全文获取类型
收费全文 | 1213篇 |
免费 | 95篇 |
国内免费 | 10篇 |
专业分类
电工技术 | 14篇 |
综合类 | 5篇 |
化学工业 | 309篇 |
金属工艺 | 39篇 |
机械仪表 | 52篇 |
建筑科学 | 31篇 |
矿业工程 | 2篇 |
能源动力 | 78篇 |
轻工业 | 137篇 |
水利工程 | 8篇 |
石油天然气 | 20篇 |
无线电 | 112篇 |
一般工业技术 | 222篇 |
冶金工业 | 50篇 |
原子能技术 | 9篇 |
自动化技术 | 230篇 |
出版年
2024年 | 6篇 |
2023年 | 37篇 |
2022年 | 55篇 |
2021年 | 101篇 |
2020年 | 78篇 |
2019年 | 66篇 |
2018年 | 80篇 |
2017年 | 66篇 |
2016年 | 83篇 |
2015年 | 57篇 |
2014年 | 60篇 |
2013年 | 101篇 |
2012年 | 65篇 |
2011年 | 81篇 |
2010年 | 51篇 |
2009年 | 37篇 |
2008年 | 42篇 |
2007年 | 36篇 |
2006年 | 28篇 |
2005年 | 19篇 |
2004年 | 17篇 |
2003年 | 20篇 |
2002年 | 13篇 |
2001年 | 15篇 |
2000年 | 17篇 |
1999年 | 13篇 |
1998年 | 11篇 |
1997年 | 12篇 |
1996年 | 3篇 |
1995年 | 3篇 |
1994年 | 4篇 |
1993年 | 6篇 |
1992年 | 6篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 4篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1980年 | 4篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1975年 | 2篇 |
1972年 | 1篇 |
1971年 | 1篇 |
1968年 | 1篇 |
排序方式: 共有1318条查询结果,搜索用时 265 毫秒
61.
62.
Gagan Kumar Ritu Rani Sucheta Sharma Khalid M. Batoo M. Singh 《Ceramics International》2013,39(5):4813-4818
Cobalt substituted Mg–Mn nanoferrites with formulae Mg0.9Mn0.1CoxFe2?xO4, x=0.0, 0.1, 0.2 and 0.3, have been synthesized for the first time by the solution combustion technique. The effects of Co2+ ions on the dc resistivity, dielectric constant and dielectric loss tangent of Mg–Mn nanoferrites at room temperature are presented in this paper. X-ray diffraction confirmed the formation of a single phase spinel structure. Particle size was found to increase, 20.9–23.9 nm, with increasing Co2+ concentration. The dc resistivity was increased by two order of magnitude with substitution of Co2+ ions while the dielectric constant was found to be decreasing with the increasing concentration of cobalt ions. The value of dc resistivity obtained for Mg0.9Mn0.1Fe2O4 nanoferrite in our work is greater than the value obtained for the same composition prepared by the conventional ceramic technique. Further, the dielectric constant and dielectric loss tangent were observed to be decreasing with the increase in frequency. 相似文献
63.
Khalid Eldrandaly 《Applied Soft Computing》2010,10(3):694-702
Multisite Land Use Allocation Problem (MLUA) refers to the problem of allocating more than one land use type in an area. MLUA problem is one of the truly NP Complete (combinatorial optimization) problems. To cope with this type of problems, intelligent techniques such as genetic algorithms, and simulated annealing, have been used. Research in the area of Spatial Decision Support Systems (SDSS) for resource allocation issues, a new scientific area of information system applications developed to support semi-structured or unstructured spatial decisions, has recently generated attention for integrating Artificial Intelligence (AI) techniques with Geographic Information Systems (GIS). In this paper we demonstrate how GIS can be integrated with Gene Expression Programming (GEP), a recently developed AI approach, for solving MLUA problems. The feasibility of the proposed approach in solving MLUA problems was checked using a fictive case study. The results indicated that the proposed approach gives good and satisfactory results. 相似文献
64.
Performance of PAM/PEI gel system for water shut‐off in high temperature reservoirs: Laboratory study 下载免费PDF全文
Khalid S. M. ElKarsani Ghaithan A. Al‐Muntasheri Abdulla S. Sultan Ibnelwaleed A. Hussein 《应用聚合物科学杂志》2015,132(17)
A polymer gel is one of the common remediate methods to either reduce or totally block excessive water production in oilfields. Some systems demonstrated an excellent performance in treating the problem like polyacrylamide tert‐butyl acrylate (PAtBA)/polyethylenimine (PEI). In this study, polyacrylamide (PAM) was introduced as a cheap alternative to PAtBA that can tolerate high salinity reservoirs. The thermal stability of the PAM/PEI polymeric gel in saline water was examined at 150°C (302F). Samples prepared in sea water showed better stability compared with distilled and field water. Dynamic rheology and core‐flooding experiments were used to evaluate the PAM / PEI gel system at high temperatures. NaCl and NH4Cl were evaluated as a possible retarders for delaying the gelation time in order to achieve a successful placement. NH4Cl was found to be more effective retarder. Core‐flooding tests were conducted in sandstone and carbonate cores. The subject polymer gel was injected at rates typical of those in field applications. The injectivity of PAM/PEI was tested in Berea sandstone cores with initial permeability of ~45 mD. The post‐treatment of the system showed a permeability reduction of ~94% for a period of two weeks. The injectivity in low permeability carbonate cores required more retardation compared with the injectivity in sandstone cores. The gel reduced the permeability to brine in Indiana limestone core by 99.8% for more than 5 months. Rheology of cured gel samples indicated that the gel strength needs about one day of curing in the core for the strength to stabilize. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41869. 相似文献
65.
The length of the transit region of a Gunn diode determines the natural frequency at which it operates in fundamental mode-the shorter the device, the higher the frequency of operation. The long-held view on Gunn diode design is that for a functioning device the minimum length of the transit region is about 1.5 μm, limiting the devices to fundamental mode operation at frequencies of roughly 60 GHz. The authors posit that this theoretical restriction is a consequence of limits of the hydrodynamic models by which it was determined. Study of these devices by more advanced Monte Carlo techniques, which simulate the ballistic transport and electron-phonon interactions that govern device behaviour, offers a new lower bound of 0.5 μm, which is already being approached by the experimental evidence shown in planar and vertical devices exhibiting Gunn operation at 0.6 μm and 0.7 μm. It is shown that the limits for Gunn domain operation are determined by the device length required for the transferred electron effect to occur(approximately 0.15 μm, which as demonstrated is largely field independent) and the fundamental size of the domain(approximately 0.3 μm). At this new length, operation in fundamental mode at much higher frequencies becomes possible-the Monte Carlo model used predicts power output at frequencies over 300 GHz. 相似文献
66.
Kamel Tourki Mohamed‐Slim Alouini Khalid A. Qaraqe Hong‐Chuan Yang 《Wireless Communications and Mobile Computing》2015,15(2):367-378
Opportunistic relaying in cooperative communication depends on careful relay selection. However, the traditional centralized method used for opportunistic amplify‐and‐forward protocols requires precise measurements of channel state information at the destination. In this paper, we adopt the max–min criterion as a relay selection framework for opportunistic amplify‐and‐forward cooperative communications, which was exhaustively used for the decode‐and‐forward protocol, and offer an accurate performance analysis based on exact statistics of the local signal‐to‐noise ratios of the best relay. Furthermore, we evaluate the asymptotical performance and deduce the diversity order of our proposed scheme. Finally, we validate our analysis by showing that performance simulation results coincide with our analytical results over Rayleigh fading channels, and we compare the max–min relay selection with their centralized channel state information‐based and partial relay selection counterparts. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
67.
Fahd Ahmed Khan Kamel Tourki Mohamed‐Slim Alouini Khalid A. Qaraqe 《Wireless Communications and Mobile Computing》2015,15(16):2004-2019
Consider a multi‐user underlay cognitive network where multiple cognitive users concurrently share the spectrum with a primary network with multiple users. The channel between the secondary network is assumed to have independent but not identical Nakagami‐m fading. The interference channel between the secondary users (SUs) and the primary users is assumed to have Rayleigh fading. A power allocation based on the instantaneous channel state information is derived when a peak interference power constraint is imposed on the secondary network in addition to the limited peak transmit power of each SU. The uplink scenario is considered where a single SU is selected for transmission. This opportunistic selection depends on the transmission channel power gain and the interference channel power gain as well as the power allocation policy adopted at the users. Exact closed form expressions for the moment‐generating function, outage performance, symbol error rate performance, and the ergodic capacity are derived. Numerical results corroborate the derived analytical results. The performance is also studied in the asymptotic regimes, and the generalized diversity gain of this scheduling scheme is derived. It is shown that when the interference channel is deeply faded and the peak transmit power constraint is relaxed, the scheduling scheme achieves full diversity and that increasing the number of primary users does not impact the diversity order. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
68.
Brajendra Kumar Singh Jeremy Coulter Mohammad Abdul Ghani Sayani Syed M. Sami Mohammad Khalid Kemal E. Tepe 《The International journal of environmental studies》2013,70(5):765-776
Communication systems are needed to integrate generated power from wind farms with the electrical grid. This paper provides a comprehensive review of available communication technologies, protocols and objectives related to wind energy and electrical grid integration. This paper summarizes the communication system solutions for wind generation. A major obstacle is an absence of unified communication architectures and standards. 相似文献
69.
Graphene nanosheets-supported Sn-Pt bimetallic nanoparticles (GNs/Sn-Pt) were prepared by precipitation method. The obtained GNs/Sn-Pt was used as a photocatalyst for photodegradation of Basic Green 5 (BG5) in aqueous solution under sunlight. The morphology and photodegradation study was performed by SEM and UV–VIS spectrophotometry, respectively. The SEM image showed the presence of Sn and Pt on GNs, being confirmed by energy dispersive X-ray (EDX) analysis. The photodegradation study of BG5 showed that the dye degradation increases as a function of irradiation time. The degradation of BG5 was found to be pH dependent and maximum degradation was found at higher pH. 相似文献