全文获取类型
收费全文 | 29965篇 |
免费 | 3613篇 |
国内免费 | 2876篇 |
专业分类
电工技术 | 2908篇 |
技术理论 | 1篇 |
综合类 | 3818篇 |
化学工业 | 2513篇 |
金属工艺 | 1935篇 |
机械仪表 | 2059篇 |
建筑科学 | 837篇 |
矿业工程 | 394篇 |
能源动力 | 358篇 |
轻工业 | 906篇 |
水利工程 | 202篇 |
石油天然气 | 351篇 |
武器工业 | 326篇 |
无线电 | 5303篇 |
一般工业技术 | 4912篇 |
冶金工业 | 636篇 |
原子能技术 | 178篇 |
自动化技术 | 8817篇 |
出版年
2024年 | 96篇 |
2023年 | 406篇 |
2022年 | 721篇 |
2021年 | 871篇 |
2020年 | 897篇 |
2019年 | 927篇 |
2018年 | 830篇 |
2017年 | 1154篇 |
2016年 | 1192篇 |
2015年 | 1461篇 |
2014年 | 2049篇 |
2013年 | 2214篇 |
2012年 | 2381篇 |
2011年 | 2508篇 |
2010年 | 2009篇 |
2009年 | 2099篇 |
2008年 | 1842篇 |
2007年 | 2014篇 |
2006年 | 1721篇 |
2005年 | 1453篇 |
2004年 | 1192篇 |
2003年 | 973篇 |
2002年 | 794篇 |
2001年 | 735篇 |
2000年 | 645篇 |
1999年 | 523篇 |
1998年 | 430篇 |
1997年 | 369篇 |
1996年 | 332篇 |
1995年 | 320篇 |
1994年 | 267篇 |
1993年 | 224篇 |
1992年 | 172篇 |
1991年 | 138篇 |
1990年 | 121篇 |
1989年 | 89篇 |
1988年 | 69篇 |
1987年 | 45篇 |
1986年 | 26篇 |
1985年 | 23篇 |
1984年 | 20篇 |
1983年 | 21篇 |
1982年 | 14篇 |
1981年 | 13篇 |
1980年 | 6篇 |
1979年 | 7篇 |
1978年 | 6篇 |
1977年 | 8篇 |
1976年 | 6篇 |
1951年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
52.
相干源二维波达方向估计 总被引:4,自引:0,他引:4
本文分析了平面阵接收信号的协方差矩阵,发现它可分解为一个广义对称矩阵与一个非广义对称矩阵之和,利用信号协方差矩阵的这一结构特征,重点研究了相干源二维波达方向(DOA)估计.该方法通过构造一个差矩阵,求出其本特征值对应的任一特征向量,利用谱函数估计相干源二维DOA.简要分析了二维DOA估计的分维处理。 相似文献
53.
54.
纵横波测井资料在储层评价中的应用 总被引:5,自引:1,他引:4
将弹性波基础理论,Gasman理论,Biot理论和实验研究结果相结合,探讨了沉积岩地层中速度和弹性模量,弹性模量和孔隙度,剪切模量和孔隙度,速度和孔隙度,孔隙度和Biot系数之间的关系,利用从各种声学测井资料中提取出的P波和S波时差(或速度)定量评价地层孔隙度和骨架物质,辅以泥质指示测井曲线,可以计算地层孔隙度,饱和度,岩性等参数,在M,Krief方法的基础上,采用优化算法寻求适合于任何岩性地层的孔隙度与Biot系数之间的关系式,提高了Biot系数的计算精度,该评价方法有坚实的实验基础和理论基础,评价结果与实验室岩心分析数据吻合。 相似文献
55.
56.
The bonding of β'-Al2O3 and pyrex glass to Al matrix composites by anodic bonding process is achieved. The microstructure of the bonded interface and the joining mechanisms are analyzed with scanning electron microscope (SEM), energy dispersive X-ray fluorescence spectrometer (EDX). It is observed that the bonding region across the interface consists of the metal layer, oxide transitional layer and the ceramic layer, with the transitional layer composed of surface region and sub-surface region. The bonding process can mainly be categorized into anodic bonding process and solid state diffusing process. The pile-up of the ions and its drift in the interface area are the main reasons for anode oxidation and joining of the interface. The temperature, voltage and the drift ions in the ceramic or glass during the bonding process are the essential conditions to solid state diffusing and oxide bonding at the interface. The voltages, temperature, pressure as well as the surface state are the main factors that influence the anodic bonding. 相似文献
57.
Vatroslav Bubalo Vjekoslav Jerolimov Ivo Bau
i Mladen Andreis Zorica Veksli 《Polymer International》2005,54(5):848-853
The electron‐spin‐resonance (ESR) spin‐probe method, was used to study the heterogeneity of denture resins based on poly(methyl methacrylate). Results for three resins processed by microwave energy, conventional curing and cold curing (depending on the curing procedure and exposed to ageing in various environmental conditions) were compared. All three cured resins were stored over the same time (1200 h) in distilled water at ambient temperature and in artificial saliva at 348 K. The temperature‐dependent ESR spectra of a spin probe dispersed in the denture resins are analyzed in terms of line‐shapes and line‐widths. The appearance of two spectral components was taken as an indication of resin heterogeneity. The results reveal that the cold‐cured resin has a lower local density in comparison with microwave and conventionally cured resin. The amount of residual monomer also contributes to the local motion of polymer segments. The change of denture resins exposed to ageing is influenced both by the structure of the original resin and the ageing conditions. Restricted motion of a spin probe incorporated into the acrylic resins exposed to accelerated ageing suggests additional crosslinking of polymer chains. The differences are observed for all the investigated resins, but the highest change is observed with the cold‐cured resin. The ESR results are accompanied by Tg and Tm measurements. Copyright © 2005 Society of Chemical Industry 相似文献
58.
1Introduction Reconstructivesurgeryisoneofthehottestre searchedsubjectsthatdealingwithbonedefects.Thetra ditionalmethodisimplantationoffreshautograftbonebe causeofitsnon immunoreactiveproperty.Butautologousbonewasnotabundantinsomecases.Sowefoundbeta trica… 相似文献
59.
The formation of aluminum matrix composites fabricated by exothermic dispersion reaction in A1-TiO2-B2O3 system was investigated. The thermal analysis results show that the reactions are spontaneous and exothermic. The Gibbs free energy of α-Al2O3 is the lowest among all the combustion products, followed by TiB2 and Al3Ti. It is noted that when the B2O3/TiO2 mole ratio is below 1, the reaction products are composed of particle-like α-Al2O3, TiB2 and rod-like Al3Ti. The α-Al2O3 crystallites, resulting from the reaction between A1 and TiO2 or B2O3, are segregated at the grain boundaries due to a lower wettability with the matrix. SEM micrographs show that rod-like Al3Ti phase distributes uniformly in the matrix. When the BEO3/TiO2 mole ratio is around 1, the Al3Ti phase almost disappears in the composites, and the distribution of α-Al2O3 particulates is improved evidently. 相似文献
60.
Jiang Minhong Gu Zhengfei Cheng Gang 《中国稀土学报(英文版)》2005,23(6):723-723
Polymer matrix RE-Fe giant magnetostrictire composite (GMPC) was prepared using bonding and magnetic field forming technique, and magnetostriction of samples was measured for different compressive stress. The experimental results show thai there is certain compressive effect in GMPC. And the influence of compressive stress on magnetostriction of sample was investigated. It offers essential reference for application and device design of GMPC. 相似文献