全文获取类型
收费全文 | 62637篇 |
免费 | 6464篇 |
国内免费 | 3701篇 |
专业分类
电工技术 | 3844篇 |
技术理论 | 2篇 |
综合类 | 4806篇 |
化学工业 | 10240篇 |
金属工艺 | 3496篇 |
机械仪表 | 4013篇 |
建筑科学 | 4337篇 |
矿业工程 | 1681篇 |
能源动力 | 1544篇 |
轻工业 | 6442篇 |
水利工程 | 1369篇 |
石油天然气 | 2669篇 |
武器工业 | 551篇 |
无线电 | 7256篇 |
一般工业技术 | 7452篇 |
冶金工业 | 2582篇 |
原子能技术 | 739篇 |
自动化技术 | 9779篇 |
出版年
2024年 | 334篇 |
2023年 | 1047篇 |
2022年 | 1916篇 |
2021年 | 2550篇 |
2020年 | 1992篇 |
2019年 | 1685篇 |
2018年 | 1937篇 |
2017年 | 2108篇 |
2016年 | 1957篇 |
2015年 | 2667篇 |
2014年 | 3349篇 |
2013年 | 4111篇 |
2012年 | 4554篇 |
2011年 | 4965篇 |
2010年 | 4561篇 |
2009年 | 4407篇 |
2008年 | 4231篇 |
2007年 | 4052篇 |
2006年 | 3766篇 |
2005年 | 3100篇 |
2004年 | 2229篇 |
2003年 | 1854篇 |
2002年 | 1842篇 |
2001年 | 1533篇 |
2000年 | 1196篇 |
1999年 | 1004篇 |
1998年 | 707篇 |
1997年 | 600篇 |
1996年 | 514篇 |
1995年 | 397篇 |
1994年 | 341篇 |
1993年 | 264篇 |
1992年 | 209篇 |
1991年 | 176篇 |
1990年 | 125篇 |
1989年 | 101篇 |
1988年 | 80篇 |
1987年 | 59篇 |
1986年 | 57篇 |
1985年 | 23篇 |
1984年 | 27篇 |
1983年 | 20篇 |
1982年 | 26篇 |
1981年 | 13篇 |
1980年 | 20篇 |
1979年 | 17篇 |
1978年 | 12篇 |
1977年 | 13篇 |
1976年 | 21篇 |
1975年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
Video transmission over IEEE 802.11e wireless networks still shows poor performance for large bandwidth demand and frequently changed environments. Thus, several enhancements of IEEE 802.11e were proposed. On the other hand, big frames and simultaneous sending of adjacent frames always cause packet dropping for buffer overflow. In the past, we proposed an IEEE 802.11e enhancement named DFAA and a content aware mechanism to solve the above problems. The motivation of this paper is to find a proper way to integrate these two mechanisms. A DFAA enhancement (DFAA-E) is proposed to make up the insufficiency of content aware mechanism. Experiments results show that the combination of DFAA-E and content aware mechanism improves the video decoded quality greatly. And its performance can be further enhanced by selecting the suitable settings of certain parameters. 相似文献
12.
The effect of biochar substituted for anthracite as reductant on magnetizing-roasting pyrite cinder was investigated.The key of magnetizing-roasting is the gasification reaction between reductants and CO2.Since biochar could react with CO2 more rapidly at lower temperature,the reactivity of biochar is better than that of anthracite.The gasification of biochar could produce reducing condition ofφCO/(φCO+φCO2)about 10%-20% between 700-800 ℃,which is in accord with the atmosphere and temperature of Fe2O3 reduction.So it is beneficial to the reduction of iron mineral of pyrite cinder.Compared with anthracite,biochar could decrease the roasting temperature from825 to 750 ℃ and roasting time from 20 to 15min,which shows that a better effect of magnetization could be obtained in the condition of lower temperature and shorter time.Using biochar as reductant,iron concentrate extracted from pyrite cinder as about 64%iron grade could be produced,and the recovery is over 90% under the condition of above 90% grinding particle less than 0.045 mm and magnetic intensity of 0.124-0.194 T. 相似文献
13.
Ye Wan Jun Tan Guangling Song Chuanwei Yan 《Metallurgical and Materials Transactions A》2006,37(7):2313-2316
The focused ion beam technique was employed to investigate the atmospheric corrosion morphology of AZ91D. It was found that
the α matrix of the alloy was preferentially corroded in the areas adjacent to intermetallic phases. The most interesting
finding was that the corrosion products in corrosion cavities were pelletlike, which has never been reported before. 相似文献
14.
Supported metal catalysts, particularly noble metals supported on SiO2, have attracted considerable attention due to the importance of the silica–metal interface in heterogeneous catalysis and in electronic device fabrication. Several important issues, e.g., the stability of the metal–oxide interface at working temperatures and pressures, are not well-understood. In this review, the present status of our understanding of the metal–silica interface is reviewed. Recent results of model studies in our laboratories on Pd/SiO2/Mo(1 1 2) using LEED, AES and STM are reported. In this work, epitaxial, ultrathin, well-ordered SiO2 films were grown on a Mo(1 1 2) substrate to circumvent complications that frequently arise from the silica–silicon interface present in silica thin films grown on silicon. 相似文献
15.
Depending on whether bidirectional links or unidirectional links are used for communications, the network topology under a
given range assignment is either an undirected graph referred to as the bidirectional topology, or a directed graph referred
to as the unidirectional topology. The Min-Power Bidirectional (resp., Unidirectional) k-Node Connectivity problem seeks a range assignment of minimum total power subject to the constraint that the produced bidirectional
(resp. unidirectional) topology is k-vertex connected. Similarly, the Min-Power Bidirectional (resp., Unidirectional) k-Edge Connectivity problem seeks a range assignment of minimum total power subject to the constraint the produced bidirectional
(resp., unidirectional) topology is k-edge connected.
The Min-Power Bidirectional Biconnectivity problem and the Min-Power Bidirectional Edge-Biconnectivity problem have been studied
by Lloyd et al. [23]. They show that range assignment based the approximation algorithm of Khuller and Raghavachari [18],
which we refer to as Algorithm KR, has an approximation ratio of at most 2(2 – 2/n)(2 + 1/n) for Min-Power Bidirectional Biconnectivity, and range assignment based on the approximation algorithm of Khuller and Vishkin [19],
which we refer to as Algorithm KV, has an approximation ratio of at most 8(1 – 1/n) for Min-Power Bidirectional Edge-Biconnectivity.
In this paper, we first establish the NP-hardness of Min-Power Bidirectional (Edge-) Biconnectivity. Then we show that Algorithm KR has an approximation ratio of at most 4 for both Min-Power Bidirectional Biconnectivity and Min-Power Unidirectional Biconnectivity,
and Algorithm KV has an approximation ratio of at most 2k for both Min-Power Bidirectional k-Edge Connectivity and Min-Power Unidirectional k-Edge Connectivity. We also propose a new simple constant-approximation algorithm for both Min-Power Bidirectional Biconnectivity
and Min-Power Unidirectional Biconnectivity. This new algorithm applies only to Euclidean instances, but is best suited for
distributed implementation.
A preliminary version of this work appeared in the proceedings of the 2nd International Conference on AD-HOC Network and Wireless
(Adhoc-Now 2003).
Research performed in part while visiting the Max-Plank-Institut fur Informatik.
Gruia Calinescu is an Assistant Professor of Computer Science at the Illinois Institute of Technology since 2000. He held postdoc or visiting
researcher positions at DIMACS, University of Waterloo, and Max-Plank Institut fur Informatik. Gruia has a Diploma from University
of Bucharest and a Ph.D. from Georgia Insitute of Technology. His research interests are in the area of algorithms.
Peng-Jun Wan has joined the Computer Science Department at Illinois Institute of Technology in 1997 and has been an Associate Professor
since 2004. He received his Ph.D. in Computer Science from University of Minnesota in 1997, M.S. in Operations Research and
Control Theory from Chinese Academy of Science in 1993, and B.S. in Applied Mathematics from Tsinghua University in 1990.
His research interests include optical networks and wireless networks. 相似文献
16.
A new detection algorithm (NDA) based on fuzzy cellular neural networks for white blood cell detection. 总被引:1,自引:0,他引:1
White blood cell detection is one of the most basic and key steps in the automatic recognition system of white blood cells in microscopic blood images. Its accuracy and stability greatly affect the operating speed and recognition accuracy of the whole system. But there are only a few methods available for cell detection or segmentation due to the complexity of the microscopic images. This paper focuses on this issue. Based on the detailed analysis of the existing two methods--threshold segmentation followed by mathematical morphology (TSMM), and the fuzzy logic method--a new detection algorithm (NDA) based on fuzzy cellular neural networks is proposed. NDA combines the advantages of TSMM and the fuzzy logic method, and overcomes their drawbacks. With NDA, we can detect almost all white blood cells, and the contour of each detected cell is nearly complete. Its adaptability is strong and the running speed is expected to be comparatively high due to the easy hardware implementation of FCN. Experimental results show good performance. 相似文献
17.
18.
19.
20.
陆东凹陷油气藏烃类组成非均质性及其意义 总被引:1,自引:1,他引:0
陆东凹陷原油和油砂抽提物中烃类的宏观组成存在着明显的非均质性。在高孔隙度(>15%)储层单元中,饱和烃的含量高,占总组成的含量均大于40%,而极性化合物则相对较低,一般不足40%;相反,在低孔隙度(<15%)储层单元中,饱和烃的含量明显降低,而极性化合物则显著增加。此外,陆东凹陷原油和油砂抽提物中烃类成熟度亦存在着非均质性:在高孔隙度储层中,原油和油砂烃类的成熟度参数高,而在低孔隙度储层中原油和油砂烃类的成熟度参数低。根据原油和油砂抽提物中烃类的宏观组成特征和成熟度参数的变化规律,提出了陆东凹陷油气聚集模式。 相似文献