全文获取类型
收费全文 | 13012篇 |
免费 | 923篇 |
国内免费 | 9篇 |
专业分类
电工技术 | 84篇 |
综合类 | 8篇 |
化学工业 | 5118篇 |
金属工艺 | 135篇 |
机械仪表 | 311篇 |
建筑科学 | 455篇 |
矿业工程 | 17篇 |
能源动力 | 333篇 |
轻工业 | 3193篇 |
水利工程 | 112篇 |
石油天然气 | 69篇 |
无线电 | 508篇 |
一般工业技术 | 1705篇 |
冶金工业 | 637篇 |
原子能技术 | 37篇 |
自动化技术 | 1222篇 |
出版年
2024年 | 41篇 |
2023年 | 179篇 |
2022年 | 901篇 |
2021年 | 1017篇 |
2020年 | 413篇 |
2019年 | 428篇 |
2018年 | 479篇 |
2017年 | 502篇 |
2016年 | 544篇 |
2015年 | 446篇 |
2014年 | 581篇 |
2013年 | 888篇 |
2012年 | 833篇 |
2011年 | 951篇 |
2010年 | 719篇 |
2009年 | 672篇 |
2008年 | 614篇 |
2007年 | 587篇 |
2006年 | 449篇 |
2005年 | 344篇 |
2004年 | 292篇 |
2003年 | 256篇 |
2002年 | 244篇 |
2001年 | 148篇 |
2000年 | 99篇 |
1999年 | 135篇 |
1998年 | 126篇 |
1997年 | 126篇 |
1996年 | 112篇 |
1995年 | 80篇 |
1994年 | 63篇 |
1993年 | 65篇 |
1992年 | 66篇 |
1991年 | 48篇 |
1990年 | 45篇 |
1989年 | 35篇 |
1988年 | 42篇 |
1987年 | 34篇 |
1986年 | 42篇 |
1985年 | 43篇 |
1984年 | 34篇 |
1983年 | 27篇 |
1982年 | 21篇 |
1981年 | 18篇 |
1980年 | 20篇 |
1979年 | 20篇 |
1978年 | 22篇 |
1977年 | 22篇 |
1976年 | 17篇 |
1975年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Maria Virginia Gelfuso Juan Oswaldo Montoya Uribe Daniel Thomazini 《International Journal of Applied Ceramic Technology》2019,16(2):868-882
The influence of the CuO–TiO2 phase (CT) on dielectric properties of the CCTO ceramic was investigated. CaCuXTiYO12 (CCXTYO) powders were prepared based on the coprecipitated method, where 2.70 ≤ x ≤ 3.30 and 3.25 ≤ y ≤ 4.75. XRD patterns confirmed the presence of CCTO and also the secondary phases as CuO, TiO2, and CaTiO3 for each sample and aided in its quantification. Scanning Electron Microscopy (SEM) shows secondary phases evolution in the grain boundaries, and its influence on size and morphology of the grains. Impedance spectroscopy measurements showed that the ceramics with lower amount of CuO and TiO2 phases (CT/deficient ceramics) exhibited the highest ε′ values (2.1 × 104 at 1 kHz for CC2.9T3.75O ceramic). Also, CT/deficient ceramics showed lower tanδ values (0.090 at 1 kHz for CC2.9T3.75O ceramic) than ceramics prepared with excessive CuO–TiO2 phase (0.241 at 1 kHz for CC3.1T4.25O ceramics). The deficiency of CuO and TiO2 phases associated with high percentage of CCTO and CaTiO3 phases resulted in ceramics with the higher ε′ values. 相似文献
992.
Gredson Keiff Souza Alexandre Diório Gracielle Johann Maria Carolina Sérgi Gomes Armando Mateus Pomini Pedro Augusto Arroyo Nehemias Curvelo Pereira 《Journal of the American Oil Chemists' Society》2019,96(1):51-61
This study investigated the effects of variations in oil contents and fatty-acid composition, density, viscosity, acid values, saponification values, specific oxidative stability, and antioxidant concentration of Acrocomia totai kernel oil during fruit maturation. Fatty acids were quantified using 1H nuclear magnetic resonance (NMR) spectroscopy, gas chromatograph-flame-ionization detector (GC-FID), and Fourier transform Raman (FT-Raman) spectroscopy analyses. The results showed that all physicochemical characteristics and oil composition changed during the ripening stage. The CG-FID analysis showed a reduction in the unsaturated fatty-acid content (from 78.8% to 22.1%), with a proportional increase in the saturated fatty-acid contents (from 21.6% to 77.9%). The difference in the fatty-acid composition was confirmed by analysis of the 1H NMR and FT-Raman spectra. The degree of unsaturation was calculated to determine the oxidative stability of oil. These results suggest that the fruit's maturation contributes to the specific oxidative stability. The antioxidant concentration revealed higher contents of carotenoids in the ripe fruit (0.16 mg of carotenoid per 100 gKERNEL) when compared to the unripe fruit (0.05 mg of carotenoid per 100 gKERNEL). In the total phenolics analysis, there was no change in concentration over ripening time. These results show that kernel oil has physicochemical properties comparable with high-quality commercial vegetable oils, suggesting that it is a promising alternative to conventional vegetable oils. 相似文献
993.
994.
995.
Systemic administration of a nanoemulsion with tributyrin reduces inflammation in experimental colitis 下载免费PDF全文
996.
New approach for the prediction of azeotropy in binary systems 总被引:1,自引:0,他引:1
Rita Maria Brito Alves Frank H. Quina Claudio Augusto Oller Nascimento 《Computers & Chemical Engineering》2003,27(12):1755-1759
A new approach for the prediction of azeotrope formation between components in a mixture, that does not require vapor–liquid equilibrium calculations, is presented. The method employs neural networks to correlate azeotropic data for binary mixtures with a series of macroscopic and microscopic properties of the pure components, without explicit consideration of non-ideality of mixture. The model fails to make a clear prediction regarding azeotropy in only a relatively small number of situations in which structurally homologous molecules are known to exhibit quite distinct azeotropic behavior. 相似文献
997.
Pier Paolo Prosini Maria Carewska Silvera Scaccia Pawel Wisniewski Mauro Pasquali 《Electrochimica acta》2003,48(28):4205-4211
Amorphous LiFePO4 was obtained by lithiation of FePO4 synthesized by spontaneous precipitation from equimolar aqueous solutions of Fe(NH4)2(SO4)2·6H2O and NH4H2PO4, using hydrogen peroxide as oxidizing agent. Nano-crystalline LiFePO4 was obtained by heating amorphous nano-sized LiFePO4 for different periods of time. The materials were characterized by TG, DTA, X-ray powder diffraction, scanning electron microscopy (SEM) and BET. All materials showed very good electrochemical performance in terms of energy and power density. Upon cycling, a capacity fading affected the materials, thus reducing the electrochemical performance. Nevertheless, the fading decreased upon cycling and after the 200th cycle the cell was able to cycle for more than 500 cycles without further fading. 相似文献
998.
Magdalena Luczak Joanna Suszynska-Zajczyk Lukasz Marczak Dorota Formanowicz Elzbieta Pawliczak Maria Wanic-Kossowska Maciej Stobiecki 《International journal of molecular sciences》2016,17(5)
The major cause of mortality in patients with chronic kidney disease (CKD) is atherosclerosis related to traditional and non-traditional risk factors. However, the understanding of the molecular specificity that distinguishes the risk factors for classical cardiovascular disease (CVD) and CKD-related atherosclerosis (CKD-A) is far from complete. In this study we investigated the disease-related differences in the proteomes of patients with atherosclerosis related and non-related to CKD. Plasma collected from patients in various stages of CKD, CVD patients without symptoms of kidney dysfunction, and healthy volunteers (HVs), were analyzed by a coupled label-free and mass spectrometry approach. Dysregulated proteins were confirmed by an enzyme-linked immunosorbent assay (ELISA). All proteomic data were correlated with kidney disease development and were subjected to bioinformatics analysis. One hundred sixty-two differentially expressed proteins were identified. By directly comparing the plasma proteomes from HVs, CKD, and CVD patients in one study, we demonstrated that proteins involved in inflammation, blood coagulation, oxidative stress, vascular damage, and calcification process exhibited greater alterations in patients with atherosclerosis related with CKD. These data indicate that the above nontraditional risk factors are strongly specific for CKD-A and appear to be less essential for the development of “classical” CVD. 相似文献
999.
Rodolpho Rodrigues Fonseca Ana Maria Frattini Fileti Ivan Carlos Franco 《Chemical Engineering Communications》2016,203(9):1251-1259
With respect to environmental concerns, biofuels have been used around the world, such as biodiesel, and any improvement in the biodiesel production process is desirable. This paper proposes three different control systems based on fuzzy logic and output control signal split-range. Regulating reaction temperature with low settling time and process variable oscillation are the process control aims, and smooth output control signal for actuators protection is also desired. An automated biodiesel production prototype was used and the experimental results demonstrate that a fuzzy/split-range structure with three input variables showed the best performance, resulting in process variable regulation in set-point value with small settling time and actuators premature wearing prevention. 相似文献
1000.
Acidity and catalytic activity of the mesoporous aluminosilicate molecular sieve MCM-41 总被引:1,自引:0,他引:1
Robert Mokaya William Jones Zhaohua Luan Maria D. Alba Jacek Klinowski 《Catalysis Letters》1996,37(1-2):113-120
The acidity and catalytic properties of aluminosilicate mesoporous molecular sieves with the MCM-41 structure and bulk Si/Al ratios in the 10–60 range have been investigated. The incorporation of 4-coordinate aluminium into the structure of MCM-41 generates both BrØnsted and Lewis acid sites in amounts increasing with the degree of incorporation. However, the BrØnsted/Lewis acid population ratio is independent of the content of aluminium. The number and strength of acid sites generated are comparable to those of a pillared acid-activated clay and lower than in zeolite H-Y with Si/Al=3.65. Aluminosilicate MCM-41 is a moderate catalyst for the conversion of cumene which proceeds predominantly via catalytic cracking to propene and benzene. The sample of MCM-41 with the highest content of framework aluminium (Si/Al=10) has the largest number of BrØnsted acid sites and exhibits highest catalytic activity. 相似文献