全文获取类型
收费全文 | 1020篇 |
免费 | 66篇 |
国内免费 | 5篇 |
专业分类
电工技术 | 27篇 |
综合类 | 1篇 |
化学工业 | 372篇 |
金属工艺 | 26篇 |
机械仪表 | 19篇 |
建筑科学 | 22篇 |
矿业工程 | 2篇 |
能源动力 | 50篇 |
轻工业 | 81篇 |
水利工程 | 9篇 |
石油天然气 | 24篇 |
无线电 | 114篇 |
一般工业技术 | 190篇 |
冶金工业 | 45篇 |
原子能技术 | 5篇 |
自动化技术 | 104篇 |
出版年
2023年 | 18篇 |
2022年 | 33篇 |
2021年 | 48篇 |
2020年 | 33篇 |
2019年 | 47篇 |
2018年 | 74篇 |
2017年 | 50篇 |
2016年 | 42篇 |
2015年 | 38篇 |
2014年 | 41篇 |
2013年 | 82篇 |
2012年 | 58篇 |
2011年 | 59篇 |
2010年 | 48篇 |
2009年 | 34篇 |
2008年 | 30篇 |
2007年 | 17篇 |
2006年 | 17篇 |
2005年 | 15篇 |
2004年 | 25篇 |
2003年 | 25篇 |
2002年 | 22篇 |
2001年 | 12篇 |
2000年 | 19篇 |
1999年 | 11篇 |
1998年 | 16篇 |
1997年 | 19篇 |
1996年 | 16篇 |
1995年 | 12篇 |
1994年 | 6篇 |
1993年 | 4篇 |
1992年 | 5篇 |
1991年 | 5篇 |
1989年 | 4篇 |
1988年 | 6篇 |
1987年 | 6篇 |
1986年 | 5篇 |
1985年 | 6篇 |
1984年 | 11篇 |
1983年 | 7篇 |
1982年 | 9篇 |
1981年 | 6篇 |
1980年 | 6篇 |
1979年 | 5篇 |
1977年 | 5篇 |
1976年 | 5篇 |
1975年 | 7篇 |
1974年 | 3篇 |
1973年 | 5篇 |
1969年 | 3篇 |
排序方式: 共有1091条查询结果,搜索用时 0 毫秒
41.
42.
Bioactive glass–ceramic with various zirconia concentrations was applied on stainless steel (SS) by the sol–gel method. Bioactive glass powder was prepared by the sol–gel method, and thermal properties of the prepared powders were studied by differential thermal analysis (DTA). The effects of zirconia were investigated to explore the growth of nanowires. The growth model of nanowires, in this study, is proposed in terms of the surface diffusion. The coatings showed the hardness values to be in the range of 3000–4500 MPa. The hardness values of prepared composite coatings increased with an increase in zirconia amounts. 相似文献
43.
The polycyclic aromatic hydrocarbons (PAH) in Egyptian condensates are analyzed for the first. A solid phase extraction (SPE) followed by gas chromatography-mass selective detection was used for their analysis. The method was calibrated for optimal extraction conditions. Excellent recoveries were found (78–114%) for the PAHs that were identified using a variety of standards and GC-MS spectra. The solid-phase extracted PAH fraction was further separated by HPLC on a Ag(I) mercaptopropanosilica gel to reduce the complexity of the sample by separating the PAHs based on the number of aromatic rings. The analytes were quantified using GC with a flame ionization detector. For this kind of sample SPE is a more convenient separation technique than an open column. PAHs containing two to four rings in the concentration range 0.6–11 μg/L were measured. Some preliminary geochemical hypotheses based on the analyzed PAHs and the previously analyzed S-containing aromatic compounds were formed as to the depositional environment and source rock type. 相似文献
44.
The refining of lubricating oils from waste lubricating oil was examined utilizing a novel blend of solvent extraction and activated alumina adsorbent. The activity of these solvent extraction blends {toluene, butanol and methanol (A)}, {toluene, butanol and ethanol (B)} and {toluene, butanol and isopropanol (C)} was evaluated experimentally, oil to solvent proportions from 1:1 to 1:3 were analyzed for mixture blend (C). The results confirm solvent mixture (A) gave good efficiency with the highest percent sludge removal. The maximum percent of sludge removal improves with the increase of solvent to oil ratios. The physical properties of the recycle oil were measured. The results show the change in the properties of recycling oil and have good efficiency. 相似文献
45.
The corrosion inhibition of steel in a closed system containing sodium sulphite at room temperature has been established. Steady-state potential as well as weight loss measurements indicated that sodium sulphite did not only remove O2 from the solution but also brought complete cathodic protection. It was found also that sodium sulphite could tolerate the presence of Cl?, SO42? and S2?. In case of sulphite—sulphate or sulphite—chloride mixtures a concentration of 5 × 10?3M Na2SO3 was required to tolerate a wide range of concentration of these aggressive ions. A linear relationship was found between log sulphite concentration and log maximum tolerated concentration of sulphide. 相似文献
46.
Hend Omar Mohamed Enas Taha Sayed M. Obaid Yun-Jeong Choi Sung-Gwan Park Siham Al-Qaradawi Kyu-Jung Chae 《International Journal of Hydrogen Energy》2018,43(46):21560-21571
The poor wettability and high cost of the carbonaceous electrodes materials prohibited the practical applications of microbial fuel cells (MFCs) on large scale. Here, a novel nanoparticles of metal sheathed with metal oxide is electrodeposited on carbon paper (CP) to introduce as high-performance anodes of microbial fuel cell (MFC). This thin layer of metal/metal oxide significantly enhance the microbial adhesion, the wettability of the anode surface and decrease the electron transfer resistance. The investigation of the modified CP anodes in an air-cathode MFCs fed by various biocatalyst cultures shows a significant improving in the MFC performance. Where, the generated power and current density was 140% and 210% higher as compared to the pristine CP. Mixed culture of exoelectrogenic microorganism in wastewater exhibited good performance and generated higher power and current density compared to yeast as pure culture. The excellent capacitance with a distinctive nanostructure morphology of the modified-CP open an avenues for practical applications of MFCs. 相似文献
47.
The IEEE Signal Processing Society is introducing a new feature that originated from a suggestion made by my colleague Athina Petropulu and a couple of associate editors. The publication of overview articles in the transactions will be a service to our readers and appeal to the broad signal processing audience. 相似文献
48.
On Analyzing the Potential of a Layer-2 Multi-hop Authentication and Credential Delivery Scheme for Vehicular Communications 总被引:1,自引:1,他引:0
Christian Tchepnda Hassnaa Moustafa Houda Labiod Gilles Bourdon 《Wireless Personal Communications》2009,51(1):31-52
In this paper we introduce a new security architecture and security mechanisms for vehicular networks providing a layer-2
multi-hop authentication and credential delivery scheme between vehicles and the network operator authentication server. We
present a performance analysis of the proposed solution under various vehicles and Access Points (APs) densities, showing
the potential of our scheme in providing a more efficient, robust and scalable authentication and credential delivery to vehicles
when compared against the classical single-hop scheme. 相似文献
49.
Takele Zeleke Ahmed Moustafa Moussa Mohamed S. El‐Manadely 《Lakes & Reservoirs: Research and Management》2013,18(4):366-371
Angereb Dam, located in Ethiopia, was constructed in early 1994 as a water supply for the town of Gondar up to the year 2020. The reservoir could not achieve this objective, however, because of significant sedimentation problems. Accordingly, one objective of this study was to simulate the historical reservoir sedimentation pattern, as well as predict the near future (until 2015) sedimentation pattern of Angereb Reservoir. The Sedimentation and River Hydraulics one‐dimensional model (SRH‐1D), version 2.6, was used for this purpose. Another objective was to propose possible mitigation measures to reduce the quantity and rate of sedimentation in the reservoir. There was generally good agreement between measurements and model simulations, with the observed trends being well simulated. The exception was that the model tended to overpredict the sediment deposition volumes in the upstream reaches of the reservoir. The two mitigation alternatives for addressing the sedimentation problem, namely managing sediments in the watershed and flushing sediment through the dam bottom outlet, appear to be technically feasibility, with a predicted reduction of the volume of deposited sediment between 63 and 80% be achievable. 相似文献
50.
M.A. Almessiere Y. Slimani H. Güngüneş H.S. El Sayed A. Baykal 《Ceramics International》2018,44(15):17749-17758
Vanadium ions substituted BaFe12O19 nanohexaferrites, BaFe12-xVxO19 (0.0?≤x?≤?0.1), were produced through the sol-gel auto-combustion route. The structure, morphology and the elemental compositions of various products were examined using X–ray powder diffraction, scanning electron microscopy coupled with EDX and EDS elemental mapping. These techniques confirmed the formation of the desired Ba-nanohexaferrite phases. The crystallites size was found to be 55–58?nm range for all products. The magnetic properties of BaFe12-xVxO19 nanohexaferrites were investigated by Mossbauer spectroscopy, ZFC-FC magnetizations and AC susceptibility. The evolutions in the values of hyperfine magnetic field, isomer shift, quadrupole splitting, and line width were deduced via Mossbauer analysis. The experiments of ZFC and FC magnetizations indicated that no blocking temperature is observed in the temperature interval 2–400?K, which signals the typical ferromagnetic (FM) behavior for the produced nanohexaferrites. A super-spin glass like behavior is noticed at lower temperatures. The experiments AC susceptibility confirmed that the strength of magnetic interactions is enhanced for lower content of V3+ (x?=?0.02). For higher amount of V3+, the magnetic interactions are weakened. The obtained results are mainly accredited to the substitutions of Fe3+ ions by V3+ ions. 相似文献