全文获取类型
收费全文 | 17407篇 |
免费 | 1139篇 |
国内免费 | 586篇 |
专业分类
电工技术 | 471篇 |
综合类 | 968篇 |
化学工业 | 908篇 |
金属工艺 | 867篇 |
机械仪表 | 1657篇 |
建筑科学 | 368篇 |
矿业工程 | 333篇 |
能源动力 | 379篇 |
轻工业 | 350篇 |
水利工程 | 64篇 |
石油天然气 | 183篇 |
武器工业 | 99篇 |
无线电 | 1678篇 |
一般工业技术 | 1284篇 |
冶金工业 | 479篇 |
原子能技术 | 288篇 |
自动化技术 | 8756篇 |
出版年
2024年 | 6篇 |
2023年 | 96篇 |
2022年 | 132篇 |
2021年 | 193篇 |
2020年 | 215篇 |
2019年 | 181篇 |
2018年 | 215篇 |
2017年 | 358篇 |
2016年 | 393篇 |
2015年 | 439篇 |
2014年 | 875篇 |
2013年 | 763篇 |
2012年 | 869篇 |
2011年 | 1427篇 |
2010年 | 856篇 |
2009年 | 831篇 |
2008年 | 895篇 |
2007年 | 1049篇 |
2006年 | 918篇 |
2005年 | 827篇 |
2004年 | 761篇 |
2003年 | 840篇 |
2002年 | 716篇 |
2001年 | 603篇 |
2000年 | 574篇 |
1999年 | 634篇 |
1998年 | 670篇 |
1997年 | 518篇 |
1996年 | 439篇 |
1995年 | 346篇 |
1994年 | 245篇 |
1993年 | 227篇 |
1992年 | 186篇 |
1991年 | 147篇 |
1990年 | 105篇 |
1989年 | 80篇 |
1988年 | 106篇 |
1987年 | 44篇 |
1986年 | 61篇 |
1985年 | 77篇 |
1984年 | 59篇 |
1983年 | 39篇 |
1982年 | 22篇 |
1981年 | 29篇 |
1980年 | 15篇 |
1979年 | 15篇 |
1978年 | 6篇 |
1977年 | 8篇 |
1976年 | 9篇 |
1974年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
993.
It is well known that the fiber-matrix interface in many composites has a profound influence on composite performance. The objective of this study is to understand the influence of composition and concentration of coupling agent on interface strength by coating E-glass fibers with solutions containing a mixture of hydrolyzed propyl trimethoxysilane (PTMS) and γ-aminopropyl trimethoxysilane (APS). The failure behavior and strength of the fiber-matrix interface were assessed by the single-fiber fragmentation test (SFFT), while the structure of silane coupling agent was studied in terms of its thickness by ellipsometry, its morphology by atomic force microscopy, its chemical composition by diffuse reflectance infrared Fourier transform (DRIFT), and its wettability by contact angle measurement. Deposition of 4.5 ×10 -3 mol/L solution of coupling agent in water resulted in a heterogeneous surface with irregular morphology. The SFFT results suggest that the amount of adhesion between the glass fiber and epoxy is dependent not only on the type of coupling agent but also on the composition of the coupling agent mixture. As the concentration of APS in the mixture increased, the extent of interfacial bonding between the fiber and matrix increased and the mode of failure changed. For the APS coated glass epoxy system, matrix cracks were formed perpendicular to the fiber axis in addition to a sheath of debonded interface region along the fiber axis. 相似文献
994.
基于离散单元法,利用建模软件Solidworks、离散单元模拟软件EDEM,对单螺杆挤出机固体颗粒输送运动进行模拟。研究内容包括物料参数如颗粒的形状、大小,螺杆转速,结构参数如螺棱数量、螺棱倾角对固体输送量的影响,以及机筒内部颗粒的运动和填充情况。结果表明,单一螺杆-机筒模型存在最佳颗粒粒径、最佳颗粒形状;颗粒直径越小,填充效果越好;螺棱倾角为105°时颗粒输送量最大。 相似文献
995.
李方伟 《化学工业与工程技术》2003,24(2):47-48
简述了三聚氰胺生产流程、冷气风机的作用和结构,介绍了冷气风机密封泄漏的计算机单元模拟过程,提出了以风机进出口温差作为判断其密封泄漏量大小的依据。 相似文献
996.
The three-dimensional morphology of polyethylene single crystals grown from dilute solution has been examined by atomic force microscopy. Single crystals were deposited on a soft ground of aqueous solution of poly(vinyl alcohol) (PVA) to avoid the collapse of thin lamellar crystals with thickness of 10 nm. The observation of single crystals on dried PVA clarifies the morphology of a chair type crystal as well as well-known hollow pyramidal type. It has been confirmed that the screw dislocations in the chair type follow a selection rule of the handedness in a manner to relieve the distortion in the chair type. 相似文献
997.
998.
Understanding interfacial behaviors of isobutane alkylation with C4 olefin catalyzed by sulfuric acid or ionic liquids 下载免费PDF全文
Weizhong Zheng Huanying Wang Wenxiu Xie Ling Zhao Weizhen Sun 《American Institute of Chemical Engineers》2018,64(3):950-960
The interfacial properties between the hydrocarbon phase including isobutane and 2‐butene and the catalyst phase including H2SO4 or ionic liquids (ILs) with various alkyl chain length on their imidazolium cations have been investigated using molecular dynamics (MD) simulations. Compared to H2SO4, ILs can obviously improve the interfacial width, solubility and diffusion of reactants at the interface. The ILs with longer chains on cations exhibit a significant density enrichment of alkyl chains at the interface and tend to orient themselves with alkyl chains perpendicular to the interface and protruding into the reactant phase, which is in good agreement with the van der Waals energy between the reactants and cations of the ILs. The ILs with longer chains can improve the interfacial width and facilitate the dissolution of isobutane in catalyst phase, and thus exhibit a better catalytic performance, which agrees well with alkylation experiments in this work. © 2017 American Institute of Chemical Engineers AIChE J, 64: 950–960, 2018 相似文献
999.
Oxy-steam combustion is a promising next-generation combustion technology. Conversions of fuel-N, volatile-N, and char-N to NO and N2O during combustion of a single coal particle in O2/N2 and O2/H2O were studied in a tube reactor at low temperature. In O2/N2, NO reaches the maximum value in the devolatilization stage and N2O reaches the maximum value in the char combustion stage. In O2/H2O, both NO and N2O reach the maximum values in the char combustion stage. The total conversion ratios of fuel-N to NO and N2O in O2/N2 are obviously higher than those in O2/H2O, due to the reduction of H2O on NO and N2O. Temperature changes the trade-off between NO and N2O. In O2/N2 and O2/H2O, the conversion ratios of fuel-N, volatile-N, and char-N to NO increase with increasing temperature, and those to N2O show the opposite trends. The conversion ratios of fuel-N, volatile-N, and char-N to NO reach the maximum values at < O2 > = 30 vol% in O2/N2. In O2/H2O, the conversion ratios of fuel-N and char-N to NO reach the maximum values at < O2 > = 30 vol%, and the conversion ratio of volatile-N to NO shows a slightly increasing trend with increasing oxygen concentration. The conversion ratios of fuel-N, volatile-N, and char-N to N2O decrease with increasing oxygen concentration in both atmospheres. A higher coal rank has higher conversion ratios of fuel-N to NO and N2O. Anthracite coal exhibits the highest conversion ratios of fuel-N, volatile-N, and char-N to NO and N2O in both atmospheres. This work is to develop efficient ways to understand and control NO and N2O emissions for a clean and sustainable atmosphere. 相似文献
1000.
Maria M Marques Susete Fernandes Sandra G Correia Susana Caroo Pedro T Gomes Alberto R Dias Joo Mano Marvin D Rausch James C
W Chien 《Polymer International》2001,50(5):579-587
Vinyl acetate, methyl methacrylate, acrylonitrile and methyl vinyl ketone were investigated for co‐ and terpolymerization with ethylene and ethylene–propylene. Precursor [bis(N,N ′‐dimesitylimino)acenaphthene]dibromonickel, activated by methylaluminoxane was used as a catalyst system and trialkylaluminium was employed to block the polar groups for these polymerizations. Polymerization activities of the order of magnitude of 106 in the case of vinyl acetate and methyl methacrylate, and 105 in the case of acrylonitrile were achieved. Microanalysis and GPC of acrylonitrile copolymers found about 17 units of acrylonitrile per polymer chain. Copolymers with very different properties from the parent homopolymers were obtained in all cases except that of methyl vinyl ketone. © 2001 Society of Chemical Industry 相似文献