全文获取类型
收费全文 | 1038篇 |
免费 | 56篇 |
国内免费 | 5篇 |
专业分类
电工技术 | 28篇 |
综合类 | 1篇 |
化学工业 | 379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 | 19篇 |
2022年 | 38篇 |
2021年 | 49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1099条查询结果,搜索用时 15 毫秒
991.
Mohammad Ali Abdelkareem Tabbi Wilberforce Khaled Elsaid Enas Taha Sayed Emad A.M. Abdelghani A.G. Olabi 《International Journal of Hydrogen Energy》2021,46(45):23529-23547
Fuel cells are potentially efficient, silent, and environmentally friendly tools for electrical power generation. One of the obstacles facing the development and the commercialization of fuel cells is the dependence on the precious metal catalyst, i.e., Platinum (Pt) and Pt - alloy, especially at the cathode where high catalyst loading used to compensate the sluggish oxygen reduction reaction (ORR). Pt is not only an expensive and rare element but also has insufficient durability. The development of an efficient non-precious catalyst, i.e., electrochemically active, chemically and mechanically stable, and electrically conductive, is one of the basic requirements for the commercialization of fuel cells. The bonding to carbon and nitrogen to form metal carbides and nitrides modify the nature of the d-band of the parent metal, thus improve its catalytic properties relative to the parent metals to be similar to those of group VIII noble metals. In this article, we summarize the progress in the development of the transition metal carbides (TMCs) and transition metals nitrides (TMNs) relative to their application as catalysts for the ORR in fuel cells. The preparation of TMCs and TMNs via different routes which significantly affects its activity is discussed. The ORR catalytic activity of the TMCs and TMNs as a non-precious catalyst or catalyst support in fuel cells is discussed and compared to that of the Pt-based catalyst in this review article. Moreover, the recent progress in the preparation of the nano-sized (which is a critical factor for increasing the activity at low temperature) TMCs and TMNs are discussed. 相似文献
992.
A.G. Olabi Adel saleh bahri Aasim Ahmed Abdelghafar Ahmad Baroutaji Enas Taha Sayed Abdul Hai Alami Hegazy Rezk Mohammad Ali Abdelkareem 《International Journal of Hydrogen Energy》2021,46(45):23498-23528
Over the past years, hydrogen has been identified as the most promising carrier of clean energy. In a world that aims to replace fossil fuels to mitigate greenhouse emissions and address other environmental concerns, hydrogen generation technologies have become a main player in the energy mix. Since hydrogen is the main working medium in fuel cells and hydrogen-based energy storage systems, integrating these systems with other renewable energy systems is becoming very feasible. For example, the coupling of wind or solar systems hydrogen fuel cells as secondary energy sources is proven to enhance grid stability and secure the reliable energy supply for all times. The current demand for clean energy is unprecedented, and it seems that hydrogen can meet such demand only when produced and stored in large quantities. This paper presents an overview of the main hydrogen production and storage technologies, along with their challenges. They are presented to help identify technologies that have sufficient potential for large-scale energy applications that rely on hydrogen. Producing hydrogen from water and fossil fuels and storing it in underground formations are the best large-scale production and storage technologies. However, the local conditions of a specific region play a key role in determining the most suited production and storage methods, and there might be a need to combine multiple strategies together to allow a significant large-scale production and storage of hydrogen. 相似文献
993.
Finding textile applications for a new or underused fiber is always very attractive, especially when the fiber is natural and indigenous. Leafiran fiber is derived form the leaves of a plant called Typha australis, which belongs to the family Typhaceae. The fiber was obtained by chemical retting. Some properties of this fiber, such as its tensile strength, chemical composition, thermal properties, moisture absorption, and IR spectra, were determined. Leafiran is a lignocellulosic fiber having a cellulose content of 54%, a moisture regain of 8–10%, and a tenacity of 29 cN/tex. The results show that Leafiran could be an ideal replacement for some widely used natural textile fibers. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 相似文献
994.
M.A. Moustafa 《Journal of Materials Processing Technology》2009,209(1):605-610
A preliminary investigation has been carried to evaluate the influence of Fe on Sr-modified and unmodified eutectic Al–Si alloys in as-cast and heat treatment conditions. The castings were produced in zircon-coated steel permanent mold and were solutionized at 500 °C for 8 h and followed by artificial aging at 155 °C for 5 h, i.e., T6-temper. The microstructure changes in the β-Al5FeSi particle morphology were analyzed. The results indicate that dendrite arm spacing is strongly related to the cooling rate rather than the chemical composition, increasing the iron content leads to increase porosity and hardness either in the as-cast condition or after T6-temper. The Sr-modified alloys have higher hardness than unmodified at all Fe-added values. The precipitated long branched β-platelets result in the formation of large shrinkage cavities due to the inability of liquid metal to feed the space between them during solidification. 相似文献
995.
Different samples of poly(vinyl chloride) (PVC) greases were formulated from PVC, triisopropylphenylphosphate plasticizer (TIPPP), and a wax gel (microcrystalline wax and transformer oil) system, together with variable proportions of phenol formaldehyde, stearyl phenol formaldehyde, or stearyl phenol formaldehyde urethane resins. The effect of resin structure on the electrical properties (dielectric constant, dielectric loss, and conductivity) of the PVC–TIPPP–wax gel system was studied to obtain a plasticized PVC grease of high electrical insulation and fire-retarding characters. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68:699–708, 1998 相似文献
996.
Polymer composites of poly(methyl methacrylate) (PMMA) and cuprous oxide (Cu2O), magnesium oxide (MgO), copper biphthalocyanine, iron (II) chloride (FeCl2), and iron metal were prepared by different filler-to-polymer percentages of 10, 20, 30, 40, and 50%. With increasing filler concentration, brinell hardness increases. Copper biphthalocyanine resulted in the highest hardness, and iron metal resulted in the lowest one. The electrical conductivity was found to increase with increasing filler concentration. The iron metal composite gave the highest effect, while the magnesium oxide composite resulted in the lowest one. The 50% concentration samples were subjected to electrical conductivity measurements at temperatures ranging from 25 to 100°C. The electrical conductivity was found to increase with increasing the temperature. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67: 637–641, 1998 相似文献
997.
This paper develops several lattice structures for RLS-Laguerre adaptive filtering including a posteriori and a priori based lattice filters with error-feedback, array-based lattice filters, and normalized lattice filters. All structures are efficient in that their computational cost is proportional to the number of taps, albeit some structures require more multiplications or divisions than others. The performance of all filters, however, can differ under practical considerations, such as finite-precision effects and regularization. Simulations are included to illustrate these facts 相似文献
998.
Ahmed I. Foudah Dr. Sandeep Jain Belnaser A. Busnena Dr. Khalid A. El Sayed 《ChemMedChem》2013,8(3):497-510
Sipholenol A, a sipholane triterpene isolated from the Red Sea sponge Callyspongia siphonella, has the ability to reverse multidrug resistance in cancer cells that overexpress P‐glycoprotein (P‐gp). Here, the antimigratory activity of sipholenol A and analogues are reported against the highly metastatic human breast cancer cell line MDA‐MB‐231 in a wound‐healing assay. Sipholenol A and sipholenone A were semisynthetically optimized using ligand‐based strategies to generate structurally diverse analogues in an attempt to maximize their antimigratory activity. A total of 22 semisynthetic ester, ether, oxime, and carbamate analogues were generated and identified by extensive one‐ and two‐dimensional NMR spectroscopy and high‐resolution mass spectrometry analyses. Sipholenol A 4β‐4‐chlorobenzoate and 19,20‐anhydrosipholenol A 4β‐4‐chlorobenzoate esters were the most potent of all tested analogues in the wound‐healing assay, with IC50 values of 5.3 and 5.9 μM , respectively. Generally, ester derivatives showed better antimigratory activities than the carbamate analogues. A KINOMEscan of 19,20‐anhydrosipholenol A 4β‐benzoate ester against 451 human protein kinases identified protein tyrosine kinase 6 (PTK6) as a potential target. In breast tumor cells, PTK6 promotes growth factor signaling and migration, and as such the semisynthetic sipholanes were evaluated for their ability to inhibit PTK6 phosphorylation in vitro. The two analogues with the highest antimigratory activities, sipholenol A 4β‐4‐chlorobenzoate and 19,20‐anhydrosipholenol A 4β‐4‐chlorobenzoate esters, also exhibited the most potent inhibition of PTK6 phosphorylation inhibition. None of the compounds exhibited cytotoxicity in a normal epithelial breast cell line. These derivatives were evaluated in an in vitro invasion assay, where sipholenol A succinate potently inhibited MDA‐MB‐231 cell invasion at 10 μM . These results highlight sipholane triterpenoids as novel antimigratory marine natural products with potential for further development as agents for the control of metastatic breast malignancies. 相似文献
999.
Efficient adaptive receivers for joint equalization and interference cancellation in multiuser space-time block-coded systems 总被引:2,自引:0,他引:2
This paper develops low-complexity adaptive receivers for space-time block-coded (STBC) transmissions over frequency-selective fading channels. The receivers are useful for equalization purposes for single user transmissions and for joint equalization and interference cancellation for multiuser transmissions. The receivers exploit the rich code structure of STBC codes in order to deliver recursive-least-squares (RLS) performance at least-mean-squares (LMS) complexity. Besides reduced complexity, the proposed adaptive receivers also lower system overhead requirements. 相似文献
1000.
John P. Frampton Brendan M. Leung Eve L. Bingham Sasha Cai Lesher‐Perez Jack D. Wang Hady T. Sarhan Mohamed E. H. El‐Sayed Stephen E. Feinberg Shuichi Takayama 《Advanced functional materials》2015,25(11):1694-1699
An entirely new approach to tissue engineering is presented that uses the interfacial forces between aqueous solutions of phase‐separating polymers to confine cells and promote their assembly into interconnected, macroscopic tissue constructs. This simple and inexpensive general procedure creates free‐standing, centimeter‐scale constructs from cell suspensions at the interface between poly(ethylene glycol) and dextran aqueous two‐phase systems in as little as 2 h. Using this method, skin constructs are produced that integrate with decellularized dermal matrices, on which they differentiate and stratify into skin equivalents. It is demonstrated that the constructs produced by this method have appropriate integrity and mechanical properties for use as in vitro tissue models. 相似文献