全文获取类型
收费全文 | 25568篇 |
免费 | 2048篇 |
国内免费 | 880篇 |
专业分类
电工技术 | 1373篇 |
技术理论 | 1篇 |
综合类 | 1437篇 |
化学工业 | 4429篇 |
金属工艺 | 1348篇 |
机械仪表 | 1351篇 |
建筑科学 | 1987篇 |
矿业工程 | 580篇 |
能源动力 | 915篇 |
轻工业 | 1666篇 |
水利工程 | 359篇 |
石油天然气 | 1379篇 |
武器工业 | 124篇 |
无线电 | 3188篇 |
一般工业技术 | 3286篇 |
冶金工业 | 1441篇 |
原子能技术 | 319篇 |
自动化技术 | 3313篇 |
出版年
2024年 | 50篇 |
2023年 | 403篇 |
2022年 | 572篇 |
2021年 | 1029篇 |
2020年 | 722篇 |
2019年 | 679篇 |
2018年 | 711篇 |
2017年 | 810篇 |
2016年 | 762篇 |
2015年 | 934篇 |
2014年 | 1269篇 |
2013年 | 1601篇 |
2012年 | 1636篇 |
2011年 | 1781篇 |
2010年 | 1444篇 |
2009年 | 1478篇 |
2008年 | 1373篇 |
2007年 | 1273篇 |
2006年 | 1390篇 |
2005年 | 1198篇 |
2004年 | 869篇 |
2003年 | 778篇 |
2002年 | 782篇 |
2001年 | 557篇 |
2000年 | 538篇 |
1999年 | 628篇 |
1998年 | 586篇 |
1997年 | 489篇 |
1996年 | 470篇 |
1995年 | 364篇 |
1994年 | 289篇 |
1993年 | 196篇 |
1992年 | 185篇 |
1991年 | 120篇 |
1990年 | 94篇 |
1989年 | 78篇 |
1988年 | 93篇 |
1987年 | 52篇 |
1986年 | 43篇 |
1985年 | 23篇 |
1984年 | 30篇 |
1983年 | 14篇 |
1982年 | 26篇 |
1981年 | 12篇 |
1980年 | 10篇 |
1979年 | 15篇 |
1977年 | 4篇 |
1976年 | 9篇 |
1975年 | 4篇 |
1965年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
981.
To better understand the distribution of words in all kinds of syntactic structures, the paper calculates the word distribution
in syntactic structures of both English and Chinese. On the basis of the calculation, the article presents the definition
of the words’ syntactic distribution complexity. After arranging the Chinese and English words according to their own syntactic
distribution complexity, respectively, the Lotka phenomenon can be clearly attested by the results. The discovery made in
the paper reveals the law of the words’ syntactic distribution in linguistic studies on one hand and the statistically proven
fact that Chinese words’ syntax is much more complex than that of the English after comparing the Lotka phenomenon of both
Chinese and English words’ syntactic distribution complexity on the other hand. 相似文献
982.
Weizhi Nie Anan Liu Xiaorong Zhu Yuting Su 《Multimedia Tools and Applications》2016,75(20):12521-12534
With the rapid development of location-based social networks (LBSNs), increasing media data is ceaselessly uploaded by users. The multimedia data is often scattered and not informative and consequently they can not directly represent the semantics of each venue. Most of prior works leverage the user’ travelling histories to recommend new venues to users. However, these works often focus on the users’ travelling histories, while ignore the concepts or the popular levels of venues. In this paper, we proposed a quality model for venue recommendation by utilizing multimedia data to predict the interested level of each venue. First, we apply the graph cut method to generate the latent textual topics. Second, we leverage visual data from Flickr to train concept detectors to automatically label visual information. Third, the weighted bipartite matching algorithm is implemented to generate the venue multimedia topics by bridging the textual information and the visual information. Finally, we utilize the matching cost to predict the popular level of venue for recommendation. The experiments have been conducted on the cross-platform datasets. The results demonstrate the superiority of the proposed model. 相似文献
983.
984.
谢素艳 《自动化与仪器仪表》2014,(2):89-90
当今社会最为突出的发展领域是无线网络技术的应用以及快速发展。本文就无线电技术即zigbee技术及其自身的特性进行了详细的分析,主要将优点与自身的构成方式进行了探讨。 相似文献
985.
Su Hang Sandoval Juan Vieyres Pierre Poisson Gérard Ferrigno Giancarlo De Momi Elena 《International Journal of Control, Automation and Systems》2018,16(6):2915-2923
International Journal of Control, Automation and Systems - In this paper, a safety-enhanced collaborative control framework is proposed for tele-operated minimally invasive surgery (MIS) using a... 相似文献
986.
采用基于密度泛函理论(DFT)的平面波赝势(PW-PP)方法,分别计算纯净以及掺杂Ti的NaAlH4和Na3AlH6的晶格结构参数、能量变化和电子态密度(DOS),分析比较Ti掺杂对NaAlH4和Na3AlH6储氢性能的影响。结果表明:Ti掺杂后的晶格结构比原纯净的NaAlH4和Na3AlH6稳定,且脱氢所需能量减少。Ti替代Na后,Ti吸引周围的H原子,使Al-H键变弱;Ti替代Al,Ti-H键比原Al-H键明显减弱,使掺杂后脱氢所需能量降低。通过对比分析Ti掺杂对NaAlH4和Na3AlH6结构和态密度的影响,得出Ti的催化作用主要发生在脱氢反应的第一步。 相似文献
987.
氧化还原电位对低煤阶煤生物甲烷生成的影响 总被引:1,自引:0,他引:1
氧化还原电位(Eh)是煤层生物甲烷生成的重要控制因素之一。为了解其对煤层生物甲烷产出的影响以及产甲烷的动力学过程,在实验室采用-102 mV、-153 mV、-208 mV、-284 mV、-315 mV这5个氧化还原电位值,对河南义马低煤阶煤样品进行了生物甲烷模拟产出实验,采用气相色谱仪对不同反应阶段生成气体的成分及生成量进行检测,同时对菌种源中微生物进行培养计数。结果表明:①不同Eh条件下的实验均有甲烷的生成,氧化还原电位较低时产甲烷菌的繁殖更加快速,在-284 mV时生物甲烷的浓度最大,-102 mV时最小;②通过平板计数法,分析了产甲烷过程和细菌生长动力学机理--整个产甲烷生成过程也是微生物生长代谢的过程,间接证明了产气量大小变化的原因。结论认为,Eh对于煤层生物甲烷的生成具有重要的控制作用。 相似文献
988.
Xi Chen Guo-Ping Wu Qiu-Feng Cai Guang-Ming Liu Kiyoshi Osatomi Wen-Jin Su Min-Jie Cao 《Food chemistry》2012,130(3):679-686
An aminopeptidase was purified from Japanese flounder skeletal muscle to homogeneity by ammonium sulphate fractionation and three chromatographies. The enzyme was approximately 100 kDa with isoelectric point of 5.7 as estimated by two-dimensional polyacrylamide gel electrophoresis. Its optimum temperature and pH were 45 °C and 7.5, respectively. According to peptide mass fingerprinting study, the enzyme revealed high identity to a puromycin-sensitive aminopeptidase. It had a broad specificity toward aminopeptidase substrates and preferred to hydrolyse Lys-MCA with kcat/Km of 8.1 × 106 M?1 s?1, and the activation energy (Ea) of 72.5 kJ M?1. Metal-chelating agents effectively inhibited the enzyme activity, and Zn2+, Mn2+ and Co2+ significantly restored the apoenzymatic activity dialysed by EDTA, whilst inhibitors to other proteinases did not show much effect. Furthermore, bestatin strongly inhibited its activity. These results indicate that the purified enzyme is a metalloaminopeptidase which would possibly contribute to free amino acids increase in fish muscle. 相似文献
989.
990.
Through melt hydrogenation, a gradient microstructure (α″ + α′)/(α + βH) has been observed in TC21 alloy. The addition of hydrogen induces martensite transformation and increases the volume fraction of β. It is found that the absorption process of hydrogen atoms can be divided into melting and cooling stages. During cooling, the continuous absorption of hydrogen and the corresponding decrease of freezing point of melt extend solidification time of melt and lead to hydrogen enrichment in the upper of the specimen, which induces the formation of the gradient structure. The hydrogenated TC21 alloy shows higher thermoplasticity compared with the unhydrogenated TC21 alloy. The flow stress of the upper part of the hydrogenated alloy is lower than that of the center part. A gradual variation has been observed in the microhardness along the gradient direction due to variation in the microstructure. The microhardness of the upper surface drops about 45% with 14.6 at.%H. 相似文献