全文获取类型
收费全文 | 73365篇 |
免费 | 11094篇 |
国内免费 | 10429篇 |
专业分类
电工技术 | 2004篇 |
技术理论 | 3篇 |
综合类 | 6007篇 |
化学工业 | 1338篇 |
金属工艺 | 605篇 |
机械仪表 | 1829篇 |
建筑科学 | 524篇 |
矿业工程 | 258篇 |
能源动力 | 1513篇 |
轻工业 | 397篇 |
水利工程 | 97篇 |
石油天然气 | 119篇 |
武器工业 | 121篇 |
无线电 | 13178篇 |
一般工业技术 | 3668篇 |
冶金工业 | 298篇 |
原子能技术 | 172篇 |
自动化技术 | 62757篇 |
出版年
2024年 | 361篇 |
2023年 | 1630篇 |
2022年 | 3176篇 |
2021年 | 3723篇 |
2020年 | 3642篇 |
2019年 | 2948篇 |
2018年 | 3273篇 |
2017年 | 4777篇 |
2016年 | 5194篇 |
2015年 | 4770篇 |
2014年 | 6797篇 |
2013年 | 6217篇 |
2012年 | 7540篇 |
2011年 | 7367篇 |
2010年 | 6128篇 |
2009年 | 6054篇 |
2008年 | 4635篇 |
2007年 | 4612篇 |
2006年 | 3629篇 |
2005年 | 2017篇 |
2004年 | 910篇 |
2003年 | 805篇 |
2002年 | 812篇 |
2001年 | 753篇 |
2000年 | 497篇 |
1999年 | 504篇 |
1998年 | 251篇 |
1997年 | 222篇 |
1996年 | 234篇 |
1995年 | 175篇 |
1994年 | 185篇 |
1993年 | 135篇 |
1992年 | 131篇 |
1991年 | 125篇 |
1990年 | 94篇 |
1989年 | 104篇 |
1988年 | 129篇 |
1987年 | 38篇 |
1986年 | 35篇 |
1985年 | 41篇 |
1984年 | 40篇 |
1983年 | 23篇 |
1982年 | 28篇 |
1981年 | 23篇 |
1980年 | 16篇 |
1979年 | 19篇 |
1978年 | 19篇 |
1977年 | 20篇 |
1975年 | 8篇 |
1974年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 217 毫秒
91.
Sleep modes are widely accepted as an effective technique for energy-efficient networking: by adequately putting to sleep and waking up network resources according to traffic demands, a proportionality between energy consumption and network utilization can be approached, with important reductions in energy consumption. Previous studies have investigated and evaluated sleep modes for wireless access networks, computing variable percentages of energy savings. In this paper we characterize the maximum energy saving that can be achieved in a cellular wireless access network under a given performance constraint. In particular, our approach allows the derivation of realistic estimates of the energy-optimal density of base stations corresponding to a given user density, under a fixed performance constraint. Our results allow different sleep mode proposals to be measured against the maximum theoretically achievable improvement. We show, through numerical evaluation, the possible energy savings in today’s networks, and we further demonstrate that even with the development of highly energy-efficient hardware, a holistic approach incorporating system level techniques is essential to achieving maximum energy efficiency. 相似文献
92.
The continuity of supply and quality of power are the two main significant aspects of today’s power delivery system. The Dynamic Voltage Restorer (DVR) is a series connected custom power device which improves the quality of power delivered to the consumers. This paper deals with the effectual exploitation of DVR for interconnecting the proton exchange membrane fuel cell (PEMFC) stack to the grid based on optimized proportional integral (PI) and fuzzy logic (FL) Controller. The real coded Genetic algorithm (GA) is used to optimize the PI controller parameters. The PEMFC operated boost converter is used to boost up the fuel cell output voltage to balance the DC side necessities of the voltage source converter (VSC). The proposed DVR provides balanced and unbalanced voltage sag/swell compensation, harmonic reduction as well as an active power injection to the grid. The designed method also protects the sensitive loads from source side power quality disturbances including short term interruption. In addition, the harmonic compensation performance of the proposed work is validated by comparing with the results of the H∞ controller based DVR under medium level voltage condition. The simulation results from MATLAB/SIMULINK are discussed to prove the effectiveness of the planned method. 相似文献
93.
94.
《Ceramics International》2019,45(13):16166-16172
Cr2O3 is a well-known corrosion resistant oxide used in refractory applications. However, it can oxidize into toxic and water-soluble Cr(VI) compounds upon reaction with calcium aluminate cement phases in the presence of oxygen, which subsequently causes disposal problems after use. This study describes the extent to which chromium in the spinel Mg(Al,Cr)2O4 phase can be oxidized to Cr(VI) when it reacts with the calcium aluminate cement phases C12A7, CA, CA2 and free CaO at 1300 °C in air, using XRD, XPS and leaching tests (TRGS 613 standard) as analytical tools. On reaction with CaO, the Mg(Al,CrIII)2O4 spinel mainly transformed into hauyne (Ca4Al6CrVIO16) and Ca5Cr3O12 which contains both Cr(IV) and Cr(VI). The reaction of C12A7 and CA with the spinel phase also resulted in the formation of Ca4Al6CrO16. Conversely, the reaction of Mg(Al,CrIII)2O4 spinel with CA2 resulted in the formation of only a trace amount of Cr(VI). Water-soluble Cr(VI) leached in large quantities (>100 mg/L) from samples where the Mg(Al,CrIII)2O4 reacted with either C12A7 or CA. Almost no Cr(VI) leached from the sample when Mg(Al,CrIII)2O4 reacted with CaO, using the standard TRGS 613 leach test, but a significant amount of Cr(VI) was released into solution when leached with a HCl solution for 12 h. Both Cr(IV) and Cr(VI) present in the Ca5Cr3O12 dissolved into acidic solution. Only a small amount of Cr(VI) leached from the sample that resulted when spinel was reacted with CA2, even after a prolonged HCl leach. Cr(III) in spinel Mg(Al,Cr)2O4 is very stable and does not leach in either distilled water or acidic solution. 相似文献
95.
Evangelopoulos Xenophon Brockmeier Austin J. Mu Tingting Goulermas John Y. 《Machine Learning》2019,108(4):595-626
Machine Learning - We propose a set of highly scalable algorithms for the combinatorial data analysis problem of seriating similarity matrices. Seriation consists of finding a permutation of data... 相似文献
96.
相似用户挖掘是提高社交网络服务质量的重要途径,在面向大数据的社交网络时代,准确的相似用户挖掘对于用户和互联网企业等都有重要的意义,而根据用户自己的兴趣话题挖掘的相似用户更符合相似用户的要求。提出了一种基于用户兴趣话题进行相似用户挖掘的方法。该方法首先使用TextRank话题提取方法对用户进行兴趣话题提取,再对用户发表内容进行训练,计算出所有词之间的相似度。提出CP(Corresponding Position similarity)、CPW(Corresponding Position Weighted similarity)、AP(All Position similarity)、APW(All Position Weighted similarity)四种用户兴趣话题词相似度计算方法,通过用户和相似用户间关注、粉丝重合率验证相似用户挖掘效果,APW similarity的相似用户的关注/粉丝重合百分比为1.687%,优于提出的其他三种算法,分别提高了26.3%、2.8%、12.4%,并且比传统的文本相似度方法Jaccard相似度、编辑距离算法、余弦相似度分别提高了20.4%、21.2%、45.0%。因此APW方法可以更加有效地挖掘出用户的相似用户。 相似文献
97.
Journal of Computer Science and Technology - DOACROSS loops are significant parts in many important scientific and engineering applications, which are generally exploited pipeline/wave-front... 相似文献
98.
Scientometrics - Due to the development of academic, more and more attentions are paid to citation recommendation. To solve the citation recommendation problem, researchers begin to focus on the... 相似文献
99.
性能效率是APP软件的重要质量属性,但目前缺乏APP软件性能效率的通用模型。分析了APP软件的性能特征,基于ISO/IEC 25010标准提出了APP软件的性能效率模型,定义了APP软件性能效率的子特性和度量指标。基于提出的APP软件性能效率模型,通过实验对APP软件的性能效率进行了度量及相关分析。 相似文献
100.
Wu Ge Mu Yi Susilo Willy Guo Fuchun Zhang Futai 《International Journal of Information Security》2019,18(3):321-331
International Journal of Information Security - Data integrity is a critical security issue in cloud storage. The data integrity checking schemes by a third-party auditor (TPA) have attracted a lot... 相似文献