全文获取类型
收费全文 | 29632篇 |
免费 | 3996篇 |
国内免费 | 2105篇 |
专业分类
电工技术 | 4932篇 |
综合类 | 2644篇 |
化学工业 | 4347篇 |
金属工艺 | 1503篇 |
机械仪表 | 2285篇 |
建筑科学 | 2062篇 |
矿业工程 | 1073篇 |
能源动力 | 1467篇 |
轻工业 | 1094篇 |
水利工程 | 1182篇 |
石油天然气 | 1492篇 |
武器工业 | 310篇 |
无线电 | 4017篇 |
一般工业技术 | 3184篇 |
冶金工业 | 1000篇 |
原子能技术 | 620篇 |
自动化技术 | 2521篇 |
出版年
2024年 | 177篇 |
2023年 | 612篇 |
2022年 | 1084篇 |
2021年 | 1316篇 |
2020年 | 1287篇 |
2019年 | 1047篇 |
2018年 | 991篇 |
2017年 | 1206篇 |
2016年 | 1252篇 |
2015年 | 1335篇 |
2014年 | 1864篇 |
2013年 | 2066篇 |
2012年 | 2225篇 |
2011年 | 2395篇 |
2010年 | 1735篇 |
2009年 | 1718篇 |
2008年 | 1537篇 |
2007年 | 1839篇 |
2006年 | 1605篇 |
2005年 | 1392篇 |
2004年 | 1177篇 |
2003年 | 934篇 |
2002年 | 905篇 |
2001年 | 701篇 |
2000年 | 587篇 |
1999年 | 504篇 |
1998年 | 370篇 |
1997年 | 333篇 |
1996年 | 294篇 |
1995年 | 253篇 |
1994年 | 232篇 |
1993年 | 158篇 |
1992年 | 132篇 |
1991年 | 102篇 |
1990年 | 76篇 |
1989年 | 74篇 |
1988年 | 59篇 |
1987年 | 27篇 |
1986年 | 22篇 |
1985年 | 17篇 |
1984年 | 19篇 |
1983年 | 10篇 |
1982年 | 18篇 |
1981年 | 2篇 |
1980年 | 8篇 |
1979年 | 9篇 |
1978年 | 4篇 |
1964年 | 2篇 |
1959年 | 10篇 |
1951年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 13 毫秒
61.
62.
广西国营水利工程管理单位运行困难,亏损严重。为此对亏损情况及存在问题进行分析,提出相应措施及扭亏为盈的弥补思路。 相似文献
63.
Poly[2‐methoxy‐5‐(2′‐ethyl‐hexyloxy)‐para‐phenylene vinylene] (MEH‐PPV)/silica nanoparticle hybrid films were prepared and characterised. Three kinds of materials were compared: parent MEH‐PPV, MEH‐PPV/silica (hybrid A films), and MEH‐PPV/coupling agent MSMA/silica (hybrid B films), in which MSMA is 3‐(trimethoxysilyl) propyl methacrylate. It was found that the hybrid B films could significantly prevent macrophase separation, as evidenced by scanning electron and fluorescence microscopy. Furthermore, the thermal characteristics of the hybrid films were largely improved in comparison with the parent MEH‐PPV. The UV‐visible absorption spectra suggested that the incorporation of MSMA‐modified silica into MEH‐PPV could confine the polymer chain between nanoparticles and thus increase the conjugation length. The photoluminescence (PL) studies also indicated enhancement of the PL intensity and quantum efficiency by incorporating just 2 wt% of MSMA‐modified silica into MEH‐PPV. However, hybrid A films did not show such enhancement of optoelectronic properties as the hybrid B films. The present study suggests the importance of the interface between the luminescent organic polymers and the inorganic silica on morphology and optoelectronic properties. Copyright © 2004 Society of Chemical Industry 相似文献
64.
T. A. Hall 《Journal of microscopy》1991,164(1):67-79
When a microregion in a thin section of frozen-dried and embedded tissue is analysed by the conventional electron-probe X-ray continuum-normalization method, the measured quantity is in mmol of element per kg of embedded specimen. As each microregion contains an unknown amount of embedding medium, this quantity generally lies indeterminately somewhere within the wide range between mmol of element per kg of hydrated tissue and mmol of element per kg of dehydrated tissue. However, if a ‘tag’ element is incorporated in the embedding medium, the contribution of the medium to the local continuum count in each probed field should be measurable, and the X-ray data may then unambiguously yield mmol of element per kg of dehydrated tissue. This result should not be affected by shrinkage on freeze-drying or by incomplete replacement of water by embedding medium. The same X-ray data can additionally provide estimates of mmol of element per unit volume, mmol of element per kg of hydrated tissue and local dry-mass fraction. However, these estimates are subject to errors due to tissue shrinkage, incomplete replacement of water and beam damage. 相似文献
65.
浅谈克东县水土流失的成因及存在的问题 总被引:1,自引:1,他引:0
克东县属丘陵地带,土壤主要是黑土。近年来由于水土流失严重,对农业生产和农民生活带来了极大的不便。虽然采取治理与开发相结合的措施,取得了一定成绩,但目前的任务仍然艰巨。 相似文献
66.
本文评价了塑料闪烁片用作软β核素探测器时的计数效率、β谱、本底谱和康普顿电子谱的特征。文中强调:采用胶合光导剂构成的系统是一种新型探测器(软β核素内部样品塑料闪烁探测器)。本文提出内部样品固体探测器、胶合光导剂和胶合闪烁光导剂的新概念。 相似文献
67.
H. Möller 《Corrosion Science》2007,49(4):1992-2001
The purpose of this study was to determine how magnesium in seawater influences the corrosion behaviour of freely corroding steel. This was done by studying if Mg(OH)2 is formed and if calcite and aragonite differ in their protective properties. No Mg(OH)2 was detected after immersion of steel in a Mg2+-containing artificial seawater. Magnesium seems to influence the corrosion behaviour of freely corroding steel by causing calcium carbonate to precipitate as aragonite. Aragonite is more effective in covering the surface than calcite and is therefore more functional in preventing oxygen from reaching the steel surface, thereby lowering the corrosion rate. 相似文献
68.
Qingzhao Yao Yuming Zhou Yanqing Sun Xiaoyun Ye 《Journal of Inorganic and Organometallic Polymers and Materials》2008,18(4):477-484
TiO2 hybrid molecular imprinted polymer (MIP) for ethofumesate using methacrylic acid (MAA) as the functional monomer and silane
coupling agent 3-(trimethoxysilyl) propylmethacrylate (KH570) as organic–inorganic connective bridge was synthesized via photo-excitation
method. Hydrogen bond was proved to act between MAA and ethofumesate for pre- and post-polymerization binding properties as
testified by UV spectrometric method. KH570 modified TiO2 nanoparticles were prepared via sonochemical reaction, which can accelerate hydrolysis, increase collision chance for the
reactive system and improve the dispersion of the nanoparticles. Scanning electron microscope (SEM), transmission electron
microscope (TEM), binding and the adsorption kinetics experiments as well as thermogravimetric analysis (TGA) were employed
for characterization. The results indicated that the hybrid MIP revealed a larger surface area and more ordered imprinting
cavities with improved thermal stability compared to organic-only MIP. Furthermore, faster adsorption kinetics and enhancive
adsorption capacity were achieved, which made it promising in chemical sensor applications. 相似文献
69.
A. Benhamida I. Djeran-Maigre H. Dumontet S. Smaoui 《International Journal of Rock Mechanics and Mining Sciences》2005,42(7-8):996-1005
The modelling of hydromechanical behavior of clayey sediments by homogenization theory is described. The rheological model of clays buried in depth requires a three-dimensional approach and laboratory experiments to quantify the model parameters. An iterative process which can be coupled to any homogenization method is used to model the porous media behavior. Hydromechanical compaction results from oedometric experiments are simulated with the proposed model. 相似文献
70.
使用液力偶合器因故障频繁,对高炉稳产、高产造成严重威胁,而且维修费用较高,对偶合器改造后,应用金属迭片挠性联轴器其故障率、维修费用都很低。 相似文献