全文获取类型
收费全文 | 109740篇 |
免费 | 10438篇 |
国内免费 | 5427篇 |
专业分类
电工技术 | 6874篇 |
技术理论 | 9篇 |
综合类 | 7663篇 |
化学工业 | 17707篇 |
金属工艺 | 6557篇 |
机械仪表 | 7390篇 |
建筑科学 | 8562篇 |
矿业工程 | 3453篇 |
能源动力 | 3126篇 |
轻工业 | 7294篇 |
水利工程 | 2153篇 |
石油天然气 | 6189篇 |
武器工业 | 1074篇 |
无线电 | 13287篇 |
一般工业技术 | 12915篇 |
冶金工业 | 5104篇 |
原子能技术 | 1386篇 |
自动化技术 | 14862篇 |
出版年
2024年 | 546篇 |
2023年 | 2011篇 |
2022年 | 3676篇 |
2021年 | 5017篇 |
2020年 | 3814篇 |
2019年 | 3059篇 |
2018年 | 3312篇 |
2017年 | 3917篇 |
2016年 | 3470篇 |
2015年 | 4843篇 |
2014年 | 6058篇 |
2013年 | 7238篇 |
2012年 | 7637篇 |
2011年 | 8378篇 |
2010年 | 7224篇 |
2009年 | 6978篇 |
2008年 | 6864篇 |
2007年 | 6230篇 |
2006年 | 5857篇 |
2005年 | 4839篇 |
2004年 | 3230篇 |
2003年 | 2682篇 |
2002年 | 2595篇 |
2001年 | 2299篇 |
2000年 | 2126篇 |
1999年 | 2118篇 |
1998年 | 1745篇 |
1997年 | 1468篇 |
1996年 | 1371篇 |
1995年 | 1131篇 |
1994年 | 932篇 |
1993年 | 680篇 |
1992年 | 504篇 |
1991年 | 410篇 |
1990年 | 314篇 |
1989年 | 251篇 |
1988年 | 205篇 |
1987年 | 115篇 |
1986年 | 115篇 |
1985年 | 67篇 |
1984年 | 51篇 |
1983年 | 54篇 |
1982年 | 45篇 |
1981年 | 30篇 |
1980年 | 29篇 |
1979年 | 18篇 |
1977年 | 5篇 |
1976年 | 10篇 |
1959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
81.
高温预析出对Al-Zn-Mg系铝合金时效硬化和应力腐蚀的影响 总被引:1,自引:0,他引:1
研究了高温固溶后降温处理工艺对中强可使预析出LC52和7039铝合金的组织、时效硬化和应力腐蚀的影响。金相观察发现,高温预析出可优先在晶界处产生,并提高随后时效状态下晶界析出相的不连续分布程度,温度降低到一定程度晶内和晶界产生大量析出。合金拉伸性能和应力腐蚀结果表明,预析出在保持强度和塑性的同时,可提高抗应力腐蚀性能。而预析出温度降低,合金强度呈下降趋势。 相似文献
82.
Triton polymers are commercial surfactants whose molecular weight distributions are conventionally determined by means of high-performance liquid chromatography (HPLC). However, in the case of the important octylphenol ethoxylates [p-C8H17-C6H4-O-(CH2CH2O)n-H], HPLC cannot resolve individual oligomers of high molecular weight Triton surfactants (e.g., greater than 2000 u or so; u = unified atomic mass unit). In this paper, we show that laser desorption Fourier transform ion cyclotron resonance mass spectrometry (LD/FT/ICR/MS) provides a simple and accurate measure of such Triton surfactant molecular weight distributions up to at least 3500 u, based on a single-shot laser pulse measurement of a few seconds duration. Comparison of LD/FT/ICR/MS and HPLC molecular weight distributions of low molecular weight surfactants shows that laser desorption/ionization produces minimal fragmentation and thus offers an accurate measure of the relative abundances of the neutral oligomers, without the need for prior chromatographic separation of the components. Moreover, for all Triton polymer molecular weight distributions (700-3000 u), LD/FT/ICR/MS provides much more highly resolved profiles of oligomer relative abundances. Finally, LD/FT/ICR/MS reveals the presence of poly(ethylene oxide) side products of the polymerization process, which are not observed by HPLC with conventional ultraviolet absorption detection. 相似文献
83.
84.
A multi-channel continuous toxicity monitoring system developed in our laboratory, based on two-stage mini-bioreactors, was successfully implemented in the form of computer-based data acquisition. The multi-channel system consists of a series of a two-stage minibioreactor systems connected by a fiber optic probe to a luminometer, and uses genetically engineered bioluminescent bacteria for the detection of the potential toxicity from the soluble chemicals. This system can be stably and continuously operated due to the separation of the culture reactor from the test reactor and accomplish easy and long-term monitoring without system shut down by abrupt inflows of severe polluting chemicals. Four different recombinant bioluminescent bacteria were used in different channels so that the modes of the samples toxicities can be reasonably identified and evaluated based upon the response signature of each channel. The bioluminescent signatures were delivered from four channels by switching one at once, while the data is automatically logged to an IBM compatible computer. We also achieved the enhancement of the system through the manipulation of the dilution rate and the use of thermo-lux fusion strains. Finally, this system is now being implemented to a drinking water reservoir and river for remote sensing as an early warning system. 相似文献
85.
86.
87.
I.H. Song 《Thin solid films》2007,515(19):7598-7602
This paper is a report on the effect of a single perpendicular grain boundary on the hot-carrier and high current stability in high performance polycrystalline silicon (poly-Si) thin film transistors (TFTs). Under a hot carrier stress condition (Vg = Vth + 1 V, Vd = 12 V), the poly-Si TFT with a single grain boundary is superior to the poly-Si without any grain boundary because of the smaller free carriers available for electric conduction. The shift of transconductance in poly-Si TFT with a single grain boundary is less than 5% after hot carrier stress during a period of 1000 s. The shift of transconductance is about 25% in the case of the poly-Si TFTs without a grain boundary in the channel. On high current stress, the poly-Si TFT without the grain boundary is less degraded than the poly-Si TFT with the grain boundary because the concentrated electric field near the drain junction is lower. 相似文献
88.
89.
90.
A new pulse stabilisation scheme for a harmonically frequency modulated (FM) modelocked erbium fibre ring laser using a distributed feedback laser diode (DFBLD) is presented. More than 65 dB supermode noise suppression in the RF spectrum was obtained with the proposed method. Effective reduction of supermode noise can be accomplished as the DFBLD in the fibre laser acts not only as a fast-gain saturated medium but also as an optical bandpass filter for suppressing supermode noise in a harmonically modelocked laser system. 相似文献