首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   217篇
  免费   4篇
  国内免费   1篇
电工技术   1篇
化学工业   36篇
金属工艺   21篇
机械仪表   3篇
建筑科学   9篇
矿业工程   1篇
能源动力   6篇
轻工业   16篇
水利工程   16篇
无线电   7篇
一般工业技术   34篇
冶金工业   54篇
自动化技术   18篇
  2020年   2篇
  2019年   3篇
  2018年   3篇
  2017年   2篇
  2016年   2篇
  2014年   3篇
  2013年   20篇
  2012年   5篇
  2011年   9篇
  2010年   15篇
  2009年   15篇
  2008年   7篇
  2007年   10篇
  2006年   9篇
  2005年   6篇
  2004年   7篇
  2003年   2篇
  2002年   7篇
  2001年   3篇
  2000年   2篇
  1999年   2篇
  1998年   10篇
  1997年   7篇
  1996年   8篇
  1995年   4篇
  1994年   6篇
  1993年   3篇
  1992年   2篇
  1989年   4篇
  1988年   2篇
  1987年   5篇
  1986年   2篇
  1985年   2篇
  1984年   5篇
  1983年   1篇
  1982年   1篇
  1981年   1篇
  1979年   2篇
  1977年   3篇
  1976年   4篇
  1975年   1篇
  1974年   1篇
  1973年   1篇
  1967年   2篇
  1963年   1篇
  1962年   1篇
  1959年   1篇
  1958年   2篇
  1957年   1篇
  1955年   1篇
排序方式: 共有222条查询结果,搜索用时 369 毫秒
151.
152.
The impact that varying qualities of wastewater may have on the movement of steroid estrogens through soils into groundwater is little understood. In this study, the steroid estrogens 17β-estradiol (E2) and estrone (E1) were followed through batch and column studies to examine the impact that organic wastewater constituents from on-site wastewater treatment systems (i.e., septic systems or decentralized systems) may have on influencing the rate of transport of estrogens through soils. Total organic carbon (TOC) content (as a surrogate indicator of overall wastewater quality) and the presence of nonyl-phenol polyethoxylate surfactants (NPEO) at concentrations well below the critical micelle concentration were independently shown to be indicative of earlier breakthrough and less partitioning to soil in batch and column experiments. Both NPEO and wastewater with increasing TOC concentrations led to shifts in the equilibrium of E1 and E2 towards the aqueous phase and caused the analytes to have an earlier breakthrough than in control experiments. The presence of nonylphenols, on the other hand, did not appreciably impact partitioning of E1 or E2. Biodegradation of the steroids in soil was also lower in the presence of septic tank effluents than in an organic-free control water. Furthermore, the data indicate that the rate of movement of E1 and E2 present in septic tank effluent through soils and into groundwater can be decreased by removing the NPEOs and TOC through wastewater treatment prior to sub-surface disposal. This study offers some insights into mechanisms which impact degradation, transformation, and retardation, and shows that TOC and NPEO surfactants play a role in estrogen transport.  相似文献   
153.
Danish architect Kay Fislcer is presented as a representative figure in the post–World War II architectural debates on functionalism, regionalism, and monumentality. Fisker participated in a transatlantic exchange on these matters that linked Scandinavia, the English conception of “new empiricism,” and the teaching and architectural practice associated with two noted American schools at the Massachusetts Institute of Technology and the University of California at Berkeley. Prominent Americans in this program for a modern architecture that confronted the more dominant ideology of the International Style included Lewis Mumford, William Wilson Wurster, Pietro Belluschi, and Lawrence B. Anderson.  相似文献   
154.
Monensin and tylosin have activity against gram-positive bacteria, and it has been theorized that their effects on the intestinal environment may promote proliferation of gram-negative bacteria such as Escherichia coli. Effects of these antibiotics on the shedding of E. coli O157:H7 were studied in a feedlot environment, using 32 finishing steers. A diet containing 85% barley grain, 10% barley silage, and 5% supplement was amended with 33 ppm monensin, 11 ppm tylosin, both of these additives, or no additives (control). All steers were orally inoculated with 10(10) CFU of a mixture of four strains of nalidixic acid-resistant E. coli O157:H7. Fecal (grab), oral (mouth swab) and water, water-water bowl interface, feed, and pen floor fecal pat samples were collected weekly for 12 weeks. Prevalence of E. coli O157:H7-positive fecal grab samples did not differ (P = 0.26) among treatments, nor did the rate (P = 0.81) or duration (P = 0.85) of shedding of the organism. Fecal grab samples were positive for E. coli O157:H7 more frequently (P < 0.001) than were oral swabs. More (P = 0.02) E. coli O157:H7-positive oral swabs were recovered from the tylosin group than from controls. E. coli O157:H7 was not detected in any of 47 water samples, but was present in 1 of 47 water bowl swabs, 7 of 48 feed samples, and 36 of 48 fecal pats. Pulsed-field gel electrophoresis suggested that differences existed among inoculated strains in their ability to persist in animals and in the environment. However, this study revealed no evidence that dietary inclusion of monensin or tylosin, alone or in combination, increased fecal shedding of E. coli O157:H7 or its persistence in the environment.  相似文献   
155.
The precipitate-hardenable aluminium alloy 2024 has been processed by rolling to develop a fine microstructure. Four alloy conditions were tested; these included two rolling temperatures and two different ageing sequences. For all four conditions there was an ideal heat-treatment time at which there was a concurrent improvement in both strength and formability. Microstructural modeling has shown that this is the result of a small processing window in which the hardening due to precipitation is larger than the softening due to recovery, while the detrimental effects of particle coarsening on ductility have not yet developed. Cryo-rolling and room-temperature rolling produced materials with similar strengths, but cryo-rolling showed inferior formability. Natural ageing before rolling significantly decreased the formability compared to rolling in the supersaturated condition, and it is proposed that the solute clusters that develop during natural aging inhibit dynamic recovery and consequently increase the dislocation density that develops during rolling.  相似文献   
156.
The effects of rumen protozoal populations on ruminal populations and fecal shedding of Escherichia coli O157:H7 were evaluated by using specifically faunated sheep. Nine fauna-free sheep (three animals per treatment) were inoculated with Dasytricha spp. (DAS sheep); with mixed population A (PopA) comprising Entodinium spp., Isotricha spp., Diplodinium spp., and Polyplastron spp.; or with mixed population B (PopB) comprising Entodinium spp., Isotricha spp., Dasytricha spp., and Epidinium spp.; six sheep were maintained fauna-free (FF sheep) to serve as controls. Sheep were fed barley silage-based diets, and treatment groups were housed in isolated rooms. Sheep were inoculated orally with 10(10) CFU of a four-strain mixture of nalidixic acid-resistant E. coli O157:H7. Samples of ruminal fluid and feces were collected over 77 days. Polyplastron spp. were detected in only one sheep in PopA, and Dasytricha spp. were detected only once within the PopB cohort. Sheep in the DAS group were 2.03 times more likely (P < 0.001) to shed E. coli O157:H7 than were those in the other three treatments, whereas the PopB sheep were less likely (0.65; P < 0.05) to shed this bacterium. The likelihood of harboring ruminal E. coli O157:H7 also tended (P = 0.06) to be higher in DAS and was lower (P < 0.01) in FF than in other cohorts. Possibly, Dasytricha spp. had a hosting effect, and Epidinium spp. had a predatory relationship, with E. coli O157:H7. Additional study into predator-prey and hosting relationships among rumen protozoa and E. coli O157:H7 is warranted.  相似文献   
157.
An epoxy resin system based on a triglycidyl p‐amino phenol (MY0510) was crosslinked using stoichiometric amounts of 4,4′‐diaminodiphenyl sulfone. The epoxy was modified with random copolymers, polyethersulfone‐poly(ether‐ethersulfone) (PES:PEES), with either amine or chlorine end groups, at 10 and 20 wt %. The reaction kinetics for both unmodified and modified epoxy systems were studied using differential scanning calorimetry in isothermal and dynamic conditions. The results show that the degree of conversion in thermoplastic‐modified epoxies at any reaction time is smaller compared with the unmodified resin. Gel point (GP) determination was done from rheological measurements. The modified system containing 20% of the PES:PEES additive showed considerable increase in the GP. The reaction rate shows the characteristic of an autocatalytic reaction where the product acts as catalyst. The activation energy, Ea calculated from the isothermal reaction depends on the extent of conversion and increases with increasing PES:PEES content. For unmodified epoxy system, the average Ea is 67.8 ± 4.1 kJ mol?1 but for systems modified with 20 wt % of amine and chlorine PES:PEES, the value increased to 74.1 ± 3.3 and 77.9 ± 4.4 kJ mol?1, respectively. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009  相似文献   
158.
A series of studies was conducted to determine the efficacy and possible modes of action of a water-soluble mixture of alcohol ethoxylate and pluronic detergents (AEPD; Blocare 4511, ANCARE, Auckland, NZ) in preventing pasture bloat in ruminants grazing or fed freshly harvested alfalfa. Ten cannulated Suffolk wethers were offered freshly harvested alfalfa; five were given a daily intraruminal dose of 40 ml of 50% AEPD (vol/vol) 1 h before feeding, and five (controls) were dosed with water. Viscosity of ruminal fluid was reduced (P < 0.001) in AEPD-treated wethers, relative to the controls, for the first 2 h after feeding but not at 4 h after feeding and beyond. Treatment with AEPD did not affect dry matter (DM) intake, digestibility of DM, acid detergent fiber, or neutral detergent fiber, or N digestion and retention, implying that AEPD likely would not affect milk production. In a crossover grazing study, five of the wethers were given AEPD in drinking water (0.1%, vol/vol); treatment with AEPD was 100% effective for preventing bloat in sheep grazing early-bloom alfalfa for 4 h daily. Replicate grazing studies were conducted with cattle in Lethbridge, AB; Lacombe, AB; and Kamloops, BC. Treated animals received AEPD in the water (0.06%, vol/vol) and grazed vegetative alfalfa for 6 h daily. As it did with sheep, AEPD treatment effectively precluded the bloat observed in control animals. Consequently, AEPD may be a valuable tool for alfalfa pasture-based dairy production although further study is required to develop an integrated model for optimal administration under a variety of climatic conditions.  相似文献   
159.
Summary The properties of RIM-copolyureas formed from a polyether triamine and containing 30 to 70% by weight of MDI/DETDA hard segments (HS) were investigated. As-moulded (mould temperature 115°C) and postcured (200°C/1h) materials were compared using DSC, DMTA and tensile stress-strain measurements. Phase separation ratios (PSR) of as-moulded materials increased from 47 to 56% with increasing HS content. Postcuring increased PSR to 70% for all materials resulting in significant intensification of HS glass transition at TgH (220 to 250°C), and reduced mechanical damping and modulus-temperature dependence between –40 and 200°C. Agreement between experimental tensile moduli and those predicted by appropriate two-phase composite theory has confirmed the co-continuous morphology of these RIM-copolyureas over the entire composition range studied.  相似文献   
160.
A special course for senior psychology majors "… in which one step has been taken in the direction away from the conservative tradition of lecturing and examining" is described. The students' first assignment is to list "… the ten most persistent and pressing problems of personal and social living… " and the second is to "… select the ten concepts, laws, or principles which you believe to be the most significant… ." From these the "… subject matter of the rest of the term is established." There is "… frequent and favorable reaction from students… ." (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号