全文获取类型
收费全文 | 838篇 |
免费 | 10篇 |
专业分类
综合类 | 1篇 |
化学工业 | 83篇 |
金属工艺 | 9篇 |
机械仪表 | 16篇 |
建筑科学 | 16篇 |
矿业工程 | 2篇 |
能源动力 | 28篇 |
轻工业 | 60篇 |
水利工程 | 2篇 |
石油天然气 | 2篇 |
无线电 | 91篇 |
一般工业技术 | 143篇 |
冶金工业 | 332篇 |
原子能技术 | 7篇 |
自动化技术 | 56篇 |
出版年
2023年 | 5篇 |
2022年 | 6篇 |
2021年 | 7篇 |
2019年 | 5篇 |
2018年 | 6篇 |
2017年 | 6篇 |
2014年 | 10篇 |
2013年 | 26篇 |
2012年 | 18篇 |
2011年 | 20篇 |
2010年 | 24篇 |
2009年 | 21篇 |
2008年 | 23篇 |
2007年 | 27篇 |
2006年 | 11篇 |
2005年 | 20篇 |
2004年 | 17篇 |
2003年 | 15篇 |
2002年 | 15篇 |
2001年 | 17篇 |
2000年 | 17篇 |
1999年 | 28篇 |
1998年 | 92篇 |
1997年 | 56篇 |
1996年 | 44篇 |
1995年 | 18篇 |
1994年 | 22篇 |
1993年 | 15篇 |
1992年 | 14篇 |
1991年 | 5篇 |
1990年 | 11篇 |
1989年 | 10篇 |
1988年 | 12篇 |
1987年 | 9篇 |
1986年 | 11篇 |
1985年 | 16篇 |
1984年 | 18篇 |
1983年 | 7篇 |
1982年 | 12篇 |
1981年 | 10篇 |
1980年 | 13篇 |
1979年 | 6篇 |
1978年 | 9篇 |
1977年 | 12篇 |
1976年 | 18篇 |
1975年 | 10篇 |
1973年 | 6篇 |
1971年 | 4篇 |
1967年 | 4篇 |
1966年 | 4篇 |
排序方式: 共有848条查询结果,搜索用时 15 毫秒
51.
52.
Experiments have been carried out to determine the effect of centrifugal force on the rate of condensation of vapors. Methanol and isopropanol vapors were condensed on a vertical rotating finned tube and it was found that the data could be correlated by the equation: Condensation film heat transfer coefficients in excess of 5,700 W/(m2 °K) and 4,200 W/(m2 °K) were obtained for methanol and isopropanol respectively at a tube rotational speed of 1,000 rpm. 相似文献
53.
The historical background and current use of getter sputtering are reviewed and it is shown that the process often occured in early apparatus because of fortuitous layout of the chamber components. Getter systems are classified into “static” and “ynamic” according to the gas flow and pumping conditions. In conclusion mass spectra are given of the gas atmospheres in an r.f. getter sputtering plant when depositing tantalum. It is shown that gettering reduces the gaseous impurities. However, provision of the extra getter target requires use of increased power input. Otherwise the deposition rate can fall (from an overall reduction in ion current density) which increases in the desired coating the proportion of sorbed impurity from gas released in the substrate coating vessel. 相似文献
54.
55.
A linearised pixel-swapping method for mapping rural linear land cover features from fine spatial resolution remotely sensed imagery 总被引:1,自引:0,他引:1
Accurate maps of rural linear land cover features, such as paths and hedgerows, would be useful to ecologists, conservation managers and land planning agencies. Such information might be used in a variety of applications (e.g., ecological, conservation and land management applications). Based on the phenomenon of spatial dependence, sub-pixel mapping techniques can be used to increase the spatial resolution of land cover maps produced from satellite sensor imagery and map such features with increased accuracy. Aerial photography with a spatial resolution of 0.25 m was acquired of the Christchurch area of Dorset, UK. The imagery was hard classified using a simple Mahalanobis distance classifier and the classification degraded to simulate land cover proportion images with spatial resolutions of 2.5 and 5 m. A simple pixel-swapping algorithm was then applied to each of the proportion images. Sub-pixels within pixels were swapped iteratively until the spatial correlation between neighbouring sub-pixels for the entire image was maximised. Visual inspection of the super-resolved output showed that prediction of the position and dimensions of hedgerows was comparable with the original imagery. The maps displayed an accuracy of 87%. To enhance the prediction of linear features within the super-resolved output, an anisotropic modelling component was added. The direction of the largest sums of proportions was calculated within a moving window at the pixel level. The orthogonal sum of proportions was used in estimating the anisotropy ratio. The direction and anisotropy ratio were then used to modify the pixel-swapping algorithm so as to increase the likelihood of creating linear features in the output map. The new linear pixel-swapping method led to an increase in the accuracy of mapping fine linear features of approximately 5% compared with the conventional pixel-swapping method. 相似文献
56.
Multivariate analysis of NMR fingerprint of the unsaponifiable fraction of virgin olive oils for authentication purposes 总被引:1,自引:0,他引:1
R.M. Alonso-Salces K. Héberger M.V. Holland J.M. Moreno-Rojas C. Mariani G. Bellan F. Reniero C. Guillou 《Food chemistry》2010
A new approach to the geographical characterisation of virgin olive oils (VOOs) based on the 1H NMR fingerprint of the unsaponifiable matter is presented. The 1H NMR spectra of the unsaponifiable fraction of virgin olive oils from Spain, Italy, Greece, Tunisia, Turkey, and Syria were analysed by several pattern recognition techniques (LDA, PLS-DA, SIMCA, and CART). PLS-DA (PLS-1 approach) obtained the best classification results for all classes. Moreover, 1H NMR spectra of the bulk oil, and its corresponding unsaponifiable fraction, as well as the subfractions of the unsaponifiable fraction (alcohol, sterol, hydrocarbon, and tocopherol fractions) were studied in the search for the markers that multivariate techniques revealed to be related to the geographical origin of olive oils. Additionally, a preliminary study regarding 1H NMR data of the bulk oil and the corresponding unsaponifiable fraction of VOOs suggested that these spectral data contained complementary information for the geographical characterisation of VOOs. 相似文献
57.
An experimental study has been carried out on a continuously operated pilot fractional distillation column equipped with an external heat pump. The distillation column was a 15 cm internal diameter glass unit containing eleven single bubble cap plates. A methanol-water mixture was fed to the column. After operating the heat pumps with R114 as the working fluid, further experiments have been conducted with R11 as the working fluid. Plots of pressure against enthalpy, condensation pressure and latent heat of vaporization against condensation temperature and theoretical Rankine coefficient of performance against gross temperature lift and condensation temperature are presented for both R114 and R11. R11 has correspondingly higher theoretical Rankine coefficients of performance than R114. The experiments show that the actual coefficients are also higher for R11 than for R114. A maximum actual coefficient of performance of 5.3 was obtained using R11 as the working fluid with a gross temperature lift of 38.4°C. The experimental data for R11 were found to be reproducible during operation over a number of weeks. This showed that the relative thermal instability of R11 compared to R114 had not apparently affected the performance of the system. 相似文献
58.
The lubrication approximation is used to investigate slender dry patches in an infinitely wide film of viscous fluid flowing steadily on an inclined plane that is either heated or cooled relative to the surrounding atmosphere. Four non-isothermal situations in which thermocapillary effects play a significant role are considered.Similarity solutions describing a thermocapillary-driven flow with a dry patch that is widening or narrowing due to either gravitational or surface-tension effects on a non-uniformly heated or cooled substrate are obtained, and examples of these solutions, when the substrate temperature gradient depends on the longitudinal coordinate according to a general power law, are presented. When gravitational effects are strong, the solution contains a free parameter, and for each value of this parameter there is a unique solution representing both a narrowing pendent dry patch and a widening sessile dry patch, whose transverse profile has a monotonically increasing shape. When surface-tension effects are strong, the solution also contains a free parameter, and for each value of this parameter there is both a unique solution representing a narrowing dry patch, whose transverse profile has a monotonically increasing shape, and a one-parameter family of solutions representing a widening dry patch, whose transverse profile has a capillary ridge near the contact line and decays in an oscillatory manner far from it.Similarity solutions are also obtained for both a gravity-driven and a constant-surface-shear-stress-driven flow with a dry patch that is widening or narrowing due to thermocapillarity on a uniformly heated or cooled substrate. The solutions in both cases contain a free parameter, and for each value of this parameter there is a unique solution representing both a narrowing dry patch on a heated substrate and a widening dry patch on a cooled substrate, whose transverse profile has a monotonically increasing shape. 相似文献
59.
Daly Raymond M.; Holland Cornelius J.; Forrest Patricia A.; Fellbaum G. Anthony 《Canadian Metallurgical Quarterly》1985,17(4):379
Assessed the permanence of the treatment effects (temporal generalization) obtained by a parent-training program, Directive Parental Counseling (DPC), developed by the 2nd author (1983). 20 parents who participated in the program completed the Walker Problem Behavior Identification Checklist and the Missouri Children's Behavior Checklist at pretreatment, treatment termination, 3 mo posttreatment, and 3 yrs posttreatment. The parents were part of a larger treatment group of 36 Ss who demonstrated superiority in altering targeted behaviors of their children (mean age 6 yrs 11 mo), in contrast to a waiting-control group, at the completion of a 10-wk program. The positive changes noted on the behavior rating scales obtained from the parents in the treatment group at the posttreatment period were still evident at the 3-mo follow-up and continued to increase over the 3-yr interval. Results are discussed in light of the issues surrounding temporal generalization and the structure of the DPC program. (French abstract) (26 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
60.
There are three sections in an evaporator tube; liquid heating, foam and climbing film. A technique is presented for estimating the lengths of these three sections and the overall heat transfer coefficients in each of them. The lower the liquid feed temperature, the longer the liquid heating length. The length of the foam section does not depend on the liquid feed temperature. In these studies it was estimated to be more than half the length of the evaporator tube. Only at the higher liquid feed temperatures was a climbing film found to exist. 相似文献