全文获取类型
收费全文 | 64596篇 |
免费 | 3889篇 |
国内免费 | 537篇 |
专业分类
电工技术 | 782篇 |
综合类 | 730篇 |
化学工业 | 13265篇 |
金属工艺 | 1387篇 |
机械仪表 | 1504篇 |
建筑科学 | 2391篇 |
矿业工程 | 306篇 |
能源动力 | 1550篇 |
轻工业 | 9816篇 |
水利工程 | 694篇 |
石油天然气 | 873篇 |
武器工业 | 99篇 |
无线电 | 3776篇 |
一般工业技术 | 10521篇 |
冶金工业 | 12204篇 |
原子能技术 | 442篇 |
自动化技术 | 8682篇 |
出版年
2024年 | 132篇 |
2023年 | 604篇 |
2022年 | 1189篇 |
2021年 | 1941篇 |
2020年 | 1424篇 |
2019年 | 1390篇 |
2018年 | 2281篇 |
2017年 | 2292篇 |
2016年 | 2360篇 |
2015年 | 1861篇 |
2014年 | 2533篇 |
2013年 | 4540篇 |
2012年 | 3991篇 |
2011年 | 3986篇 |
2010年 | 3159篇 |
2009年 | 2863篇 |
2008年 | 3047篇 |
2007年 | 2682篇 |
2006年 | 2162篇 |
2005年 | 1774篇 |
2004年 | 1538篇 |
2003年 | 1408篇 |
2002年 | 1248篇 |
2001年 | 930篇 |
2000年 | 870篇 |
1999年 | 1037篇 |
1998年 | 4059篇 |
1997年 | 2500篇 |
1996年 | 1688篇 |
1995年 | 1042篇 |
1994年 | 870篇 |
1993年 | 791篇 |
1992年 | 300篇 |
1991年 | 296篇 |
1990年 | 282篇 |
1989年 | 286篇 |
1988年 | 273篇 |
1987年 | 211篇 |
1986年 | 217篇 |
1985年 | 257篇 |
1984年 | 225篇 |
1983年 | 176篇 |
1982年 | 196篇 |
1981年 | 201篇 |
1980年 | 198篇 |
1979年 | 147篇 |
1978年 | 140篇 |
1977年 | 224篇 |
1976年 | 464篇 |
1973年 | 98篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
72.
Ricardo Martínez-Corona Gerardo Vázquez Marrufo Carlos Cortés Penagos Luis Alberto Madrigal-Pérez Juan Carlos González-Hernández 《Yeast (Chichester, England)》2020,37(1):149-162
Lipases are hydrolytic enzymes that break the ester bonds of triglycerides, generating free fatty acids and glycerol. Extracellular lipase activity has been reported for the nonconventional yeast Kluyveromyces marxianus, grown in olive oil as a substrate, and the presence of at least eight putative lipases has been detected in its genome. However, to date, there is no experimental evidence on the physiological role of the putative lipases nor their structural and catalytic properties. In this study, a bioinformatic analysis of the genes of the putative lipases from K. marxianus L-2029 was performed, particularly identifying and characterizing the extracellular expected enzymes, due to their biotechnological relevance. The amino acid sequence of 10 putative lipases, obtained by in silico translation, ranged between 389 and 773 amino acids. Two of the analysed putative proteins showed a signal peptide, 25 and 33 amino acids long for KmYJR107Wp and KmLIP3p, and a molecular weight of 44.53 and 58.23 kDa, respectively. The amino acid alignment of KmLIP3p and KmYJR107Wp with the crystallized lipases from a patatin and the YlLip2 lipase from Yarrowia lipolytica, respectively, revealed the presence of the hydrolase characteristic motifs. From the 3D models of putative extracellular K. marxianus L-2029 lipases, the conserved pentapeptide of each was determined, being GTSMG for KmLIP3p and GHSLG for KmYJR107Wp; besides, the genes of these two enzymes (LIP3 and YJR107W) are apparently regulated by oleate response elements. The phylogenetic analysis of all K. marxianus lipases revealed evolutionary affinities with lipases from abH15.03, abH23.01, and abH23.02 families. 相似文献
73.
74.
75.
Abdeljaoued Emna Brulé Mathieu Tayibi Saida Manolakos Dimitris Oukarroum Abdallah Monlau Florian Barakat Abdellatif 《Clean Technologies and Environmental Policy》2020,22(10):1967-1997
Clean Technologies and Environmental Policy - Biochar has caught great attention over the last decade, yielding a large number of publications in a broad range of disciplines. This scientometric... 相似文献
76.
77.
Meza-Espinoza Libier de los Ángeles Vivar-Vera María de Lourdes García-Magaña María Sáyago-Ayerdi Sonia G. Chacón-López Alejandra Becerrea-Verdín Eduardo M. Montalvo-González Efigenia 《Food science and biotechnology》2018,27(2):509-517
Food Science and Biotechnology - The enzymatic activity and partial characterization of proteases from Bromelia karatas fruits were evaluated and compared with Bromelia pinguin proteases. The... 相似文献
78.
Marcia Cristina Kaezer Fran a Rosane Aguiar da Silva San Gil Jean-Guillaume Eon 《Catalysis Today》2003,78(1-4):105-115
γ-Al2O3 supported vanadium oxides were modified by tungsten and molybdenum oxides in order to improve dispersion and selectivity towards olefins in propane oxidative dehydrogenation (ODH). Both vanadium–tungsten and vanadium–molybdenum catalysts were obtained by adsorption of mixed isopolyanions (VW5O195−, V2W4O194−, VMo5O195− and V2Mo4O194−) from aqueous solutions. The isopolyanion solutions were characterized by UV-Vis and 51V NMR spectroscopy. Vanadium, vanadium–tungsten and vanadium–molybdenum precursors and catalysts were also characterized by UV-Vis (diffuse reflectance) and solid state 51V NMR spectroscopy. An improved selectivity to propene in the presence of tungsten and molybdenum in VOx/γ-Al2O3 was observed and attributed to dilution of vanadium by tungsten or molybdenum oxides on the γ-Al2O3 surface. 相似文献
79.
Sébastien Ambellouis Fran?ois Cabestaing Jack-Gérard Postaire 《IEEE transactions on image processing》2006,15(6):1601-1609
Energy-based methods for motion estimation in image sequences process the input data either in the spatiotemporal or in the frequency domain. In both cases, the algorithms already described in the literature often require a huge number of elementary operations. In this paper, we describe a class of velocity selective filters which yield an accurate detection of the edges moving in the sequence. We first present a filtering scheme based on a convolution operation computed on a finite size neighborhood and describe its properties in the spatiotemporal and frequency domains. Then, we show that filters with similar properties can be implemented recursively, i.e., as convolutions computed on infinite-size neighborhoods. As an example, we finally show the filters' responses in the case of two superimposed translational motions. 相似文献
80.
Quality of service has become today a major concern for operators of mobile communication networks. The massive development of networks and strong competition between operators has lead to the necessary and daily follow-up of network quality of service, a key factor for its subscriber’s fidelity. This article aims at presenting the optimization methodology and proposes its illustration with a case of RNO (Radio Network Optimisation) software usage, one of the Alcatel optimization toolchain component. After a short presentation of cellular network, the optimization basic principles are described. RNO software and its main functionnalities are then detailed before a last part dedicated to a real case of optimization done with RNO software. 相似文献