全文获取类型
收费全文 | 125630篇 |
免费 | 14557篇 |
国内免费 | 8066篇 |
专业分类
电工技术 | 8764篇 |
技术理论 | 6篇 |
综合类 | 10298篇 |
化学工业 | 19102篇 |
金属工艺 | 12219篇 |
机械仪表 | 9943篇 |
建筑科学 | 9804篇 |
矿业工程 | 5487篇 |
能源动力 | 3145篇 |
轻工业 | 12707篇 |
水利工程 | 3519篇 |
石油天然气 | 5999篇 |
武器工业 | 1363篇 |
无线电 | 12117篇 |
一般工业技术 | 14927篇 |
冶金工业 | 6874篇 |
原子能技术 | 1478篇 |
自动化技术 | 10501篇 |
出版年
2024年 | 593篇 |
2023年 | 2053篇 |
2022年 | 3440篇 |
2021年 | 4333篇 |
2020年 | 4765篇 |
2019年 | 4170篇 |
2018年 | 4051篇 |
2017年 | 4842篇 |
2016年 | 5130篇 |
2015年 | 5300篇 |
2014年 | 7631篇 |
2013年 | 7945篇 |
2012年 | 9460篇 |
2011年 | 9616篇 |
2010年 | 6722篇 |
2009年 | 6929篇 |
2008年 | 6364篇 |
2007年 | 8148篇 |
2006年 | 7323篇 |
2005年 | 6125篇 |
2004年 | 5111篇 |
2003年 | 4604篇 |
2002年 | 4015篇 |
2001年 | 3505篇 |
2000年 | 3023篇 |
1999年 | 2500篇 |
1998年 | 1890篇 |
1997年 | 1607篇 |
1996年 | 1417篇 |
1995年 | 1085篇 |
1994年 | 946篇 |
1993年 | 712篇 |
1992年 | 598篇 |
1991年 | 432篇 |
1990年 | 391篇 |
1989年 | 282篇 |
1988年 | 256篇 |
1987年 | 142篇 |
1986年 | 139篇 |
1985年 | 130篇 |
1984年 | 97篇 |
1983年 | 65篇 |
1982年 | 74篇 |
1981年 | 49篇 |
1980年 | 54篇 |
1979年 | 25篇 |
1978年 | 16篇 |
1964年 | 23篇 |
1963年 | 13篇 |
1959年 | 22篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
61.
62.
Porous polyimide (PI) films with low dielectric constants and excellent thermal properties have been a pressing demand for the next generation of high-performance, miniature, and ultrathin microelectronic devices. A series of novel porous PI films containing fluorenyl-adamantane groups were prepared successfully via thermolysis of poly(ethylene glycol) (PEG) added in the PI matrix. The cross-sectional morphologies of porous PI films showed closed pores with diameters ranging from 135 to 158 nm, which were uniform and regular in shape without interconnectivity. These porous PI films exhibited excellent thermal properties with a glass-transition temperature at 376 °C whereas the 5% weight loss temperature in air excess of 405 °C due to enhanced rigidity afforded by fluorenyl-adamantane groups. Accompanied by thermolysis content of PEG increasing from 0 to 20 wt %, the density of porous PI films decreased, and the corresponding porosity grew significantly from 0 to 11.48%. Depending on porosity, the dielectric constant and dielectric loss of porous PI films significantly declined from 2.89 to 2.37 and from 0.050 to 0.021, respectively. These excellent properties benefit the as-prepared porous PI films for application as interlayer dielectrics, integrated circuit chips, or multichip modules in microelectronic fields. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47313. 相似文献
63.
In this article, we study a linear array of bowtie nanoantennas placed between two metallic strips that can work from 800 to 1420 nm (600 nm linewidth), with an electric field enhancement factor close to 20. We study the dynamical change of the position of the electric field enhancement amongst different elements in the array and, at the same time, the effects of dispersion on the scalability of the array elements. A systematic analysis and methodology to produce an array that can operate over a large bandwidth whilst maintaining the electric field enhancement without significant variation is provided. 相似文献
64.
高浓度聚合物驱提高采收率方法实验研究 总被引:3,自引:0,他引:3
为探索一种新的提高原油采收率的方法,在外形尺寸为4.5 cm×4.5 cm×30 cm、气测渗透率0.9~1.0μm2、变异系数为0.72的二维纵向非均质人造岩心上,模拟大庆油田油藏流体性质及温度条件,研究了高浓度聚合物(HPAM)驱注入时机、聚合物相对分子质量、聚合物段塞体积及段塞组合对驱油效果的影响。通过注入大分子量、高浓度聚合物,结合合理的注入方式,在化学剂成本与三元复合驱相当的情况下,采收率比水驱提高20个百分点以上,接近或超过三元复合驱的水平。实验表明,采用高浓度聚合物驱油是一种较好的提高原油采收率的方法。 相似文献
65.
Defects are often present in rolled products, such as wire rod. The market demand for wire rod without any defects has increased. In the final wire rod products, defects originating from steel making, casting, pre‐rolling of billets and during wire rod rolling can appear. In this work, artificial V‐shaped longitudinal surface cracks have been analysed experimentally and by means of FEM. The results indicate that the experiments and FEM calculations show the same tendency except in two cases, where instability due to fairly “round” false round bars disturbed the experiment. FE studies in combination with practical experiments are necessary in order to understand the behaviour of the material flows in the groove and to explain whether the crack will open up as a V‐shape or if it will be closed as an I‐shape. 相似文献
66.
67.
An adaptive numerical dissipation control in a class of high order filter methods for compressible MHD equations is systematically discussed. The filter schemes consist of a divergence-free preserving high order spatial base scheme with a filter approach which can be divergence-free preserving depending on the type of filter operator being used, the method of applying the filter step, and the type of flow problem to be considered. Some of these filter variants provide a natural and efficient way for the minimization of the divergence of the magnetic field (∇·B) numerical error in the sense that commonly used divergence cleaning is not required. Numerical experiments presented emphasize the performance of the ∇·B numerical error. Many levels of grid refinement and detailed comparison of the filter methods with several commonly used compressible MHD shock-capturing schemes will be illustratedA condensed version appears in the Proceedings of the International Conference on High Performance Scientific Computing, March 10-14, 2003, Hanoi, Vietnam. This is a revised version of a longer internal report, Feb. 19, 2004. The longer internal report was published as a RIACS Technical Report TR03.10, July 2003, NASA Ames Research Center 相似文献
68.
四川盆地上三叠统划分对比研究 总被引:36,自引:6,他引:30
四川盆地上三叠统对比长期存在混乱,给盆地整体评价带来困难。通过岩石地层、地震地层、事件地层及高分辨率旋回地层等多种方法讨论了须家河组与香溪群各岩性段的对比关系,得出了全盆地上三叠统的对比关系;指出须四段底可近似看成等时界面;须家河组下部地层自西向东、向南逐层超覆在雷口坡组之上,上部地层在盆地西北部自东南向西北方向剥蚀层位渐次变老。文章建议四川盆地上三叠统废除“香溪群”,统一使用“须家河组”,以利于对全盆地上三叠统进行油气资源整体评价与深化研究。 相似文献
69.
An optoelectronic method is considered for noncontacting reconstruction of the surface profile of three-dimensional objects of large dimensions. The optimal conditions for performing measurements are identified. It is shown that the proposed method, in contrast to the already known methods, does not require fine tuning of the equipment. A numerical method is given for compensating distortions caused by aberrations. A method is described for reconstructing the surface profile cell by cell which increases the accuracy of measurements. 相似文献
70.