全文获取类型
收费全文 | 430602篇 |
免费 | 7130篇 |
国内免费 | 1386篇 |
专业分类
电工技术 | 7764篇 |
综合类 | 334篇 |
化学工业 | 65417篇 |
金属工艺 | 16923篇 |
机械仪表 | 14039篇 |
建筑科学 | 9146篇 |
矿业工程 | 2216篇 |
能源动力 | 12040篇 |
轻工业 | 33025篇 |
水利工程 | 4530篇 |
石油天然气 | 8010篇 |
武器工业 | 22篇 |
无线电 | 50324篇 |
一般工业技术 | 87669篇 |
冶金工业 | 81189篇 |
原子能技术 | 9279篇 |
自动化技术 | 37191篇 |
出版年
2022年 | 2889篇 |
2021年 | 4585篇 |
2020年 | 3514篇 |
2019年 | 4484篇 |
2018年 | 7650篇 |
2017年 | 7552篇 |
2016年 | 8091篇 |
2015年 | 5185篇 |
2014年 | 8188篇 |
2013年 | 22210篇 |
2012年 | 13014篇 |
2011年 | 16770篇 |
2010年 | 13391篇 |
2009年 | 14802篇 |
2008年 | 15131篇 |
2007年 | 14790篇 |
2006年 | 13071篇 |
2005年 | 11676篇 |
2004年 | 11070篇 |
2003年 | 10897篇 |
2002年 | 10275篇 |
2001年 | 10054篇 |
2000年 | 9447篇 |
1999年 | 9860篇 |
1998年 | 26085篇 |
1997年 | 17957篇 |
1996年 | 13584篇 |
1995年 | 10001篇 |
1994年 | 8751篇 |
1993年 | 8840篇 |
1992年 | 6219篇 |
1991年 | 5869篇 |
1990年 | 5806篇 |
1989年 | 5451篇 |
1988年 | 5179篇 |
1987年 | 4538篇 |
1986年 | 4398篇 |
1985年 | 4930篇 |
1984年 | 4527篇 |
1983年 | 4078篇 |
1982年 | 3766篇 |
1981年 | 3860篇 |
1980年 | 3559篇 |
1979年 | 3392篇 |
1978年 | 3404篇 |
1977年 | 3998篇 |
1976年 | 5398篇 |
1975年 | 2895篇 |
1974年 | 2711篇 |
1973年 | 2789篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
271.
272.
Semiconductors - The optical properties of dielectric nanostructures strongly depend on dielectric nanoparticles (NP) polarizability which can take the high values even interacting with... 相似文献
273.
Silicon - Nano-crystalline powders of Zn1−xCoxO with $\left (0.0\le x\le 0.07 \right )$ have been synthesized by sol-gel method. X-ray diffraction patterns of the prepared samples confirm the... 相似文献
274.
Ahmed Obaid M. Alzahrani M. Sh. Abdel-wahab Meshari Alayash M. S. Aida 《Journal of Materials Science: Materials in Electronics》2018,29(19):16317-16324
In this work, p-NiO/n-ZnO heterostructures were successfully prepared at room temperature using RF sputtering technique. The influence of ZnO layer thickness on the performance of the heterojunction was investigated. The deposited ZnO layers have a hexagonal Wurtzite structure with preferable growth orientations along (002) and (103) for thinner films. Increasing the thickness results in more crystallographic orientation randomness. The current–voltage measurements of the realized heterojunctions showed a clear rectifying behavior. The measured ideality factor varies from 2.5 to 1.6 according to the thickness of ZnO layer. The series resistance of the device is enlarged with increasing ZnO thickness. The deduced parameters from the I–V characteristics suggest that 200 nm is the optimal thickness of the ZnO layer according to our experimental conditions. We attribute the relatively better performance of this thickness to achieving reasonable compensation between serial resistance and ideality factor. The best heterojunction was tested and successfully used as a UV detector. 相似文献
275.
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
276.
277.
Basic insulating refractories were fabricated by the pressing route using dead-burned magnesia, pure calcined alumina, expanded perlite, and calcined waste serpentine as starting raw materials in four compositions from F1 to F4. Periclase and forsterite were major phases in F1 and F2 compositions, while spinel was also detected in the XRD patterns of F3 and F4 samples. Quantitative phase analysis showed that F4 sample sintered at 1450?°C has the highest forsterite content among all other samples. On the other hand, it has lower thermal conductivity compared to F1 to F3, and even lower than aluminosilicate IFBs with the same bulk density. It is concluded that forsterite is a highly insulating material, compared to periclase, corundum, periclase-spinel, aluminosilicates, such as mullite, etc. 相似文献
278.
279.
Alfredo M. Gravagnuolo Eden Morales‐Narváez Charlene Regina Santos Matos Sara Longobardi Paola Giardina Arben Merkoçi 《Advanced functional materials》2015,25(38):6084-6092
Class I hydrophobin Vmh2, a peculiar surface active and versatile fungal protein, is known to self‐assemble into chemically stable amphiphilic films, to be able to change wettability of surfaces, and to strongly adsorb other proteins. Herein, a fast, highly homogeneous and efficient glass functionalization by spontaneous self‐assembling of Vmh2 at liquid–solid interfaces is achieved (in 2 min). The Vmh2‐coated glass slides are proven to immobilize not only proteins but also nanomaterials such as graphene oxide (GO) and quantum dots (QDs). As models, bovine serum albumin labeled with Alexa 555 fluorophore, anti‐immunoglobulin G antibodies, and cadmium telluride QDs are patterned in a microarray fashion in order to demonstrate functionality, reproducibility, and versatility of the proposed substrate. Additionally, a GO layer is effectively and homogeneously self‐assembled onto the studied functionalized surface. This approach offers a quick and simple alternative to immobilize nanomaterials and proteins, which is appealing for new bioanalytical and nanobioenabled applications. 相似文献
280.
Dr. Manuel Nieto-Domínguez Dr. Pablo I. Nikel 《Chembiochem : a European journal of chemical biology》2020,21(18):2551-2571
The diversity of life relies on a handful of chemical elements (carbon, oxygen, hydrogen, nitrogen, sulfur and phosphorus) as part of essential building blocks; some other atoms are needed to a lesser extent, but most of the remaining elements are excluded from biology. This circumstance limits the scope of biochemical reactions in extant metabolism – yet it offers a phenomenal playground for synthetic biology. Xenobiology aims to bring novel bricks to life that could be exploited for (xeno)metabolite synthesis. In particular, the assembly of novel pathways engineered to handle nonbiological elements (neometabolism) will broaden chemical space beyond the reach of natural evolution. In this review, xeno-elements that could be blended into nature's biosynthetic portfolio are discussed together with their physicochemical properties and tools and strategies to incorporate them into biochemistry. We argue that current bioproduction methods can be revolutionized by bridging xenobiology and neometabolism for the synthesis of new-to-nature molecules, such as organohalides. 相似文献