全文获取类型
收费全文 | 28506篇 |
免费 | 3353篇 |
国内免费 | 2497篇 |
专业分类
电工技术 | 1582篇 |
技术理论 | 1篇 |
综合类 | 3401篇 |
化学工业 | 1212篇 |
金属工艺 | 3936篇 |
机械仪表 | 2112篇 |
建筑科学 | 7733篇 |
矿业工程 | 2617篇 |
能源动力 | 702篇 |
轻工业 | 409篇 |
水利工程 | 2210篇 |
石油天然气 | 807篇 |
武器工业 | 312篇 |
无线电 | 1223篇 |
一般工业技术 | 3298篇 |
冶金工业 | 1477篇 |
原子能技术 | 100篇 |
自动化技术 | 1224篇 |
出版年
2024年 | 115篇 |
2023年 | 405篇 |
2022年 | 731篇 |
2021年 | 958篇 |
2020年 | 998篇 |
2019年 | 779篇 |
2018年 | 783篇 |
2017年 | 992篇 |
2016年 | 1155篇 |
2015年 | 1165篇 |
2014年 | 1838篇 |
2013年 | 1681篇 |
2012年 | 2214篇 |
2011年 | 2381篇 |
2010年 | 1779篇 |
2009年 | 1802篇 |
2008年 | 1671篇 |
2007年 | 2004篇 |
2006年 | 1768篇 |
2005年 | 1501篇 |
2004年 | 1193篇 |
2003年 | 1113篇 |
2002年 | 909篇 |
2001年 | 770篇 |
2000年 | 753篇 |
1999年 | 603篇 |
1998年 | 441篇 |
1997年 | 370篇 |
1996年 | 262篇 |
1995年 | 257篇 |
1994年 | 225篇 |
1993年 | 140篇 |
1992年 | 128篇 |
1991年 | 100篇 |
1990年 | 96篇 |
1989年 | 79篇 |
1988年 | 62篇 |
1987年 | 31篇 |
1986年 | 21篇 |
1985年 | 11篇 |
1984年 | 12篇 |
1983年 | 8篇 |
1982年 | 14篇 |
1981年 | 3篇 |
1980年 | 7篇 |
1979年 | 18篇 |
1975年 | 1篇 |
1962年 | 1篇 |
1959年 | 7篇 |
1955年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 218 毫秒
11.
This paper discusses the effects of the grinding-induced cyclic heating on the properties of the hardened layer in a plunge cylindrical grinding process on the high strength steel EN26. It was found that a multi-pass grinding brings about a uniform and continuous hardened layer along the circumference of the cylindrical workpiece. An increase of the number of grinding passes, leads to a thicker layer of hardening, a larger compressive residual stress and a deeper plastic deformation zone. Within the plastic deformation zone, the martensitic grains are refined by the thermo-mechanical loading, giving rise to a hardness of 12.5% higher than that from a conventional martensitic transformation. The coupled effects of heat accumulation and wheel wear in the multi-pass grinding are the main causes for the thickening of the hardened layer. A too small infeed per workpiece revolution would result in insufficient grinding heat, and in turn, bring about an undesirable tempered hardened layer and a reduction of its hardness. 相似文献
12.
The flame front deformation instability of low-velocity filtration combustion within an inert packed bed is studied based on the initial preheating non-uniformity. Based on the experimental phenomena, an initial thermal perturbation model is numerically proposed so as to predict the deformation behaviors of the flame front instabilities. The numerical prediction indicates that the assumption of an initial thermal perturbation is a feasible explanation as the cause of the flame front inclination instability. As the initial thermal perturbation increases, the phenomena of the flame front break and shrinking instabilities could easily occur at high filtration velocity or low equivalence ratio. Moreover, the evolutions of the flame front break rate and the shrinking rate are quantitatively analyzed. 相似文献
13.
最大塑性功原理在烧结体上限分析中的应用 总被引:1,自引:0,他引:1
最大塑性功原理又称第二塑性变分原理,在致密体塑性变形分析叶l是运用能量法进行变形力能计算的基础。本文从分析Drucker公设的亢要条件出发,证明了烧结体塑性变形最大塑性功原理的存在,片在该原理的荩础卜,推导出塑性变形的上限功率表达式,并以平面挤压条件下的上限法应用作为实例加以说明。 相似文献
14.
Dong‐Wook Kim 《ETRI Journal》2006,28(1):84-86
This letter presents a small‐sized, high‐power single‐pole double‐throw (SPDT) switch with defected ground structure (DGS) for wireless broadband Internet application. To reduce the circuit size by using a slow‐wave characteristic, the DGS is used for the quarter‐wave (°/4) transmission line of the switch. To secure a high degree of isolation, the switch with DGS is composed of shunt‐connected PIN diodes. It shows an insertion loss of 0.8 dB, an isolation of 50 dB or more, and power capability of at least 50 W at 2.3 GHz. The switch shows very similar performance to the conventional shunt‐type switch, but the circuit size is reduced by about 50% simply with the use of DGS patterns. 相似文献
15.
16.
Deformation behavior of stoichiometric blends made from poly(styrene-co-styrenesulfonic acid) (SPS) and poly(styrene-co-4-vinylpyridine) (SVP) was investigated by TEM observation of strained thin films. An FTIR investigation revealed that ionic cross-links were formed between the component polymers upon blending due to intermolecular ion-ion interactions, which arose from proton transfer from sulfonic acid groups to pyridine groups. TEM observations indicate that the deformation mode of the blends changed from crazing only to crazing plus shear deformation, with the shear contribution becoming larger, as the ion content in the blends increased. Such changes in deformation mode can be understood as arising from an increase in the ‘effective’ strand density due to the formation of ionic cross-links upon blending. It was also found that the ionic cross-links via pyridinium cation/sulfonate anion ion pairs were more effective in inducing the transition of deformation mode than ionic cross-links via -SO3−/Na+ or -SO3−/Ca2+ ion pairs. 相似文献
17.
连续波半主动雷达制导空空导弹截获跟踪距离计算 总被引:1,自引:1,他引:0
分析了连续波半主动雷达制导导弹导引头工作电磁环境和对武器系统攻击区的影响,建立了热噪声和杂波干扰环境下导引头截获距离方程,分析推导了直波泄漏干扰,地杂波干扰的计算公式,并在此基础上给出了导弹允许攻击区计算公式。 相似文献
18.
WC/Cu复合材料制备及其高温性能 总被引:11,自引:0,他引:11
用机械合金化法结合冷变形,制备了WC/Cu复合材料,研究了冷变形后复合材料的组织特征和高温退火时韵性能变化。结果表明:烧结后的材料经冷变形,组织呈显著纤维状,WC颗粒弥散分布,密度明显提高,达到理论密度的99.2%;复合材料经600~900℃高温退火,强度和硬度略有下降,塑性则有大幅提高;900℃退火时未发生明显的再结晶,界面结合良好;所制备的WC/Cu复合材料有优良的综合性能。 相似文献
19.
A three-dimensional FE analysis of large deformations for impact loadings using tetrahedral elements
A three-dimensional dynamic program for the anaysis of large deformations in contact-penetration problems is developed using
the finite element Lagrangian method with explicit time integration. By incorporating a tetrahedral element, which allows
a single-point integration without a special hourglass control scheme, this program can be more effective to the present problem.
The position code algorithm is used to search contact surface. Eroding surfaces are also considered. The defense node algorithm
was slightly modified for the calculation of contact forces. A study of obliquity effects on metallic plate perforation and
ricochet processes in thin plates impacted by a sphere was conducted. It is well simulated that on separation of two parts
of the sphere, the portion still within the crater tends to perforate, while the portion in contact with the plate surface
ricochets. This deformation pattern is observed in experiments, especially at high obliquities. A long rod that impacts an
oblique steel plate at high impact velocity was also simulated in order to study the dynamics of the rod caused by the three
dimensional asymmetric contact. The agreement between simulated and experimental results is quite good. Fracture phenomena
occuring at high obliquity deserves further investigations.
Received: 20 February 2002 / Accepted: 20 September 2002 相似文献
20.
本文就利用诸如蛋白石这样的疏松多孔矿料同灰土构成的混合料,在路面结构中表现出的独特有效的抗冻作用机理作了深入分析,并结合足尺试验数据加以验证。阐述了所谓多孔板体结构的概念、机制和材料组成要求。 相似文献