全文获取类型
收费全文 | 1259篇 |
免费 | 75篇 |
国内免费 | 5篇 |
专业分类
电工技术 | 40篇 |
综合类 | 6篇 |
化学工业 | 324篇 |
金属工艺 | 21篇 |
机械仪表 | 40篇 |
建筑科学 | 36篇 |
矿业工程 | 1篇 |
能源动力 | 74篇 |
轻工业 | 91篇 |
水利工程 | 24篇 |
石油天然气 | 10篇 |
无线电 | 137篇 |
一般工业技术 | 224篇 |
冶金工业 | 118篇 |
原子能技术 | 9篇 |
自动化技术 | 184篇 |
出版年
2024年 | 3篇 |
2023年 | 25篇 |
2022年 | 48篇 |
2021年 | 84篇 |
2020年 | 66篇 |
2019年 | 75篇 |
2018年 | 87篇 |
2017年 | 66篇 |
2016年 | 65篇 |
2015年 | 47篇 |
2014年 | 61篇 |
2013年 | 110篇 |
2012年 | 62篇 |
2011年 | 65篇 |
2010年 | 48篇 |
2009年 | 33篇 |
2008年 | 22篇 |
2007年 | 32篇 |
2006年 | 20篇 |
2005年 | 19篇 |
2004年 | 17篇 |
2003年 | 17篇 |
2002年 | 16篇 |
2001年 | 12篇 |
2000年 | 13篇 |
1999年 | 10篇 |
1998年 | 37篇 |
1997年 | 22篇 |
1996年 | 20篇 |
1995年 | 11篇 |
1994年 | 11篇 |
1993年 | 21篇 |
1992年 | 7篇 |
1991年 | 6篇 |
1989年 | 3篇 |
1988年 | 3篇 |
1987年 | 11篇 |
1986年 | 5篇 |
1985年 | 3篇 |
1984年 | 13篇 |
1983年 | 4篇 |
1982年 | 6篇 |
1981年 | 3篇 |
1980年 | 6篇 |
1979年 | 4篇 |
1978年 | 4篇 |
1977年 | 4篇 |
1976年 | 2篇 |
1974年 | 3篇 |
1966年 | 2篇 |
排序方式: 共有1339条查询结果,搜索用时 19 毫秒
71.
Significant improvement of semi-solid microstructure and mechanical properties of A356 alloy by ARB process 总被引:2,自引:0,他引:2
Roohollah Jamaati Sajjad AmirkhanlouMohammad Reza Toroghinejad Behzad Niroumand 《Materials Science and Engineering: A》2011,528(6):2495-2501
Accumulative roll bonding (ARB) process was used in this study as an effective method for manufacturing high-strength, finely-dispersed and highly-uniform A356 alloy. It was found that when the number of ARB cycles was increased, the uniformity of silicon particles in the aluminum matrix improved, the particles became finer and spheroider and therefore, the tensile strength (TS) and ductility of the samples improved. The microstructure of the manufactured A356 alloy after five ARB cycles indicated a totally modified structure such that it's TS and elongation values reached 269 MPa and 5.3% which were 2.6 and 2.5 times greater than those of the as-cast material, respectively. Also, the hardness value increased from 55.4 (for as-cast sample) to 100.2 HV (after the fifth cycle of ARB), and registered 81% increase. 相似文献
72.
Colour assays: An inside look into Alentejo traditional limewash paintings and coloured lime mortars
Milene Gil Jose Aguiar Ana Seruya Rosário Veiga Luisa Carvalho Helena Vargas Jose Mirão Antonio Candeias 《Color research and application》2011,36(1):61-71
A series of colour assays were conducted taking into account old bibliographic recommendations and oral testimony regarding traditional lime painting technology from the Alentejo (South Portugal) region. The main objectives were: (a) the colorimetric analysis of paintings made with different limewash preparation methods; (b) the comparison between natural processed red and yellows ochre pigments (“home made” and from industrial origin) and synthetic iron oxides in different concentrations and lime proportions; (c) the evaluation of the colorimetric CIELAB coordinates during the lime carbonation process in coloured mortars and limewashes. The results shows that the evolution of L*, a*, and b* during the carbonation process is independent of pigment concentration and paint thickness but dependent of pigment composition and finishing technique (lime painting or coloured mortar). They also emphasize the importance of surface appearance attributes and its influence on the colorimetric parameters. © 2010 Wiley Periodicals, Inc. Col Res Appl, 36, 61–71, 2011 相似文献
73.
Texture analysis of CT images 总被引:5,自引:0,他引:5
Mir A.H. Hanmandlu M. Tandon S.N. 《IEEE engineering in medicine and biology magazine》1995,14(6):781-786
The present study has shown some promise in the use of texture for the extraction of diagnostic information from CT images. A number of features are obtained from abdominal CT scans of the liver using the spatial domain statistical texture analysis methods: SGLDM, GLRLM, and GLDM. This study investigated whether (a) the texture could be used to discriminate among the various tissue types that are inaccessible to human perception and, (b) if so, then what are the most useful feature parameters for such an application? The efficacies of the different methods were evaluated from the consistency of the computed values within a class and from their differences with other classes. The study has demonstrated the use of texture for tissue characterization of CT images. In particular, we have been successful in identifying the onset of disease in liver tissue, which can not be recognized even by trained human observers. Three useful features, namely entropy (H), local homogeneity (L) and grey level distribution (GLD), have been found effective for pattern recognition. The performance of these features has been compared on the basis of statistical significance. The results show that, except for L, (Direction 0°) all feature parameters perform equally well and detect early malignancy with a confidence level of above 99%-a finding that will not only help in automation, but more importantly, in early detection of malignancy in the liver 相似文献
74.
75.
The -514 polymorphism in the hepatic lipase gene (LIPC) is associated with decreased hepatic lipase activity. In the present study, the interaction between body mass index (BMI), the -514 polymorphism, and hepatic lipase activity was examined in 118 white men and in 51 African American men. BMI was significantly positively correlated with hepatic lipase activity in both populations. BMI was similar in men with genetic differences in hepatic lipase activity, indicating that high hepatic lipase activity did not cause increased BMI. The data therefore suggest that high BMI leads to increased hepatic lipase activity. The actions of BMI and the -514 polymorphism on hepatic lipase activity appear to be additive and independent, rather than synergistic. This finding indicates that hepatic lipase activity is a multifactorial trait, determined in part by polymorphism within the LIPC gene as well as by factors that influence BMI. 相似文献
76.
The multipath tree-encoding of speech at 8 kbits/s is investigated. Tree coding proceeds along the lines of Anderson, et al, but at this lower bit rate, frequency weighting of the error process and adaptation of the coding process are found to be beneficial. Coding results for a stationary speech-like source are found to agree well with rate-distortion theoretic ideas, and when applied to speech, tree coding at 8000 bits/s yielded frequency-weighted SNR's of 15-20 dB. 相似文献
77.
This is the first study to analyze variations in time estimation during 60 h of sleep deprivation and the relation between time estimation performance and the activation measures of skin resistance level, body temperature, and Stanford Sleepiness Scale (SSS) scores. Among 30 healthy participants 18 to 24 years of age, for a 10-s interval using the production method, we found a lengthening in time estimations that was modulated by circadian oscillations. No differences in gender were found in the time estimation task during sleep deprivation. The variations in time estimation correlated significantly with body temperature, skin resistance level, and SSS throughout the sleep deprivation period. When body temperature is elevated, indicating a high level of activation, the interval tends to be underestimated, and vice versa. When the skin resistance level or SSS is elevated (low activation), time estimation is lengthened, and vice versa. This lengthening is important because many everyday situations involve duration estimation under moderate to severe sleep loss. Actual or potential applications of this research include transportation systems, emergency response work, sporting activities, and industrial settings in which accuracy in anticipation or coincidence timing is important for safety or efficiency. 相似文献
78.
The modal spectral response of an antiresonant reflecting optical waveguide (ARROW) with periodic corrugations or grating is calculated for both shallow and deep gratings with the Method of Lines. The effect of the ARROW layer thickness and the grating depth on the spectral response is studied. It is found that when the ARROW-layer thickness is close to resonance, the ripples in the reflection spectra become smooth and the peak reflectivity drops. This is attributed to the large increase in the leakage loss of the ARROW waveguide near resonance. The ARROW grating is characterized by modal reflectivity spectra, which exhibit a strong polarization discrimination property, in favor of the TE polarization. 相似文献
79.
The dc conductivity and dielectric parameters of glassy system of a-Se70Te30−x
Sn
x
(x = 0, 2, 4, 6, 8 and 10) glasses have been investigated. Frequency and temperature dependence of dielectric constants (ε′)
and dielectric loss (ε′′) are studied in the frequency range 120–100 kHz and temperature range 300–390 K. Dielectric dispersion
is observed when Tin (Sn) is incorporated to a-Se–Te system in the entire temperature range. These results explain that the
dc conduction loss is dominated in the present system. From dc conductivity studies it is observed that the dc conductivity
and activation energy increases with increasing tin concentration in the present system. 相似文献
80.
Sushil Kumar M. A. Majeed Khan M. Zulfequar M. Husain 《Journal of Materials Science》2007,42(1):363-367
The fabrication of devices with lead salts and their alloys with detecting and lasing capabilities has been an important technological
development. The high quality polycrystalline thin films of PbTe1−x
S
x
with variable composition (0 ≤ x ≤ 1) have been deposited onto ultra clean glass substrates by vacuum evaporation technique. Optical, structural and electrical
properties of PbTe1−x
S
x
thin films have been examined. Absorption coefficient and band gap of the films were determined by absorbance measurements
in wavelength range 2,500–5,000 nm using FTIR spectrophotometer. Sample nature, crystal structure and lattice parameter of
the films were determined from X-ray diffraction patterns. DC conductivity and activation energy of the films were measured
in temperature range 300–380 K through I–V measurements. 相似文献