全文获取类型
收费全文 | 54614篇 |
免费 | 6273篇 |
国内免费 | 2712篇 |
专业分类
电工技术 | 13036篇 |
技术理论 | 4篇 |
综合类 | 4852篇 |
化学工业 | 3189篇 |
金属工艺 | 1918篇 |
机械仪表 | 5488篇 |
建筑科学 | 2742篇 |
矿业工程 | 2464篇 |
能源动力 | 1433篇 |
轻工业 | 2097篇 |
水利工程 | 1023篇 |
石油天然气 | 2210篇 |
武器工业 | 1233篇 |
无线电 | 8226篇 |
一般工业技术 | 3189篇 |
冶金工业 | 1977篇 |
原子能技术 | 456篇 |
自动化技术 | 8062篇 |
出版年
2025年 | 14篇 |
2024年 | 930篇 |
2023年 | 868篇 |
2022年 | 1333篇 |
2021年 | 1729篇 |
2020年 | 1780篇 |
2019年 | 1299篇 |
2018年 | 1180篇 |
2017年 | 1558篇 |
2016年 | 1829篇 |
2015年 | 2115篇 |
2014年 | 3893篇 |
2013年 | 3164篇 |
2012年 | 4705篇 |
2011年 | 4619篇 |
2010年 | 3443篇 |
2009年 | 3289篇 |
2008年 | 3080篇 |
2007年 | 3822篇 |
2006年 | 3270篇 |
2005年 | 2815篇 |
2004年 | 2339篇 |
2003年 | 2039篇 |
2002年 | 1550篇 |
2001年 | 1419篇 |
2000年 | 1194篇 |
1999年 | 948篇 |
1998年 | 676篇 |
1997年 | 583篇 |
1996年 | 490篇 |
1995年 | 369篇 |
1994年 | 295篇 |
1993年 | 204篇 |
1992年 | 159篇 |
1991年 | 115篇 |
1990年 | 105篇 |
1989年 | 92篇 |
1988年 | 57篇 |
1987年 | 34篇 |
1986年 | 25篇 |
1985年 | 30篇 |
1984年 | 36篇 |
1983年 | 27篇 |
1982年 | 28篇 |
1981年 | 6篇 |
1980年 | 6篇 |
1979年 | 6篇 |
1978年 | 5篇 |
1976年 | 5篇 |
1975年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
61.
直流输电线路对电信线路的危险影响、影响机理和计算方法,国内外资料及文献中尚无系统的介绍,我国也尚无统一的计算、设计标准。为便于工程设计,可以采用理论计算与实测对比相结合的方法推导出的简化公式进行计算。 相似文献
62.
介绍了河北省南部电网500 kV输电线路复合绝缘子的运行与试验情况,分析了复合绝缘子憎水性能明显下降的原因。 相似文献
63.
64.
Martensitic stabilization caused by deformation in a TiNi shape memory alloy was studied.Special attention was paid to the deformed microstructures to identify the cause of martensitic stabilization.Martensitic stabilization was demonstrated by differential scanning calorimetry for the tensioned TiNi shape memory alloy.Transmission electron microscopy revealed that antiphase boundaries were formed because of the fourfold dissociation of[110]B19'super lattice dislocations and were preserved after reverse transformation due to the lattice correspondence.Martensitic stabilization was attributed to dislocations induced by deformation,which reduced the ordering degree of the microstructure,spoiled the reverse path from martensite to parent phase compared with thermoelastic transformation,and imposed resistance on phase transformation through the stress field. 相似文献
65.
Extreme winds, hurricanes, and tornadoes produce significant damage to electrical transmission and distribution line structures. The damage produces loss of power to the affected communities for a variable length of time, depending on severity of damage. Most institutions whose operations would be life threatening in the event of power failure have emergency power. However, loss of power to both residences and businesses can have economic impact on the community in the form of temporary housing shortages and loss of business. Utility companies seem to cope with wind damage fairly well, following risk management procedures in designing for wind and in providing alternate routing for distribution lines. However, continuing research and developments are needed to keep abreast of the problem. 相似文献
66.
67.
提出了一种求解含抛物线型有损非均匀线网络频域灵敏度的方法。该方法首先将抛物线型有损非均匀线用科罗达(Kuroda)等效方法变换成有损均匀线及若干集中元件组成的等效电路,然后借助伴随网络方程法求出抛物线型有损非均匀传输线等参数的频域灵敏度。给出了计算实例,并通过扰动法进行了验证。 相似文献
68.
Thomas R. Hammant 《Cryptologia》2013,37(1):50-60
The importance of radio communications, both in controlling military forces and for purposes of intelligence collection, was recognized from the beginning by the new Soviet leaders in Russia. By January 1919, a radio intelligence service had been established in the Red Army, although shortages of equipment and comint personnel limited its operations during the civil war. Both sides in the civil war suffered from poor communications security. 相似文献
69.
提出了一种新型的机液集成变速器,介绍了其结构、工作原理和结构特点,总参数选择及系统设计方法,可指导新产品的研究开发,满足众多领域对低转速、大扭矩、高效率、低能耗变速器的需要. 相似文献
70.
Iwona Mazur-Michaek Katarzyna Kowalska Daniel Zielonka Marta Leniczak-Staszak Paulina Pietras Witold Szaflarski Mark Isalan Michal Mielcarek 《International journal of molecular sciences》2022,23(10)
Huntington’s disease (HD) is a fatal neurodegenerative disorder caused by a polyglutamine expansion in the huntingtin protein. HD-related pathological remodelling has been reported in HD mouse models and HD carriers. In this study, we studied structural abnormalities in the optic nerve by employing Spectral Domain Optical Coherence Tomography (SD-OCT) in pre-symptomatic HD carriers of Caucasian origin. Transmission Electron Microscopy (TEM) was used to investigate ultrastructural changes in the optic nerve of the well-established R6/2 mouse model at the symptomatic stage of the disease. We found that pre-symptomatic HD carriers displayed a significant reduction in the retinal nerve fibre layer (RNFL) thickness, including specific quadrants: superior, inferior and temporal, but not nasal. There were no other significant irregularities in the GCC layer, at the macula level and in the optic disc morphology. The ultrastructural analysis of the optic nerve in R6/2 mice revealed a significant thinning of the myelin sheaths, with a lamellar separation of the myelin, and a presence of myelonoid bodies. We also found a significant reduction in the thickness of myelin sheaths in peripheral nerves within the choroids area. Those ultrastructural abnormalities were also observed in HD photoreceptor cells that contained severely damaged membrane disks, with evident vacuolisation and swelling. Moreover, the outer segment of retinal layers showed a progressive disintegration. Our study explored structural changes of the optic nerve in pre- and clinical settings and opens new avenues for the potential development of biomarkers that would be of great interest in HD gene therapies. 相似文献