全文获取类型
收费全文 | 41210篇 |
免费 | 1763篇 |
国内免费 | 957篇 |
学科分类
工业技术 | 43930篇 |
出版年
2024年 | 36篇 |
2023年 | 177篇 |
2022年 | 445篇 |
2021年 | 655篇 |
2020年 | 472篇 |
2019年 | 405篇 |
2018年 | 471篇 |
2017年 | 655篇 |
2016年 | 1044篇 |
2015年 | 1738篇 |
2014年 | 2192篇 |
2013年 | 2080篇 |
2012年 | 2370篇 |
2011年 | 3837篇 |
2010年 | 3363篇 |
2009年 | 3559篇 |
2008年 | 3070篇 |
2007年 | 3145篇 |
2006年 | 2698篇 |
2005年 | 2473篇 |
2004年 | 2102篇 |
2003年 | 1959篇 |
2002年 | 1608篇 |
2001年 | 716篇 |
2000年 | 522篇 |
1999年 | 475篇 |
1998年 | 321篇 |
1997年 | 263篇 |
1996年 | 197篇 |
1995年 | 162篇 |
1994年 | 119篇 |
1993年 | 86篇 |
1992年 | 74篇 |
1991年 | 43篇 |
1990年 | 40篇 |
1989年 | 42篇 |
1988年 | 40篇 |
1987年 | 19篇 |
1986年 | 24篇 |
1985年 | 24篇 |
1984年 | 25篇 |
1983年 | 15篇 |
1982年 | 21篇 |
1981年 | 33篇 |
1980年 | 72篇 |
1979年 | 8篇 |
1978年 | 9篇 |
1977年 | 7篇 |
1975年 | 5篇 |
1973年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 296 毫秒
61.
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
62.
63.
《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
64.
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
65.
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
66.
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
67.
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
68.
This paper deals with the investigation of the effect of hygrothermal conditions on the bending of nanoplates using Levy type solution model employing the state-space concept. The nanoplates are assumed to be subjected to a hygrothermal environment. The two-unknown function plate theory is used to derive the governing differential equations on the basis of Eringen's nonlocal elasticity theory. The governing equations contain the small scale effect as well as hygrothermal and mechanical effects. These equations are converted into a set of first-order linear ordinary differential equations with constant coefficients. Analytical solution of bending response for nanoplates under combinations of simply supported, clamped and free boundary conditions is obtained. Comparison of the results with those being in the open literature is made. The influences played by small scale parameter, temperature rise, the degree of moisture concentration, boundary conditions, plate aspect ratio and side-to-thickness ratio are studied. 相似文献
69.
We demonstrate that alkali-halide salts, particularly potassium bromide, can reduce the photothermal emission (PTE) from single walled carbon nanotubes (SWNT). PTE is a prominent spectral feature in Raman spectroscopy when a near infrared laser is used to analyze a dark colored sample. We subsequently show that trapping salts inside SWNT and coating SWNT with the salt has a more pronounced impact on not only reducing PTE, but also enhancing the intensity of the Raman spectral features. The effect, which we have called nanotube enhanced Raman spectroscopy (NERS), has differences and similarities to the widely studied surface enhanced Raman spectroscopy (SERS). 相似文献
70.
实时操作系统DSP/BIOS在DSP开发中的应用 总被引:2,自引:0,他引:2
本文介绍了RTOS(实时操作系统)DSP/BIOS在DSP的开发设计中的应用。在简述了DSP的一般模型后,论述了RTOS在DSP/BIOS外设管理,实时性能分析以及程序流程控制中的应用。 相似文献