全文获取类型
收费全文 | 93666篇 |
免费 | 8384篇 |
国内免费 | 5399篇 |
专业分类
电工技术 | 3744篇 |
技术理论 | 4篇 |
综合类 | 9756篇 |
化学工业 | 14378篇 |
金属工艺 | 6457篇 |
机械仪表 | 5406篇 |
建筑科学 | 19035篇 |
矿业工程 | 3575篇 |
能源动力 | 2543篇 |
轻工业 | 5361篇 |
水利工程 | 2503篇 |
石油天然气 | 4368篇 |
武器工业 | 926篇 |
无线电 | 5558篇 |
一般工业技术 | 11082篇 |
冶金工业 | 3505篇 |
原子能技术 | 700篇 |
自动化技术 | 8548篇 |
出版年
2024年 | 319篇 |
2023年 | 1270篇 |
2022年 | 2472篇 |
2021年 | 2858篇 |
2020年 | 2736篇 |
2019年 | 2316篇 |
2018年 | 2177篇 |
2017年 | 2734篇 |
2016年 | 2867篇 |
2015年 | 3107篇 |
2014年 | 5688篇 |
2013年 | 5200篇 |
2012年 | 6435篇 |
2011年 | 7108篇 |
2010年 | 5521篇 |
2009年 | 5936篇 |
2008年 | 5381篇 |
2007年 | 6420篇 |
2006年 | 5848篇 |
2005年 | 5103篇 |
2004年 | 4169篇 |
2003年 | 3732篇 |
2002年 | 3190篇 |
2001年 | 2647篇 |
2000年 | 2291篇 |
1999年 | 1893篇 |
1998年 | 1489篇 |
1997年 | 1281篇 |
1996年 | 950篇 |
1995年 | 830篇 |
1994年 | 774篇 |
1993年 | 520篇 |
1992年 | 470篇 |
1991年 | 373篇 |
1990年 | 307篇 |
1989年 | 215篇 |
1988年 | 166篇 |
1987年 | 87篇 |
1986年 | 66篇 |
1985年 | 79篇 |
1984年 | 64篇 |
1983年 | 57篇 |
1982年 | 66篇 |
1981年 | 24篇 |
1980年 | 71篇 |
1979年 | 14篇 |
1978年 | 12篇 |
1975年 | 11篇 |
1959年 | 10篇 |
1951年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
221.
海洋平台损伤检测的发展现状与展望 总被引:2,自引:0,他引:2
针对海洋平台损伤检测技术进行了分析,总结了国内外海洋平台损伤检测技术的最新进展。对各种检测方法进行了分类与比较,分析了不同检测方法的基本原理及其适用范围,提出了海洋工程结构损伤检测的二步法,可以综合利用不同的损伤检测方法,更准确、有效地对平台进行损伤检测。 相似文献
222.
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
223.
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
224.
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
225.
Maisto Stephen A.; Chung Tammy A.; Cornelius Jack R.; Martin Christopher S. 《Canadian Metallurgical Quarterly》2003,17(2):98
This study investigated the Stages of Change Readiness and Treatment Eagerness Scale (SOCRATES: W. R. Miller & J. S. Tonigan, 1996) in adolescents presenting for treatment of alcohol use disorder (AUD). The participants were 80 males and 43 females (mean age=16.8 years) who presented for AUD treatment (95.1% outpatient, 4.9% inpatient). Participants completed assessments at baseline and 1 year and provided information on alcohol use and related variables monthly between these 2 assessments. Principal-components and confirmatory factor analyses of the baseline SOCRATES identified 2 factors, Taking Steps and Recognition, which showed good internal consistency and concurrent and predictive evidence of validity. The results were interpreted as supporting the use of the SOCRATES with clinical samples of adolescents. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
226.
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
227.
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
228.
通过对Cholesky分解法求解线性方程组的分析,建立Cholesky分解法三角化对称正定阵的图模型,并基于该模型及Mesh结构P/G网络的自身特点,提出一个P/G网快速分析算法.实验证明,该算法能大大降低Mesh结构P/G网络的分析运算时间和内存占用. 相似文献
229.
It has been revealed, that in Ir subjected to severe plastic deformation, an ultrafine grained structure (UFG) is formed (the grain size of 20-30 nm). Practically no defects have been detected within the grains, while, in the case of Ar+ implantation, the subgrain structure with characteristic sizes of about 3-5 nm is formed; defects have been detected within subgrains.The subgrain structure was also revealed in UFG Ni and Cu after severe plastic deformation (SPD) (subgrain size of 3-15 nm), but in the latter case the observed boundary region is broader and subgrain is highly disoriented. 相似文献
230.
Hydrothermal process was applied to synthesize zinc oxide nanocrystals. X-ray powder diffraction and scanning electron microscopy were used to analyze the crystal structure and surface morphology. XRD pattern analysis showed that the ZnO clusters are single hexagonal phase of wurtzite structure (space group P63 mc) with no impurity of Zn and Zn(OH)2. Also, SEM images revealed that the size of a single ZnO crystal is between 200-500 nm in diameter and 2-5 μm in length. The influence of potassium iodide (KI) as a surfactant on the crystallinity of ZnO has been investigated. 相似文献