全文获取类型
收费全文 | 1512786篇 |
免费 | 30488篇 |
国内免费 | 8870篇 |
专业分类
电工技术 | 36750篇 |
技术理论 | 7篇 |
综合类 | 9037篇 |
化学工业 | 276525篇 |
金属工艺 | 66123篇 |
机械仪表 | 43990篇 |
建筑科学 | 48655篇 |
矿业工程 | 12770篇 |
能源动力 | 51038篇 |
轻工业 | 113969篇 |
水利工程 | 15458篇 |
石油天然气 | 40227篇 |
武器工业 | 580篇 |
无线电 | 199538篇 |
一般工业技术 | 283131篇 |
冶金工业 | 147622篇 |
原子能技术 | 34246篇 |
自动化技术 | 172478篇 |
出版年
2021年 | 17190篇 |
2020年 | 13072篇 |
2019年 | 15506篇 |
2018年 | 16160篇 |
2017年 | 15487篇 |
2016年 | 22032篇 |
2015年 | 18872篇 |
2014年 | 30494篇 |
2013年 | 90028篇 |
2012年 | 37559篇 |
2011年 | 49766篇 |
2010年 | 44582篇 |
2009年 | 52883篇 |
2008年 | 46405篇 |
2007年 | 43643篇 |
2006年 | 46824篇 |
2005年 | 40774篇 |
2004年 | 41977篇 |
2003年 | 41754篇 |
2002年 | 40965篇 |
2001年 | 37409篇 |
2000年 | 36087篇 |
1999年 | 34794篇 |
1998年 | 39765篇 |
1997年 | 36421篇 |
1996年 | 33598篇 |
1995年 | 29760篇 |
1994年 | 28049篇 |
1993年 | 27817篇 |
1992年 | 26162篇 |
1991年 | 23084篇 |
1990年 | 23415篇 |
1989年 | 22469篇 |
1988年 | 20995篇 |
1987年 | 19240篇 |
1986年 | 18576篇 |
1985年 | 21897篇 |
1984年 | 22282篇 |
1983年 | 20201篇 |
1982年 | 19193篇 |
1981年 | 19291篇 |
1980年 | 17848篇 |
1979年 | 18480篇 |
1978年 | 17695篇 |
1977年 | 17115篇 |
1976年 | 17742篇 |
1975年 | 15957篇 |
1974年 | 15509篇 |
1973年 | 15553篇 |
1972年 | 13044篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
831.
Tseluikin V. N. Yakovlev A. V. 《Protection of Metals and Physical Chemistry of Surfaces》2020,56(2):374-378
Protection of Metals and Physical Chemistry of Surfaces - Nickel-based composite electrochemical coatings (CECs) modified with graphite nitrate have been obtained. Their microstructure and... 相似文献
832.
Brusov V. S. Korchagin P. O. Malyshev V. V. Piyavsky S. A. 《Journal of Computer and Systems Sciences International》2020,59(1):83-94
Journal of Computer and Systems Sciences International - The article considers the problem of making multicriteria decisions in which the decision maker (DM) has the opportunity to indicate the... 相似文献
833.
Wan Huan Wang Hui Scotney Bryan Liu Jun Ng Wing W. Y. 《Multimedia Tools and Applications》2020,79(39-40):29327-29352
Multimedia Tools and Applications - In many real-world classification problems there exist multiple subclasses (or clusters) within a class; in other words, the underlying data distribution is... 相似文献
834.
In order to improve the process effectiveness and joint quality, ultrasonic vibrations were integrated with friction stir lap welding. Effect of ultrasonic exertion on the process and joint quality of AA 6061-T6 were investigated. Upon ultrasonic exertion, joints owned larger effective lap width, shorter hooks and improved strength. Weld fracture mode changed from a ductile–brittle mixed mode to a more ductile mode while the fracture path shifted from lap interface to beyond the stir zone. Material flow and interface defects were characterised using lap welded dissimilar aluminium alloy joints. Ultrasonic vibration improved the material flow and reduced the interfacial defects. Variations in failure load of joints were found in accordance with the variations in material flow and interfacial defects. 相似文献
835.
The relatively low capacitance of negative electrodes, as compared to the capacitance of advanced positive electrodes, poses a serious problem, since this limits the development of asymmetric supercapacitor (SC) devices with a large voltage window and enhanced power-energy characteristics. We fabricate negative SC electrodes with a high capacitance that match the capacitance of advanced positive electrodes at similar active mass loadings, as high as 37?mg?cm?2. Cyclic voltammetry, impedance spectroscopy, galvanostatic charge-discharge data and the power-energy characteristics of the asymmetric SC device exhibit good electrochemical performance for a voltage window of 1.6?V. Our approach involves the development and application of particle extraction through liquid-liquid interface (PELLI) methods, new extraction mechanisms and efficient extractors to synthesize α-FeOOH and β-FeOOH electrode materials. The use of PELLI allows agglomerate-free processing of powders, which facilitates their efficient mixing with multiwalled carbon nanotubes (MWCNT) and allows improved electrolyte access to the particle surface. Experiments to determine the properties of FeOOH-MWCNT composites provided insight into the influence of the electrode material and the structure of extractor molecules on the composite properties. The highest capacitance of 5.86?F?cm?2 for negative electrodes and low impedance were achieved using α-FeOOH-MWCNT composites and a 16-phosphonohexadecanoic acid (PHDA) extractor. This extractor allows adsorption on particles, not only at the liquid-liquid interface, but also in the bulk aqueous phase and can potentially be used as a capping agent for particle synthesis and as an extractor in the PELLI method. 相似文献
836.
The in-situ fabrication of an electron-blocking layer between the Ba-containing anode and the ceria-based electrolyte is an effective approach in suppressing the internal electronic leakage in ceria-based solid oxide fuel cell (SOFC). To improve the thickness of the electron-blocking layer and to research the effect of the layer thickness on the improvement of SOFC, a Ba-containing compound (0.6NiO-0.4BaZr0.1Ce0.7Y0.2O3-δ) modified by Y stabilized zirconia (YSZ) was employed as a composite anode in this research. SEM analyses demonstrated that the thickness of the interlayer can be simply controlled by regulating the proportion of YSZ at anode. The in-situ formed interlayer in the cell with the anode modified by 20?mol% YSZ possesses a thickness of 0.9?µm which is more suitable for the cell achieving an enhanced performance. 相似文献
837.
Nano crystalline pure and Mg doped ceriaparticles were synthesized by simple chemical co-precipitation method using cerium nitrate hexahydrate as a source material and magnesium nitrate as doping precursor at room temperature. The effect of doping were investigated by X-ray diffraction pattern(XRD), FT-Raman,fourier transform infrared spectroscopy(FTIR), Ultraviolet spectroscopy(UV), photoluminescence spectroscopy(PL), field emission scanning electron microscope(FESEM) and high resolution transmission electron microscopy with energy dispersive spectroscopy (HRTEM &EDS). The X-ray diffraction pattern and FT-Raman studies showed that the prepared samples were nano particulates with cubic fluorite structure. The XRD pattern analysis showed that the size of the particles ranged from 13 to 20?nm, however 4?wt% Mg doping results in reduction of particle size compared with other doping concentrations. The effects of Mg concentration on various structural parameters of the prepared samples were also determined. The slight blue shift observed upon doping in UV–Vis absorption region around 330–360nmrecorded for reduction in particle size. The FTIR unveils the presence of Metal oxygen bonds below 700?cm?1in the prepared samples. All samples showed a broad emission band at 430?nm with linearly increasing intensity with respect to dopant concentrations. The Spherical morphology with weak agglomeration was identified through FESEM and HRTEM analysis. The elemental analysis of Ce, O and Mg were confirmed through EDS analysis. 相似文献
838.
Y.K. Yang F.L. Liu Y.W. Zhang M.F. Li F. Ling H.T. Wu 《Ceramics International》2018,44(11):12238-12244
In this work, ultra-low loss Li2MgTi0.7(Mg1/3Nb2/3)0.3O4 ceramics were successfully prepared via the conventional solid-state method. X-ray photoelectron spectroscopy (XPS), thermally stimulated depolarization current (TSDC) and bond energy were used to determine the distinction between intrinsic and extrinsic dielectric loss in (Mg1/3Nb2/3)4+ ions substituted ceramics. The addition of (Mg1/3Nb2/3)4+ ions enhances the bond energy in unit cell without changing the crystal structure of Li2MgTiO4, which results in high Q·f value as an intrinsic factor. The extrinsic factors such as porosity and grain size influence the dielectric loss at lower sintering temperature, while the oxygen vacancies play dominant role when the ceramics densified at 1400?°C. The Li2MgTi0.7(Mg1/3Nb2/3)0.3O4 ceramics sintered at 1400?°C can achieve an excellent combination of microwave dielectric properties: εr =?16.19, Q·f?=?160,000?GHz and τf =??3.14?ppm/°C. In addition, a certain amount of LiF can effectively lower the sintering temperature of the matrix, and the Li2MgTi0.7(Mg1/3Nb2/3)0.3O4-3?wt% LiF ceramics sintered at 1100?°C possess balanced properties with εr?=?16.32, Q·f?=?145,384?GHz and τf =??16.33?ppm/°C. 相似文献
839.
Radiochemistry - Spent reactor graphite constitutes a significant part of the accumulated solid radioactive wastes, and a search for its isolation from the biosphere is a topical task. Radioactive... 相似文献
840.