全文获取类型
收费全文 | 2211篇 |
免费 | 25篇 |
国内免费 | 6篇 |
专业分类
电工技术 | 8篇 |
综合类 | 5篇 |
化学工业 | 121篇 |
金属工艺 | 31篇 |
机械仪表 | 33篇 |
建筑科学 | 7篇 |
能源动力 | 44篇 |
轻工业 | 79篇 |
水利工程 | 3篇 |
石油天然气 | 3篇 |
无线电 | 48篇 |
一般工业技术 | 138篇 |
冶金工业 | 1664篇 |
原子能技术 | 3篇 |
自动化技术 | 55篇 |
出版年
2023年 | 6篇 |
2022年 | 21篇 |
2021年 | 44篇 |
2020年 | 32篇 |
2019年 | 29篇 |
2018年 | 39篇 |
2017年 | 26篇 |
2016年 | 28篇 |
2015年 | 14篇 |
2014年 | 30篇 |
2013年 | 36篇 |
2012年 | 30篇 |
2011年 | 37篇 |
2010年 | 31篇 |
2009年 | 17篇 |
2008年 | 25篇 |
2007年 | 29篇 |
2006年 | 17篇 |
2005年 | 14篇 |
2004年 | 12篇 |
2003年 | 6篇 |
2002年 | 3篇 |
2001年 | 4篇 |
2000年 | 3篇 |
1999年 | 52篇 |
1998年 | 501篇 |
1997年 | 272篇 |
1996年 | 210篇 |
1995年 | 98篇 |
1994年 | 85篇 |
1993年 | 105篇 |
1992年 | 22篇 |
1991年 | 22篇 |
1990年 | 26篇 |
1989年 | 25篇 |
1988年 | 23篇 |
1987年 | 52篇 |
1986年 | 29篇 |
1985年 | 34篇 |
1984年 | 3篇 |
1983年 | 4篇 |
1982年 | 9篇 |
1981年 | 11篇 |
1980年 | 10篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1977年 | 32篇 |
1976年 | 71篇 |
1975年 | 5篇 |
1955年 | 1篇 |
排序方式: 共有2242条查询结果,搜索用时 15 毫秒
71.
Islam S. Humail F. Akhtar S.J. Askari M. Tufail Xuanhui Qu 《International Journal of Refractory Metals and Hard Materials》2007,25(5-6):380-385
Tungsten heavy alloys (WHAs) are metal–metal composites consisting of nearly pure spherical tungsten particles embedded in a Ni–Fe–W or Ni–Co–W or Ni–Cu–W ductile matrix. In this dual phase alloy, there are several complicated relations between the ductile matrix and hard tungsten particles. The aim of this research was to examine the effect of varying tungsten content on the microstructure and mechanical properties of tungsten heavy alloys. The microstructural parameters (grain size, connectivity, contiguity and solid volume fraction) were measured and were found to have a significant effect on the mechanical properties of tungsten-based heavy alloys. The result shows that the binding strength between the W and the matrix phase has a major influence on the ductility of tungsten-based alloys. The larger this binding force is, the better the ductility is. 相似文献
72.
Merzouk SA Saker M Reguig KB Soulimane N Merzouk H Guermouche B Berrouiguet AY Hichami A Narce M Khan NA 《Lipids》2008,43(6):485-497
In this work, we assessed the in-vitro effects of eicosapentaenoic acid (EPA; C20:5n-3) and docosahexaenoic acid (DHA; C22:6n-3) (final concentration, 15 microM) on T cell blastogenesis, interleukin-2 and -4 (IL-2, IL-4) secretion, fatty acid composition and intracellular oxidative status in type I diabetic patients with or without complications. Con A stimulated lymphocyte proliferation, glucose uptake, intracellular reduced glutathione levels and catalase activity were lower in diabetics as compared to controls, regardless to the presence of complications. EPA and DHA diminished T-lymphocyte proliferation and IL-2 production but enhanced IL-4 secretion in both diabetic and control groups. No changes in the levels of reduced glutathione and in the activities of catalase and SOD were observed in control T cells cultured in the presence of EPA and DHA. However, in diabetic patients, addition of n-3 PUFA to culture induced an increase in T cell levels of reduced glutathione and hydroperoxide, and in activities of catalase and SOD. Low levels of arachidonic acid (C20:4n-6) were found in plasma membrane phospholipids of lymphocytes from diabetic patients compared to controls. Incubation of lymphocytes with EPA and DHA was associated with an incorporation of these fatty acids in membrane phospholipids. In conclusion, the beneficial effects of n-3 PUFA on T cell functions in type I diabetes could be attributed to their suppressive action and modulation of cytokine secretion, and to the improvement of intracellular oxidative status. 相似文献
73.
Maria Yousaf Lodhi Muhammad Azhar Khan Majid Niaz Akhtar Muhammad Farooq Warsi Asif Mahmood Shahid M. Ramay 《Ceramics International》2018,44(3):2968-2975
The influence of neodymium and nickel substitution on structural and dielectric parameters was investigated in strontium-barium X-type hexagonal ferrites having composition SrBaCu2?xNixNdyFe28?yO46 (x = 0, 0.2, 0.4, 0.6, 0.8, 1 and y = 0, 0.02, 0.04, 0.06, 0.08, 0.1). Sol-gel method was employed for synthesizing these hexagonal ferrites. The XRD plots of all studied materials which were annealed at 1250 °C show single phase characteristics. Lattice parameter ‘c’ increased as a consequence of larger radius of rare earth ion (Nd3+) as compared to (Fe3+), while lattice parameter ‘a’ showed very small variation. The cell volume was obtained in the range 2508.32–2523.75 (Å3). The inclusion of Nd-Ni also affected X-ray density, bulk density and porosity. The FTIR spectroscopy indicated the particular absorption peaks of hexagonal ferrites and it was performed in the range of 500–700 cm?1. On account of Nd-Ni doping, the dielectric constant, dielectric loss and AC-conductivity showed decreasing trend. The occupancy of Nd3+ ions at octahedral site impedes the valence alternation of Fe3+; therefore there was decrease in dielectric permittivity. Ac conductivity has been decreased from 9.14 to 6.49 (Ω cm)?1 at frequency of 2.7 GHz. The Cole-Cole plots of synthesized materials noticeably revealed grain boundary contribution. The appearance of single semi-circle in impedance Cole-Cole graphs confirms the exceptional role of grain boundaries in the conduction process. The considerably lower dielectric parameters of investigated nano X-type ferrites propose their feasibility for high-frequency applications (phase shifters, dielectric resonators, stealth technology etc). 相似文献
74.
Jawad Arif Suhail Akhtar 《International Journal of Adaptive Control and Signal Processing》2010,24(4):275-286
Adaptive interference cancelation is of vital importance in a broad array of scientific and engineering disciplines. In this paper we develop a closed‐loop discrete‐time interference cancelation algorithm. The novel features of this algorithm are its ability to deal with multiple channels being affected by interferences with different frequency spectrums. Also we provide a proof of Lyapunov stability of closed‐loop system and asymptotically perfect interference cancelation for a class of interference signals. Furthermore, we introduce a new approach for updating the estimator through the use of staggered estimate. The goal of staggered estimation is to minimize the total number of estimates/calculations done within a time period while ensuring that there is no estimator aliasing. Finally, the proposed algorithm is implemented on an TMS320C6713 DSP Kit and an experimental verification is obtained. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
75.
Bekir Sami Yilbas A. F. M. Arif C. Karatas S. Akhtar B. J. Abdul Aleem 《The International Journal of Advanced Manufacturing Technology》2010,48(9-12):1009-1018
In this paper, bees algorithm (BA) has been used for determine the optimal number of material handling equipment (MHE) used on the production centers. The unmet demands become zero at the end of the planning horizon, i.e., the part demands are totally satisfied through the horizon. The newly developed model provides network information, such as unmet demands and number of loaded and empty of MHE at any given time and centers. Consequently, the model provides a tool for helping managers with planning and decision-making in manufacturing systems. Computational tests showed that small-sized instances can be solved by the exact approach in a fair amount of central processing unit time, but it is not feasible for medium and large-sized instances. To tackle this problem, a bees algorithm is proposed to solve the model. The algorithm is a search procedure inspired by the way honeybees forage for food. The results obtained show the robust performance of the bees algorithm. 相似文献
76.
Naveed Akhtar Stephen P. Decent Kevin Kendall 《International Journal of Hydrogen Energy》2009,34(18):7807-7810
In the present study, structural stability of silver under single-chamber conditions has been examined. Micro-tubular cells made of conventional solid oxide fuel cell materials (Ni-YSZ/YSZ/LSM) with silver paste and silver current-collecting wires (for both electrodes) were prepared. The cells were operated with methane/air mixture of 25/60 mL min−1, furnace temperature of 750 °C, and at an operating voltage of 0.5 V. The results showed increasing porosity in the current-collecting silver wire with time, leading to rupture, finally. It is postulated that the porosity formation could be due to the formation of silver oxide which is highly unstable (volatile) at operating temperature considered in this study. Furthermore, vaporization and melting of silver due to cell overheating under mixed-reactant conditions is expected. Based on experimental evidences, it is concluded that silver may not be a good choice to be employed under the above specified operating conditions, as it lacks long-term structural stability. 相似文献
77.
Snowboarding is a popular winter sport that involves riding a single board down a ski slope or on a half-pipe snow ramp. Compared with injuries resulting from traditional alpine skiing, snowboarding injuries occur more frequently in the upper extremities and ankles and less frequently in the knees. Different types of snowboard equipment, rider stance and snowboarding activity tend to result in different types of injury. Snowboarder's ankle, a fracture of the lateral talus, must be considered in a snowboarder with a "severe ankle sprain" that has not responded to treatment. Risk of injury may be lowered by using protective equipment, such as a helmet and wrist guards. 相似文献
78.
79.
R de Bree RP Chung J van Aken MW van den Brekel 《Canadian Metallurgical Quarterly》1998,142(29):1676-1680
Laryngeal tuberculosis was diagnosed in two men, a 73-year-old man Dutch by birth and a 40-year-old one Turkish by birth. In the former patient it was probably primary tuberculosis, in the latter secondary (he had lung tuberculosis as well). The clinical picture was highly suggestive of laryngeal carcinoma in both patients. They both recovered with chemotherapy. Laryngeal tuberculosis may mimic laryngeal carcinoma. The diagnosis is based on Ziehl-Neelsen staining, culture and polymerase chain reaction (PCR) on Mycobacterium tuberculosis. Because laryngeal tuberculosis is highly infectious, the patient has to be nursed in isolation and people in his or her environment have to be screened. The response of laryngeal tuberculosis to chemotherapy is good. 相似文献
80.
J Rossjohn G Polekhina SC Feil N Allocati M Masulli C De Illio MW Parker 《Canadian Metallurgical Quarterly》1998,6(6):721-734
BACKGROUND: Glutathione S-transferases (GSTs) are a multifunctional group of enzymes, widely distributed in aerobic organisms, that have a critical role in the cellular detoxification process. Unlike their mammalian counterparts, bacterial GSTs often catalyze quite specific reactions, suggesting that their roles in bacteria might be different. The GST from Proteus mirabilis (PmGST B1-1) is known to bind certain antibiotics tightly and reduce the antimicrobial activity of beta-lactam drugs. Hence, bacterial GSTs may play a part in bacterial resistance towards antibiotics and are the subject of intense interest. RESULTS: Here we present the structure of a bacterial GST, PmGST B1-1, which has been determined from two different crystal forms. The enzyme adopts the canonical GST fold although it shares less than 20% sequence identity with GSTs from higher organisms. The most surprising aspect of the structure is the observation that the substrate, glutathione, is covalently bound to Cys 10 of the enzyme. In addition, the highly structurally conserved N-terminal domain is found to have an additional beta strand. CONCLUSIONS: The crystal structure of PmGST B1-1 has highlighted the importance of a cysteine residue in the catalytic cycle. Sequence analyses suggest that a number of other GSTs share this property, leading us to propose a new class of GSTs - the beta class. The data suggest that the in vivo role of the beta class GSTs could be as metabolic or redox enzymes rather than conjugating enzymes. Compelling evidence is presented that the theta class of GSTs evolved from an ancestral member of the thioredoxin superfamily. 相似文献