全文获取类型
收费全文 | 37293篇 |
免费 | 4023篇 |
国内免费 | 2525篇 |
专业分类
电工技术 | 852篇 |
综合类 | 1866篇 |
化学工业 | 8271篇 |
金属工艺 | 3240篇 |
机械仪表 | 1158篇 |
建筑科学 | 2322篇 |
矿业工程 | 716篇 |
能源动力 | 1440篇 |
轻工业 | 1490篇 |
水利工程 | 260篇 |
石油天然气 | 264篇 |
武器工业 | 473篇 |
无线电 | 4227篇 |
一般工业技术 | 13848篇 |
冶金工业 | 1972篇 |
原子能技术 | 358篇 |
自动化技术 | 1084篇 |
出版年
2024年 | 167篇 |
2023年 | 896篇 |
2022年 | 938篇 |
2021年 | 1357篇 |
2020年 | 1612篇 |
2019年 | 1401篇 |
2018年 | 1275篇 |
2017年 | 1394篇 |
2016年 | 1345篇 |
2015年 | 1367篇 |
2014年 | 1964篇 |
2013年 | 2213篇 |
2012年 | 2341篇 |
2011年 | 3110篇 |
2010年 | 2219篇 |
2009年 | 2431篇 |
2008年 | 2187篇 |
2007年 | 2487篇 |
2006年 | 2181篇 |
2005年 | 2043篇 |
2004年 | 1619篇 |
2003年 | 1437篇 |
2002年 | 1169篇 |
2001年 | 856篇 |
2000年 | 778篇 |
1999年 | 525篇 |
1998年 | 501篇 |
1997年 | 360篇 |
1996年 | 293篇 |
1995年 | 227篇 |
1994年 | 234篇 |
1993年 | 165篇 |
1992年 | 133篇 |
1991年 | 132篇 |
1990年 | 120篇 |
1989年 | 98篇 |
1988年 | 46篇 |
1987年 | 30篇 |
1986年 | 32篇 |
1985年 | 22篇 |
1984年 | 35篇 |
1983年 | 21篇 |
1982年 | 32篇 |
1981年 | 8篇 |
1980年 | 11篇 |
1979年 | 4篇 |
1976年 | 3篇 |
1963年 | 2篇 |
1955年 | 4篇 |
1951年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
A route to synthesize ZSM‐5 crystals with a bimodal micro/mesoscopic pore system has been developed in this study; the successful incorporation of the mesopores within the ZSM‐5 structure was performed using tetrapropylammonium hydroxide (TPAOH)‐impregnated mesoporous materials containing carbon nanotubes in the pores, which were encapsulated in the ZSM‐5 crystals during a solid rearrangement process within the framework. Such mesoporous ZSM‐5 zeolites can be readily obtained as powders, thin films, or monoliths. 相似文献
3.
4.
机械合金化Fe-Ni粉末的相结构 总被引:1,自引:0,他引:1
使用XRD和Moessbauer等方法,研究了在Ar气氛下机械合金化Fe—Ni粉末相结构的变化.结果表明,在机械合金化Fe64-Ni36粉末过程中,fcc相的数量随着球磨时间的增加先增加然后减少,与加乙醇球磨Fe64-Ni36的情形相同.当Ni的含量(原子分数)大于50%时,有fcc相、顺磁相和FeNi3形成,当Ni的含量低于50%时,bcc相的数量随着Ni含量减少而增加.Moessbauer谱的结果表明,因球磨时间或Fe、Ni比例的不同,Fe—Ni球磨粉末固溶体具有不同结构的原子配比。 相似文献
5.
J. B. Quinn G. E. Schumacher L. W. Schultheis 《Journal of Failure Analysis and Prevention》2004,4(1):41-46
Several days after heart surgery, a patient discovered his upper right canine tooth had broken at the root. Such tooth damage,
recognized post-operatively, is usually assumed to be caused by blunt mechanical force from an instrument used by the anesthesiologist
during placement of a breathing tube at the start of surgery.
In this case, the patient had saved the crown portion of the broken tooth, and it was possible to examine the root fracture
characteristics. The curvature and direction of the crack path and natural tooth situation suggested that failure could be
described through a cantilever beam model. This was confirmed when a whole extracted sample tooth was embedded and broken
by a measured force in a manner consistent with the model. The resulting fracture surface matched that of the patient’s broken
canine tooth. However, the high load and force direction necessary to fracture the root was inconsistent with forces applied
during the anesthesia procedure. The failure analysis and further investigation indicated tooth clenching on the breathing
tube during recovery was the likely cause of fracture.
This paper presents an alternate explanation for intubation-related dental injury, demonstrates the practicality of fractographic
analysis of biological materials, and introduces a methodology for simulating in vitro tooth settings for mechanical testing. 相似文献
6.
金属/Al2O3基纳米复合材料研究最新进展 总被引:2,自引:0,他引:2
金属/Al2O3纳米复合材料在保持原有金属的功能特性时,还可以获得 很好的力学性能,是有良好发展前景的一种纳米复合材料。本文回顾了近年来金属/Al2O3基纳米复合材料在制备工艺,微观结构和力学性能,增韧强化机理方面的最新进展,并指出了今后的研究方向。 相似文献
7.
核电材料在模拟反应堆环境中应力腐蚀破裂测试技术与性能评价 总被引:1,自引:0,他引:1
杨武 《理化检验(物理分册)》1996,32(5):7-12
简要介绍了采用慢应变速率试验,U型弯曲和C形环试验等技术,分别对800合金,304和316及316Ti不锈钢A533B压力容器用多在模拟核反应堆环境中的应力腐蚀破裂敏感性性进行的试验研究的一些主要结果;并结合电化学测试和表面膜俄歇电子能谱分析结果进行了讨论。 相似文献
8.
Hyun-Goo Kim Wha-Nam Myung K. Sumiyama K. Suzuki 《Journal of Alloys and Compounds》2002,340(1-2):270-274
We report upon the chemical leaching and magnetic properties of nanoscale crystalline Al0.6(Co25Cu75)0.4 alloy powders produced by rod milling. X-Ray diffractometry (XRD), transmission electron microscopy, differential scanning calorimetry, vibrating sample magnetometry, and superconducting quantum interference device magnetometry were used to characterize the as-milled and leached specimens. After 400 h of milling, only the b.c.c. phase of the intermetallic compound γ-Al3.892Cu6.10808 was detected by XRD. After annealing the leached specimen at 600 °C for 1 h, the nanoscale crystalline phase was transformed into the f.c.c. Cu phase, and this was accompanied by a change in the magnetic properties. The peaks of the magnetization shifted towards lower temperature with increasing external field. The temperature behavior at Tf (45 K) for direct current (d.c.) magnetic susceptibility measurements was quite different for field cooling and zero-field cooling. After cooling the leached specimen from 800 °C, magnetization increased gradually. 相似文献
9.
A theory related to the statistics of the structure and properties of inhomogeneous materials has been proposed, dealing with the distribution of properties from sampling of inhomogeneous structures by line transects. It is demonstrated that the empirical cumulative distribution functions of the intercepts from the microstructural constituents and their variances are important fingerprints of the inhomogeneous structures.Simulated sampling of the images of the microstructure by line transects has been proposed as a powerful method for characterization the distribution of properties of inhomogeneous structures. One of the advantages of the method based on the expected values of the order statistics of the intercepts is that the probability bounds of the property are determined without prior knowledge of the functional relationship between the property and the intercepts from the structural constituents.The concept intercept variance has an important application in determining the minimum transect length that stabilizes the variation of the intercept at a low value. Additionally, the concept ‘intercept variance’ can be used for topological optimization of the microstructure regarding the risk of intercepting a large amount of the weaker constituent. Equations regarding the variance of the intercepted fraction characterizing transect lengths with a specified distribution have also been derived. 相似文献
10.
新型高k栅介质材料研究进展 总被引:5,自引:0,他引:5
随着半导体技术的不断发展,MOSFET(metal-oxide-semiconductor field effect transistor)的特征尺寸不断缩小,栅介质等效氧化物厚度已小至nm数量级。这时电子的直接隧穿效应将非常显著,将严重影响器件的稳定性和可靠性。因此需要寻找新型高k介质材料,能够在保持和增大栅极电容的同时,使介质层仍保持足够的物理厚度来限制隧穿效应的影响。本文综述了研究高k栅介质材料的意义;MOS栅介质的要求;主要新型高k栅介质材料的最新研究动态;展望了高k介质材料今后发展的主要趋势和需要解决的问题。 相似文献