全文获取类型
收费全文 | 1886887篇 |
免费 | 55228篇 |
国内免费 | 22114篇 |
专业分类
电工技术 | 54686篇 |
技术理论 | 45篇 |
综合类 | 31228篇 |
化学工业 | 328354篇 |
金属工艺 | 84137篇 |
机械仪表 | 65153篇 |
建筑科学 | 73968篇 |
矿业工程 | 22992篇 |
能源动力 | 59277篇 |
轻工业 | 141892篇 |
水利工程 | 22327篇 |
石油天然气 | 59325篇 |
武器工业 | 2916篇 |
无线电 | 232242篇 |
一般工业技术 | 324877篇 |
冶金工业 | 208869篇 |
原子能技术 | 37435篇 |
自动化技术 | 214506篇 |
出版年
2022年 | 19779篇 |
2021年 | 28847篇 |
2020年 | 21870篇 |
2019年 | 22676篇 |
2018年 | 25022篇 |
2017年 | 25473篇 |
2016年 | 30788篇 |
2015年 | 30644篇 |
2014年 | 45441篇 |
2013年 | 107311篇 |
2012年 | 58191篇 |
2011年 | 72829篇 |
2010年 | 63965篇 |
2009年 | 70879篇 |
2008年 | 65300篇 |
2007年 | 61750篇 |
2006年 | 64604篇 |
2005年 | 56875篇 |
2004年 | 53287篇 |
2003年 | 51935篇 |
2002年 | 50364篇 |
2001年 | 46585篇 |
2000年 | 44772篇 |
1999年 | 44998篇 |
1998年 | 59860篇 |
1997年 | 49783篇 |
1996年 | 44214篇 |
1995年 | 37288篇 |
1994年 | 34165篇 |
1993年 | 32653篇 |
1992年 | 28580篇 |
1991年 | 25488篇 |
1990年 | 25325篇 |
1989年 | 24257篇 |
1988年 | 22730篇 |
1987年 | 20568篇 |
1986年 | 19920篇 |
1985年 | 23144篇 |
1984年 | 22923篇 |
1983年 | 20884篇 |
1982年 | 19670篇 |
1981年 | 19756篇 |
1980年 | 18406篇 |
1979年 | 18895篇 |
1978年 | 18062篇 |
1977年 | 18479篇 |
1976年 | 20755篇 |
1975年 | 16251篇 |
1974年 | 15763篇 |
1973年 | 15827篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
H.C. Weigele L. Gygax A. Steiner B. Wechsler J.-B. Burla 《Journal of dairy science》2018,101(3):2370-2382
Lameness is one of the most prevalent diseases affecting the welfare of cows in modern dairy production. Lameness leads to behavioral changes in severely lame cows, which have been investigated in much detail. For early detection of lameness, knowledge of the effects of moderate lameness on cow behavior is crucial. Therefore, the behavior of nonlame and moderately lame cows was compared on 17 Swiss dairy farms. On each farm, 5 to 11 nonlame (locomotion score 1 of 5) and 2 to 7 moderately lame (locomotion score 3 of 5) cows were selected for data collection in two 48-h periods (A, B) separated by an interval of 6 to 10 wk. Based on visual locomotion scoring, 142 nonlame and 66 moderately lame cows were examined in period A and 128 nonlame and 53 moderately lame cows in period B. Between these 2 periods, the cows underwent corrective hoof trimming. Lying behavior, locomotor activity, and neck activity were recorded by accelerometers (MSR145 data logger, MSR Electronics GmbH, Seuzach, Switzerland), and feeding and rumination behaviors by noseband sensors (RumiWatch halter, ITIN + HOCH GmbH, Liestal, Switzerland). Furthermore, visits to the brush and the concentrate feeder, and the milking order position were recorded. In comparison with nonlame cows, moderately lame cows had a longer lying duration, a longer average lying bout duration, and a greater lateral asymmetry in lying duration. Average locomotor activity, locomotor activity during 1 h after feed delivery or push-ups, and average neck activity were lower in moderately lame cows. Eating time and the number of eating chews (jaw movements) were reduced in moderately lame compared with nonlame cows, whereas no effect of moderate lameness was evident for ruminating time, number of ruminating chews and boluses, and average number of ruminating chews per bolus. Moderately lame cows visited the concentrate feeder and the brush less frequently, and they were further back in the milking order compared with nonlame cows. In conclusion, nonlame and moderately lame cows differed in a biologically relevant way in many of the behavioral variables investigated in this study. Therefore, the use of these behavioral changes seems to be promising to develop a tool for early lameness detection. 相似文献
992.
993.
Roberto C. Dante Pablo Martín-Ramos Pedro Chamorro-Posada Dario Rutto José Vázquez-Cabo Denisse G. Dante 《Fullerenes, Nanotubes and Carbon Nanostructures》2020,28(7):533-540
AbstractIn this work, a new g-C3N4-based Z-scheme with γ-Fe2O3 and β-Ag2Se both n-type semiconductors, and graphite to favor electron exchange is presented. The composite material was studied by XRD, FTIR, UV-Vis, TEM, XPS, TGA, DSC and TOF-SIMS, and the ability of this photocatalytic system to act as a photo-reductant was assessed using crystal violet (CV+) dye. Solar light driven photo-reduction of CV+ in the presence of tri-sodium citrate evidenced a synergistic enhancement of the activity of the composite toward reduction, with ~20 times higher conversion rates per unit of surface area than those of g-C3N4. Photo-oxidation experiments under Xe lamp irradiation in the presence of H2O2 also showed that the AgFeCN composite featured a higher activity (~8×) than g-C3N4. This Z-scheme may deserve further study as a photo-reductant to obtain hydrogen or hydrogenated compounds. Moreover, the use of CV+ may represent a facile procedure that can aid in the selection of new photocatalysts to be used in hydrogen production. 相似文献
995.
热轧态中锰TRIP钢首先经650 ℃退火2 h,随后在550 ℃进行等温时效热处理,采用场发射扫描电镜(FE-SEM)研究该钢中P的偏聚和时效析出行为的变化情况。结果表明,中锰TRIP钢中P在晶界的偏聚是一种非平衡偏聚现象,临界时间约为50 h,与理论计算结果48 h较为吻合。在局部偏聚区域内,C与P存在共偏聚的关系,即P偏聚量高的地方,C含量也高。而合金元素Nb具有抑制P偏聚的效果,在20~70 h时效时间内,可以相对降低6.57%~19.5%的最大P偏聚量。根据电子背散射衍射(EBSD)菊池线分析,P偏聚量低于2.28at%时,P为固溶状态,高于2.28at.%时,P为析出状态。 相似文献
996.
997.
L. S. Belevskii N. V. Koptseva I. V. Belevskaya Yu. Yu. Efimova 《Russian Metallurgy (Metally)》2015,2015(9):753-758
The microstructure and properties of the functional coatings formed by impact friction processing of product surfaces with a flexible tool are studied. It is established that the processing produces a hard nanostructured surface layer with fragments up to 0.13 µm in size, as it is achieved by severe plastic deformation. 相似文献
998.
999.
1000.