全文获取类型
收费全文 | 142175篇 |
免费 | 8210篇 |
国内免费 | 6357篇 |
专业分类
电工技术 | 5822篇 |
技术理论 | 6篇 |
综合类 | 11070篇 |
化学工业 | 25833篇 |
金属工艺 | 6649篇 |
机械仪表 | 5635篇 |
建筑科学 | 5091篇 |
矿业工程 | 2138篇 |
能源动力 | 4880篇 |
轻工业 | 17807篇 |
水利工程 | 2208篇 |
石油天然气 | 23072篇 |
武器工业 | 753篇 |
无线电 | 7114篇 |
一般工业技术 | 15358篇 |
冶金工业 | 3330篇 |
原子能技术 | 2269篇 |
自动化技术 | 17707篇 |
出版年
2024年 | 320篇 |
2023年 | 943篇 |
2022年 | 1731篇 |
2021年 | 2315篇 |
2020年 | 2728篇 |
2019年 | 2728篇 |
2018年 | 2525篇 |
2017年 | 2832篇 |
2016年 | 3501篇 |
2015年 | 3951篇 |
2014年 | 6824篇 |
2013年 | 7970篇 |
2012年 | 7601篇 |
2011年 | 8358篇 |
2010年 | 6501篇 |
2009年 | 7730篇 |
2008年 | 7442篇 |
2007年 | 8437篇 |
2006年 | 8194篇 |
2005年 | 6951篇 |
2004年 | 6044篇 |
2003年 | 5866篇 |
2002年 | 5651篇 |
2001年 | 4411篇 |
2000年 | 4596篇 |
1999年 | 4149篇 |
1998年 | 3477篇 |
1997年 | 3208篇 |
1996年 | 3199篇 |
1995年 | 3162篇 |
1994年 | 2797篇 |
1993年 | 1718篇 |
1992年 | 1731篇 |
1991年 | 1208篇 |
1990年 | 884篇 |
1989年 | 758篇 |
1988年 | 683篇 |
1987年 | 421篇 |
1986年 | 251篇 |
1985年 | 426篇 |
1984年 | 465篇 |
1983年 | 468篇 |
1982年 | 357篇 |
1981年 | 414篇 |
1980年 | 286篇 |
1979年 | 117篇 |
1978年 | 115篇 |
1977年 | 70篇 |
1976年 | 44篇 |
1975年 | 56篇 |
排序方式: 共有10000条查询结果,搜索用时 234 毫秒
11.
Nowadays, oil pollution has become more serious, which causes great threats both to the ecological environment and human life. In this study, a novel type of multifunctional deacetylated cellulose acetate/polyurethane (d-MCA:MTPU) composite nanofiber membranes for oil/water separation are successfully fabricated by electrospinning, which show super-amphiphilicity in air, super-hydrophilicity in oil, and oleophobicity in water. All the d-MCA:MTPU composite nanofiber membranes with different mass ratios can be used as water-removing, oil-removing, and emulsion separation substance only by gravity driving force. The highest separation flux for water and oil reaches up to 37 000 and 74 000 L m−2 h−1, respectively, and all the separation efficiencies are more than 99%. They have outstanding comprehensive mechanics performance, which can be controlled by simply adjusting the mass ratios. They show excellent antifouling and self-cleaning ability, endowing powerful cyclic stability and reusability. Those results show that d-MCA:MTPU composite nanofiber membranes have great application prospects in oil/water separation. 相似文献
12.
13.
With the increase of industrialization and urbanization, humankind faces massive oil-based pollution due to tanker accidents, human error, and natural disasters. For this, hydrophobic sorbents are fabricated and their applications for the removal of oil from polluted water sources are investigated. These hydrophobic sorbents are prepared by the condensation reaction of poly(dimethylsiloxane) and tris[3-(trimethoxysilyl)propyl]isocyanurate cross-linker via bulk polymerization. The obtained sorbents exhibit high oil sorption capacity, fast absorption–desorption kinetics, and great reusability. Moreover, they can selectively absorb oil from the water surface, thus making them practical for water clean-up applications. 相似文献
14.
15.
In this work, the longitudinal permeability of squarely packed dual-scale fiber preforms is studied theoretically. These fiber preforms are composed of aligned porous tows and the tows are tightly packed. The effective permeability is calculated as a parallel-like network of intra-tow permeability and inter-tow permeability, which are quantified by Darcy’s law and the inscribed radius between tows, respectively. The jump velocity at the interface between inter-tow fluids and porous tows is considered, as derived by substituting Beavers and Joseph’s correlation into Brinkman’s equation. We further examine the effects of intra-tow permeability on the effective permeability of the fibrous system with three interface conditions: (1) interface velocity = 0, (2) interface velocity = mean intra-tow velocity, and (3) interface velocity = jump velocity. The jump-velocity-based model is found to be closest to numerical data. The influence of the fiber volume fraction of tows on the effective permeability is also analyzed. 相似文献
16.
17.
18.
19.
The main objective of the present work is to improve the performance of bonded joints in carbon fiber composite structures through introducing Multi-Walled Carbon Nanotubes (MWCNTs) into Epocast 50-A1/946 epoxy, which was primarily developed for joining and repairing of composite aircraft structures. Results from tension characterizations of structural adhesive joints (SAJs) with different scarf angles (5–45°) showed improvement up to 40% compared to neat epoxy (NE)–SAJs. Special attention was considered to investigate the performance of SAJs with 5° scarf angle under different environments. The tensile strength and stiffness of both NE-SAJs and MWCNT/E-SAJs were dramatically decreased at elevated temperature. Water absorption showed a marginal drop of about 2.0% in the tensile strength of the moist SAJs compared to the dry one. Cracks initiation and propagation were detected effectively using instrumented-SAJs with eight strain gauges. The experimental results agree well with the predicted using three-dimensional finite element analysis model. 相似文献
20.
This paper presents the Kriging model approach for stochastic free vibration analysis of composite shallow doubly curved shells. The finite element formulation is carried out considering rotary inertia and transverse shear deformation based on Mindlin’s theory. The stochastic natural frequencies are expressed in terms of Kriging surrogate models. The influence of random variation of different input parameters on the output natural frequencies is addressed. The sampling size and computational cost is reduced by employing the present method compared to direct Monte Carlo simulation. The convergence studies and error analysis are carried out to ensure the accuracy of present approach. The stochastic mode shapes and frequency response function are also depicted for a typical laminate configuration. Statistical analysis is presented to illustrate the results using Kriging model and its performance. 相似文献