全文获取类型
收费全文 | 506336篇 |
免费 | 7107篇 |
国内免费 | 1362篇 |
专业分类
电工技术 | 9948篇 |
综合类 | 858篇 |
化学工业 | 71559篇 |
金属工艺 | 18493篇 |
机械仪表 | 15204篇 |
建筑科学 | 12198篇 |
矿业工程 | 1839篇 |
能源动力 | 13556篇 |
轻工业 | 46337篇 |
水利工程 | 4652篇 |
石油天然气 | 6959篇 |
武器工业 | 75篇 |
无线电 | 65650篇 |
一般工业技术 | 96465篇 |
冶金工业 | 95762篇 |
原子能技术 | 9622篇 |
自动化技术 | 45628篇 |
出版年
2021年 | 3631篇 |
2019年 | 3792篇 |
2018年 | 6399篇 |
2017年 | 6349篇 |
2016年 | 6660篇 |
2015年 | 4450篇 |
2014年 | 7687篇 |
2013年 | 23379篇 |
2012年 | 12540篇 |
2011年 | 17307篇 |
2010年 | 13549篇 |
2009年 | 15459篇 |
2008年 | 16421篇 |
2007年 | 16239篇 |
2006年 | 14675篇 |
2005年 | 13427篇 |
2004年 | 13018篇 |
2003年 | 12660篇 |
2002年 | 11721篇 |
2001年 | 11745篇 |
2000年 | 11033篇 |
1999年 | 11691篇 |
1998年 | 28413篇 |
1997年 | 20458篇 |
1996年 | 15958篇 |
1995年 | 12827篇 |
1994年 | 11515篇 |
1993年 | 11176篇 |
1992年 | 8628篇 |
1991年 | 8159篇 |
1990年 | 7997篇 |
1989年 | 7519篇 |
1988年 | 7321篇 |
1987年 | 6272篇 |
1986年 | 6278篇 |
1985年 | 7436篇 |
1984年 | 6816篇 |
1983年 | 6283篇 |
1982年 | 5737篇 |
1981年 | 6000篇 |
1980年 | 5554篇 |
1979年 | 5405篇 |
1978年 | 5142篇 |
1977年 | 6086篇 |
1976年 | 7736篇 |
1975年 | 4605篇 |
1974年 | 4440篇 |
1973年 | 4482篇 |
1972年 | 3659篇 |
1971年 | 3304篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Seniz R. Kushan Akin Emrah Dolekcekic Thomas J. Webster 《Ceramics International》2021,47(13):18213-18217
The main drawback of bioglasses is their restricted use in load bearing applications and the consequent need to develop stronger glassy materials. This has led to the consideration of oxynitride glasses for numerous biomedical applications. This paper investigated two different types of glasses at a constant cationic ratio, with and without nitrogen (a N containing and a N-free glass composition) to better understand the effect of N on the biological properties of glasses. The results revealed that the addition of N increased the glass transition temperature, isoelectric point (IEP) and slightly increased wettability. Moreover, compared to N including glass, N-free glass exhibited better anti-bacterial activity against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus), two key bacteria that infect implants. In summary, these in vitro results indicated that amine functional groups existing in N containing glasses which are missing in N-free glasses, caused a slight difference in wetting behavior and a more obvious change in isoelectric point and in bacterial response. N-free glasses exhibited better inhibitory results both against E. coli and S. aureus compared to N including glass suggesting that oxygen rich glasses should be further studied for their novel antibacterial properties. 相似文献
2.
3.
Protection of Metals and Physical Chemistry of Surfaces - The present review is devoted to the sorption properties of magnetite towards hexavalent chromium ions and the possibility of its use as a... 相似文献
4.
Leucokinins (LKs) constitute a family of neuropeptides identified in numerous insects and many other invertebrates. LKs act on G-protein-coupled receptors that display only distant relations to other known receptors. In adult Drosophila, 26 neurons/neurosecretory cells of three main types express LK. The four brain interneurons are of two types, and these are implicated in several important functions in the fly’s behavior and physiology, including feeding, sleep–metabolism interactions, state-dependent memory formation, as well as modulation of gustatory sensitivity and nociception. The 22 neurosecretory cells (abdominal LK neurons, ABLKs) of the abdominal neuromeres co-express LK and a diuretic hormone (DH44), and together, these regulate water and ion homeostasis and associated stress as well as food intake. In Drosophila larvae, LK neurons modulate locomotion, escape responses and aspects of ecdysis behavior. A set of lateral neurosecretory cells, ALKs (anterior LK neurons), in the brain express LK in larvae, but inconsistently so in adults. These ALKs co-express three other neuropeptides and regulate water and ion homeostasis, feeding, and drinking, but the specific role of LK is not yet known. This review summarizes Drosophila data on embryonic lineages of LK neurons, functional roles of individual LK neuron types, interactions with other peptidergic systems, and orchestrating functions of LK. 相似文献
5.
Wireless Personal Communications - A GPS spoofing attack broadcasts counterfeit signals to resemble standard GPS satellite signals to take control of the correlation peaks of GPS signals to force... 相似文献
6.
Barium strontium alumino silicate (BSAS); (Ba0.6Sr0.4Al2Si2O8) was synthesized through solid state reaction between BaCO3, SrCO3, Al2O3 and SiO2 subjected to wet milling in isopropanol for about 24 h. The sequence of the solid state reaction was studied by subjecting to DG/DTG from room temperature to 1550 °C. The crystallographic phase evolution was confirmed by X-ray diffraction of the powders calcined in the range 1000 to 1300 °C for 2 h. The monoclinic celsian phase obtained at 1300 °C, pelletized through uniaxial pressing was sinterable to 67 to 78% density in the temperature range of 1300 to 1500 °C. The density improved to 75 to 94% after ball milling for 76 h, while ZrO2 addition further improved the density by 2%. The celcian phase of BSAS was dispersed in isopropyl alcohol, milled for about 24 h and spray coated on to plain SiC and mullite precoated SiC substrates. Sintering of coated samples and characterization for weight gain/loss, microstructure, scratch test prove that mullite + BSAS coating is more effective than single layer coating of BSAS on SiC substrates. 相似文献
7.
Avdeev Ya. G. Kuznetsov D. S. Kuznetsov Yu. I. 《Protection of Metals and Physical Chemistry of Surfaces》2021,57(7):1307-1312
Protection of Metals and Physical Chemistry of Surfaces - Impedance spectroscopy was used to study the adsorption of the IFKhAN-92 inhibitor, a triazole derivative, on cathodically polarized... 相似文献
8.
Seplyarskii B. S. Kochetkov R. A. Lisina T. G. Abzalov N. I. 《Combustion, Explosion, and Shock Waves》2021,57(3):334-342
Combustion, Explosion, and Shock Waves - This paper touches upon the effect of a polyvinyl butyral content (0–2.3%) on the combustion of a Ti + C granular... 相似文献
9.
Lalitha Kodumudi Venkataraman Tingting Zhu Monica Pinto Salazar Kathrin Hofmann Aamir Iqbal Waidha J. C. Jaud Pedro B. Groszewicz Jürgen Rödel 《Journal of the American Ceramic Society》2021,104(5):2201-2212
Na1/2Bi1/2TiO3-based materials have been earmarked for one of the first large-volume applications of lead-free piezoceramics in high-power ultrasonics. Zn2+-doping is demonstrated as a viable route to enhance the thermal depolarization temperature and electromechanically harden (1-y)Na1/2Bi1/2TiO3-yBaTiO3 (NBT100yBT) with a maximum achievable operating temperature of 150 °C and mechanical quality factor of 627 for 1 mole % Zn2+-doped NBT6BT. Although quenching from sintering temperatures has been recently touted to enhance TF-R, with quenching the doped compositions featuring an additional increase in TF-R by 17 °C, it exhibits negligible effect on the electromechanical properties. The effect is rationalized considering the missing influence on conductivity and therefore, negligible changes in the defect chemistry upon quenching. High-resolution diffraction indicates that Zn2+-doped samples favor the tetragonal phase with enhanced lattice distortion, further corroborated by 23Na Nuclear Magnetic Resonance investigations. 相似文献
10.
Mechanical properties and thermal shock in thin ZrO2–Y2O3–Al2O3 films obtained by the sol-gel method
Antonio Díaz-Parralejo M. Ángeles Díaz-Díez José Sánchez-González Antonio Macías-García Juan Pablo Carrasco-Amador 《Ceramics International》2021,47(1):80-86
Thin multilayer coatings of ZrO2–Y2O3–Al2O3 were prepared using the sol-gel method and dip-coating technique in order to advance in the study of what influence the incorporation of Al2O3 has on films of Y2O3-doped ZrO2, investigating its role in the synthesis of the solutions and in the characteristics and properties of the coatings. After the characterization of the solutions used in the process, the microstructure of the films was studied and their mechanical behaviour and resistance to thermal shock were determined so as to optimize the characteristics and functionality of these coatings. With increased alumina content, 3YSZ-Al2O3 (20 mol%), the cubic phase of the zirconia disappeared completely at the sintering temperature used (700 °C), resulting in the tetragonal phase with Al in solution. There was also a decrease in the coatings' hardness and Young's modulus, and an increase in toughness and resistance to thermal shock. These results allow guidelines to be established for the design of multilayer structures that are, tougher, more resistant, and have improved surface properties. 相似文献