全文获取类型
收费全文 | 923篇 |
免费 | 21篇 |
国内免费 | 7篇 |
专业分类
电工技术 | 15篇 |
综合类 | 2篇 |
化学工业 | 147篇 |
金属工艺 | 9篇 |
机械仪表 | 15篇 |
建筑科学 | 42篇 |
矿业工程 | 4篇 |
能源动力 | 22篇 |
轻工业 | 60篇 |
水利工程 | 15篇 |
石油天然气 | 5篇 |
武器工业 | 1篇 |
无线电 | 40篇 |
一般工业技术 | 147篇 |
冶金工业 | 311篇 |
原子能技术 | 2篇 |
自动化技术 | 114篇 |
出版年
2022年 | 4篇 |
2021年 | 21篇 |
2020年 | 11篇 |
2019年 | 17篇 |
2018年 | 18篇 |
2017年 | 5篇 |
2016年 | 17篇 |
2015年 | 17篇 |
2014年 | 11篇 |
2013年 | 63篇 |
2012年 | 51篇 |
2011年 | 60篇 |
2010年 | 57篇 |
2009年 | 54篇 |
2008年 | 46篇 |
2007年 | 59篇 |
2006年 | 48篇 |
2005年 | 41篇 |
2004年 | 35篇 |
2003年 | 34篇 |
2002年 | 26篇 |
2001年 | 10篇 |
2000年 | 12篇 |
1999年 | 15篇 |
1998年 | 34篇 |
1997年 | 28篇 |
1996年 | 17篇 |
1995年 | 14篇 |
1994年 | 15篇 |
1993年 | 13篇 |
1992年 | 16篇 |
1991年 | 4篇 |
1990年 | 6篇 |
1989年 | 7篇 |
1988年 | 5篇 |
1987年 | 10篇 |
1986年 | 8篇 |
1985年 | 2篇 |
1984年 | 6篇 |
1983年 | 6篇 |
1982年 | 4篇 |
1981年 | 4篇 |
1980年 | 2篇 |
1978年 | 2篇 |
1976年 | 3篇 |
1975年 | 3篇 |
1974年 | 2篇 |
1960年 | 1篇 |
1955年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有951条查询结果,搜索用时 397 毫秒
171.
Mohammad Karkhaneh Brian H. Rowe L. Duncan Saunders Don C. Voaklander Brent E. Hagel 《Accident; analysis and prevention》2013
Background
Bicycling related head injuries (HIs) can be severe. Helmet use reduces head injury risk; however, there are few controlled studies of the effect of helmet legislation. We conducted this study to investigate changes in HIs after bicycle helmet legislation targeting those <18 in Alberta, Canada in 2002.Methods
Bicyclist and pedestrian (control) HI rates and HIs as a proportion of all injuries were compared for the three years (1999–2001) before and four years (2003–2006) after bicycle helmet legislation in three age groups (children: <13, adolescents: 13–17, and adults: 18+).Results
There were 41,270 ED visits and 2782 hospitalizations for bicyclists and 9836 ED visits and 2029 hospitalizations for pedestrians (excluding the legislation year 2002). The rate of ED HIs declined for child bicyclists and child pedestrians, while the rate of non-HIs declined in adult bicyclists and child pedestrians. The rate of hospitalized HIs declined in child bicyclists and all ages of pedestrians while non-HI rates declined for child and adult pedestrians. Non-HI rates for adolescent and adult bicyclists increased. After adjusting for sex and location, the proportion of ED bicycle HIs declined by 9% (APR = 0.91; 95% CI: 0.86, 0.95) in children, was unchanged among adolescents and increased in adults (APR = 1.08; 95% CI: 1.01, 1.15). The proportion of bicycle HI related hospitalizations decreased by 30% (APR = 0.70; 95% CI: 0.55, 0.90) in children, 36% (APR = 0.64; 95% CI: 0.49, 0.84) in adolescents and 24% (APR = 0.76; 95% CI: 0.63, 0.91) in adults. There were no observed changes in the proportion of pedestrian HIs resulting in ED visits or hospitalizations.Interpretation
Our data indicate significant declines in the proportion of child bicyclist ED HIs and child, adolescent and adult bicyclist HI hospitalizations. This is in contrast to no significant trends in the proportion of ED or hospitalized HIs among pedestrians and the unexpected increases in the proportion of ED HIs for adult bicyclists. Comparing bicyclist and pedestrian trends in the proportion of child and adolescent HIs suggests a bicycle helmet legislation effect. 相似文献172.
Harish K. Patney Christina Nordlund Adam Moy Harry Rose Brent Young Michael A. Wilson 《Fullerenes, Nanotubes and Carbon Nanostructures》2013,21(6):941-971
Abstract Graphite has normally been used to synthesise fullerenes and nanotubes. However, coal is a cheaper and more suitable industrial material. Because coal is a molecular solid, unlike graphite, the mechanism by which fullerene and nanotubes are formed is different. Moreover, other products such as polyaromatic hydrocarbons (PAHs) and microfibres are also formed. In this review, the mechanism of formation of fullerene and nanotubes from coal is discussed. It is shown that the pathway involved is other than through the C1 intermediate route. The influence of other elements in coal such as hydrogen, oxygen, sulfur and iron is also discussed. It appears that, hydrogen, oxygen, iron and sulfur affect the yield and type of fullerenes and nanotubes formed. 相似文献
173.
Jon Scott Michael Miles David Fullwood Brent Adams Ali Khosravani Raja K. Mishra 《Metallurgical and Materials Transactions A》2013,44(1):512-516
Failure mechanisms were studied in wrought AZ31B magnesium alloy after forming under different strain paths. Optical micrographs were used to observe the shear band formation and regions of high twin density in samples strained under uniaxial, biaxial, and plane strain conditions. Interrupted testing at 4?pct effective strain increments, until failure, was used to observe the evolution of the microstructure. The results showed that shear bands, with a high percentage of twinned grains, appeared early in the samples strained under biaxial or plane strain tension. These bands are similar to those seen in uniaxial tension specimens just prior to failure where the uniaxial tensile ductility was much greater than that observed for plane strain or biaxial tension conditions. A forming limit diagram for AZ31B, which was developed from the strain data, showed that plane strain and biaxial tension had very similar limit strains; this contrasts with materials like steel or aluminum alloys, which typically have greater ductility in biaxial tension compared to plane strain tension. 相似文献
174.
Microstructures and Mechanical Properties of Ti6Al4V Parts Fabricated by Selective Laser Melting and Electron Beam Melting 总被引:1,自引:0,他引:1
H. K. Rafi N. V. Karthik Haijun Gong Thomas L. Starr Brent E. Stucker 《Journal of Materials Engineering and Performance》2013,22(12):3872-3883
This work compares two metal additive manufacturing processes, selective laser melting (SLM) and electron beam melting (EBM), based on microstructural and mechanical property evaluation of Ti6Al4V parts produced by these two processes. Tensile and fatigue bars conforming to ASTM standards were fabricated using Ti6Al4V ELI grade material. Microstructural evolution was studied using optical and scanning electron microscopy. Tensile and fatigue tests were carried out to understand mechanical properties and to correlate them with the corresponding microstructure. The results show differences in microstructural evolution between SLM and EBM processed Ti6Al4V and their influence on mechanical properties. The microstructure of SLM processed parts were composed of an α′ martensitic phase, whereas the EBM processed parts contain primarily α and a small amount of β phase. Consequently, there are differences in tensile and fatigue properties between SLM- and EBM-produced Ti6Al4V parts. The differences are related to the cooling rates experienced as a consequence of the processing conditions associated with SLM and EBM processes. 相似文献
175.
Karkhaneh M Naghavi M Rowe BH Hagel BE Jafari N Saunders LD 《Accident; analysis and prevention》2008,40(1):192-199
Bicyclists are vulnerable road users for severe injury all over the world. The nature and extent of such injuries are less well known in Iran. Using data from a comprehensive survey conducted by the Ministry of Health and Medical Education in 13 health divisions of Iran, in 2003, we examined circumstances around bicyclist injury and death. Trained health workers completed the survey instruments by interviewing patients who stayed more than 24h in hospitals and/or relatives, hospital personnel and by reviewing patient charts. Data were cross-matched with medico-legal documents to prevent missing deaths. The information that was collected from 64 cities/towns' emergency departments (EDs), over the study period, showed that 440 injured cyclists were hospitalized and/or died due to traffic collisions. Most injuries occurred in males (94.8%) and in the young (median age: 14 years with 75% =18 years). Head injury occurred in 14% of all hospitalized and in 90% of fatally injured bicyclists. Striking a moving vehicle increased the odds of death (OR: 32.3; 95% CI 3.5-291.0) as well as the odds of severe injury (OR: 1.9; 95% CI 1.2-3.2) compared with other mechanisms of injury. As a conclusion, bicyclists in Iran, particularly males and young children, are vulnerable to severe injury and death when struck by moving vehicles on highways. 相似文献
176.
177.
Tianfu Wang Yomaira J. Pagán-Torres Elliot J. Combs James A. Dumesic Brent H. Shanks 《Topics in Catalysis》2012,55(7-10):657-662
Water-compatible lanthanide-based Lewis acids for the efficient conversion of glucose and other carbohydrates to produce 5-hydroxymethylfurfural (HMF) were demonstrated in a biphasic reactor using sec-butyl phenol as the extracting solvent. The reaction of glucose dehydration to HMF was found to proceed under near-neutral conditions (pH?=?5.5) and a moderately high yield of 42?mol?% could be obtained. The combined catalytic system also showed effectiveness to convert other polysaccharides to HMF. Furthermore, the aqueous phase was recycled and used for multiple times without significant loss of catalytic performance. 相似文献
178.
M Aslam S Checkley B Avery G Chalmers V Bohaychuk G Gensler R Reid-Smith P Boerlin 《Food microbiology》2012,32(1):110-117
This study determined the prevalence of Salmonella serovars, antimicrobial resistance (AMR) and resistance genes in Salmonella isolated from retail meats purchased in Alberta, Canada. Samples were collected during one year period (May 2007–April 2008) on weekly basis from 19 census divisions in Alberta. A total of 564 samples including chicken (n = 206), turkey (n = 91), beef (n = 134) and pork (n = 133) were purchased. Salmonella were recovered from chicken (40%), turkey (27%) and pork (2%) samples and was not found in ground beef. A total of 21, 8, and 3 different serovars were recovered from chicken, turkey and pork meats, respectively. Salmonella Hadar was most common in chicken whereas S. Heidelberg was common in turkey meat. Overall 29% (32/110) of isolates were susceptible to tested antimicrobials and resistance to ciprofloxacin, amikacin and nalidixic acid was not found in any isolate. Multiresistance (≥2 antimicrobials) was found in 56% of isolates. Resistance to amoxicillin–clavulanic acid (AMC), ceftiofur (TIO), and ceftriaxone (CRO) was found in about 21% of chicken and 25% of turkey isolates. Resistance to either of tetracycline (TET), streptomycin (STR) or ampicillin (AMP) was unconditionally associated with S. Hadar but resistance to either of TET, AMP, AMC, TIO, CRO or cefoxitin was associated with S. Heidelberg. The strA/B (42% isolates), tet(A) (28% isolates), blaCMY-2 (21% isolates) and blaTEM (17% isolates) were the most common resistance genes found. The blaCMY-2 and blaTEM genes were unconditionally associated with S. Heidelberg; tet(A) and strA/B with S. Hadar and tet(B) gene with S. Kentucky. The strA/B genes were not associated with S. Heidelberg. Our data suggests that the prevalence of Salmonella serovars varied by the meat type and that AMR and resistance genes varied by the Salmonella serovars. 相似文献
179.
Pautler BG Woods GC Dubnick A Simpson AJ Sharp MJ Fitzsimons SJ Simpson MJ 《Environmental science & technology》2012,46(7):3753-3761
Glaciers and ice sheets are the second largest freshwater reservoir in the global hydrologic cycle, and the onset of global climate warming has necessitated an assessment of their contributions to sea-level rise and the potential release of nutrients to nearby aquatic environments. In particular, the release of dissolved organic matter (DOM) from glacier melt could stimulate microbial activity in both glacial ecosystems and adjacent watersheds, but this would largely depend on the composition of the material released. Using fluorescence and (1)H NMR spectroscopy, we characterize DOM at its natural abundance in unaltered samples from a number of glaciers that differ in geographic location, thermal regime, and sample depth. Parallel factor analysis (PARAFAC) modeling of DOM fluorophores identifies components in the ice that are predominantly proteinaceous in character, while (1)H NMR spectroscopy reveals a mixture of small molecules that likely originate from native microbes. Spectrofluorescence also reveals a terrestrial contribution that was below the detection limits of NMR; however, (1)H nuclei from levoglucosan was identified in Arctic glacier ice samples. This study suggests that the bulk of the DOM from these glaciers is a mixture of biologically labile molecules derived from microbes. 相似文献
180.
Colloid transport in dolomite rock fractures: effects of fracture characteristics, specific discharge, and ionic strength 总被引:1,自引:0,他引:1
The effects of fracture characteristics, specific discharge, and ionic strength on microsphere transport in variable-aperture dolomite rock fractures were studied in a laboratory-scale system. Fractures with different aperture distributions and mineral compositions were artificially created in two dolomite rock blocks. Transport tests were conducted with bromide and carboxylate-modified latex microspheres (20, 200, and 500 nm diameter). Under overall unfavorable attachment conditions, there was significant retention of the 20 nm microsphere and minimal retention of the 500 nm microsphere for all conditions examined. Aperture variability produced significant spatial variation in colloid transport. Flushing with low ionic strength solution (1 mM) following microsphere transport at 12 mM ionic strength solution produced a spike in effluent microsphere concentrations, consistent with retention of colloids in secondary energy minima. Surface roughness and charge heterogeneity effects may have also contributed to the effect of microsphere size on retention. Matrix diffusion influenced bromide transport but was not a dominant factor in transport for any microsphere size. Calibrated one-dimensional, two-site kinetic model parameters for colloid transport in fractured dolomite were sensitive to the physical and chemical properties of both the fractured dolomite and the colloids, indicating the need for mechanistic modeling for accurate prediction. 相似文献