全文获取类型
收费全文 | 27763篇 |
免费 | 1853篇 |
国内免费 | 1851篇 |
专业分类
电工技术 | 431篇 |
综合类 | 1803篇 |
化学工业 | 5213篇 |
金属工艺 | 3036篇 |
机械仪表 | 2103篇 |
建筑科学 | 3421篇 |
矿业工程 | 936篇 |
能源动力 | 635篇 |
轻工业 | 1016篇 |
水利工程 | 645篇 |
石油天然气 | 1696篇 |
武器工业 | 470篇 |
无线电 | 962篇 |
一般工业技术 | 7078篇 |
冶金工业 | 951篇 |
原子能技术 | 498篇 |
自动化技术 | 573篇 |
出版年
2024年 | 97篇 |
2023年 | 474篇 |
2022年 | 945篇 |
2021年 | 1123篇 |
2020年 | 953篇 |
2019年 | 804篇 |
2018年 | 901篇 |
2017年 | 977篇 |
2016年 | 1052篇 |
2015年 | 1349篇 |
2014年 | 1712篇 |
2013年 | 2008篇 |
2012年 | 1560篇 |
2011年 | 2486篇 |
2010年 | 1538篇 |
2009年 | 1585篇 |
2008年 | 1401篇 |
2007年 | 1471篇 |
2006年 | 1394篇 |
2005年 | 1190篇 |
2004年 | 974篇 |
2003年 | 946篇 |
2002年 | 852篇 |
2001年 | 652篇 |
2000年 | 560篇 |
1999年 | 465篇 |
1998年 | 353篇 |
1997年 | 319篇 |
1996年 | 294篇 |
1995年 | 215篇 |
1994年 | 153篇 |
1993年 | 120篇 |
1992年 | 88篇 |
1991年 | 109篇 |
1990年 | 67篇 |
1989年 | 56篇 |
1988年 | 45篇 |
1987年 | 27篇 |
1986年 | 27篇 |
1985年 | 20篇 |
1984年 | 16篇 |
1983年 | 10篇 |
1982年 | 24篇 |
1981年 | 6篇 |
1980年 | 14篇 |
1979年 | 10篇 |
1966年 | 3篇 |
1965年 | 3篇 |
1964年 | 3篇 |
1959年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 328 毫秒
171.
172.
双头螺栓失效分析 总被引:4,自引:3,他引:1
金蔚静 《理化检验(物理分册)》2003,39(5):268-270
与汽车电机装配在一起的双头螺栓在拧紧后不久便发生断裂。采用扫描电镜、化学分析、金相检验等方法对失效件进行了检测,同时又进行了氢脆试验验证。结果表明,螺栓在进行表面酸洗及电镀时,氢向金属内部扩散和富集,当氢浓度达到一定临界值后,促使氢致裂纹的产生和扩展。在外应力的作用下,即出现氢脆现象导致螺栓断裂。 相似文献
173.
钢管机械扩径工艺研究 总被引:3,自引:0,他引:3
介绍了大口径直缝焊管机械扩径的优点,原理及扩径力的计算,找出影响扩径力及扩径头寿命的因素。 相似文献
174.
用屏蔽暂堵技术封堵水平井裂缝性漏层 总被引:1,自引:1,他引:0
克拉玛依油田HW702水平井的大斜度段和水平段,将穿越纵向裂缝发育的二叠系佳木河组储层。为安全钻进和保护油层,用超细碳酸钙和磺化沥青复配后加入复合离子钻井液中成屏蔽暂堵的堵漏钻井液。室内用岩心试验,屏蔽暂堵后渗透率可降为0,暂堵深度小于3cm,可用酸化和射孔解堵。现场使用效果也很好,使HW702水平井顺利完钻,并获得工业油气流。 相似文献
175.
用自蔓燃高温合成(SHS)技术及电弧熔融法制备的(Nb,Ti)C固溶体作基体,制备(Nb,Ti)C-35Ni金属陶瓷。结果表明用电弧熔融法制备的(Nb,Ti)C为基的试样具较优的室温力学性能(σ=1630MPa,KIC=18.0MPa),其陶瓷颗粒均匀分行粘结相之中并是包裹结构;而用SHS法制备的(Nb,Ti)C为基的试样其力学性能相对较差,其陶瓷颗粒无包裹结构. 相似文献
176.
System reliability is evolving as an important design method for selecting components and topology. It should be used to investigate the original intact structure behavior as well as providing sufficient reserve capacity under likely accident and damage scenarios. Highway bridges are an area of special concern since effort to optimize the cost of construction may not provide adequate redundant capacity. The paper describes an example in which a typical girder bridge structure is optimized (both size and girder spacing) to achieve target system performance. System reliability constraints are imposed on the behavior of the intact structure under highway loads. Also, residual system reliability constraints are imposed to control safety under specified accident scenarios corresponding to damage and “lost” members due to corrosion, fatigue, fire or accidental collisions. An optimal design framework for controlling safety under all these life cycle situations is thus provided. 相似文献
177.
Unidirectional (UD) and multidirectional (MD) flax/polypropylene composites were studied. Flax with varying retting degree and boiled flax was used as reinforcement for the UD composites and unmodified and maleic acid anhydride modified polypropylene (MAA-PP) was used as matrix. Multidirectional flax/polypropylene composites were manufactured on laboratory scale and on pilot scale. They were made from needle-punched hybrid flax/PP non-wovens. Normally retted flax as well as boiled flax was used. For the specimens made on pilot scale, a third kind of flax, namely bleached flax was also studied. The influence of different process times and temperatures on the mechanical properties of the composites was analysed. Generally, the composites have adequate good mechanical properties. The unidirectional composites of boiled flax combined with MAA-PP show the best mechanical properties. Contrary to the UD composites, flax treatment did not lead to the expected property improvements for MD composites. 相似文献
178.
179.
简述了钢筋混凝土正截面强度计算理论的发展历程,介绍了其计算理论的特点及其存在的问题,并对今后需要进一步研究的问题进行了展望,为工程设计提供参考。 相似文献
180.
Z.M. Zhong J. Chen P. Zhong J.B. Wu 《The International Journal of Advanced Manufacturing Technology》2006,28(9):855-862
As the result of vibration emission in air, a machine sound signal carries important information about the working condition
of machinery. But in practice, the sound signal is typically received with a very low signal-to-noise ratio. To obtain features
of the original sound signal, uncorrelated sound signals must be removed and the wavelet coefficients related to fault condition
must be retrieved. In this paper, the blind source separation technique is used to recover the wavelet coefficients of a monitored
source from complex observed signals. Since in the proposed blind source separation (BSS) algorithms it is generally assumed
that the number of sources is known, the Gerschgorin disk estimator method is introduced to determine the number of sound
sources before applying the BSS method. This method can estimate the number of sound sources under non-Gaussian and non-white
noise conditions. Then, the partial singular value analysis method is used to select these significant observations for BSS
analysis. This method ensures that signals are separated with the smallest distortion. Afterwards, the time-frequency separation
algorithm, converted to a suitable BSS algorithm for the separation of a non-stationary signal, is introduced. The transfer
channel between observations and sources and the wavelet coefficients of the source signals can be blindly identified via
this algorithm. The reconstructed wavelet coefficients can be used for diagnosis. Finally, the separation results obtained
from the observed signals recorded in a semi-anechoic chamber demonstrate the effectiveness of the presented methods . 相似文献