全文获取类型
收费全文 | 327750篇 |
免费 | 24111篇 |
国内免费 | 12308篇 |
专业分类
电工技术 | 17605篇 |
技术理论 | 56篇 |
综合类 | 19631篇 |
化学工业 | 54970篇 |
金属工艺 | 18356篇 |
机械仪表 | 21125篇 |
建筑科学 | 25409篇 |
矿业工程 | 10801篇 |
能源动力 | 9742篇 |
轻工业 | 18533篇 |
水利工程 | 5180篇 |
石油天然气 | 22686篇 |
武器工业 | 2600篇 |
无线电 | 36192篇 |
一般工业技术 | 39292篇 |
冶金工业 | 17829篇 |
原子能技术 | 3193篇 |
自动化技术 | 40969篇 |
出版年
2024年 | 564篇 |
2023年 | 4911篇 |
2022年 | 7257篇 |
2021年 | 11872篇 |
2020年 | 9537篇 |
2019年 | 7729篇 |
2018年 | 8983篇 |
2017年 | 10194篇 |
2016年 | 9131篇 |
2015年 | 12132篇 |
2014年 | 15785篇 |
2013年 | 19092篇 |
2012年 | 20167篇 |
2011年 | 22434篇 |
2010年 | 19194篇 |
2009年 | 18326篇 |
2008年 | 17974篇 |
2007年 | 17393篇 |
2006年 | 18276篇 |
2005年 | 16131篇 |
2004年 | 10345篇 |
2003年 | 9124篇 |
2002年 | 8133篇 |
2001年 | 7472篇 |
2000年 | 8005篇 |
1999年 | 9615篇 |
1998年 | 8112篇 |
1997年 | 6704篇 |
1996年 | 6224篇 |
1995年 | 5290篇 |
1994年 | 4319篇 |
1993年 | 3053篇 |
1992年 | 2463篇 |
1991年 | 1937篇 |
1990年 | 1480篇 |
1989年 | 1212篇 |
1988年 | 989篇 |
1987年 | 634篇 |
1986年 | 507篇 |
1985年 | 323篇 |
1984年 | 225篇 |
1983年 | 190篇 |
1982年 | 191篇 |
1981年 | 122篇 |
1980年 | 125篇 |
1979年 | 67篇 |
1978年 | 33篇 |
1977年 | 38篇 |
1976年 | 55篇 |
1975年 | 20篇 |
排序方式: 共有10000条查询结果,搜索用时 767 毫秒
991.
StudyonHotDeformationCracksofSteelD2UsingProcesingMapGaoShan,LiuXianghua,WangGuodongABSTRACTThehotdeformationbehaviorsofsteel... 相似文献
992.
利用宽300mm、长/宽=1的横向CTT试样对国产铝钛双金属板做了常规力学性能测定,并按航标测定了KR曲线,经过柔度法和K值计算,分别测得了KRi和ai数据,确定了临界的KC值通过性能数据对比,研制的材料达到了进口料的性能要求。 相似文献
993.
Chi-Chang Wang Jiin-Chuan Wu 《Solid-State Circuits, IEEE Journal of》1997,32(6):852-860
Conventional charge pump circuits use a fixed switching frequency that leads to power efficiency degradation for loading less than the rated loading. This paper proposes a level shifter design that also functions as a frequency converter to automatically vary the switching frequency of a dual charge pump circuit according to the loading. The switching frequency is designed to be 25 kHz with 12 mA loading on both inverting and noninverting outputs. The switching frequency is automatically reduced when loading is lighter to improve the power efficiency. The frequency tuning range of this circuit is designed to be from 100 Hz to 25 kHz. A start-up circuit is included to ensure proper pumping action and avoid latch-up during power-up. A slow turn-on, fast turn-off driving scheme is used in the clock buffer to reduce power dissipation. The new dual charge pump circuit was fabricated in a 3-μm p-well double-poly single-metal CMOS technology with breakdown voltage of 18 V, the die size is 4.7×4.5 mm2. For comparison, a charge pump circuit with conventional level shifter and clock buffer was also fabricated. The measured results show that the new charge pump has two advantages: (1) the power dissipation of the charge pump is improved by a factor of 32 at no load and by 2% at rated loading of 500 Ω and (2) the breakdown voltage requirement is reduced from 19.2 to 17 V 相似文献
994.
995.
结合本钢的生产实际,对炼焦煤的最佳配比作了比较具体的分析,同时对资源,质量、成本也作了比较详细的调查,并提出了本钢焦化厂最佳配煤比方案,由此可看出,最大限度地降低采购成本,继续开发合理的配煤比例,具有广阔的前景。 相似文献
996.
997.
FATIGUE CRACK GROWTH UNDER MODE II LOADING 总被引:1,自引:0,他引:1
M. O. Wang R. H. Hu C. F. Qian J. C. M. Li 《Fatigue & Fracture of Engineering Materials & Structures》1995,18(12):1443-1454
Abstract— The behavior of fatigue crack growth for low and medium carbon steels, an austenitic stainless steel and an aluminum alloy under pure Mode II loading was investigated experimentally, using cruciform specimens. The results show that under pure Mode II loading, fatigue crack propagation has three possibilities, namely, bifurcation into two branches, propagation along the original Mode II direction, and the mixture of these two situations, depending on the material. The growth rate da/dN vs. ΔKII relation for Mode II propagation is similar to a Pans type law for Mode I growth. Fractographic observations by optical microscopy and SEM were made also on all specimens tested. When a crack branched, striations parallel to the crack front which were often associated with Mode I fatigue crack growth were observed and long marks parallel to the crack propagation direction were also found for slanted fracture surfaces. When a crack propagated along the original Mode II direction, many frictional marks parallel to the crack propagation direction were observed. 相似文献
998.
Formulas for the two-carrier third-order intermodulation distortion in semiconductor lasers have been reported by many authors. The authors refine the formula further and illustrates the difference in results arising from the refinement, for typical laser parameters.<> 相似文献
999.
Rongdong Wang 《野外机器人技术杂志》1994,11(7):657-663
New transform matrices and their multiplications and inversion are defined. Properties of these matrices and operations are derived. The new notation is suitable for both conceptual formula derivation and actual computation. An example of using the new notation for computation of kinematics of robotic manipulators is given. © 1994 John Wiley & Sons, Inc. 相似文献
1000.
This paper demonstrates the use of simple optimization techniques in the production of two advanced materials - a fibre-reinforced composite laminate and a transformation toughened ceramic - having enhanced mechanical properties. Both example materials are based on a brittle matrix prone to cracking at very low applied stresses. The optimization process aims at altering the microstructure so that the materials have enhanced resistance to crack propagation without any undesirable side effects. 相似文献