全文获取类型
收费全文 | 71265篇 |
免费 | 7885篇 |
国内免费 | 2688篇 |
专业分类
电工技术 | 1108篇 |
技术理论 | 1篇 |
综合类 | 2854篇 |
化学工业 | 25877篇 |
金属工艺 | 10667篇 |
机械仪表 | 1660篇 |
建筑科学 | 1906篇 |
矿业工程 | 973篇 |
能源动力 | 1394篇 |
轻工业 | 9679篇 |
水利工程 | 318篇 |
石油天然气 | 1212篇 |
武器工业 | 348篇 |
无线电 | 2710篇 |
一般工业技术 | 16673篇 |
冶金工业 | 3230篇 |
原子能技术 | 270篇 |
自动化技术 | 958篇 |
出版年
2024年 | 467篇 |
2023年 | 1706篇 |
2022年 | 2389篇 |
2021年 | 3178篇 |
2020年 | 3064篇 |
2019年 | 2566篇 |
2018年 | 2894篇 |
2017年 | 3270篇 |
2016年 | 3309篇 |
2015年 | 3411篇 |
2014年 | 4060篇 |
2013年 | 5174篇 |
2012年 | 4528篇 |
2011年 | 5645篇 |
2010年 | 3774篇 |
2009年 | 4070篇 |
2008年 | 3364篇 |
2007年 | 3666篇 |
2006年 | 3511篇 |
2005年 | 2749篇 |
2004年 | 2717篇 |
2003年 | 2316篇 |
2002年 | 1873篇 |
2001年 | 1289篇 |
2000年 | 1205篇 |
1999年 | 959篇 |
1998年 | 823篇 |
1997年 | 711篇 |
1996年 | 536篇 |
1995年 | 480篇 |
1994年 | 353篇 |
1993年 | 263篇 |
1992年 | 269篇 |
1991年 | 216篇 |
1990年 | 262篇 |
1989年 | 252篇 |
1988年 | 87篇 |
1987年 | 59篇 |
1986年 | 60篇 |
1985年 | 68篇 |
1984年 | 68篇 |
1983年 | 33篇 |
1982年 | 55篇 |
1981年 | 8篇 |
1980年 | 35篇 |
1979年 | 6篇 |
1978年 | 6篇 |
1975年 | 6篇 |
1974年 | 6篇 |
1951年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 788 毫秒
971.
Blends based on ethylene–propylene–diene monomer rubber (EPDM) and acrylonitrile butadiene rubber (NBR) was prepared. Sulfur was used as the vulcanizing agent. The effects of blend ratio on the cure characteristics and mechanical properties, such as stress–strain behavior, tensile strength, elongation at break, hardness, rebound resilience, and abrasion resistance have been investigated. Tensile and tear strength showed synergism for the blend containing 30% of NBR, which has been explained in terms of morphology of the blends attested by scanning electron micrographs. A relatively cocontinuous morphology was observed for 70 : 30, EPDM/NBR blend system. The experimental results have been compared with the relevant theoretical models. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007 相似文献
972.
Behavior of high strength concrete with and without steel fiber reinforcement in triaxial compression 总被引:4,自引:0,他引:4
Based on an extensive experimental program, this paper studies the behavior of high strength concrete and steel fiber reinforced high strength concrete under uniaxial and triaxial compression. Triaxial stress-strain relations and failure criteria are used to evaluate the effect of steel fiber reinforcement on the mechanical properties of high strength concrete in triaxial compression, which is found to be insignificant. 相似文献
973.
Molecular sieve properties of activated carbon fibers modified by cracking treatment with methane are studied herein. The effect of methane treatment on the porous texture of the samples has been studied while varying temperature and time. These materials have been evaluated for their selectivity during CO2 and CH4 separation; their uptakes have been compared with non-treated activated carbon fibers (studied previously), which were considered suitable to be used as molecular sieves. Kinetics of CO2 and CH4 uptake have also been investigated in this research. The treatment produced materials exhibiting fast kinetics and high selectivity during CO2 and CH4 separation; at the same time however, the CO2 uptake capacity was diminished. 相似文献
974.
R.D. Toledo Filho J.P. Gonçalves E.M.R. Fairbairn 《Cement and Concrete Research》2007,37(9):1357-1365
The Brazilian ceramic industry generates large amounts of calcined-clay waste. This paper examines the factors that influence its potential for use as a partial replacement of Portland cement. Superplasticized mortars of equal workability containing ground crushed waste calcined-clay brick (GCWCCB) in the proportions of 10, 20, 30 and 40% as a cement replacement were analyzed through mechanical tests, pore structure characterization and durability tests. The results indicated the optimal percentages of substitution lies between 10% to 20%. The potential reduction of CO2 emissions could be as high as 10% of current Brazilian cement industry emissions if this approach were to be fully implemented, and it could be eligible for “Clean Development Mechanism” credits under Kyoto protocol. 相似文献
975.
The dielectric constant, dielectric loss, and ac conductivity of polyblends of cellulose acetate hydrogen phthalate (CAP) and poly (vinyl pyrrolidone) (PVP) of different compositions were measured in the temperature range of 300–430 K and in the frequency range of 50 Hz–100 kHz. In the blends, the dielectric constant as well as the dielectric loss as a function of the temperature display a single peak corresponding to the glass transition temperature (Tg) in the region between the Tg values of the pure polymers. The Tg values observed agree well with those values obtained from DSC. Dielectric studies show that CAP forms a miscible blend with PVP. Ac conductivity values were calculated from the dielectric data and the conduction mechanism is discussed. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1702–1708, 2002 相似文献
976.
977.
The surface and mechanical properties of copolymers of hydroxyalkyl acrylates and methacrylates have been examined by a variety of techniques. This work is complementary to earlier parts of this series which describe the effect of copolymer structure on water binding properties. Water structure has been demonstrated to exert a profound effect upon mechanical properties whether measured in compression or in tension. In particular, water that is characterized by differential scanning calorimetry as ‘freezing’ water is observed to have a marked plasticizing effect upon the gel, whereas ‘non-freezing’ water has little such effect. Similarly, the ‘freezing’ water produces a more marked effect on thermally induced transitions. Two distinct transition points are observed as a result of its presence. One corresponds to the freezing point of water and the other to a glass transition temperature, whose value depends upon the proportion of ‘freezing’ or ‘plasticizing’ water in the gel. Several predictive and direct measurement techniques have been used to study the surface properties of the copolymers in both hydrated and dehydrated states. Taken together they have established a sound understanding of the way in which polar and dispersive components of surface free energy vary as a function of copolymer composition and water content. Use of protein adsorption and fibroblast cell interaction techniques demonstrate that biological phenomena respond to changes at a molecular level which current macroscopic surface energy techniques are unable to discern. 相似文献
978.
The influence of the electron beam modification of a dual‐phase filler on the dynamic mechanical properties of styrene‐butadiene rubber (SBR) is investigated in the presence and absence of trimethylol propane triacrylate or triethoxysilylpropyltetrasulfide. Electron beam modification of the filler results in reduction of the tan δ at 70°C, a parameter for rolling resistance, and an increase in the tan δ at 0°C, a parameter for wet skid resistance of SBR vulcanizates. These modified fillers give significantly better overall performance in comparison with the control dual‐phase filler. This variation in properties is explained in terms of filler parameters such as the filler structure that leads to rubber occlusion and filler networking. These results are further corroborated using the master curves obtained by the time–temperature superposition principle. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2992–3004, 2003 相似文献
979.
以扩链剂ADR4370S 和硅烷偶联剂KH550为原料,合成了一种含硅相容剂(K-ADR)并应用于滑石增强PBAT基复合材料中。采用FTIR、1HNMR、TGA对K-ADR的结构进行了表征,通过转矩流变仪制备PBAT/K-ADR/滑石体系复合材料,并对复合材料的流变性能、力学性能、冲击断面微观形貌和元素分布进行了表征。结果表明,当相容剂K-ADR添加质量是体系质量的6‰时,PBAT/K-ADR/滑石复合材料拉伸强度、冲击强度和弯曲模量分别为19.11MPa、67.68KJ/m2和378.36MPa,相比于纯PBAT样品分别提高了5.3%、110.7%和346.7%。复合薄膜的水蒸气透过率系数(WVP)为5.70×10-12g·cm/cm2·s,氧气透过率系数(OP)为3.17×10-13cm3·cm/(cm2·s·Pa),分别降低为纯PBAT样品的2.1%和1.0%。 相似文献
980.
The optimum conditions for crosslinking rigid poly(vinyl chloride) with trimethylolpropane trimethacrylate (TMPTMA) and peroxide have been examined. The extent of crosslinking was measured by determining gel content by Soxhlet extraction in tetrahydrofuran. Mechanical properties were measured at 130°C and dynamic viscoelastic measurements were carried out to detect changes in the glass transition temperature (Tg). It was found that 15 phr of TMPTMA and 0.3 phr of peroxide were optimum concentrations for maximizing the extent of crosslinking, tensile strength, and Tg. The lower molding temperature of 170°C was preferred to minimize thermal degradation. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2904–2909, 2007 相似文献