全文获取类型
收费全文 | 4785篇 |
免费 | 447篇 |
国内免费 | 13篇 |
专业分类
电工技术 | 2篇 |
综合类 | 263篇 |
化学工业 | 567篇 |
金属工艺 | 5篇 |
机械仪表 | 11篇 |
建筑科学 | 16篇 |
矿业工程 | 2篇 |
能源动力 | 4篇 |
轻工业 | 4236篇 |
水利工程 | 2篇 |
石油天然气 | 17篇 |
无线电 | 3篇 |
一般工业技术 | 109篇 |
冶金工业 | 1篇 |
原子能技术 | 1篇 |
自动化技术 | 6篇 |
出版年
2024年 | 46篇 |
2023年 | 84篇 |
2022年 | 156篇 |
2021年 | 187篇 |
2020年 | 215篇 |
2019年 | 189篇 |
2018年 | 141篇 |
2017年 | 162篇 |
2016年 | 175篇 |
2015年 | 182篇 |
2014年 | 215篇 |
2013年 | 262篇 |
2012年 | 315篇 |
2011年 | 346篇 |
2010年 | 213篇 |
2009年 | 182篇 |
2008年 | 206篇 |
2007年 | 269篇 |
2006年 | 316篇 |
2005年 | 265篇 |
2004年 | 214篇 |
2003年 | 178篇 |
2002年 | 134篇 |
2001年 | 84篇 |
2000年 | 80篇 |
1999年 | 61篇 |
1998年 | 60篇 |
1997年 | 42篇 |
1996年 | 27篇 |
1995年 | 32篇 |
1994年 | 37篇 |
1993年 | 40篇 |
1992年 | 30篇 |
1991年 | 27篇 |
1990年 | 21篇 |
1989年 | 8篇 |
1988年 | 11篇 |
1987年 | 11篇 |
1986年 | 2篇 |
1985年 | 6篇 |
1984年 | 3篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 8篇 |
1973年 | 1篇 |
排序方式: 共有5245条查询结果,搜索用时 31 毫秒
61.
Food shortage experienced by juvenile insects affects adult morphology and life-history traits. Developmental plasticity and trade-off between ecological and sexual traits helps maximise individual fitness. Ephestia kuehniella were reared at different larval densities to investigate phenotypic shifts in adult males. Variation in ecological traits (sizes of forewing, head and thorax and adult longevity) and sexual traits (valva and aedeagus, sperm number, mating frequency) were compared. Males that emerged from highest density population (800) had lower body mass and small forewings, head and thorax, suggesting that they could not completely compensate for food shortage. The allometric relationship between body mass and forewing length also changed, and these males had relatively longer wings. This arrangement may enhance dispersal and assist in mate-searching at higher densities. Males from all larval densities achieved similar mating frequency but those from higher density produced fewer eupyrene sperm and had shorter adult lifespan. By mating more frequently and maintaining apyrene sperm production, males increase their reproductive success at sperm competition observed at higher densities. Food stress associated with high density populations did not affect valva and aedeagus size indicating that these traits may be insensitive to external environmental changes because they incur fitness costs to males. 相似文献
62.
63.
64.
A novel adhesive that is solely based on natural materials of defatted soy flour (SF) and magnesium oxide (MgO) has been investigated for preparation of five‐ply plywood panels. The resulting plywood panels met the industrial water‐resistant requirement for interior plywood. In this study, mechanisms by which an aqueous mixture of SF and MgO served as a strong and water‐resistant adhesive for bonding wood were investigated. SF was first fractionated into soy protein isolates (SPI), a water‐soluble fraction, and insoluble carbohydrates (ICs) that were mixed with MgO, respectively, for preparation of maple laminates. The water resistance of the resulting maple laminates was evaluated by a three‐cycle water‐soaking‐and‐drying (WSAD) test and a two‐cycle boiling‐water test (BWT). The mixture of MgO and the soluble fraction was not able to bond maple veneers together. The shear strengths of the resulting maple laminates before and after WSAD and BWT all had the following order: MgO–SPI > MgO–SF > SF only > MgO–IC. The water solubility of SF in the heat‐cured SF–MgO mixture was much lower than that of the heat‐cured SF. We believe that the low water solubility of SF–MgO and close interactions between MgO and soy proteins instead of soy carbohydrates were responsible for the superior strengths and high water resistance of the soy‐MgO adhesive. 相似文献
65.
加入HDPE-g-MAH、CG-8831和KH-550制备HDPE/木粉改性复合材料。研究其长效吸水性,发现吸水率随时间延长先快速增加,浸水35 d后缓慢增至平衡,HDPE-g-MAH改性效果最好,其饱和吸水率仅为1.503%。利用Fick第二扩散定律拟合吸水动力学曲线,得扩散系数D的顺序:HDPE-g-MAH增容HDPE/木粉复合材料HDPE/木粉复合材料KH-550改性HDPE/木粉复合材料CG-8831改性HDPE/木粉复合材料。并证明该吸水过程符合Fick第二扩散定律,相关系数R2值达0.99以上。HDPE/木粉改性复合材料尺寸变化系数CDCWCT。 相似文献
66.
67.
68.
69.
70.