全文获取类型
收费全文 | 100913篇 |
免费 | 9068篇 |
国内免费 | 5670篇 |
专业分类
电工技术 | 3999篇 |
技术理论 | 4篇 |
综合类 | 10901篇 |
化学工业 | 14354篇 |
金属工艺 | 6755篇 |
机械仪表 | 6039篇 |
建筑科学 | 22363篇 |
矿业工程 | 3742篇 |
能源动力 | 2470篇 |
轻工业 | 5889篇 |
水利工程 | 2495篇 |
石油天然气 | 4431篇 |
武器工业 | 964篇 |
无线电 | 6235篇 |
一般工业技术 | 10810篇 |
冶金工业 | 3843篇 |
原子能技术 | 546篇 |
自动化技术 | 9811篇 |
出版年
2024年 | 412篇 |
2023年 | 1391篇 |
2022年 | 2615篇 |
2021年 | 2947篇 |
2020年 | 2945篇 |
2019年 | 2393篇 |
2018年 | 2321篇 |
2017年 | 2961篇 |
2016年 | 3134篇 |
2015年 | 3347篇 |
2014年 | 6265篇 |
2013年 | 5388篇 |
2012年 | 6950篇 |
2011年 | 7807篇 |
2010年 | 5996篇 |
2009年 | 6457篇 |
2008年 | 5850篇 |
2007年 | 6983篇 |
2006年 | 6332篇 |
2005年 | 5506篇 |
2004年 | 4505篇 |
2003年 | 4022篇 |
2002年 | 3430篇 |
2001年 | 2845篇 |
2000年 | 2440篇 |
1999年 | 2014篇 |
1998年 | 1583篇 |
1997年 | 1325篇 |
1996年 | 1011篇 |
1995年 | 860篇 |
1994年 | 822篇 |
1993年 | 529篇 |
1992年 | 485篇 |
1991年 | 385篇 |
1990年 | 316篇 |
1989年 | 222篇 |
1988年 | 186篇 |
1987年 | 99篇 |
1986年 | 71篇 |
1985年 | 76篇 |
1984年 | 60篇 |
1983年 | 60篇 |
1982年 | 69篇 |
1981年 | 21篇 |
1980年 | 72篇 |
1979年 | 14篇 |
1978年 | 11篇 |
1976年 | 10篇 |
1975年 | 13篇 |
1959年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
71.
References: 《中国炼油与石油化工》2007,(3):35-42
The proton nuclear magnetic resonance spectroscopy (1H-NMR), the synchronous fluorescence spectrometry (SFS) and the ruthenium ions catalyzed oxidation (RICO) method were used to determine the chemical structure of polyaromatic nucleus in Oman residue fractions. The results of 1H-NMR analyses showed that the average numbers of aromatic rings in the aromatics, resins and asphaltenes units were 3.2, 5.6 and 8.2, respectively. SFS was used to investigate the distribution of aromatic rings in residue fractions, the main distribution range of aromatic rings in aromatics, resins and asphaltenes were 3 4 rings, 3--5 rings and more than 5 rings, respectively. The aromatic network in residue fractions was oxidized to produce numerous carboxylic acids. The types and content of benzenepolycarboxylic acids, such as phthalic acid, benzenetricarboxylic acids, benzenetetracarboxylic acids, benzenepentacarboxylic acid and benzenehexacarboxylic acid disclosed the condensed types of aromatic nuclei in the core. The biphenyl fraction (BIPH), the cata-condensed fraction (CATA), the peri-condensed fraction (PERI) and the condensed index (BCI) were calculated based on the benzenepolycarboxylic acids formed. The results implied that there was less biphenyl type structures in all residue fractions. The aromatics fraction was almost composed of the cata-condensed type system, and the asphaltenes fraction was wholly composed of the peri-condensed type system, while in the resins fraction co-existed the two types, herein the peri-con- densed type was predominant over the cata-condensed type. Based on the analytical results obtained in the study, the components --aromatics, resins and asphaltenes -- were given the likely structural models. 相似文献
72.
对省煤器开裂管进行了化学成分及宏、微观分析。分析结果表明,在高温高压条件下,在其焊缝溶合区出现粗大的魏氏组织,管材中的珠光体组织产生了不同程度的球化,而母材组织又存在严重的带状组织。在过热条件下熔合区极易出现裂纹,并由此快速扩展,造成省煤器管开裂。 相似文献
73.
74.
V. G. Khoruzhaya K. E. Kornienko P. S. Martsenyuk T. Ya. Velikanova 《Powder Metallurgy and Metal Ceramics》2006,45(5-6):251-258
Methods of differential thermal analysis, x-ray diffraction, microstructural analysis and electron probe microanalysis are
used to study alloys of the Al-Rh system over the whole concentration range. It is established that the phase of equiatomic
composition AlRh melts congruently at 2060°C and it has an extended range of homogeneity (45.1–54.2 at.% Rh). The solubility
of aluminum in rhodium reaches 9 at.%, decreasing to 6 at.% at 850°C. Coordinates are determined for the eutectic point l
⇆ AlRh + 〈Rh〉 as 70 at.% Rh and 1715°C. The existence of intermediate phases, their crystal structure, and also the method
of forming phases in the field of composition rich in aluminum given in publications are confirmed.
__________
Translated from Poroshkovaya Metallurgiya, Nos. 5–6(449), pp. 48–56, May–June, 2006. 相似文献
75.
76.
Wei Hui 《Frontiers of Computer Science in China》2007,1(3):361-372
Almost all applications of Artificial Neural Networks (ANNs) depend mainly on their memory ability. The characteristics of
typical ANN models are fixed connections, with evolved weights, globalized representations, and globalized optimizations,
all based on a mathematical approach. This makes those models to be deficient in robustness, efficiency of learning, capacity,
anti-jamming between training sets, and correlativity of samples, etc. In this paper, we attempt to address these problems
by adopting the characteristics of biological neurons in morphology and signal processing. A hierarchical neural network was
designed and realized to implement structure learning and representations based on connected structures. The basic characteristics
of this model are localized and random connections, field limitations of neuron fan-in and fan-out, dynamic behavior of neurons,
and samples represented through different sub-circuits of neurons specialized into different response patterns. At the end
of this paper, some important aspects of error correction, capacity, learning efficiency, and soundness of structural representation
are analyzed theoretically. This paper has demonstrated the feasibility and advantages of structure learning and representation.
This model can serve as a fundamental element of cognitive systems such as perception and associative memory. 相似文献
77.
A compact dipole antenna for the terrestrial digital multimedia broadcasting (TDMB) application is presented. The length of the antenna is about 0.06λ at the TDMB resonance frequency of 190 MHz. Miniaturization of the antenna is achieved by using meander structures and lumped elements. The proposed antenna has two resonance frequencies and covers the TDMB band from 174 MHz to 216 MHz in Korea. The antenna has good impedance bandwidth and radiation characteristics for the TDMB. The experimental results of the designed dipole antenna are presented and analyzed. 相似文献
78.
An optimal control problem with nonsmooth performance criterion described by a system of ordinary differential equations is considered. Necessary first-order optimality conditions are obtained. 相似文献
79.
耀江大厦顶层屋面热泵的振动治理 总被引:1,自引:0,他引:1
本文通过耀江大厦27层屋面上六台热泵振动治理前后的振动和噪声测试数据的对比,简要阐述了安装在屋面上热泵的振动影响的程度和范围、产生振动影响和固体噪声传递的原因,并介绍了热泵双层隔振的方法和隔振效果。 相似文献
80.
采用种子乳液聚合法制备了含有PBA\PMMA\PS三种组分的丙烯酸酯类抗冲型改性剂ACR,在ACR的幔层结构中引入接枝剂甲基丙烯酸烯丙酯(ALMA)来完善幔层结构,从而实现核一壳之间良好的结合,用红外光谱(FTIR)和差示扫描量热法(DSC)对ACR的组成和结构进行表征。研究结果表明:由PBA\PMMA\PS三组分构成的ACR在抗冲击性能上要略优于由简单的PBA\PMMA构成的ACR,苯乙烯单体(St)最多可以取代大约1/3壳层的甲基丙烯酸甲酯(MMA),甲基丙烯酸烯丙酯(ALMA)的引入对幔层结构的完善起了显著的作用。 相似文献