全文获取类型
收费全文 | 6799篇 |
免费 | 216篇 |
国内免费 | 27篇 |
专业分类
电工技术 | 105篇 |
综合类 | 2篇 |
化学工业 | 1355篇 |
金属工艺 | 284篇 |
机械仪表 | 183篇 |
建筑科学 | 103篇 |
矿业工程 | 8篇 |
能源动力 | 312篇 |
轻工业 | 267篇 |
水利工程 | 56篇 |
石油天然气 | 15篇 |
无线电 | 972篇 |
一般工业技术 | 1486篇 |
冶金工业 | 862篇 |
原子能技术 | 72篇 |
自动化技术 | 960篇 |
出版年
2023年 | 66篇 |
2022年 | 121篇 |
2021年 | 172篇 |
2020年 | 154篇 |
2019年 | 144篇 |
2018年 | 226篇 |
2017年 | 191篇 |
2016年 | 195篇 |
2015年 | 105篇 |
2014年 | 204篇 |
2013年 | 397篇 |
2012年 | 221篇 |
2011年 | 303篇 |
2010年 | 232篇 |
2009年 | 275篇 |
2008年 | 244篇 |
2007年 | 198篇 |
2006年 | 207篇 |
2005年 | 153篇 |
2004年 | 127篇 |
2003年 | 129篇 |
2002年 | 129篇 |
2001年 | 126篇 |
2000年 | 129篇 |
1999年 | 112篇 |
1998年 | 264篇 |
1997年 | 182篇 |
1996年 | 132篇 |
1995年 | 130篇 |
1994年 | 104篇 |
1993年 | 129篇 |
1992年 | 106篇 |
1991年 | 95篇 |
1990年 | 83篇 |
1989年 | 74篇 |
1988年 | 72篇 |
1987年 | 74篇 |
1986年 | 86篇 |
1985年 | 105篇 |
1984年 | 96篇 |
1983年 | 95篇 |
1982年 | 78篇 |
1981年 | 60篇 |
1980年 | 49篇 |
1979年 | 45篇 |
1978年 | 48篇 |
1977年 | 62篇 |
1976年 | 82篇 |
1975年 | 43篇 |
1973年 | 37篇 |
排序方式: 共有7042条查询结果,搜索用时 296 毫秒
991.
Achintya Kumar Sen Gupta 《Zeitschrift für Lebensmitteluntersuchung und -Forschung A》1975,158(2):71-72
Zusammenfassung Eine Schnellmethode zur routinemäßigen Bestimmung des Ölanteils in Handelsleeithin und ähnlichen Phospholipidproben wurde ausgearbeitet. Sie beruht auf der Beobachtung, dam 1 g Phospholipid an 45 g mit Wasser desaktiviertem Kieselgel unter den Versuchsbedingungen vollständig adsorbiert werden.Die Lecithinprobe wird in ätherischer Lösung durch eine mit desaktiviertem Kieselgel gefüllte Säule filtriert und mit etwas Äther nacheluiert. Das gesamte Äther-Eluat wird i. Vak. eingedampft und der Rückstand gewogen. Dieser Rückstand entspricht dem Ölanteil, der aus Mono-, Di- und Triglyceriden, freien Fettsäuren, Sterinen und deren Derivaten besteht. Eine Bestimmung dauert etwa 20 min.
Vorgetragen anläßlich des 11. ISF-Kongresses in Göteborg, Juni 1972. 相似文献
A rapid method for determination of oil in lecithins
Summary A rapid method for routine determination of oil in commercial lecithins and similar phospholipid samples has been worked out. This based on the observation that under the described experimental conditions 1 g of phospholipids is completely adsorbed on 45 g silica gel which has previously been disactivated by the addition of 15% water.The lecithin sample is filtered in ethereal solution through a column filled with disactivated silica gel which is subsequently washed with a little ether. The combined ether eluates are evaporated to drynessin vacuo and the residue weighed. This residue is the oil part of the sample and is constituted of mono-, di-, and triglycerides, free fatty acids, sterols and their derivatives. The duration for one such determination is about 20 min.
Vorgetragen anläßlich des 11. ISF-Kongresses in Göteborg, Juni 1972. 相似文献
992.
An understanding of the work hardening behavior of particulate reinforced metal -matrix composites is crucial in optimizing the parameters for deformation processing of these materials. In the case of particulate reinforced composites with an age hardenable aluminum alloy matrix, the microstructure and mechanical properties can be altered by a suitable aging treatment as well as by changing the content of alloying elements in the matrix. In this study MMCs with different levels of Cu in the matrix were prepared and aged to peak hardness. A modified continuum model was then used to relate the work hardening behavior of the composites to microstructural parameters. The model is shown to be accurate for all the composite materials investigated in the present study. 相似文献
993.
M Shams MD Kilby DA Somerset AJ Howie A Gupta PJ Wood M Afnan PM Stewart 《Canadian Metallurgical Quarterly》1998,13(4):799-804
The evolutionary theory of aging predicts that the equilibrium gene frequency for deleterious mutations should increase with age at onset of mutation action because of weaker (postponed) selection against later-acting mutations. According to this mutation accumulation hypothesis, one would expect the genetic variability for survival (additive genetic variance) to increase with age. The ratio of additive genetic variance to the observed phenotypic variance (the heritability of longevity) can be estimated most reliably as the doubled slope of the regression line for offspring life span on paternal age at death. Thus, if longevity is indeed determined by late-acting deleterious mutations, one would expect this slope to become steeper at higher paternal ages. To test this prediction of evolutionary theory of aging, we computerized and analyzed the most reliable and accurate genealogical data on longevity in European royal and noble families. Offspring longevity for each sex (8409 records for males and 3741 records for females) was considered as a dependent variable in the multiple regression model and as a function of three independent predictors: paternal age at death (for estimation of heritability of life span), paternal age at reproduction (control for parental age effects), and cohort life expectancy (control for cohort and secular trends and fluctuations). We found that the regression slope for offspring longevity as a function of paternal longevity increases with paternal longevity, as predicted by the evolutionary theory of aging and by the mutation accumulation hypothesis in particular. 相似文献
994.
Significant structure theory (SST) of Eyring has been employed to calculate theoretically the viscosity of binary molten electrolytes on the basis of rigid sphere model. For KClNaCl and KClKBr systems the agreement between theoretical and experimental values is found to be satisfactory. 相似文献
995.
996.
997.
The solid state processing of a high density polyethylene by hydrostatic extrusion at room temperature has been investigated. The extrusion pressure for a given extrusion ratio is found to depend on the pressure fluid used, the die angle and the velocity of extrusion. The strain hardening behaviour of the resulting extrudates is found to be independent of the extrusion ratio. An effective flow stress equation which accounts for the dependence of the flow stress of high density polyethylene on strain, strain rate and hydrostatic pressure is developed and used in an analysis of the extrusion process based on the upper bound approach. The calculated values of the extrusion pressure as a function of the various extrusion variables are in reasonable agreement with the experimental results. 相似文献
998.
Crosslinking of 4,4′(bismaleimido)diphenyl ether (BM) was investigated in presence of bis(m-aminophenyl)methylphosphine oxide (BAP), tris(m-aminophenyl)phosphine oxide (TAP), diaminodiphenyl ether (E) and 3,3-bis(p-aminophenyl)phthalide (AP). These crosslinked resins were examined for thermal stability by thermogravimetric analysis. A slight decrease in initial decomposition temperature, the temperature of maximum rate of weight loss, was observed, though the char yield in nitrogen atmosphere at 800°C did not change appreciably. Glass-cloth-reinforced laminates were fabricated from BM and amine mixtures. An improvement in mechanical properties was observed in the presence of phosphorus-containing di- and triamines. 相似文献
999.
1000.
R. Thangaraj S. B. Gadgil B. K. Gupta J. Vaidhyanathan Iyer O. P. A. Agnihotri 《国际能源研究杂志》1982,6(2):169-173
High absorptance and low thermal emittance selective surfaces have been formed by evaporating lead sulphide onto Al evaporated Al substrates. The dependence of selectivity, α/?, on thickness has been studied. The maximum selectivity was obtained for PbS thickness of 400 Å. The emissivity is found to increase with temperature. The coatings are stable up to a temperature of 240°C in air. Long term ultraviolet irradiation causes the photo-oxidation of PbS to PbSO4 which results in the increase of emittance and a decrease in absorptance. When cycled between 0°C and 200°C, the coatings do not show any signs of degradation. 相似文献