers, the resulting polymers exhibited moderate melting points and good processing properties. The polymers prepared showed initial decomposition temperatures above 340 °C, excellent thermal stability, high char yields at 850 °C and very high limited oxygen index values of 56–59. The polymers' char yields and their (P + Si) contents showed linear relationships. © 2003 Society of Chemical Industry 相似文献
38.
39.
L. Sheeney‐Haj‐Ichia S. Pogorelova Y. Gofer I. Willner 《Advanced functional materials》2004,14(5):416-424
Three different configurations of Au‐nanoparticle/CdS‐nanoparticle arrays are organized on Au/quartz electrodes for enhanced photocurrent generation. In one configuration, Au‐nanoparticles are covalently linked to the electrode and the CdS‐nanoparticles are covalently linked to the bare Au‐nanoparticle assembly. The resulting photocurrent, φ = 7.5 %, is ca. 9‐fold higher than the photocurrent originating from a CdS‐nanoparticle layer that lacks the Au‐nanoparticles, φ = 0.8 %. The enhanced photocurrent in the Au/CdS nanoparticle array is attributed to effective charge separation of the electron–hole pair by the injection of conduction‐band electrons from the CdS‐ to the Au‐nanoparticles. Two other configurations involving electrostatically stabilized bipyridinium‐crosslinked Au/CdS or CdS/Au nanoparticle arrays were assembled on the Au/quartz crystal. The photocurrent quantum yields in the two systems are φ = 10 % and φ = 5 %, respectively. The photocurrents in control systems that include electrostatically bridged Au/CdS or CdS/Au nanoparticles by oligocationic units that lack electron‐acceptor units are substantially lower than the values observed in the analogous bipyridinium‐bridged systems. The enhanced photocurrents in the bipyridinium‐crosslinked systems is attributed to the stepwise electron transfer of conduction‐band electrons to the Au‐nanoparticles by the bipyridinium relay bridge, a process that stabilizes the electron–hole pair against recombination and leads to effective charge separation. 相似文献
40.
N. Jongen M. Donnet P. Bowen J. Lemaître H. Hofmann R. Schenk C. Hofmann M. Aoun‐Habbache S. Guillemet‐Fritsch J. Sarrias A. Rousset M. Viviani M.T. Buscaglia V. Buscaglia P. Nanni A. Testino J.R. Herguijuela 《化学工程与技术》2003,26(3):303-305
The synthesis of powders with controlled shape and narrow particle size distributions is still a major challenge for many industries. A continuous Segmented Flow Tubular Reactor (SFTR) has been developed to overcome homogeneity and scale‐up problems encountered when using batch reactors. Supersaturation is created by mixing the co‐reactants in a micromixer inducing precipitation; the suspension is then segmented into identical micro‐volumes by a non‐miscible fluid and sent through a tube. These micro‐volumes are more homogeneous when compared to large batch reactors leading to narrower size distributions, better particle morphology, polymorph selectivity and stoichiometry. All these features have been demonstrated on single tube SFTR for different chemical systems. To increase productivity for commercial application the SFTR is being “scaled‐out” by multiplying the number of tubes running in parallel instead of scaling‐up by increasing their size. The versatility of the multi‐tube unit will allow changes in type of precipitate with a minimum of new investment as new chemistry can be researched, developed and optimised in a single tube SFTR and then transferred to the multi‐tube unit for powder production. 相似文献