全文获取类型
收费全文 | 104048篇 |
免费 | 9601篇 |
国内免费 | 4721篇 |
专业分类
电工技术 | 6264篇 |
技术理论 | 15篇 |
综合类 | 6790篇 |
化学工业 | 17692篇 |
金属工艺 | 5768篇 |
机械仪表 | 6419篇 |
建筑科学 | 7469篇 |
矿业工程 | 3065篇 |
能源动力 | 3251篇 |
轻工业 | 6541篇 |
水利工程 | 1857篇 |
石油天然气 | 5886篇 |
武器工业 | 1101篇 |
无线电 | 12640篇 |
一般工业技术 | 12960篇 |
冶金工业 | 5251篇 |
原子能技术 | 1352篇 |
自动化技术 | 14049篇 |
出版年
2024年 | 475篇 |
2023年 | 1763篇 |
2022年 | 3261篇 |
2021年 | 4541篇 |
2020年 | 3415篇 |
2019年 | 2825篇 |
2018年 | 3177篇 |
2017年 | 3527篇 |
2016年 | 3169篇 |
2015年 | 4271篇 |
2014年 | 5289篇 |
2013年 | 6531篇 |
2012年 | 6812篇 |
2011年 | 7276篇 |
2010年 | 6270篇 |
2009年 | 6034篇 |
2008年 | 5905篇 |
2007年 | 5588篇 |
2006年 | 5524篇 |
2005年 | 4644篇 |
2004年 | 3380篇 |
2003年 | 2938篇 |
2002年 | 2990篇 |
2001年 | 2679篇 |
2000年 | 2454篇 |
1999年 | 2463篇 |
1998年 | 2116篇 |
1997年 | 1777篇 |
1996年 | 1544篇 |
1995年 | 1233篇 |
1994年 | 977篇 |
1993年 | 750篇 |
1992年 | 586篇 |
1991年 | 459篇 |
1990年 | 348篇 |
1989年 | 309篇 |
1988年 | 252篇 |
1987年 | 140篇 |
1986年 | 139篇 |
1985年 | 105篇 |
1984年 | 61篇 |
1983年 | 48篇 |
1982年 | 60篇 |
1981年 | 48篇 |
1980年 | 30篇 |
1979年 | 27篇 |
1977年 | 18篇 |
1976年 | 25篇 |
1974年 | 13篇 |
1973年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 811 毫秒
61.
测向误差的减小一直以来都是无线电测向精度提高的一个难点,对于不同的测向体制所采用的减小测向误差的方法都不尽相同。本文主要介绍的是相关干涉仪测向体制的基本原理以及通过内插法的应用来减小测向误差的方法。 相似文献
62.
The support flux was first investigated as a separate influencing factor for its effect on performances of ceramic filtration membranes. Three pre-membranes were prepared by tape-casting and then transfer-coated to supports to form dual-layer ceramic membranes after sintering. Experiments demonstrated that membrane layers with almost the same properties were obtained despite the huge difference in support flux. When the support flux increases from 3.120 to 97.53 m3m?2h?1, the flux of these three membrane series have increased by 75%, 186% and 228%, respectively. Experimental rules can provide structural design and evaluation from the perspective of permeability. The limit membrane flux of a certain system was derived according to the resistance distribution law of internal membrane structure and the Darcy's theorem. On this basis, a method for designing support flux was proposed. Furthermore, we present a criterion to quickly and easily evaluate the match between the support and the top layer, which is the ratio of membrane resistance to total resistance. Finally, the filtration resistance of penetration caused by suction of membrane particles into the support was measured for the first time, taking the advantage of the transfer-coating method that inherently free of penetration. Our works are expected to deepen the understanding of the ceramic membrane structure and provided guidance for its rational design and optimization. 相似文献
63.
64.
66.
67.
Sowoon Seo Yunjeong Song Sun Mi Gu Hyun Kyu Min Jin Tae Hong Hye Jin Cha Jaesuk Yun 《International journal of molecular sciences》2020,21(23)
Background: Epilepsy is a chronic neurological disorder characterized by the recurrence of seizures. One-third of patients with epilepsy may not respond to antiseizure drugs. Purpose: We aimed to examine whether D-limonene, a cyclic monoterpene, exhibited any antiseizure activity in the pentylenetetrazole (PTZ)-induced kindling mouse model and in vitro. Methods: PTZ kindling mouse model was established by administering PTZ (30 mg/kg) intraperitoneally to mice once every 48 h. We performed immunoblot blots, immunohistochemistry (IHC), and high-performance liquid chromatography (HPLC) analysis after the behavioral study. Results: An acute injection of PTZ (60 mg/kg) induced seizure in mice, while pretreatment with D-limonene inhibited PTZ-induced seizure. Repeated administration of PTZ (30 mg/kg) increased the seizure score gradually in mice, which was reduced in D-limonene (10 mg/kg)-pretreated group. In addition, D-limonene treatment increased glutamate decarboxylase-67 (GAD-67) expression in the hippocampus. Axonal sprouting of hippocampal neurons after kindling was inhibited by D-limonene pretreatment. Moreover, D-limonene reduced the expression levels of Neuronal PAS Domain Protein 4 (Npas4)-induced by PTZ. Furthermore, the adenosine A2A antagonist and ZM241385 inhibited anticonvulsant activity and gamma-aminobutyric acid (GABA)ergic neurotransmission-induced by D-limonene. Conclusion: These results suggest that D-limonene exhibits anticonvulsant activity through modulation of adenosine A2A receptors on GABAergic neuronal function. SCH58261相似文献
68.
69.
针对反射面成型的复杂影响因素,提出平面桁架构建的定日镜面形支撑结构优化技术路线. 利用模拟仿真、数值计算和优化算法等方法,解析20 m2定日镜面形定义技术路线的4个组成环节:面形规格及宽高比、上弦杆的截面矩、平面桁架组间距的最优值、机加工中工艺控制要点的量化. 试制小型定日镜进行实验,分析光斑形状和能流密度分布特性,并与理想球面形光斑比较,两者的拟合优度大于0.98. 实验结果表明,当反射镜宽高比取1.2,上弦杆截面矩取40 000 mm4,桁架组间距取950 mm,上弦杆和斜杆的开孔公差小于0.9 mm时,反射面形的质量提升. 研究从原理和实践上证明了该优化技术路线的可行性. 相似文献
70.
Hechun Cao Hui Zheng Lining Fan Zifeng Cheng Jianwei Zhou Qiong Wu Peng Zheng Liang Zheng Yang Zhang 《International Journal of Applied Ceramic Technology》2020,17(2):813-822
In this study, yttrium iron garnet co-doped with Zn and Zr atoms with a chemical formula Y3ZnxZrxFe(5−2x)O12 (x = 0.0-0.3) has been successfully prepared by the solid-state reaction method. The effects of doping concentration on the microstructure, crystal structure, magnetic properties, and dielectric properties of Y3ZnxZrxFe(5−2x)O12 were investigated. The microstructure analysis indicates that co-doping of YIG with Zn and Zr can effectively reduce the grain size of the ceramic. The crystal structure results reveal that the doping concentration of Zn–Zr has substantial influence on the lattice parameters of YIG, such as, increases the lattice constant, crystal cell size, and interplanar spacing. However, the second phase of ZrO2 appears once x ≥ 0.15. Additionally, the dielectric properties of YIG ferrite can be regulated using this Zn–Zr co-doping method. Zn–Zr co-doping can improve the dielectric stability and reduce the dielectric loss at high temperature. The magnetization measurement shows that the saturation magnetization is stabilized at x < 0.15, and the magnetic loss is decreased with the increase in the doping concentration. Overall, the findings show that the ceramic with x = 0.1 exhibits better properties included high saturation magnetization (24.607 emu/g), low magnetic loss (0.0025 @ 1 MHz), and relatively low dielectric loss (496 @ 400°C). 相似文献