全文获取类型
收费全文 | 192554篇 |
免费 | 22826篇 |
国内免费 | 15670篇 |
专业分类
电工技术 | 18743篇 |
技术理论 | 4篇 |
综合类 | 19231篇 |
化学工业 | 23771篇 |
金属工艺 | 13076篇 |
机械仪表 | 13272篇 |
建筑科学 | 15743篇 |
矿业工程 | 7395篇 |
能源动力 | 5290篇 |
轻工业 | 19375篇 |
水利工程 | 6539篇 |
石油天然气 | 6830篇 |
武器工业 | 2906篇 |
无线电 | 21534篇 |
一般工业技术 | 16774篇 |
冶金工业 | 7662篇 |
原子能技术 | 3129篇 |
自动化技术 | 29776篇 |
出版年
2024年 | 1207篇 |
2023年 | 3242篇 |
2022年 | 7284篇 |
2021年 | 9520篇 |
2020年 | 6919篇 |
2019年 | 5052篇 |
2018年 | 5405篇 |
2017年 | 6274篇 |
2016年 | 5443篇 |
2015年 | 8649篇 |
2014年 | 10743篇 |
2013年 | 12564篇 |
2012年 | 15781篇 |
2011年 | 16662篇 |
2010年 | 15553篇 |
2009年 | 15315篇 |
2008年 | 15364篇 |
2007年 | 14810篇 |
2006年 | 13159篇 |
2005年 | 10838篇 |
2004年 | 7754篇 |
2003年 | 5031篇 |
2002年 | 4665篇 |
2001年 | 4309篇 |
2000年 | 3515篇 |
1999年 | 1688篇 |
1998年 | 741篇 |
1997年 | 611篇 |
1996年 | 546篇 |
1995年 | 473篇 |
1994年 | 334篇 |
1993年 | 310篇 |
1992年 | 275篇 |
1991年 | 186篇 |
1990年 | 154篇 |
1989年 | 144篇 |
1988年 | 108篇 |
1987年 | 73篇 |
1986年 | 66篇 |
1985年 | 29篇 |
1984年 | 24篇 |
1983年 | 19篇 |
1982年 | 22篇 |
1981年 | 25篇 |
1980年 | 47篇 |
1979年 | 38篇 |
1978年 | 4篇 |
1976年 | 3篇 |
1959年 | 33篇 |
1951年 | 26篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
采用直流磁控溅射和后退火氧化工艺在p型GaAs单晶衬底上成功制备了n-VO_2/pGaAs异质结,研究了不同退火温度和退火时间对VO_2/GaAs异质结性能的影响,并分析其结晶取向、化学组分、膜层质量以及光电特性。结果表明,在退火时间2 h和退火温度693 K下能得到相变性能最佳的VO_2薄膜,相变前后电阻变化约2个数量级。VO_2/GaAs异质结在308 K、318 K和328 K温度下具有较好的整流特性,对应温度下的阈值跳变电压分别为6.9 V、6.6 V和6.2 V,该结果为基于VO_2相变特性的异质结光电器件的设计与应用提供了可行性。 相似文献
2.
3.
Pengfei Chen Honggang Chang Tao Peng Yongfan Tang Youquan Liu Chao Xiang 《应用聚合物科学杂志》2021,138(30):50314
Hydraulic fracturing with slickwater is a field-proven stimulation technology used in tight reservoirs. Because of the high pumping rate associated with slickwater fracturing, drag reduction (DR) is critical in minimizing pressure drop and the success of oilfield operations. In this paper, a new type of drag reducer (SPR) was synthesized with acrylamide and 12-allyloxydodecyl acid sodium, and its drag reduction performance was evaluated. The results showed that the new drag reducer features low molecular weight, fast-dissolving rate and low interfacial tension. The algorithm of estimating the drag reduction rate of non-Newtonian fluid SPR was proposed and validated. Empirical or semianalytical models for estimating the friction ratio (σ) or friction factor (λ or f) were used to simulate the turbulence behavior of the SPR drag reducer under different Reynolds numbers (Re). The modified Virk's correlation could accurately model the turbulent behavior of the SPR drag reducer. A unified calculation formula was established in this study for different pipe diameters. 相似文献
4.
针对煤矸石粉替代率50%、聚酯纤维掺量0.4%的沥青混合料,开展盐冻耦合作用(NaCl溶液质量分数为0%、7.0%、13.0%、26.5%,冻融循环次数为0、2、4、6、8)下的半圆弯曲(SCB)试验,分析了盐冻耦合作用对SCB试件内部损伤劣化过程的影响.结果表明:NaCl溶液质量分数为13.0%、冻融循环为8次时,盐冻耦合作用对沥青混合料的侵蚀破坏作用最强,试件内部损伤最严重;在煤矸石粉与矿粉质量比为1∶1、聚酯纤维掺量为0.4%的条件下,沥青混合料能够形成高黏性、致密、厚实的沥青膜以及由纤维形成的三维网状结构,从而显著降低盐冻侵蚀对沥青混合料的损伤.通过Poly2D模型对SCB试件的极限拉应力损伤量进行拟合,拟合系数为0.944. 相似文献
5.
Yixuan ZHOU Huajie WANG Yi YU Yihang CHEN Rui KE Min XU Chijie XIAO Zhanhui WANG Jiquan LI Xuru DUAN Minyou YE 《等离子体科学和技术》2021,23(7):75105-52
In this article, we present the optical design of a novel diagnostic on the HL-2 A tokamak, i.e. the20-channel edge Lyman-alpha beam emission spectroscopy, which is a promising solution for edge density turbulence research on tokamaks, as it offers the possibility of density fluctuation measurement with a 3.3 mm spatial resolution while maintains a high temporal resolution of1 μs. The optical path, including the reflective collection optics, the high-dispersion spectrometer, and the linear detector array, is carefully optimized to obtain a good image quality and a high throughput. The maximum root mean square radius of the collection optics is 64 μm.The detected photon flux is estimated to be about 10~(11) photons/s/channel. 相似文献
6.
人工智能的普及促进了语音交互技术的发展,语音传感器阵列作为智能语音交互的硬件前端,成为语音交互领域的前沿研究方向.矢量语音传声器自有的偶极子指向性、零点深度以及阵列体积小便于集成的特点特别符合语音交互技术对硬件设备的要求.基于此,通过采用两组矢量敏感单元"共点正交"形成矢量微阵列实现声源空间锐化波束指向,其不受瑞利限与空间采样率限制,与传统空间离散分布的声压麦克风阵列有着本质区别,是矢量微阵列的核心优势所在.矢量微阵列传声器弥补了现有双麦阵列的不足,具有更为广阔的应用前景,作为智能语音交互的硬件前端,对推动智能语音交互领域的发展具有重要意义. 相似文献
7.
Tao Feng Mingde Tong Shuotian Yao Hejun Li Shifeng Wen Hongjiao Lin 《Journal of the European Ceramic Society》2021,41(1):158-166
Composites based on hafnium carbide and reinforced with continuous naked carbon fiber with and without PyC interface were prepared at low temperature by precursor infiltration and pyrolysis and chemical vapor deposition method. The microstructure, mechanical property, cyclic ablation and fiber bundle push-in tests of the composites were investigated. The results show that after three times ablation cycles, the bending strength of samples without PyC interface decreased by 63.6 %; the bending strength of samples with PyC interface only decreased by 37.8 %. The force displacement curve of the samples with PyC interface presented a well pseudoplastic deformation state. The mechanical behavior difference of two kinds of composites was due to crucial function of PyC interface phase including protection of fiber and weakening of fiber/matrix interface. 相似文献
8.
Zhenkun Ke Xin Cao Chuanli Shan Lifen Shi Pingping Wang Yong Yang Fengyang Zhao Jiedong Cui Jinwei Li Gang Zhou Min Guan Tao Yu 《Ceramics International》2021,47(14):19605-19613
The purpose of the current work was to research the effect of alkali metal oxide on the structure, thermal properties, viscosity and chemical stability in the glass system (R2O–CaO–B2O3–SiO2) systematically. Because the glass would emulsify when Li2O was added to the glass batch, this article did not discuss Li2O. The results showed that when the amount of Na2O was less than 4 mol.%, there was a higher interconnectivity of borate and silicate sub-networks in glass, as more mixed Si–O–B bonds were present in glass. The glass samples exhibited excellent thermal properties and chemical stabilities. As the amount of Na2O exceeded 4 mol.%, the interconnectivity of borate and silicate sub-networks was weakened. The thermal properties and chemical stabilities of the glass samples were reduced. The connectivity of the silicate sub-network was weakened slightly as the Na/K ratio varied, and the coefficient of thermal expansion (CTE) of the glass samples gradually increased, and the resistance to thermal shock (RTS) value gradually decreased. Moreover, the viscosity of the glass samples decreased with the ratio of Na/Si and Na/K increased. 相似文献
9.
10.
三维异质异构集成技术是实现电子信息系统向着微型化、高效能、高整合、低功耗及低成本方向发展的最重要方法,也是决定信息化平台中微电子和微纳系统领域未来发展的一项核心高技术。文章详细介绍了毫米波频段三维异质异构集成技术的优势、近年来的发展趋势以及面临的挑战。利用硅基MEMS 光敏复合薄膜多层布线工艺可实现异质芯片的低损耗互连,同时三维集成高性能封装滤波器、高辐射效率封装天线等无源元件,还能很好地处理布线间的电磁兼容和芯片间的屏蔽问题。最后介绍了一款新型毫米波三维异质异构集成雷达及其在远距离生命体征探测方面的应用。 相似文献