全文获取类型
收费全文 | 76262篇 |
免费 | 7098篇 |
国内免费 | 4766篇 |
专业分类
电工技术 | 5732篇 |
技术理论 | 6篇 |
综合类 | 6164篇 |
化学工业 | 11602篇 |
金属工艺 | 4518篇 |
机械仪表 | 5146篇 |
建筑科学 | 6062篇 |
矿业工程 | 2154篇 |
能源动力 | 2287篇 |
轻工业 | 4815篇 |
水利工程 | 1587篇 |
石油天然气 | 3934篇 |
武器工业 | 926篇 |
无线电 | 9123篇 |
一般工业技术 | 8523篇 |
冶金工业 | 3218篇 |
原子能技术 | 1073篇 |
自动化技术 | 11256篇 |
出版年
2024年 | 325篇 |
2023年 | 1093篇 |
2022年 | 1978篇 |
2021年 | 2933篇 |
2020年 | 2240篇 |
2019年 | 1827篇 |
2018年 | 2029篇 |
2017年 | 2308篇 |
2016年 | 2168篇 |
2015年 | 3070篇 |
2014年 | 3871篇 |
2013年 | 4756篇 |
2012年 | 5103篇 |
2011年 | 5585篇 |
2010年 | 5283篇 |
2009年 | 5145篇 |
2008年 | 4947篇 |
2007年 | 4627篇 |
2006年 | 4419篇 |
2005年 | 3721篇 |
2004年 | 2853篇 |
2003年 | 2693篇 |
2002年 | 2803篇 |
2001年 | 2578篇 |
2000年 | 1909篇 |
1999年 | 1622篇 |
1998年 | 1179篇 |
1997年 | 938篇 |
1996年 | 857篇 |
1995年 | 690篇 |
1994年 | 575篇 |
1993年 | 451篇 |
1992年 | 361篇 |
1991年 | 242篇 |
1990年 | 207篇 |
1989年 | 163篇 |
1988年 | 125篇 |
1987年 | 75篇 |
1986年 | 83篇 |
1985年 | 45篇 |
1984年 | 35篇 |
1983年 | 36篇 |
1982年 | 35篇 |
1981年 | 29篇 |
1980年 | 15篇 |
1979年 | 16篇 |
1978年 | 7篇 |
1976年 | 16篇 |
1973年 | 8篇 |
1951年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 21 毫秒
71.
72.
Organic‐acid‐catalyzed sol–gel route for preparing poly(methyl methacrylate)–silica hybrid materials
Jui‐Ming Yeh Kuan‐Yeh Huang Chung‐Feng Dai B. G. Chand Chang‐Jian Weng 《应用聚合物科学杂志》2008,110(4):2108-2114
In this study, a series of organic–inorganic hybrid sol–gel materials consisting of a poly(methyl methacrylate) (PMMA) matrix and dispersed silica (SiO2) particles were successfully prepared through an organic‐acid‐catalyzed sol–gel route with N‐methyl‐2‐pyrrolidone as the mixing solvent. The as‐synthesized PMMA–SiO2 nanocomposites were subsequently characterized with Fourier transform infrared spectroscopy and transmission electron microscopy. The solid phase of organic camphor sulfonic acid was employed to catalyze the hydrolysis and condensation (i.e., sol–gel reactions) of tetraethyl orthosilicate in the PMMA matrix. The formation of the hybrid membranes was beneficial for the physical properties at low SiO2 loadings, especially for enhanced mechanical strength and gas barrier properties, in comparison with the neat PMMA. The effects of material composition on the thermal stability, thermal conductivity, mechanical strength, molecular permeability, optical clarity, and surface morphology of the as‐prepared hybrid PMMA–SiO2 nanocomposites in the form of membranes were investigated with thermogravimetric analysis, differential scanning calorimetry, dynamic mechanical analysis, gas permeability analysis, ultraviolet–visible transmission spectroscopy, and atomic force microscopy, respectively. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献
73.
A series of novel block polymers of polyurethane (PU) and chitosan have been prepared in two steps. The first step is the preparation of PU prepolymer, obtained from polytetramethylene oxide glycol (PTMO, Mn = 1000), isophrone diisocyanate (IPDI), and 2,2′-dimethylol propionic acid (DMPA), followed by ionizing PU prepolymer with triethylamine (TEA). The second step involves PU chain-extended by water-soluble chitosan of low molecular weight (Mn = 5000) by self-emulsion polymerization method. The sizes of the latex particles, morphology, and copolymer architecture have been characterized by dynamic light scattering (DLS), general tensile test, infrared spectroscopy (IR), surface contact angle measurement, and transmission electron microscopy (TEM). Furthermore, it shows that the addition of chitosan remarkably increases anticoagulative property of PU elastomers confirmed by the recalcification time. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献
74.
Associations (dimer or aggregate) of anthracene (An) fluorophores tend to interrupt the monomer emission and reduce the quantum yield (ΦPL); therefore, poly(methyl methacrylate) (PMMA) chain was used in this study to chemically link to anthracene and to block the mutual associations among the anthracene fluorophores. With this aim, the target polymers were prepared by anionic polymerizations with 9,10‐dibromoanthracene/s‐butyllithium as initiating system to proceed polymerizations of methyl methacrylate (MMA) directly or in the presence of 1,1‐diphenylethylene (DPE). Use of DPE before addition of MMA produces stable initiating anionic species and avoids potential side reactions during polymerization; however, it also introduces four β‐phenylene rings around the central anthracene ring, which interfere with the corresponding emission pattern and reduce the ΦPL (32%) value due to potential interactions between phenylene rings and anthracene. On the contrast, polymerization without participation of DPE results in polymer with central anthracene ring directly connected to two PMMA chains, which gives clean vibronic emission pattern with limited association emissions and enhanced ΦPL (52%) value. Physical blending of anthracene by PMMA is less efficient to restrain the associations and results in a film of lower ΦPL (20%). © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献
75.
Branched polyacrylonitrile (PAN) was prepared through a self‐condensing vinyl copolymerization of acrylonitrile and 2‐(2‐bromopropionyloxy)ethyl acrylate (BPEA). The branched architecture of the product was confirmed by NMR spectra and the average degree of branching (DB ) was estimated. Through a comparison of the intrinsic viscosity of the product with that of its linear analogue, the contraction factor g′ was calculated. It was found that the viscosity of the branched PAN was obviously lower that that of linear PAN. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献
76.
Defeng Wu Yisheng Zhang Lanfeng Wu Lifeng Jin Ming Zhang Weidong Zhou Changhao Yan 《应用聚合物科学杂志》2008,108(3):1934-1941
Polyarylene ether nitriles (PEN)/thermotropic liquid crystalline polymer (TLCP) blend was prepared via melt mixing. The immiscible phase morphologies, linear and nonlinear, as well as transient viscoelastic properties of the blend were studied using SEM, rheometer, and DMA. The linear dynamic viscoelastic behavior of the blend shows temperature dependence due to further evolution of the immiscible morphology and, as a result, the principle of time‐temperature superposition (TTS) is invalid. In the steady shear flow, the discrete TLCP phase is difficult to be broken up because of the high viscosity ratio of the blend systems, while is easy to be coarsened and followed by elongation, and finally, to form fibrous morphology at high TLCP content and high shear level. During this morphological evolution process, the transient stress response presents step increase and nonzero residual relaxation behavior, leading to increase of the dynamic viscoelastic responses after steady preshear. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献
77.
78.
79.
80.
Kuo‐Hsiung Wang Tzong‐Ming Wu Yeng‐Fong Shih Chien‐Ming Huang 《Polymer Engineering and Science》2008,48(9):1833-1839
The water bamboo husk is one of major agricultural wastes in Taiwan. In this study, the powder obtained from the water bamboo husk was added to poly(lactic acid) (PLA) to form novel reinforced biodegradable composites. Morphologies, mechanical properties, and heat resistance of these water bamboo powder reinforced composites were investigated. The results indicate that the char yields were increased as plant powder was incorporated to PLA. In addition, the mechanical properties were also enhanced due to the addition of powders. The increments of storage moduli of PLA were about 50–200%. Moreover, the increments of loss moduli of PLA were about 70–200%. On the other hand, the Tg of PLA was slightly decreased by the addition of powder, and this may improve the brittle characteristics of PLA. Furthermore, this type of reinforced PLA would be more environmental friendly than the artificial additive‐reinforced one. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers 相似文献