全文获取类型
收费全文 | 605篇 |
免费 | 30篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 3篇 |
综合类 | 1篇 |
化学工业 | 183篇 |
金属工艺 | 7篇 |
机械仪表 | 24篇 |
建筑科学 | 19篇 |
能源动力 | 53篇 |
轻工业 | 54篇 |
水利工程 | 13篇 |
石油天然气 | 2篇 |
无线电 | 50篇 |
一般工业技术 | 120篇 |
冶金工业 | 19篇 |
原子能技术 | 1篇 |
自动化技术 | 87篇 |
出版年
2024年 | 7篇 |
2023年 | 7篇 |
2022年 | 33篇 |
2021年 | 32篇 |
2020年 | 34篇 |
2019年 | 38篇 |
2018年 | 30篇 |
2017年 | 39篇 |
2016年 | 23篇 |
2015年 | 20篇 |
2014年 | 18篇 |
2013年 | 75篇 |
2012年 | 34篇 |
2011年 | 41篇 |
2010年 | 26篇 |
2009年 | 31篇 |
2008年 | 21篇 |
2007年 | 20篇 |
2006年 | 11篇 |
2005年 | 13篇 |
2004年 | 12篇 |
2003年 | 4篇 |
2002年 | 9篇 |
2001年 | 7篇 |
2000年 | 2篇 |
1999年 | 7篇 |
1998年 | 7篇 |
1997年 | 1篇 |
1996年 | 5篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1993年 | 4篇 |
1992年 | 2篇 |
1991年 | 4篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1978年 | 1篇 |
排序方式: 共有636条查询结果,搜索用时 15 毫秒
101.
A tapered fiber is fabricated by heating and stretching a piece of optical fiber after the polymer protective cladding has been removed. An equidistant comb-like transmission spectrum, with a spacing of 1.6?nm and an extinction ratio of more than 5?dB, was obtained by the tapered fiber due to the multibeam interferences of the cladding modes. The tapered fiber was applied in a ring erbium-doped fiber laser (EDFL) to generate dual-wavelength lasing oscillations. The EDFL operates at wavelengths of 1557.0?nm and 1558.6?nm with a stable peak power and a signal-to-noise ratio of more than 40?dB. 相似文献
102.
Mohd Faizal B. Ismail Mohamad Dernaika Amin Khodaei Sulaiman Wadi Harun 《Journal of Modern Optics》2013,60(11):892-896
This study describes a proposal and experimental demonstration of a tunable thulium-doped fiber laser with a multi-wavelength output operating at 1.8 μm. The introduction of a multi-mode non-adiabatic taper fiber into a single-mode cavity induces spatial-mode beating and a consequent narrow band filter mechanism. The fiber laser can be tuned by changing the state of the polarization in a ring cavity via adjustment of a polarization controller. The resulting outputs for single and dual wavelengths with different spacing are reported in detail. 相似文献
103.
M. Masturah I. Norezan A. K. Yahya A. Zakaria M. S. Mohd Deni M. K. Talari 《Transactions of the Indian Institute of Metals》2013,66(4):325-328
CaCu3Ti4O12 (CCTO) is well known to have colossal dielectric constant in the range of 105. However, CCTO has considerably high dielectric loss values (tanδ > 0.1) at room temperature and 1 kHz. In this work, addition of glass to CCTO was suggested in order to improve its dielectric properties. The effect of V2O5–TeO2 (VT) glass addition on microstructure and dielectric properties of CCTO ceramics were investigated. Dielectric measurements were carried out for (1 ? x) CCTO-(x) V2O5–TeO2 (x = 0, 0.03, 0.05, 0.10) samples in the frequency range of 102–106 Hz using impedance spectrometer. Electron micrographs showed that low melting VT glass addition facilitated the grain growth of CCTO. As VT glass amount increased, dielectric constant decreased. The drop, though within reasonable values (~105), may related to the presence of grain boundary glassy phase which itself has low dielectric constant. However, the dielectric loss of the composite has decreased after VT glass addition. The low melting V2O5–TeO2 glass aided in liquid phase sintering and improved the grain boundary resistance which resulted in decreased leakage currents. 相似文献
104.
Rafidah Razuan Nur Aimi Jani Mohamad Kamal Harun Mahesh Kumar Talari 《Transactions of the Indian Institute of Metals》2013,66(4):309-312
Properties of pure metals can be enhanced by alloying with other metallic or non-metallic elements according to the need. However, as multiple alloying elements in an alloy may lead to the formation of many intermetallic compounds with complex microstructures and poor mechanical properties, new types of metallic alloys called high entropy alloys with at least five elements with equimolar ratios were developed. In this study, FeNiAlCuCrTi x Nb y (x, y = 0, 0.5, 1.0, 1.5) alloys have been prepared using Ar arc melting technique. Microstructural studies using scanning electron microscope and XRD showed that Ti addition promoted secondary BCC2 phase whereas, Nb acted as FCC stabilizer. Samples with combined Nb and Ti addition showed FCC1 and FCC2 structure with Nb-rich FCC2 dendritic phase as dominant phase. Though, individual Nb and Ti additions have resulted in increased hardness, combined additions have resulted in highest hardness of 797 HV under 1 kg load. 相似文献
105.
Samiaah M. Hassen Al-Tmeemy Hamzah Abdul- Rahman Zakaria Harun 《International Journal of Project Management》2012
While conforming on the findings of prior researches regarding quality cost system in building companies, current research successfully illustrates the contractors' perceptions on the importance of the quality cost system and the barriers that may constrain the implementation of the system for recording and collecting quality cost data. A postal and email surveys were undertaken on Malaysian building companies, focusing on the benefits and difficulties associated with the implementation of quality cost system. Statistical analyses based on Chi-Squared test and Relative Importance Index techniques were used to investigate the significance of the findings and determine the relative importance of the factors. The most important benefit of measuring quality costs is “getting management attention and increase quality awareness” as perceived by the sample of the study. The possible barriers that may affect the management's decision to implement quality cost system are identified and grouped into three categories, which are culture and knowledge; system; and company. The study suggests that the level of the site staff's knowledge should be as important as that of the management to successfully collect and record quality costs data. The findings of this research will raise the level of awareness and sensitize managers and those involved with building industry about the importance of quality cost system and collecting quality costs data. 相似文献
106.
A. Zuraini M.N. Somchit M.H. Solihah Y.M. Goh A.K. Arifah M.S. Zakaria N. Somchit M.A. Rajion Z.A. Zakaria A.M. Mat Jais 《Food chemistry》2006
The objective of this current study was to analyze the biochemical compositions of three Malaysian Channa spp. fish. The proximate analysis revealed that the protein content of Channa lucius, Channa micropeltes and Channa striatus was 19.9%, 22.1%, 23.0% (% of dry weight), respectively. The total lipid content was generally high, ranging from 5.7% to 11.9% and crude ash ranged from 1.0% to 1.8%. The major amino acids were glutamic acid, aspartic acid and lysine, ranging from 9.7% to 21.7%, and the most abundant fatty acid in Channa spp. was C16:0, ranging from 25.6% to 30.4%. The other major fatty acids detected were C22:6, C18:1 and C18:0. The level of arachidonic acid (C20:4) was unusually high in C. striatus (19.02%). The levels of DHA in these fish would also explain the use of Channa spp., especially C. striatus, which has been used for centuries for reducing pain, inflammation and promote wound healing in Malaysia. 相似文献
107.
A rapid, sensitive and economic method for the detection, quantification and confirmation of aflatoxins is described. Aflatoxins B1, B2, G1, and G2, are extracted by methanol/water (85 + 15) and partitioned into methylene dichloride. The methylene dichloride solution is cleaned up on a polypropylene column, filled with 0.5 g silica gel 60. The aflatoxins are eluted with chloroform-acetone (90:10) and are detected using bidirectional thin-layer chromatography (TLC) with aluminium silica gel foil. The mean recovery of aflatoxins B1, B2, G1, and G2 in corn samples was 73, 78, 80, and 64%, respectively; the limit of detection was 0.5 micrograms/kg. The results can also be confirmed by derivative formation using trifluoroacetic acid on the TLC plate. The method has been applied to a wide range of foods with good results. 相似文献
108.
Ghazali MS Zakaria A Rizwan Z Kamari HM Hashim M Zaid MH Zamiri R 《International journal of molecular sciences》2011,12(3):1496-1504
The optical band-gap energy (E(g)) is an important feature of semiconductors which determines their applications in optoelectronics. Therefore, it is necessary to investigate the electronic states of ceramic ZnO and the effect of doped impurities under different processing conditions. E(g) of the ceramic ZnO + xBi(2)O(3) + xTiO(2), where x = 0.5 mol%, was determined using a UV-Vis spectrophotometer attached to a Reflectance Spectroscopy Accessory for powdered samples. The samples was prepared using the solid-state route and sintered at temperatures from 1140 to 1260 °C for 45 and 90 minutes. E(g) was observed to decrease with an increase of sintering temperature. XRD analysis indicated hexagonal ZnO and few small peaks of intergranular layers of secondary phases. The relative density of the sintered ceramics decreased and the average grain size increased with the increase of sintering temperature. 相似文献
109.
Vahab Vaezzadeh Mohamad Pauzi Zakaria Chui Wei Bong Najat Masood Sami Mohsen Magam Sadeq Alkhadher 《Polycyclic Aromatic Compounds》2013,33(5):470-485
ABSTRACTRapid industrialization and urbanization in the west coast of Peninsular Malaysia has caused increasing pollution particularly of petroleum and petroleum by-products. Surface sediment and mangrove oyster (Crassostrea belcheri) were collected from five mangrove ecosystems in the west coast of Peninsular Malaysia and investigated for bioavailability of polycyclic aromatic hydrocarbons (PAHs). Sampling locations were selected from both remote areas with few or no previous records of petroleum pollution such as Pulau Merambong and polluted areas that are under international attention such as Klang mangrove ecosystem. PAH fractions were obtained through soxhlet extraction and two-step column chromatography and the fractions were injected to gas chromatography-mass spectrometry (GC-MS) for analysis. The concentrations of PAHs ranged from 151 to 4973 ng g?1 dw in the sediments, while from 309 to 2225 ng g?1 dw in the oysters. When tested for diagnostic ratios, a predominance of pyrogenic source PAHs was detected in the sediments, whereas PAHs in the oysters had mixed petrogenic and pyrogenic sources. A significant correlation (p < 0.05) was found between high molecular weight (HMW) PAHs in the sediments and oysters and biota accumulation factors (BAFs) of PAHs were approaching or exceeding unity indicating the ability of mangrove oyster in bioaccumulation of PAHs. Overall, this study indicates that mangrove oyster (C. belcheri) can be used as a biomonitor species for PAHs in an aquatic environment. 相似文献
110.
MA Harun RJ Veeneklaas M Van Kampen M Mabasso 《Canadian Metallurgical Quarterly》1998,77(9):1280-1286
A breeding biology study of a genetically unselected variety of Muscovy duck Cairina moschata was conducted in an experimental duck unit in Maputo, Mozambique (25 degrees 58' S, 32 degrees 35' E), to gain insight into factors affecting hatchability during natural incubation. Nesting and incubation behaviors were recorded by daily nest visits. Of 1,338 nests investigated, 70% were incubated until hatching. In 23% of the incubated nests, eggs were laid by more than one duck in the same nest, indicated as dump nests. Artificial dump nests (15% of the incubated nests) were created by adding eggs (690 eggs) from nests abandoned by the duck before incubation had started. A total of 37% of the incubated nests contained eggs that were laid after the onset of incubation (nonterm eggs). Similar hatching rate was found between ducks raised in parks with or without access to swimming water. No significant difference was found in hatchability between normal (0.76) and dump nests (0.77). Artificial dump nests showed higher hatching rates than nests containing nonterm eggs. Dump nesting appears to be a reproductive strategy used by the Muscovy duck to enhance duckling production. Hatching rate was strongly influenced by the length of laying period (period between the ovoposition of the first egg until the onset of incubation) and reproduction cycle (laying period and incubation period). Hatchability was higher for clutches with a shorter reproduction cycle. It is concluded that nesting behavior of the domesticated Muscovy duck is similar to that of its wild ancestor. 相似文献