全文获取类型
收费全文 | 507179篇 |
免费 | 5573篇 |
国内免费 | 1532篇 |
专业分类
电工技术 | 9252篇 |
综合类 | 341篇 |
化学工业 | 76194篇 |
金属工艺 | 19888篇 |
机械仪表 | 15065篇 |
建筑科学 | 12272篇 |
矿业工程 | 2536篇 |
能源动力 | 13155篇 |
轻工业 | 43607篇 |
水利工程 | 5078篇 |
石油天然气 | 9488篇 |
武器工业 | 27篇 |
无线电 | 61480篇 |
一般工业技术 | 99391篇 |
冶金工业 | 95539篇 |
原子能技术 | 11461篇 |
自动化技术 | 39510篇 |
出版年
2021年 | 4023篇 |
2019年 | 3637篇 |
2018年 | 6445篇 |
2017年 | 6410篇 |
2016年 | 6799篇 |
2015年 | 4415篇 |
2014年 | 7644篇 |
2013年 | 22141篇 |
2012年 | 12163篇 |
2011年 | 16661篇 |
2010年 | 13571篇 |
2009年 | 15493篇 |
2008年 | 16143篇 |
2007年 | 16004篇 |
2006年 | 14213篇 |
2005年 | 12884篇 |
2004年 | 12179篇 |
2003年 | 12206篇 |
2002年 | 11774篇 |
2001年 | 12159篇 |
2000年 | 11312篇 |
1999年 | 11828篇 |
1998年 | 29729篇 |
1997年 | 21311篇 |
1996年 | 16425篇 |
1995年 | 12397篇 |
1994年 | 11183篇 |
1993年 | 10962篇 |
1992年 | 8074篇 |
1991年 | 7872篇 |
1990年 | 7625篇 |
1989年 | 7457篇 |
1988年 | 7273篇 |
1987年 | 6209篇 |
1986年 | 6180篇 |
1985年 | 6936篇 |
1984年 | 6464篇 |
1983年 | 6061篇 |
1982年 | 5714篇 |
1981年 | 5737篇 |
1980年 | 5529篇 |
1979年 | 5303篇 |
1978年 | 5196篇 |
1977年 | 6166篇 |
1976年 | 8171篇 |
1975年 | 4618篇 |
1974年 | 4428篇 |
1973年 | 4413篇 |
1972年 | 3829篇 |
1971年 | 3436篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
The catalytic activities of alumina prepared from an Al alkoxide-amine adduct monomer for the reaction of cyclopentene oxide with piperidine was determined after various pretreatments, including calcination and exposure to moisture. They were compared with the activity of alumina prepared by the conventional hydrolysis method. It was found that the as-prepared sample from the alkoxide-amine monomer preparation was five times more active than a conventional preparation, suggesting that it has a higher density of surface Lewis acid sites. However, its activity was much more severely suppressed by exposure to moisture. 相似文献
32.
This paper describes techniques for the on-chip measurement of high-frequency and/or high-bandwidth electrical phenomena in ultra large-scale integration environments. The techniques rely on the integration of multiple compact and robust electronic test devices, or cores, at various locations within an integrated circuit. The cores consist primarily of signal generators that approximate the output of a sigma-delta modulator using finite repetitious bit patterns and a small set of highly robust analog components. They are capable of digitizing on-chip signals at gigahertz rates even using low-cost manufacturing processes. Simple communication between the multiple cores enables the migration of many "board-level" type measurements down to the chip level. 相似文献
33.
34.
35.
36.
37.
The present work deals with the modelling of damage behaviour for sheet moulding compound (SMC) composite materials using a finite element analysis package. Specifically, a comparison is made between the results obtained experimentally for a three-point bending test, and those obtained from numerical simulation using a material model already implemented. The simulation has been performed for the material models available within the PAM-CRASH software. The simulation results are compared and validated with respect to experimentation. 相似文献
38.
The Boundary Element Method (BEM) incorporating the Embedded Cell Approach (ECA) has been used to analyse the effects of constituent material properties, fibre spatial distribution and microcrack damage on the localised behaviour of transversely fractured, unidirectional fibre-reinforced composites. Three specific composites, i.e., glass fibre reinforced polyester, carbon fibre reinforced epoxy and a glass-carbon hybrid, are considered. The geometrical structures examined were perfectly periodic, uniformly spaced fibre arrangements in square and hexagonal embedded cells. In addition, numerical simulations were also conducted using embedded cells containing randomly distributed fibres. The models involve both elastic fibres and matrix, with the interfaces between the different phases being fully bonded. The results indicate that the constituent material properties (two phase composite) and spatial distribution have a significant effect on the localised stress distributions around the primary crack tip. However, the strain energy release rate associated with crack propagation is predominantly influenced by the material composition. The three-phase hybrid composite exhibited an apparent intermediate fracture toughness value, compared to the all-glass and all-carbon models. Furthermore, the strain energy release rate for the macrocrack lowers as it enters a zone of localised damage (microcracking). The presence of microcracks relaxes the stress field, which can result in a significant reduction in the energetics of the primary crack. 相似文献
39.
Yu. V. Baldokhin V. V. Vavilova P. Ya. Kolotyrkin Yu. K. Kovneristyi N. A. Palii A. S. Solomatin 《Inorganic Materials》2003,39(6):562-567
Mössbauer effect measurements and physicochemical analysis demonstrate that annealing of amorphous Fe–P–Mn alloys leads to the formation of a nanocrystalline structure. 相似文献
40.
H. L. Du S. R. Rose Z. D. Xiang P. K. Datta X. Y. Li 《Materialwissenschaft und Werkstofftechnik》2003,34(4):421-426
The oxidation/sulphidation behaviour of a Ti‐46.7Al‐1.9W‐0.5Si alloy with a TiAl3 diffusion coating was studied in an environment of H2/H2S/H2O at 850oC. The kinetic results demonstrate that the TiAl3 coating significantly increased the high temperature corrosion resistance of Ti‐46.7Al‐1.9W‐0.5Si. The SEM, EDX, XRD and TEM analysis reveals that the formation of an Al2O3 scale on the surface of the TiAl3‐coated sample was responsible for the enhancement of the corroison resistance. The Ti‐46.7Al‐1.9W‐0.5Si alloy was also modified by Nb ion implantation. The Nb ion implanted and as received sampels were subjected to cyclic oxidation in an open air at 800oC. The Nb ion implantation not only increased the oxidation resistance but also substantially improved the adhesion of scale to the substrate. 相似文献