全文获取类型
收费全文 | 81740篇 |
免费 | 7925篇 |
国内免费 | 4189篇 |
专业分类
电工技术 | 5461篇 |
技术理论 | 8篇 |
综合类 | 6043篇 |
化学工业 | 13353篇 |
金属工艺 | 4236篇 |
机械仪表 | 5255篇 |
建筑科学 | 7374篇 |
矿业工程 | 2364篇 |
能源动力 | 2516篇 |
轻工业 | 6367篇 |
水利工程 | 1602篇 |
石油天然气 | 3794篇 |
武器工业 | 772篇 |
无线电 | 9736篇 |
一般工业技术 | 9380篇 |
冶金工业 | 3370篇 |
原子能技术 | 1008篇 |
自动化技术 | 11215篇 |
出版年
2024年 | 426篇 |
2023年 | 1570篇 |
2022年 | 2892篇 |
2021年 | 3872篇 |
2020年 | 2818篇 |
2019年 | 2353篇 |
2018年 | 2562篇 |
2017年 | 2836篇 |
2016年 | 2563篇 |
2015年 | 3407篇 |
2014年 | 4264篇 |
2013年 | 5009篇 |
2012年 | 5595篇 |
2011年 | 5769篇 |
2010年 | 5462篇 |
2009年 | 5158篇 |
2008年 | 4892篇 |
2007年 | 4420篇 |
2006年 | 4339篇 |
2005年 | 3545篇 |
2004年 | 2475篇 |
2003年 | 2152篇 |
2002年 | 2240篇 |
2001年 | 1981篇 |
2000年 | 1765篇 |
1999年 | 1826篇 |
1998年 | 1323篇 |
1997年 | 1179篇 |
1996年 | 1135篇 |
1995年 | 879篇 |
1994年 | 769篇 |
1993年 | 519篇 |
1992年 | 433篇 |
1991年 | 309篇 |
1990年 | 232篇 |
1989年 | 212篇 |
1988年 | 144篇 |
1987年 | 102篇 |
1986年 | 80篇 |
1985年 | 56篇 |
1984年 | 38篇 |
1983年 | 31篇 |
1982年 | 29篇 |
1981年 | 21篇 |
1980年 | 27篇 |
1979年 | 17篇 |
1962年 | 42篇 |
1961年 | 39篇 |
1960年 | 16篇 |
1951年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
An experimental study of an optical burst switching network based on wavelength-selective optical switches 总被引:1,自引:0,他引:1
Li Xinwan Chen Jianping Wu Guiling Wang Hui Ye Ailun 《Communications Magazine, IEEE》2005,43(5):S3-10
In this article we report the system structure and test results of an experimental optical burst switching network with three edge router's and one core node. Wavelength-selective switches developed for this system and their characteristics are depicted. The implementation and performance of our new scheme for the just-in-time protocol are described. We also report experimental results of FTP and VOD services on this system. Some parameters, including traffic rate, average burst data length, and assembly time, are studied. 相似文献
62.
2008年29届奥运会在北京举行,使得有关奥运的话题成为热门中的热门,与运动有关或无关的众多品牌、厂商对北京奥运年均寄予厚望,为赢取更大的收获和提升品牌知名度作最大的努力。其实早在几年前,国内外运动鞋品牌企业就已经大张旗鼓,在产品研发与广告宣传等多方面投入重金,为在这次北京奥运年带来的难得契机中处于市场制高点或明或隐地博杀着。 相似文献
63.
The effects of key parameters on the preparation and regeneration of protoplast from the β-carotene-producing fungus Blakeslea trispora were discussed in this paper, including the combination of various enzymes, mycelial age, digesting time and temperature,
pH value, osmotic stabilizers, pretreatment, culture medium and culture method. Under the condition of mixed enzymes in osmotic
stabilizer (0.6 M NaCl) combined with 2% lysozyme, 3% cellulase and 3% snailase, the highest protoplast yield, as high as
7.48×106 protoplasts/mL, was obtained when mycelial age was 60 h at pH 5.0–6.0 with digesting for 14–16 h at 28 °C. After
purification of the obtained protoplasts, they were regenerated in PDA regenerative medium using bilayer plate culture method.
To validate the usability of the protoplasts, a novel plasmid with green fluorescent protein (GFP) was used in transformation
for easy visual observation. The results showed that the protoplasts prepared by the optimized method were active and applicable
in further gene manipulation experiments.
This work was presented at 13
th
YABEC symposium held at Seoul, Korea, October 20–22, 2007. 相似文献
64.
Qingzhao Yao Yuming Zhou Yanqing Sun Xiaoyun Ye 《Journal of Inorganic and Organometallic Polymers and Materials》2008,18(4):477-484
TiO2 hybrid molecular imprinted polymer (MIP) for ethofumesate using methacrylic acid (MAA) as the functional monomer and silane
coupling agent 3-(trimethoxysilyl) propylmethacrylate (KH570) as organic–inorganic connective bridge was synthesized via photo-excitation
method. Hydrogen bond was proved to act between MAA and ethofumesate for pre- and post-polymerization binding properties as
testified by UV spectrometric method. KH570 modified TiO2 nanoparticles were prepared via sonochemical reaction, which can accelerate hydrolysis, increase collision chance for the
reactive system and improve the dispersion of the nanoparticles. Scanning electron microscope (SEM), transmission electron
microscope (TEM), binding and the adsorption kinetics experiments as well as thermogravimetric analysis (TGA) were employed
for characterization. The results indicated that the hybrid MIP revealed a larger surface area and more ordered imprinting
cavities with improved thermal stability compared to organic-only MIP. Furthermore, faster adsorption kinetics and enhancive
adsorption capacity were achieved, which made it promising in chemical sensor applications. 相似文献
65.
We report the growth of highly C-axis orientation of Sr
x
Ba1−x
Nb2O6 (SBN) thin films on p-type (100) Si substrates by using a potassium-substituted SBN template layer with the sol–gel method. The crystallization of SBN thin films was found closely related to the potassium ion doping concentration and the postannealing temperature of the K-SBN template layer. Secondary ion mass spectrometry analysis showed that potassium elements were accumulated at the interface of the template layer and silicon substrate. SBN films postannealed at 750 °C with K-SBN template layer has a smaller full width at half maximum of X-ray rocking curve of 2.45° than that of 5.40° for the pure SBN films. By introducing a template layer, the surface morphologies of SBN films fabricated on silicon substrate were greatly improved. 相似文献
66.
针对碳酸盐岩气藏部分气井生产效能低的状况,决定在长庆气田下古生界尝试开展加砂压裂重复改造试验,以期提高低产、低效气井的产量,延长气田稳产期。通过潜心研究、精细设计及现场质检监控,优选了4口老井进行加砂压裂重复改造现场试验。从试验结果来看,虽然只有1口井取得明显的改造效果,但4口井加砂压裂施工都是成功的,说明对碳酸盐岩气藏实施加砂压裂是可以实现的,但在选井思路和压裂工艺方面还有待探索和研究。 相似文献
67.
Average consensus in networks of dynamic agents with switching topologies and multiple time-varying delays 总被引:5,自引:0,他引:5
In this paper, we discuss average consensus problem in undirected networks of dynamic agents with fixed and switching topologies as well as multiple time-varying communication delays. By employing a linear matrix inequality method, we prove that all the nodes in the network achieve average consensus asymptotically for appropriate communication delays if the network topology is connected. Particularly, several feasible linear matrix inequalities are established to determine the maximal allowable upper bound of time-varying communication delays. Numerical examples are given to demonstrate the effectiveness and the sharpness of the theoretical results. 相似文献
68.
简单介绍了广州地铁二号线民用移动通信工程概况,并就地铁民用移动通信系统引入地铁的主要技术难点进行了论述。 相似文献
69.
70.
An innovative method for modelling biological processes under anaerobic conditions is presented and discussed. The method is based on titrimetric and off-gas measurements. Titrimetric data is recorded as the addition rate of hydroxyl ions or protons that is required to maintain pH in a bioreactor at a constant level. An off-gas analysis arrangement measures, among other things, the transfer rate of carbon dioxide. The integration of these signals results in a continuous signal which is solely related to the biological reactions. When coupled with a mathematical model of the biological reactions, the signal allows a detailed characterisation of these reactions, which would otherwise be difficult to achieve. Two applications of the method to the enhanced biological phosphorus removal processes are presented and discussed to demonstrate the principle and effectiveness of the method. 相似文献