全文获取类型
收费全文 | 2855篇 |
免费 | 3篇 |
专业分类
电工技术 | 16篇 |
综合类 | 1篇 |
化学工业 | 50篇 |
金属工艺 | 3篇 |
机械仪表 | 1篇 |
建筑科学 | 28篇 |
矿业工程 | 2篇 |
能源动力 | 13篇 |
轻工业 | 32篇 |
水利工程 | 4篇 |
石油天然气 | 3篇 |
无线电 | 45篇 |
一般工业技术 | 59篇 |
冶金工业 | 2581篇 |
原子能技术 | 3篇 |
自动化技术 | 17篇 |
出版年
2022年 | 4篇 |
2021年 | 5篇 |
2018年 | 3篇 |
2017年 | 5篇 |
2016年 | 5篇 |
2015年 | 5篇 |
2014年 | 9篇 |
2013年 | 21篇 |
2012年 | 4篇 |
2011年 | 7篇 |
2010年 | 5篇 |
2009年 | 13篇 |
2008年 | 12篇 |
2007年 | 22篇 |
2006年 | 14篇 |
2005年 | 3篇 |
2004年 | 10篇 |
2003年 | 9篇 |
2002年 | 15篇 |
2001年 | 10篇 |
2000年 | 4篇 |
1999年 | 76篇 |
1998年 | 796篇 |
1997年 | 476篇 |
1996年 | 291篇 |
1995年 | 205篇 |
1994年 | 112篇 |
1993年 | 162篇 |
1992年 | 23篇 |
1991年 | 31篇 |
1990年 | 28篇 |
1989年 | 17篇 |
1988年 | 29篇 |
1987年 | 38篇 |
1986年 | 19篇 |
1985年 | 15篇 |
1984年 | 4篇 |
1983年 | 7篇 |
1982年 | 13篇 |
1981年 | 30篇 |
1980年 | 23篇 |
1979年 | 2篇 |
1978年 | 7篇 |
1977年 | 87篇 |
1976年 | 155篇 |
1975年 | 8篇 |
1973年 | 3篇 |
1972年 | 4篇 |
1968年 | 2篇 |
1955年 | 3篇 |
排序方式: 共有2858条查询结果,搜索用时 15 毫秒
991.
The concentration of n-hexanal in low fat, dehydrated foods can be determined in 10 min by the gas chromatographic analysis
of the vapors from a 15 g sample suspended in boiling water. With 4-heptanone as an internal standard good day-to-day reproducibility
was obtained and the results could be expressed as ppm hexanal in the sample. The onset of rancid odors was found to occur
when the hexanal concentration increased to between 5 and 10 ppm. With an oat cereal good correlation between sensory evaluations
and hexanal concentration between 0.3 and 5 ppm was obtained. The rate of hexanal increase at 55 and 45 C for a corn and a
wheat cereal could be reliably projected to 37 and 21 C. Antioxidants applied to a wheat cereal reduced the rate of hexanal
increase. 相似文献
992.
Gerami-Nejad M Hausauer D McClellan M Berman J Gale C 《Yeast (Chichester, England)》2004,21(5):429-436
The recent availability of genome sequence information for the opportunistic pathogen Candida albicans has greatly facilitated the ability to perform genetic manipulations in this organism. Two important molecular tools for studying gene function are regulatable promoters for generating conditional mutants and fluorescent proteins for determining the subcellular localization of fusion gene products. We describe a set of plasmids containing promoter-GFP cassettes (P(MET3)-GFP, P(GAL1)-GFP, and P(PCK1)-GFP), linked to a selectable nutritional marker gene (URA3). PCR-mediated gene modification generates gene-specific promoter, or gene-specific promoter-GFP, fusions at the 5'-end of the gene of interest. One set of primers can be used to generate three strains expressing a native protein of interest, or an amino-terminal GFP-tagged version, from three different regulatable promoters. Thus, these promoter cassette plasmids facilitate construction of conditional mutant strains, overexpression alleles and/or inducible amino-terminal GFP fusion proteins. 相似文献
993.
This work outlines the fundamental scaling laws associated with electrical field flow fractionation channels. Although general FFF theory indicates few advantages from miniaturization, EFFF theory indicates clear advantages to miniaturization of the EFFF channel. Retention, plate heights, resolution, equilibration times, and time constants are examined. The outlined theory predicts scaling advantages in each of these areas after miniaturization. Potential applications, such as the use of these systems for sample preparation in microscale total analysis systems, and improvements associated with these theoretical predictions are also discussed. 相似文献
994.
Evans H. Gale P. Aljibouri B. Lim E.G. Korolkwiwicz E. Sambell A. 《Electronics letters》2000,36(24):1987-1988
A 5.8 GHz circularly polarised 2×2 patch antenna array is presented, employing sequential rotation of dual-feed circularly polarised elements; appropriate phase-shifting and power splitting are achieved via a serial feed arrangement. The feed has been optimised using simulated annealing; the resulting structure has a voltage standing wave ratio 2:1 bandwidth of 9.8%. Results obtained by full wave simulation and practical measurement confirm the integrity of the design 相似文献
995.
Carbon dioxide (CO2) capture and storage has the potential to reduce CO2 emissions from fossil fuel combustion. Although leakage from monitored CO2 injection sites has been minimal to non-existent, experience from the natural gas storage industry suggests that, if it becomes a widely deployed technology, leaks may be expected from some storage sites. Natural occurrences of CO2 in the geosphere, some of which have been exploited, provide insights into the types of emissions that might be expected from anthropogenic CO2 storage sites. CO2 emission sites are commonly found in clusters in CO2-prone geological provinces: the most common natural emissions sites in sedimentary basins consist of carbonated springs and mofettes. These represent at worst only a local hazard. In volcanic and hydrothermal provinces, more energetic emissions may occur due to active supply from degassing magma. These include rare, sudden emissions from fissures and craters that have caused fatalities. It is unlikely that such provinces would be considered for CO2 storage Major lake overturn events such as occurred at Lake Nyos in 1986 are considered highly unlikely to occur as a result of CO2 storage, not least because CO2 levels in lake waters can be monitored and remediated. Natural CO2 fields indicate that under favourable conditions CO2 can be retained in the subsurface for millions of years. The main risk from man-made CO2 storage sites that does not have any close analogy in nature is considered to be a well blowout. A blowout that took place at a natural CO2 field provides some indication of the likely hazard. 相似文献
996.
Noise on Residential Power Distribution Circuits 总被引:22,自引:0,他引:22
Vines R.M. Trissell H.J. Gale L.J. Ben O'neal J. 《Electromagnetic Compatibility, IEEE Transactions on》1984,(4):161-168
This paper presents electromagnetic noise measurements on power distribution circuits in the frequency range of 5-100 kHz. Since this noise is due primarily to appliances such as universal motors, light dimmers, television receivers, and certain switching power supplies located on the secondary side of the distribution transformer, the noise varies dramatically with time as these appliances are turned on and off. Measurements of the noise inserted into the distribution circuit by several representative appliances are presented. The noise measurement technique itself, as well as the resulting measurements, are described. Background noise which is present in the absence of such appliances was also measured. These noise measurements are important for the design of communications systems, such as distribution-line carrier, which operate in the 5-20 kHz region and use the distribution line as a communications medium. 相似文献
997.
998.
Methods for the reduction of spoilage, of lamb, by psychrotolerant clostridia were investigated including exposure to air, hot and cold water spray washing and tyndallisation. Initially vegetative cells of psychrotolerant clostridia associated with spoilage of chilled vacuum-packed meat were exposed to aerobic cooked meat medium at room temperature (21 °C) to determine how long they remained viable. Survival of strains varied from 2 h to 3 days. Vegetative cells of Clostridium estertheticum subsp. estertheticum survived 7 days at 10 °C with little reduction in viable numbers. This ruled out exposure to air as a practical method for reducing spoilage. Trials were also carried out on chilled vacuum-packed lamb inoculated with spores of Cl. estertheticum subsp. estertheticum. The time until inoculated packs reached the loss of vacuum stage varied from 38 to 53 days. Hot and cold water washing extended the shelf life by 12 to 13 days in comparison to untreated packs. 相似文献
999.
WA Berg CI Caskey UM Hamper ND Anderson BW Chang S Sheth EA Zerhouni JE Kuhlman 《Canadian Metallurgical Quarterly》1993,13(6):1323-1336
A total of 135 symptomatic women with 262 breast implants were examined with magnetic resonance (MR) imaging performed with a body coil, ultrasound (US), or both to determine imaging features of implant rupture. Surgical proof was available for 33 women with 62 implants; 24 were ruptured and 38 were intact. Complicated internal structure was the most reliable predictor of implant rupture: Diffuse low-level echoes were seen on sonograms in 56% of ruptured implants; internal membranes (which correspond to the collapsed implant shell) were seen on MR images in 58% of ruptured implants. Fluid droplets were seen within the silicone in 26% of ruptured implants on MR images. Irregular implant contour can be a sign of rupture but is unreliable. Fluid collections around silicone implants are not a sign of rupture. At present, neither US nor conventional MR imaging with a body coil is sufficiently reliable to advocate routine screening of asymptomatic women with breast implants. Evaluation with MR imaging performed with a surface coil is more reliable. 相似文献
1000.
Dustin L.M. Harper Julie Horrocks Jessica Barber Gale A. Bravener Carl J. Schwarz Robert L. McLaughlin 《Journal of Great Lakes research》2018,44(6):1362-1372
We evaluated statistical methods for estimating abundances of adult sea lamprey (Petromyzon marinus) migrating in Great Lakes tributaries. The sea lamprey is the target of a basin-wide, bi-national control program. Abundance estimates from mark-recapture data are used to evaluate program success and the efficiency of sea lamprey trapping. Recent tracking studies suggested the mark-recapture estimates of abundance could be biased. We compared four estimators of abundance using stratified (weekly) mark-recapture data for 19?years of trapping in the St. Marys River. Abundances from the pooled Petersen estimator were similar to abundances from the stratified Schaefer and stratified Petersen estimators, but substantially lower than abundances from a stratified Bayesian P-spline estimator. In simulations of virtual populations, pooled Petersen and Bayesian P-spline estimates were similar across a range of conditions where catchability differed between marked and unmarked lamprey and changed over the trapping season, with one exception. Abundances from the Bayesian P-spline estimator were strongly positively biased when catchability of marked lamprey increased over the season, while catchability of unmarked lamprey did not. Estimates from both estimators were negatively biased when lamprey displayed consistent individual differences in catchability and positively biased when a proportion of marked lamprey fell back. Discrepancies between mark-recapture and tracking studies cannot be reconciled by the choice of abundance estimator, but could be an outcome of bias due to individual differences in catchability. Sea lamprey managers could also switch from the stratified Schaefer to the pooled Petersen estimator to simplify field operations without losing accuracy and precision. 相似文献