全文获取类型
收费全文 | 269338篇 |
免费 | 33830篇 |
国内免费 | 28023篇 |
专业分类
电工技术 | 27207篇 |
技术理论 | 9篇 |
综合类 | 20489篇 |
化学工业 | 49939篇 |
金属工艺 | 14422篇 |
机械仪表 | 20186篇 |
建筑科学 | 12563篇 |
矿业工程 | 5223篇 |
能源动力 | 8386篇 |
轻工业 | 20392篇 |
水利工程 | 4459篇 |
石油天然气 | 7110篇 |
武器工业 | 2870篇 |
无线电 | 40297篇 |
一般工业技术 | 30642篇 |
冶金工业 | 7165篇 |
原子能技术 | 4023篇 |
自动化技术 | 55809篇 |
出版年
2024年 | 1009篇 |
2023年 | 4388篇 |
2022年 | 7125篇 |
2021年 | 9573篇 |
2020年 | 9346篇 |
2019年 | 8376篇 |
2018年 | 7811篇 |
2017年 | 10476篇 |
2016年 | 11424篇 |
2015年 | 13029篇 |
2014年 | 14115篇 |
2013年 | 17847篇 |
2012年 | 20612篇 |
2011年 | 22694篇 |
2010年 | 16455篇 |
2009年 | 16252篇 |
2008年 | 17279篇 |
2007年 | 19745篇 |
2006年 | 18525篇 |
2005年 | 15655篇 |
2004年 | 13105篇 |
2003年 | 10593篇 |
2002年 | 8410篇 |
2001年 | 6561篇 |
2000年 | 5530篇 |
1999年 | 4635篇 |
1998年 | 3793篇 |
1997年 | 3112篇 |
1996年 | 2576篇 |
1995年 | 2091篇 |
1994年 | 1855篇 |
1993年 | 1404篇 |
1992年 | 1117篇 |
1991年 | 880篇 |
1990年 | 772篇 |
1989年 | 537篇 |
1988年 | 439篇 |
1987年 | 266篇 |
1986年 | 263篇 |
1985年 | 299篇 |
1984年 | 270篇 |
1983年 | 189篇 |
1982年 | 246篇 |
1981年 | 114篇 |
1980年 | 124篇 |
1979年 | 47篇 |
1978年 | 20篇 |
1977年 | 25篇 |
1959年 | 29篇 |
1957年 | 18篇 |
排序方式: 共有10000条查询结果,搜索用时 243 毫秒
991.
The effects of glycol methacrylate as a dehydrating agent on the dimensional changes of liver tissue
The dimensional changes of liver sections during the course of processing with glycol methacrylate (GMA) or with ethanol are described. Tissue processing with ethanol served as a control. During prolonged processing steps (24 h each), linear shrinkage of tissue specimens dehydrated with GMA at room temperature was 13.2%. Subsequent infiltration with GMA resulted in trivial swelling, and polymerization in slight shrinkage (2.3%). In comparison, processing with cold GMA resulted in shrinkage during dehydration (about 10.8%), a slight swelling in pure GMA, followed by shrinkage during polymerization (2.2%). Short routine processing schedules resulted in similar shrinkage/swelling patterns, although precise values differed slightly. In all experiments, ethanolic dehydration resulted in smaller dimensional tissue changes than did GMA dehydration. The dimensional changes of tissue sections during stretching on water, mounting and drying compensated for the major part of the shrinkage manifested during processing. 相似文献
992.
K. Y. Cheah T. S. Tang Fujio Mizukami Shu-ichi Niwa Makoto Toba Y. M. Choo 《Journal of the American Oil Chemists' Society》1992,69(5):410-416
A new catalyst, ruthenium-tin-alumina is found to selectively hydrogenate oleic acid to 9-octadecen-1-ol (oleyl + elaidyl
alcohol) at low pressure with high yield. Catalyst preparation methods, catalyst raw materials and activation conditions have
a significant effect on the activity of the catalyst. The optimum atomic ratio of ruthenium to tin is about 1:2. Catalyst
prepared by an improved sol-gel method shows higher activity and selectivity than catalysts prepared by impregnation and coprecipitation
methods. Chloride is found to have a negative effect on catalytic activity. The best catalyst is prepared from chloride-free
ruthenium and tin raw materials. Under the optimum reaction conditions of 250°C and 5.6 MPa, the selectivities for 9-octadecen-1-ol
and total alcohol (9-octadecen-1-ol + stearyl alcohol) formation are 80.9% and 97%, respectively, at a conversion of 81.3%. 相似文献
993.
电力系统微机型产品的电磁兼容设计 总被引:2,自引:1,他引:1
从分析电力系统中电磁干扰的来源、传输途径入手,对应用于电力系统的微机型产品设计中的电磁兼容问题进行了较为系统的探讨,并提出了行有效的解决措施。 相似文献
994.
本文利用矩量法和广义散射矩阵理论分析了多层频率选择表面的散射特性。通过引入广义波导概念,可以统一分析单元形状为任意的多层频率选择表面。作为示例,计算了几种不同结构频率选择表面的散射特性,结果与文献中给出的数据相符。 相似文献
995.
996.
997.
998.
999.
J. Gegner Priv.‐Doz. Dr. W. Nierlich M. Brückner 《Materialwissenschaft und Werkstofftechnik》2007,38(8):613-623
Due to clearly distinguishable damage symptoms, it is differentiated between the surface and sub‐surface failure mode of rolling bearings. Material states red out by X‐ray diffraction (XRD) residual stress measurements point to a variety of loading conditions especially at raceway surfaces that are associated with several competing failure mechanisms. The corresponding lifetime reduction can range from the lower fatigue strength region to material ratcheting in extreme cases. Relevant position of the microstructural changes and nature of the failure mechanisms are characterized. The time alteration of the XRD material parameters measured at or near the surface and at the depth of the maximum equivalent stress correlates, in a different manner, with the statistical parameter of the 10 % bearing life. Both failure modes are illustrated by concrete examples. Contaminated lubricant and boundary lubrication, which represent practically important surface‐induced failures, are discussed in more detail. Gray staining, i.e. shallow pitting, often occurs without distinct indication of global material aging by means of XRD characteristics. Here, scanning electron microscopy observations and electron microprobe analyses point to corrosion fatigue as acting surface failure mechanism. The interaction between material and lubricant under complex loading regimes particularly of mixed friction and corrosion opens further failure research areas in the field of tribology. 相似文献
1000.