全文获取类型
收费全文 | 94986篇 |
免费 | 14166篇 |
国内免费 | 9823篇 |
专业分类
电工技术 | 9622篇 |
技术理论 | 1篇 |
综合类 | 9815篇 |
化学工业 | 7262篇 |
金属工艺 | 5999篇 |
机械仪表 | 6367篇 |
建筑科学 | 2189篇 |
矿业工程 | 1297篇 |
能源动力 | 1786篇 |
轻工业 | 2429篇 |
水利工程 | 1391篇 |
石油天然气 | 1229篇 |
武器工业 | 1376篇 |
无线电 | 14065篇 |
一般工业技术 | 11613篇 |
冶金工业 | 965篇 |
原子能技术 | 567篇 |
自动化技术 | 41002篇 |
出版年
2024年 | 548篇 |
2023年 | 1406篇 |
2022年 | 2961篇 |
2021年 | 3186篇 |
2020年 | 3240篇 |
2019年 | 2704篇 |
2018年 | 2735篇 |
2017年 | 3279篇 |
2016年 | 4035篇 |
2015年 | 5307篇 |
2014年 | 6562篇 |
2013年 | 6315篇 |
2012年 | 7487篇 |
2011年 | 8986篇 |
2010年 | 7253篇 |
2009年 | 7337篇 |
2008年 | 7214篇 |
2007年 | 7506篇 |
2006年 | 5798篇 |
2005年 | 4981篇 |
2004年 | 4231篇 |
2003年 | 3655篇 |
2002年 | 2888篇 |
2001年 | 1801篇 |
2000年 | 1517篇 |
1999年 | 1275篇 |
1998年 | 988篇 |
1997年 | 792篇 |
1996年 | 603篇 |
1995年 | 434篇 |
1994年 | 361篇 |
1993年 | 262篇 |
1992年 | 272篇 |
1991年 | 152篇 |
1990年 | 161篇 |
1989年 | 115篇 |
1988年 | 98篇 |
1987年 | 42篇 |
1986年 | 57篇 |
1985年 | 54篇 |
1984年 | 48篇 |
1983年 | 36篇 |
1982年 | 46篇 |
1981年 | 46篇 |
1980年 | 93篇 |
1979年 | 18篇 |
1978年 | 19篇 |
1977年 | 15篇 |
1975年 | 14篇 |
1959年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
101.
In this paper, debonding phenomena between carbon fiber reinforced polymer (CFRP) strips and masonry support were investigated on the basis of single-lap shear tests, considering different dimensions of the bond length. To capture the post-peak response of the CFRP–masonry joint, the slip between the support and the reinforcement strip was controlled using a clip gauge positioned at the end of the reinforcement. The tests were simulated by means of a finite element model able to capture the post-peak snap-back behavior due to the failure process. The numerical model is based on zero-thickness interface elements and on a proper non-linear cohesive law. The comparison between experimental and numerical results was performed in terms of overall response, measured by both the machine stroke and the clip gauge positioned at the free end of the reinforcement. The cases of effective bond length greater and lesser than the minimum anchorage length, suggested by the CNR Italian recommendation, were considered. 相似文献
102.
103.
Fresh and frozen-thawed (F-T) pork meats were classified by Vis–NIR hyperspectral imaging. Eight optimal wavelengths (624, 673, 460, 588, 583, 448, 552 and 609 nm) were selected by successive projections algorithm (SPA). The first three principal components (PCs) obtained by principal component analysis (PCA) accounted for over 99.98% of variance. Gray-level-gradient co-occurrence matrix (GLGCM) was applied to extract 45 textural features from the PC images. The correct classification rate (CCR) was employed to evaluate the performance of the partial least squares-discriminate analysis (PLS-DA) models, by using (A) the reflected spectra at full wavelengths and (B) those at the optimal wavelengths, (C) the extracted textures based on the PC images, and (D) the fused variables combining spectra at the optimal wavelengths and textures. The results showed that the best CCR of 97.73% was achieved by applying (D), confirming the high potential of textures for fresh and F-T meat discrimination. 相似文献
104.
《Intermetallics》2015
Drop-tube processing was used to rapidly solidify droplets of Ni64.7Fe10Si25.3 and Ni59.7Fe15Si25.3 alloys. In the larger droplets, and therefore at low cooling rates, only two phases, γ-Ni31Si12 and β1-Ni3Si were observed. Conversely, in the smaller droplets, and therefore at higher cooling rates, the metastable phase Ni25Si9 was also observed. The critical cooling rate for the formation of Ni25Si9 was estimated as 5 × 103 K s−1. SEM and TEM analysis reveals three typical microstructures: (I) a regular structure, comprising single-phase γ-Ni31Si12 and a eutectic structure between γ-Ni31Si12 and β1-Ni3Si; (II) a refined lamellar structure with a lamellar spacing <50 nm comprising γ-Ni31Si12 and β1-Ni3Si; (III) an anomalous structure with a matrix of Ni25Si9 and only a very small proportion of a second, and as yet unidentified, phase. These results indicate that there is an extended stability field for Ni25Si9 in the Ni-rich part of the Ni–Fe–Si ternary system in comparison to the Ni–Si binary system. With an increase of cooling rate, an increasing fraction of small droplets experience high undercoolings and, therefore, can be undercooled into the Ni25Si9 stability field forming droplets consisting of only the anomalous structure (III). The Fe atoms are found to occupy different substitutional sites in different phase, i.e. Fe substitutes for Ni in the γ phase and Si in the L12 (β1) phase respectively. 相似文献
105.
106.
目前,基于因素空间理论的背景基提取算法计算过程复杂,初始化必须依赖各因素极值,基点数量提取冗余等原因,未能在应用中取得很好效果。为此,结合内点判别法和知识可继承、可扩展的思想,提出一种计算简单、初始化独立、基点数量小的改进的背景基提取算法。然后,利用改进的背景基提取算法构造出一种全新的数据分类算法-基点分类算法,基点分类算法以提取每一类样本的背景基为预测模型,再通过新定义的λ-背景基,优化预测模型。数值实验表明:基点分类算法原理简单、构造难度小、分类模型泛化能力强,预测能力准确率高,同时严格的模型限定区域又能为识别新类别提供新方法。 相似文献
107.
Aleksandra Czumaj Sylwia Szrok-Jurga Areta Hebanowska Jacek Turyn Julian Swierczynski Tomasz Sledzinski Ewa Stelmanska 《International journal of molecular sciences》2020,21(23)
The importance of coenzyme A (CoA) as a carrier of acyl residues in cell metabolism is well understood. Coenzyme A participates in more than 100 different catabolic and anabolic reactions, including those involved in the metabolism of lipids, carbohydrates, proteins, ethanol, bile acids, and xenobiotics. However, much less is known about the importance of the concentration of this cofactor in various cell compartments and the role of altered CoA concentration in various pathologies. Despite continuous research on these issues, the molecular mechanisms in the regulation of the intracellular level of CoA under pathological conditions are still not well understood. This review summarizes the current knowledge of (a) CoA subcellular concentrations; (b) the roles of CoA synthesis and degradation processes; and (c) protein modification by reversible CoA binding to proteins (CoAlation). Particular attention is paid to (a) the roles of changes in the level of CoA under pathological conditions, such as in neurodegenerative diseases, cancer, myopathies, and infectious diseases; and (b) the beneficial effect of CoA and pantethine (which like CoA is finally converted to Pan and cysteamine), used at pharmacological doses for the treatment of hyperlipidemia. 相似文献
108.
Static stresses analysis of carbon nano-tube reinforced composite (CNTRC) cylinder made of poly-vinylidene fluoride (PVDF) is investigated in this study. Non-axisymmetric thermo-mechanical loads are applied on cylinder in presence of uniform longitudinal magnetic field and radial electric field. The surrounded elastic medium is modeled by Pasternak foundation because of its advantages to the Winkler type. Distribution of radial, circumferential and effective stresses, temperature field and electric displacements in CNTRC cylinder are determined based on Mori–Tanaka theory. The detailed parametric study is conducted, focusing on the remarkable effects of magnetic field intensity, elastic medium, angle orientation and volume fraction of carbon nano-tubes (CNTs) on distribution of effective stress. Results demonstrated that fatigue life of CNTRC cylinder will be significantly dependent on magnetic intensity, angle orientation and volume fraction of CNTs. Results of this research can be used for optimum design of thick-walled cylinders under multi-physical fields. 相似文献
109.
针对现代消费类电子产品快速更新换代的现状, 介绍了该类产品的自动化生产线成组技术,阐述了通过度量消费类电子产品相似性和派生性特征,对产线进行成组编码的原理,研究产线工位单元的建模方法,描述了建模内容,并通过有无装载板的产线结构,论述了产线成组编码集成的途径和方法. 相似文献
110.
A metal matrix composite has been obtained by a novel synthesis route, reacting Al3Ti and graphite at 1000 °C for about 1 min after ball-milling and compaction. The resulting composite is made of an aluminium matrix reinforced by nanometer sized TiC particles (average diameter 70 nm). The average TiC/Al ratio is 34.6 wt.% (22.3 vol.%). The microstructure consists of an intimate mixture of two domains, an unreinforced domain made of the Al solid solution with a low TiC reinforcement content, and a reinforced domain. This composite exhibits uncommon mechanical properties with regard to previous micrometer sized Al–TiC composites and to its high reinforcement volume fraction, with a Young’s modulus of ∼110 GPa, an ultimate tensile strength of about 500 MPa and a maximum elongation of 6%. 相似文献