全文获取类型
收费全文 | 141073篇 |
免费 | 20958篇 |
国内免费 | 3274篇 |
专业分类
电工技术 | 5496篇 |
技术理论 | 9篇 |
综合类 | 5278篇 |
化学工业 | 34790篇 |
金属工艺 | 5283篇 |
机械仪表 | 6637篇 |
建筑科学 | 9473篇 |
矿业工程 | 2159篇 |
能源动力 | 3848篇 |
轻工业 | 13667篇 |
水利工程 | 1973篇 |
石油天然气 | 4691篇 |
武器工业 | 516篇 |
无线电 | 19140篇 |
一般工业技术 | 24427篇 |
冶金工业 | 8809篇 |
原子能技术 | 1003篇 |
自动化技术 | 18106篇 |
出版年
2024年 | 272篇 |
2023年 | 1336篇 |
2022年 | 2325篇 |
2021年 | 3681篇 |
2020年 | 3858篇 |
2019年 | 5241篇 |
2018年 | 5430篇 |
2017年 | 6020篇 |
2016年 | 6340篇 |
2015年 | 6977篇 |
2014年 | 8128篇 |
2013年 | 10657篇 |
2012年 | 8526篇 |
2011年 | 8638篇 |
2010年 | 8064篇 |
2009年 | 7833篇 |
2008年 | 7140篇 |
2007年 | 6994篇 |
2006年 | 6897篇 |
2005年 | 6041篇 |
2004年 | 4724篇 |
2003年 | 4753篇 |
2002年 | 4748篇 |
2001年 | 4227篇 |
2000年 | 3917篇 |
1999年 | 3534篇 |
1998年 | 3732篇 |
1997年 | 2756篇 |
1996年 | 2375篇 |
1995年 | 1868篇 |
1994年 | 1534篇 |
1993年 | 1232篇 |
1992年 | 850篇 |
1991年 | 700篇 |
1990年 | 556篇 |
1989年 | 500篇 |
1988年 | 443篇 |
1987年 | 281篇 |
1986年 | 272篇 |
1985年 | 256篇 |
1984年 | 177篇 |
1983年 | 152篇 |
1982年 | 139篇 |
1981年 | 154篇 |
1980年 | 136篇 |
1979年 | 93篇 |
1977年 | 134篇 |
1976年 | 208篇 |
1975年 | 66篇 |
1973年 | 63篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
Recent experiments have shown that metallic materials display significant size effects when the characteristic length scale of non-uniform plastic deformation is close to a micron. Couple stress plasticity has been developed to explain such phenomena by Fleck and Hutchinson. The mechanical behaviors of ultra-thin nickel beams in different boundary conditions were studied with the hybrid element developed for couple stress plasticity before. Strong scale effects are found when the beam's thickness is close to the material characteristic length scale. Such phenomena will disappear if the beam' s thickness is greatly larger than the material characteristic length scale. The scale effect is the beams inherent property and it does not change with the change of support conditions. 相似文献
982.
983.
984.
985.
黄亚斌 《石油化工管理干部学院学报》2003,(1):9-11
多数国有大中型企业实行公司化改制后经营状况依然不佳,直接原因在于公司的治理存在严重的问题和缺陷。规范的公司治理结构能有效缓解代理问题。国有企业的产权残缺性,使公司治理结构中的直接监督和间接监督等有效手段不能充分发挥。通过股权结构的分散化调整,充分发挥非国有股权所有者的作用,建立有效的公司治理结构。 相似文献
986.
聚烯烃/纳米SiO2复合材料研究进展 总被引:4,自引:0,他引:4
论述了纳米SiO2的表面处理方法、复合材料的制备技术及其力学和光学性能。表明纳米SiO2分散于聚烯烃(PP、HDPE)中,可以提高基体的韧性、强度和模量。以纳米SiO2作为填料的聚乙烯棚膜,呈现优良的红外线吸收性能和可见光透过性能。为此,纳米SiO2可作为一种聚乙烯农膜的新型保温剂。 相似文献
987.
Comparative Study of Models on Confinement of Concrete Cylinders with Fiber-Reinforced Polymer Composites 总被引:4,自引:0,他引:4
The use of fiber-reinforced polymer (FRP) composites for strengthening and/or rehabilitation of concrete structures is gaining increasing popularity in the civil engineering community. One of the most attractive applications of FRP materials is their use as confining devices for concrete columns, which may result in remarkable increases of strength and ductility as indicated by numerous published experimental results. Despite a large research effort, a proper analytical tool to predict the behavior of FRP-confined concrete has not yet been established. Most of the available models are empirical in nature and have been calibrated against their own sets of experimental data. On the other hand, the experimental results available in the literature encompass a wide range of values of the significant variables. The objective of this work is a systematic assessment of the performance of the existing models on confinement of concrete columns with FRP materials. The study is conducted in the following steps: the experimental data on confinement of concrete cylinders with FRP available in the technical literature are classified according to the values of the significant variables; the existing empirical and analytical models are reviewed, pointing out their distinct features; the whole set of available experimental results is compared with the whole set of analytical models; and strengths and weaknesses of the various models are analyzed. Finally, a new equation is proposed to evaluate the axial strain at peak stress of FRP-confined concrete cylinders. 相似文献
988.
989.
Feng‐Ge Wu Fu‐Chun Sun Ke Yu Chang‐Wen Zheng 《International Journal of Satellite Communications and Networking》2005,23(6):359-371
How to evaluate the performance of satellite networks is a prerequisite to the construction of satellite networks, and is also one of challenges in the researches on satellite networks. In this paper, generalized stochastic Petri net (GSPN) models are presented to carry out the performance analysis of a double‐layered satellite network. Firstly, the GSPN model of a double‐layered satellite network is simplified by proper analysis. Then, two sets of experiments are conducted to analyse the performance of the satellite networks, and show that the double‐layered satellite network outperforms single‐layered ones on the heavy traffic load. Finally, the feasibility and effectiveness of the proposed approach is verified by simulation experiments. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
990.
D. Surek Prof. Dr.‐Ing. habil. 《真空研究与实践》2007,19(3):32-36
Helium leak test devices for the quality inspection of housings for vacuum compressors The well‐known and wide‐spread helium leak test method is a safe and fast quality testing method for construction units of any kind. Due to its safe examination and the short time of examination it is predominantly inserted into automated production lines as e.g. in the automobile supporting industry up to the examination by Airbags and rims of wheel. Likewise in addition, for the construction units, machines and devices of the vacuum engineering. From this the demand results simple and in particular economical devices for the helium leak test of construction units with small numbers of items of under 200 pieces per day. For these manufacturing profiles economical ways for the helium leak test are pointed out. 相似文献