全文获取类型
收费全文 | 48346篇 |
免费 | 4719篇 |
国内免费 | 3082篇 |
专业分类
电工技术 | 1429篇 |
综合类 | 3667篇 |
化学工业 | 13444篇 |
金属工艺 | 7717篇 |
机械仪表 | 1722篇 |
建筑科学 | 2734篇 |
矿业工程 | 1096篇 |
能源动力 | 754篇 |
轻工业 | 5511篇 |
水利工程 | 405篇 |
石油天然气 | 2551篇 |
武器工业 | 550篇 |
无线电 | 2250篇 |
一般工业技术 | 7394篇 |
冶金工业 | 3272篇 |
原子能技术 | 242篇 |
自动化技术 | 1409篇 |
出版年
2024年 | 218篇 |
2023年 | 800篇 |
2022年 | 1379篇 |
2021年 | 1626篇 |
2020年 | 1658篇 |
2019年 | 1451篇 |
2018年 | 1486篇 |
2017年 | 1947篇 |
2016年 | 1971篇 |
2015年 | 2089篇 |
2014年 | 2509篇 |
2013年 | 2616篇 |
2012年 | 3313篇 |
2011年 | 3599篇 |
2010年 | 2713篇 |
2009年 | 2846篇 |
2008年 | 2241篇 |
2007年 | 3236篇 |
2006年 | 2983篇 |
2005年 | 2597篇 |
2004年 | 2186篇 |
2003年 | 1897篇 |
2002年 | 1625篇 |
2001年 | 1332篇 |
2000年 | 1126篇 |
1999年 | 1005篇 |
1998年 | 832篇 |
1997年 | 611篇 |
1996年 | 548篇 |
1995年 | 428篇 |
1994年 | 372篇 |
1993年 | 238篇 |
1992年 | 229篇 |
1991年 | 138篇 |
1990年 | 76篇 |
1989年 | 63篇 |
1988年 | 43篇 |
1987年 | 29篇 |
1986年 | 19篇 |
1985年 | 11篇 |
1984年 | 11篇 |
1983年 | 6篇 |
1982年 | 6篇 |
1981年 | 8篇 |
1980年 | 9篇 |
1979年 | 4篇 |
1975年 | 1篇 |
1973年 | 2篇 |
1959年 | 6篇 |
1951年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
研究了某种环氧树脂阻尼灌封胶在热氧老化的作用下分子结构、硬度、断面形貌以及动态力学性能随时间的变化.傅立叶红外光谱图表明,所制备的样品环氧基团反应比较完全,热氧老化后试样表面由仲胺和环氧基团形成的酯键发生了部分断裂和氧化;邵氏硬度的增加、瓦向高温区移动则表明在老化过程中复杂的固化反应仍然继续进行;最大损耗因子(tanδmax)波动较小表明试样老化后分子结构几乎保持不变;SEM图片显示试样的冲击断裂由老化前的韧性转变为老化后的脆性断裂. 相似文献
12.
M.G. Pujar N. Parvathavarthini Sidhartha S. Jena B.V.R. Tata R.K. Dayal H.S. Khatak 《Journal of Materials Engineering and Performance》2008,17(6):793-801
In the present work 316LN as well as 316 stainless steel (SS) coupons each of dimensions (0.025 × 0.018 × 0.006 m3) in well-polished condition were used as two nominal electrodes which were immersed in the aerated solution of 0.5 M NaCl.
Correlated current and potential electrochemical noise (EN) signals were collected at 1 Hz sampling frequency for 1 h daily
over a period of 30 days. The detrended EN data were used to calculate the noise resistance (R
N) as well as the spectral noise resistance at zero frequency (R
SNo) values and other statistical parameters. To study the nature of pits and distribution of their diameters as well as depths,
extensive observations of the pitted and the blank specimens were carried out using Confocal Laser Scanning Microscopy (CLSM).
The current and the potential records of the two alloys showed distinct differences in their corrosion behavior. It was observed
that within less than 4 h of immersion, 316SS showed signals indicative of unstable pitting and onset of stable pitting was
noticed after 48 h of exposure. However, until about 24 h, 316LN showed just the random signals and unstable pitting was observed
after 28 h. The signals clearly indicated continuous growth of the stable pits in 316SS as against the repassivation of the
unstable pits in 316LN after 7 days exposure. It was observed that R
N values showed a continuous decrease in the case of 316SS, but were quite stable in the case of 316LN over the exposure period.
Concurrent to these observations it was observed that 316SS specimen was extensively pitted. The frequency distributions of
pit diameters as well pit depths were observed to be highest at 10-20 μm and 5-10 μm, respectively. However, pits with as
large as 70-80 μm diameter and as deep as 20-25 μm too were observed. No pits were observed in case of 316LN even after 30 days
of exposure, an observation that corroborates well with the stable R
N values. Thus, in the present investigation, the long-term tests using EN technique coupled with CLSM studies conclusively
prove that many unstable pits initiated in 316SS turn into stable ones resulting in insidious localized corrosion attack whereas
the unstable pits initiated in 316LN get passivated in the simulated coastal environment. 相似文献
13.
14.
镍氢电池负极用低成本储氢合金的研究 总被引:1,自引:0,他引:1
研究了ABS型储氢合金在低Co含量条件下,随B组元替代元素Co,Al,Si等含量的变化对合金电化学性能的影响规律,同时研究了A组元中不同La/Ce比对合金电化学性能的影响情况。结果表明,随合金中Co含量的降低,合金的活化性能和放电容量得以改善,但合金的循环寿命下降也比较明显;在试验范围内,随Al元素的加入,合金的循环寿命得以改善,但材料的放电容量和活化性能均有所下降;随合金La/Ce比的降低,合金的放电容量略有下降,但其循环寿命和放电电压平台有较大提高。 相似文献
15.
16.
The effects of yttrium and cerium on microstructures and properties of Nb-Si system composites were investigated by scanning electron microscopy( SEM), energy dispersive spectrum(EDS), X-ray diffraction(XRD) and high temperature oxidation experiments.It is found that the coarse primary silicide phase became finer and more homogeneous with Y and Ce addition.The results of high temperature oxidation experiments show that the oxidation rates of NbSi system composites with an appropriate amount of Y and Ce decrease compared with those of alloys without Y or Ce addition, and oxidation products mainly distribute along the phase boundaries between the Nb solid solution and silicide. 相似文献
17.
18.
通过对国内外大量石油套管螺纹参数的测量和全尺寸的模拟试验,以及对测量和试验数据的理论分析,找出了影响国产套管发生粘扣的原因,并在实际生产中实施验证。采取相应的措施改善了套管的抗粘结性能,同时套管的密封和抗滑脱性能并未下降。 相似文献
19.
杨加峰 《武汉理工大学学报(材料科学英文版)》2005,20(Z1)
1Introduction HA(hydroxyapatite)wasakindofbioactiveceram ics,whichhadexcellentbiocompatibilityandtissueaffin ityinthatitscomponentsweresimilartothoseofhuman bone[1].Soitwasthebestknownhumanbonesubstitute,andunprecedentedeffecthadbeenharvestedinrecenttwo d… 相似文献
20.
通过测试比较,分析了酶制剂练、高温皂碱练由精练方法不同而造成纤维在微观、外观、机械、吸湿及电学等方面的异同点。提出酶制剂练对提高纤维梳折、提高成纱品质、提高劳动生产率、降低工人劳动强度等方面均优于高温皂碱练,是精练工程改造方向之一。 相似文献